AMERICAN JOURNAL OF Respiratory and Critical Care Medicine · Respiratory Disease (1). The target...

AMERICAN JOURNAL OF

Respiratory andCritical Care Medicine

September 1997 Volume 156, Number 3, Part 2

Supplement:

American Thoracic Society Workshop

Achieving Healthy Indoor AirReport of the ALA/ATS Workshop

Santa Fe, New MexicoNovember 16-19, 1995

WORKSHOP MADE POSSIBLE BY AN EDUCATIONAL PARTNERSHIP GRANT FROMHONEYWELL, INC.

American Thoracic SocietvMEDICAL SECTION OF THE AMERICAN LUNG ASSOCIATION

Achieving Healthy Indoor AirReport of the ATS Workshop: Santa Fe, New Mexico, November 16-19, 1995T HIS W ORKSHOP R EPORT W AS APPROVEII BY THE ATS B OARD OF D I R E C T O R S, MARCH 1 9 9 7

OVERALL INTRODUCTION

In 1988, the American Thoracic Society and the AmericanLung Association convened an interdisciplinary workshop onimproving indoor air quality (IAQ) and health. The workshopwas prompted by the emerging literature on the health effectsof air pollution, and by the need for a critical review of the ev-idence on control strategies directed at the adverse healthconsequences of indoor air pollution. The focus of the 1988workshop was primarily on specific pollutants; also addressedwere source control and building-related problems. A work-shop report was published in 1990 in the American Review ofRespiratory Disease (1). The target audience for the workshopincluded the many health professionals providing clinical careto patients with respiratory diseases, the American Lung As-sociation and its constituents, and the wide range of other pro-fessionals concerned with indoor air quality.

In the ensuing years, our understanding of the adverse ef-fects of indoor air pollution on health and comfort has broad-ened, supplying a stronger framework for developing and im-plementing control strategies. During these years, the array ofprofessionals offering commercial services related to indoorair quality has grown steadily, as have the types of productsand services advertised as improving indoor air quality (e.g.,air cleaners, vacuum cleaners, radon measurement and mitiga-tion, and air duct cleaning). Products with low emission ratesof volatile compounds arc available, and homes can now bedesigned and constructed to offer lower concentrations of pol-lutants than in the past.

Health problems linked to indoor air quality have persisted,however, and the scope of the health concerns has broadened.We continue to identify buildings with occupants who are af-fected by building-associated illnesses, and we have learnedthat these outbreaks may reduce productivity and perhapsresult in costly litigation. The number of people who report re-sponding adversely to environmental contaminants has in-creased, with many receiving the label of “multiple chemicalsensitivity,” for which the World Health Organization has re-cently suggested an alternative term: “Idiopathic Environmen-tal Intolerance.” Changing patterns of infectious disease havebrought new concerns. Tuberculosis, a waning disease at thetime of the last meeting, has returned, and multi-drug-resistantorganisms are becoming more prevalent, particularly in innercities. Substantial time is spent today in often-crowded mi-croenvironments such as airplanes and day care, where thereis enhanced opportunity for disease transmission.

This report gives the proceedings of the workshop. There was no attempt toachieve group consensus on all issues; consequently, the report should not benecessarily construed as reflecting the views of all participants.

Am J Respir Crit Care Med Vol. 156. pp. 533-564, 1997

In response to these dynamic changes since 1988, theAmerican Lung Association and the American Thoracic Soci-ety convened a second workshop in 1995. Additional sponsor-ing organizations included the American Academy of Allergy,Asthma and Immunology, the American Academy of Pediat-rics, the American Society of Heating, Refrigerating, and AirConditioning Engineers (ASHRAE), the Centers for DiseaseControl and Prevention, the U.S. Environmental ProtectionAgency, and the National Association of Home Builders Re-search Center, Inc. Attendees represented the broad range ofprofessional disciplines concerned with indoor air quality andhealth: architects, engineers, building diagnosticians, physi-cians, public health professionals, facilities managers, lawyers,and others. The target audience for the report was construedas broadly as in 1988.

The charges to the workshop participants reflected thechanges in the problems and in the evidence base between1988 and 1995. Solutions to problems and the technology de-veloped to improve health and comfort through better indoorair quality received greater emphasis. After an opening ses-sion that addressed the concept of healthy indoor air, five dif-ferent working groups were convened, and during the threedays of the meeting they focused on: (I) problem-solving: de-sign, construction, and operation of buildings; (2) source con-trol; (3) ventilation; (4) air cleaning and treatment; (5) poten-tially susceptible populations. This workshop report providessummaries of the five groups’ responses to these charges, andincludes overarching recommendations. The report also pro-vides a general background for readers on the conceptual ba-sis of healthy indoor air and on institutional jurisdiction forvarious dimensions of indoor air quality. A brief description isincluded of the complex factors in the design and constructionof a building that affect the air quality within the building as itis commissioned, and the diverse factors that determine airquality in a building during its use.

What Is Healthy Indoor Air?

The meeting began with a discussion of the key elements inthe concept of healthy indoor air, with Richard Diamond,Thad Godish, William Cain, Ronald White, and JonathanSamet reviewing and addressing component issues related toarchitectural design, the residential environment, irritation,public health, and clinical medicine, respectively.

Diamond described the multiple perspectives from whicharchitects may approach indoor air pollution. In the tradi-tional “one-point” perspective, architects view their work pri-marily for its visual impact-architecture as art-with littleconcern for occupant comfort and health. A more pragmaticor “two-point” perspective recognizes that architecture hasaesthetic value but also needs to reflect a broader range offunctional considerations such as providing for human needs,

S34 AMERICAN JOURNAL OF RESPIRATORY AND CRITICAL CARE MEDICINE VOL. 156 1997

allowing construction within budget, and avoiding costly liti-gation. The architect assumes that conventional practice willprovide acceptable conditions for occupant health and com-fort. A third, more comprehensive, perspective, advanced byLevin (2) and others, adds to the previous perspective a fullyintegrated “ecological approach, ” incorporating explicit con-cerns for a building’s effects on the health of its occupants andon the environment.

Godish began by referring to the difficulty of defining“healthy air.” He then discussed the characteristics of residen-tial environments that pose unique issues: the large number ofbuildings and the diversity of environments, ownership status(owned or leased), diversity of construction characteristics,the limited complexity of building systems, and special expo-sure concerns. Godish emphasized diversity and the frequencyof problems in manufactured housing. With regard to exposure,he pointed to the length of time spent at home; the diversity ofthe exposed population, which includes infants, children, theelderly, and persons with underlying illness; particular expo-sures such as radon, formaldehyde, environmental tobaccosmoke, and releases from craft activities; and the limited po-tential for dilution through ventilation.

Cain noted that the effects of irritants may or may not bepredictable. Although body odors and environmental tobaccosmoke (ETS) have predictable effects, other agents may notaffect everyone in a uniform way. He commented that, for irri-tation, the response reflects the additive contributions fromthe individual agents. He noted that ventilation approacheshave been based largely on odor control, and he considers thatsince this odor-based approach has been generally successful,it should not be abandoned. He advocated for research to sup-port a mass-balance approach and raised the problem of fund-ing sources.

The presentations by White and Samet emphasized thebroadness of the concept of health. Implied in the WorldHealth Organization definition of health is a need for consid-ering a wide range of responses to indoor air pollution, includ-ing irritation and symptoms. Samet noted the substantial bur-den of clinically diagnosed disease associated with indoor airpollution.

In the discussion prompted by these presentations, andduring subsequent open discussions at the workshop, therewere reminders that comfort in indoor environments reflectsnot only indoor air quality but the thermal environment, light-ing, physical stressors, and diverse psychological and socialfactors.

A Conceptual Framework for Considering IndoorAir Quality and Health

Indoor air pollutants are linked to health responses through asequence that moves from emission by the source through ex-posure, dose, and ultimately to the health response, as illus-trated in Figure 1. This model, designed by the conferenceparticipants, simplifies a complex set of interactions but indi-cates the critical points at which control strategies have ef-fects. The schema points to the central role that source controlshould play in any control strategy. Air cleaning and treat-ment can lower concentrations and thereby reduce exposures,and time-activity patterns can be modified to limit source useand exposures. Ventilation reduces pollutant concentrationsthrough dilution. The materials selected in the design phasemay determine the potential for future adverse health effects,depending on associated emission rates. As a building is used,new and unintended sources may be introduced and the origi-nal design ventilation may be either inadequate or compro-

/ source Control Altered Time Activity

Mitigationstrategy

Determinateof Response S o u r c e _ _ _ _ _ _ , T i m e

+Dosa -W Response

t

Susceptibility

Figure 1. Sequence of health responses linked to indoor air pollu-tion.

mised by inadequate maintenance. This model also acknowl-edges the range of susceptibility in the population.

General Recommendations

On issues transcending the charges of the individual workinggroups, the workshop participants offered a series of generalrecommendations reflective of the interdisciplinary nature ofthe group.

Exposure reduction. Many products have been developedto benefit indoor air quality, including room and central aircleaners and low emission products for construction and fur-nishing. It is doubtful that experimental data from controlledclinical trials will become available for most of these products,and observational data, if available, may be difficult to inter-pret because of the multiplicity of factors determining re-sponses to indoor environments. However, there still exists aneed for recommendations concerning the purchase and useof these products. Persons seeking relief from health problemsassociated with indoor air quality may turn to health provid-ers, the American Lung Association, or other organizations forguidance when considering the purchase of products promisinghealth benefits. Even though there are no data on most spe-cific products, the workshop participants considered that re-duction of exposures could be generally recommended. Per-sons seeking relief from problems related to indoor air qualityor attempting to minimize risk for developing problems can becounseled that using products that reduce exposure is reason-able. They need to be aware, however, that purported healthbenefits may not follow and they should balance costs and po-tential benefits.

Interdisciplinary meetings. The 1988 and 199.5 workshopparticipants were multidisciplinary in background and reflec-tive of the broad range of professionals concerned with indoorair quality. As at the previous meeting, the 1995 participantscommented on the lack of similar meetings and of venues formultidisciplinary interactions. Participants recommended thatthe American Thoracic Society and the American Lung Asso-ciation take the lead in conducting regular interdisciplinaryworkshops that promote in-depth discussion of key and timelyissues.

Institutional interactions. Institutional alignments related toindoor air quality were also discussed. A specific focus of dis-cussion was the development of ventilation standards byASHRAE; the standard-setting process continues without for-mal participation from organizations concerned with clinicalillnesses of individuals and with public health, although per-sons with health backgrounds have served on the ASHRAEcommittee that developed the ventilation standard and onother ASHRAE committees. The group encourages discus-sion of ASHRAE’s unique role regarding ventilation and in-door air quality and involvement of other organizations suchas the American Thoracic Society and the American Public

American Thoracic Society

Health Association. The possible roie of governmental agen-cies should also be explored.

Voluntary guidelines. There was discussion on establishingvoluntary guidelines for indoor air quality practices for use incommercial buildings. The participants agreed that theseguidelines already existed in the Environmental ProtectionAgency/NIOSH’s Building Air Quality guide and that the realissue was the adoption of these good indoor air quality prac-tices. To promote their use, the participants recommendedbringing together a group similar to the Building Air QualityAlliance initiated by the EPA, which would implement a vol-untary program by encouraging building owners and opera-tors to adopt good indoor air quality practices through oppor-tunities and incentives.

Communication. The group commented on the lack of ef-fective strategies and processes for educating the public aboutindoor air quality. The American Lung Association has pro-duced printed and video documents, but no process is in placefor communicating with the public systematically and compre-hensively at key times of need-to-know such as during the de-sign or purchase of a home. The participants encourage thedevelopment of strategies for assuring consumer understand-ing of options and consequences as key decisions are madewith regard to residences.

Needs for research. Like participants in the previous work-shop, the 199.5 attendees lamented the lack of information inkey areas. They expressed concern about product marketingthat promises health benefits without appropriate data, as ab-sence of data handicaps those formulating recommendationson the use of such products. These large gaps in our under-standing of control strategies reflect the regrettable lack offunding for research on indoor air quality. The workshop par-ticipants encouraged the American Lung Association to advo-cate for increased funding for indoor air research, to urgemanufacturers of products related to indoor air quality to sup-port research, and to seek a mechanism for contributing to re-search on indoor air quality in general.

This report is intended for professionals in a variety offields who need to increase their understanding of how abuilding’s indoor air quality affects its inhabitants and whatcan be done to eliminate or reduce potential adverse reactionsto pollutants in indoor air. It is a workshop report and pre-sents the findings of the participants. Anyone who is inter-ested in a more in-depth treatment of the topics discussed orof other dimensions of indoor air quality should refer to thelist of recently published general references at the end of thedocument. These references provide information on the healtheffects on indoor air pollution, not a topic of this report. Anumber of comprehensive references have been published,and the proceedings of the Triennial Indoor Air Conferencesoffer invaluable coverage of the subject.

Organization of This Report

The five sections of this document reflect the tasks of themeeting’s five working groups. The first section provides basicinformation on how a building’s design, construction, and op-eration affect the quality of its indoor air, how to prevent airquality-related problems, and how to address them when theydo occur. The section that follows looks at sources of indoorair pollution and identifies strategies for minimizing or elimi-nating potential risks. Section three deals with ventilation asan approach to managing indoor air. It explores how a build-ing’s inhabitants are affected by the quality of its ventilationsystem. The fourth section discusses air cleaning and filtrationand the impact of these technologies on improving indoor airquality. The fifth and final section is a brief overview of se-

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lected populations who, for various reasons, appear to be espe-cially susceptible to the adverse effects of indoor air pollution.

PROBLEM SOLVING IN THE DESIGN, CONSTRUCTION,AND OPERATION OF BUILDINGS: THE RELATIONSHIPTO INDOOR AIR QUALITY

This section considers two aspects of indoor air quality (IAQ)as it relates to commercial and residential buildings: (I) howbuildings are designed, constructed, and operated to achievelow concentrations of pollutants and prevent problems fromoccurring; and (2) how to mitigate problems related to indoorair in buildings when they do occur. Delivering and operatinga “healthy building” is key to health and comfort. It beginswith an extensive discussion of the design, construction, andoperation of buildings. An understanding of the complex se-quence that leads from design to building use is essential forpreventing and diagnosing problems.

Current Nonresidential Design and ConstructionPractices: Description and Deficiencies

The quality of a building’s indoor air reflects in part the pro-cesses by which it is designed and constructed. Current prac-tices, each with advantages and disadvantages, have not con-sistently delivered buildings and building systems that performas designed reliably over a building’s lifetime. These perfor-mance deficiencies often lead to indoor air quality problems.What follows is a review of two common design/constructiondelivery practices for nonresidential buildings in use today,each with many variations.

Design/bid/build. The design/bid/build approach is by farthe most common practice in most areas in the country for in-stitutional and large commercial projects. In this approach,the owner retains an architect who takes the lead through thedesign phase. The architect typically hires consultants to de-sign specific elements of the building such as structural, me-chanical, electrical, and plumbing systems. Once the design iscomplete and documented by plans and specifications, it is letout for bid by general contractors. After award of the project,the general contractor usually subcontracts most or all of theconstruction to specialty subcontractors. Because the bid doc-uments are in the form of plans and specifications, this ap-proach is commonly referred to as the plan & spec’ approachby contractors.

There are several variations of the plan & spec’ approach.The general contractor may be selected before or during de-sign on a fixed-fee basis. The contractor is then brought on toassist in developing some design details as well as to controland ultimately guarantee the budget. In another variation, aconstruction manager is hired by the owner to oversee boththe design and construction process and to ensure that theowner receives the lowest possible price. The plan & spec’ ap-proach has two key elements: the designers are independentprofessionals (architects and consulting engineers), and all ormost of the subcontractors who build the building and its sys-tems are selected based on low bid.

Design/build. In the design/build approach, the designerswork for the contractor. A design/build general contractorfirm, for instance, would have its own architectural and struc-tural engineering staff; a design/build heating, ventilation, andair conditioning (HVAC) contractor firm would have its ownmechanical engineering staff. On occasion, instead of in-housedesigners, contractors retain local architects or consultants.The contractor may also be selected based on low bid using aperformance specification as the basis of design. This ap-proach shares many of the characteristics of the plan & spec’

536 AMERICAN IOURNAL OF RESPIRATORY AND CRITICAL CARE MEDICINE VOL. 156 1997

approach and there is a potential to compromise quality tosave costs.

A dichotomy has developed in the building industry thatcan adversely affect occupational health. On the one hand, in-creasing litigation in the construction industry has indirectlyencouraged design professionals to take less responsibility forthe ultimate product of their work (the building), leavingmany construction details to the contractors. On the otherhand, the emergence of more sophisticated HVAC systemsand control systems has made competence in design, construc-tion, operation, and maintenance even more important. Minordeficiencies in one aspect of the building defeat excellent per-formance in other areas.

Attempts have been made to change these processes, butnone offers a complete solution. Possibly, the most encourag-ing attempt has been the design/build approach in which thedesigner is employed directly by the contractor. This organiza-tional approach eliminates the separation of design and con-struction responsibilities and should improve the design aswell as reduce costs because of the close contact between de-signer and builder. However, this approach places the de-signer, who is licensed and professionally responsible, in a po-tentially compromising role.

The Integration of the Project Team

The need for communication among stakeholders increases asproject development objectives become more sophisticatedand increasingly demanding of interdisciplinary discussion. Ifpossible, a commitment to design team integration should bemade at the outset of the project. Each stakeholder then has arole and can contribute to the project development. What fol-lows is an idealized approach showing how indoor air qualityissues can be identified and addressed throughout the designand construction process.

In the Project Planning Phase, a commitment is made bythe owner or developer to a project schedule, budget, and de-sign team that will provide for indoor air quality requirements.The schedule should provide adequate time for airing-out ofnew construction materials and for commissioning buildingsystems before occupancy. Project feasibility studies and as-sembly of the design team involve consultation with all rele-vant participants in the process. A design team should be se-lected on the basis of proven indoor air quality experience aswell as commitment to integration of stakeholders into the de-sign process. Budgeting fully anticipates both capital and hold-ing cost requirements of additional time, expertise, and spe-cialized systems or materials to address indoor air qualityrequirements.

In the early Site Planning and Design Stage, the architectand the building owner or developer define the site, parking,landscape, and future area requirements. Together with thelandscape architect, they evaluate options for landscape areasto enhance the outdoor air requirements. Previous land useevaluation and testing for soil contaminants may be under-taken. The location of parking areas and vehicle access areasrelative to building openings and air intakes is identified as anissue for consideration as the building mass is developed. Themechanical engineer contributes information on HVAC op-tions and develops filter and air-cleaning options, assuring thequality of outdoor air to be used for ventilation. The site andthe building need to complement each other and to be de-signed to work together to optimize IAQ.

During the Overall Architectural Design Stage, the build-ing owner/developer, the architect, and the mechanical engi-neer work together to develop the most appropriate buildingform and preliminary window design strategies in conjunction

with an overall environmental control concept covering venti-lation, thermal control, lighting, and acoustics. Locations ofbuilding openings are related to vehicle access and parking ar-eas to minimize pollutant entry.

Pollutant-generating activities located within the buildingare identified and separation/ventilation strategies are devel-oped if needed. Wherever there is a potential moisture source,ventilation and dehumidification should be adequate to pro-tect against microbial growth. Regardless, attention to dehu-midification is needed throughout the building. Smoking loungerequirements and locations are determined, if necessary.

The building envelope, including roof, walls, doors, win-dows, and floor, is developed. Depending on ambient air qual-ity, as identified in the previous stage, operable windows areconsidered by the architect, and their potential impact on theHVAC system is assessed by the mechanical engineer. Thebuilding owner/developer considers reasonable occupant useand interlock or pressure control requirements, if any. The en-velope and structural materials are selected with input fromthe architect, the building owner/developer, the structural en-gineer, and the mechanical engineer.

Once the overall building and site have been selected, Ven-tilation and Climate Control Strategies are developed by thearchitect, the building owner/developer, the mechanical engi-neer, and the landscape architect. Outdoor air dilution de-pends on ambient air quality as affected by perimeter trees,shrubs, and landscape materials. Air intakes, exhaust loca-tions, air cleaning, and space air distribution are developed bythe mechanical engineer in conjunction with the team. Heatrecovery systems and microbial development control strate-gies are considered at this stage. Strategies related to ventila-tion rates, filters, cleaning, and air distribution are selected,and a choice is made between using either ducted or plenumreturn air.

In the Materials Selection and Specifications Stage, theteam explores source control options. Low-emitting materialsfor the envelope and the interior finishes are selected wher-ever possible. Materials that might support molds are reducedand design strategies are developed to ensure that moisturedoes not accumulate. Strategies are designed to reduce off-gassing of materials in the enclosed spaces; to manage anycondensation in HVAC systems; to ensure proper curing ofconcrete before covering; and to generally address issues of in-door air quality and make them part of the construction con-tract and of the operations and maintenance plan. The con-tractor, if available, is invited to assist in the development ofthe specification and selection of materials. Ideally, futurebuilding operations and maintenance staff would be involvedto ensure that specification strategies are practical and will beimplemented during the building operations and handoverstage.

During construction, the issue of Product Substitution mayarise. A contractor may make a request to substitute a productthat carries consequences for indoor air quality performance.This can present a temptation to owners for cost-cutting be-cause these substitution requests are made in isolation; theconsequences for indoor air quality may not be fully apparent.

The Construction Process and Initial Occupancy Stages in-volve the entire team. Some decisions regarding the commis-sioning of the building are made at this time, but comprehen-sive plans and the commissioning process should begin withdesign. The importance of special ventilation during construc-tion and of avoiding premature occupancy is clearly communi-cated to the contractor and the building owner/developer toensure indoor air quality throughout construction and occu-pancy phases. The HVAC system is handed over to the build-


ing’s operations and maintenance staff with a hands-on trainingsession to ensure the building will be operated to maximize po-tential performance.

A recent and successful development in the managementof IAQ is the System Commissioning Process. Commissioningis a formal process verifying that systems have been installedand are operating as designed. It involves a comprehensive re-view of design drawings to ensure that systems meet design in-tent and are readily maintainable, inspections to ensure thatsystems and equipment are installed per the design docu-ments, and testing of all equipment and control systems. Sev-eral case studies have shown that a formal commissioning pro-cedure can be highly effective (3).

The cost of building commissioning may be erroneouslyperceived as high and as a reason for not implementing com-missioning of HVAC systems in commercial buildings. In fact,experience with commissioning to date has clearly demon-strated its financial advantage (3). Savings are realized fromthe rcduccd riced for corrections of deficiencies late in theconstruction process and during the early occupancy period.Further savings, in some cases shown to be quite dramatic,have come from reducing energy costs in new buildings. Be-cause the commissioning process provides complete documen-tation of systems and training of building operators, design in-tent is more likely to be executed in a fully commissionedbuilding. A recent study in Switzerland found that symptomprevalence in occupants varied inversely with how closelybuilding ventilation rates conformed to the original design (4).Documentation of design intent and commissioning, therefore,can be cost cffcctivc by reducing problems and their severityand by reducing lost work time from absenteeism because ofbuilding-associated illness or by contributing to optimal workerproductivity.

Mitigating IAQ Problems in Commercial Buildings

The management of indoor air quality in an occupied buildingoften starts with simple preventive measures and may includemore advanced technological approaches as needed.

Housekeep~ngproced1lre.s. Indoor environments are contin-uously contaminated with dirt and dust tracked in by buildingoccupant’s footwear, from dust in the supply air, and fromdust sources in the building, such as office machines and paperhandling, by spillage, by residues, and from other sources.Proper housekeeping prevents build-up of dust deposits, andthus is a most important measure in controlling secondarydust sources. To date, there are very few scientific attempts todemonstrate an effect of cleaning on occurrence of Sick Build-ing Syndrome (5).

Building entrances designed to minimize track-in of dirtmay consist of grilles followed by removable, washable mats.The mats should be washed at regular intervals. If an officeroom is disturbed by computer cables, printer paper boxes onthe floor, or other obstacles, the cleaning staff cannot carryout the cleaning job as effectively as intended in the time as-signed; untidy workplaces may interfere with cleaning andthereby affect IAQ.

The building owner should take care in selecting a cleaningcontractor and phrasing the final contract. Proper cleaningcontributes significantly to the expenses of running a building,whereas insufficient cleaning results in an unacceptable envi-ronment. The customer should specify the degree of cleanli-ness to be maintained and the cleaning loads placed on rooms.The professional cleaning contractor then can design a cost-effective cleaning procedure while considering other factorssuch as types of room surfaces and accessibility. The contrac-tor should specify how the proposed cleaning procedures-

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along with quality assurance-will be documented. Specialemphasis should be put on carpets, particularly in rooms withhigh person/dirt loads.

Cost-effective cleaning consists of a carefully chosen com-bination of cleaning agents, tools, and machines applied in aspecified cleaning program. The program should specify themethod by which an object is cleaned and how frequently. Thecleaning contractor should document procedures for selectingthe least toxic cleaning agents to do the job. Cleaning person-nel should be properly trained, as improper use or dosing ofcleaning agents may degrade surfaces. Use of cleaning agentscan be reduced by more frequent inclusion of dry moppingmethods. Occupants should be informed about cleaning pro-grams specified for each room in a building.

Computer-supported quality control procedures are avail-able, based on subjective assessment of the quality of thecleaning (6). Assessors select a random sample of cleaning ob-jects for inspection and count the number of “failures” such asspots, heel marks, greasy fingerprints, and visible dust depos-its. The procedures can only help to assess if a given cleaningprocedure has been followed, not if the quality is appropriatein relation to the indoor air quality.

A comprehensive approach to evaluating the quality ofcleaning, including a method for on-site measurement by non-specialist personnel has been proposed (6). The method isapplicable to nontextile surfaces and measures the degree ofsurface soiling by the percentage of surface area covered byparticles (see Table 1). Proposed guidelines for the quality ofcleaning, based on what is reasonably achievable, are as follows:

1.

2.3.

Baseline quality. The potential dust sources can readilybe controlled to this level by using appropriate cleaningmethods.Improved quality.Indoor environment quality. Surface cleanliness can bemaintained by the best currently used cleaning methodsand programs. Control of secondary dust sources at this

TABLE 1

PROPOSED NORMS FOR CLEANING NONTEXTILE SURFACES

Cleaning ObjectArea Covered by Dust

Hard furniture surfaceIndoor environment quality

Close to personEasily accessibleOther

Improved qualityClose to personEasily accessibleOther

Baseline qualityClose to personEasily accessibleOther

Hard floorsIndoor environment quality

Walk areaOther

Improved quality*Walk areaOther

Improved quality*Walk areaOther

* Provided polish film is not sampled.Source: Schneider et al., 1994 (6).

W)

1.5

2

10

4

15

5

10

1218

S38 AMERICAN IOURNAL OF RESPIRATORY AND CRITICAL CARE MEDICINE VOL. 156 1997

level does not imply that sick building symptoms will notoccur. The limits specify the levels not be exceeded duringthe period between cleanings. The cleaning contractor se-lects appropriate cleaning methods and frequencies.

Commercial IAQ assessments. To increase assurance thatcommercial buildings offer thermal, air quality, lighting, andacoustic conditions conducive to health ar,d comfort, periodicassessments of spaces should be conducted by trained facilitiesstaff. One readily available document that can be used by thestaff for this purpose is the EPA’s Building Air Quality Man-ual (7). Although its procedures do not require quantitativemeasurements or formal surveys of occupants, they can be im-plemented with the expectation of achieving reasonable assur-ance that occupant exposures are “acceptable” according toapplicable guidelines (8-l 1). If a higher level of assurance isrequired, then quantitative and simultaneously obtained sys-tem performance, human response, and exposure measure-ments should be obtained and evaluated against a rigorousand established protocol.

Commerciul system performance assessments. To carry outperiodic systems assessments, ASHRAE’s Guideline 1: SystemCommissioning and Guideline 4: Operations and MaintenanceManuals are useful (I 0, 11). These procedures demand exten-sive knowledge of building systems and may require addi-tional training for staff or the services of a competent test andair balance (TAB) outside contractor. If system performanceis deficient, a system performance assessment should be con-ducted using a comprehensive protocol. Air flow should bemeasured and compared with the original TAB report. How-ever, if there have been modifications to the building struc-ture, use, or occupancy, the original design TAB specificationmust be evaluated and modified if needed. A third partyshould direct and evaluate the TAB assessment or provide as-surance of the competency of the selected firm.

The “healthy” building should include sensors for real-timemonitoring of supply and return air flow. Cost can be reducedby placing the sensors within the fan, eliminating the need fora large expanse of straight duct to minimize turbulence andprovide accurate measurements.

The transfer of HVAC building operations and preventivemaintenance. In this step, information on operations and pre-ventive maintenance is transferred from the designer and con-structor of the facility to the owner and/or tenant operatingthe facility. The approach to the transfer varies widely. At oneextreme, the owner/operator is simply handed instructionsfrom the equipment manufacturers without any operatortraining. At the other, systems are formally “commissioned,”including thorough system inspection and testing and carefulon-site training of the operators. Detailed approaches to ac-complishing this hand-off are covered in ASHRAE’s Guide-line I: System Commissioning and Guideline 4: Operationsand Maintenunce Munuals (10, 11). At a minimum, wall dis-plays of the HVAC system should be provided in mechanicalrooms and should include a brief description of the HVACsystems that serve the facility and of the ASHRAE designstandards used. Basic assumptions should be given, includingthe maximum number of human occupants that each HVACsystem was intended to serve and the major pollutant sourcesin the ventilated areas. The information should also includethe basic central operating sequence and the schedule for pre-ventive maintenance.

Evaluation of current HVAC performance. Many facilitieslack any routine evaluation of the ongoing performance ofH V A C systems. A few states, through state OSHA regula-tions, do require periodic maintenance and verification of per-

formance. One prudent approach to ensure proper perfor-mance is to conduct periodic audits of HVAC systems and tomaintain records of these audits by an identified, responsibleperson.

If problems are found by the HVAC audit, a careful diag-nostic procedure by trained professionals (i.e., mechanical en-gineers and HVAC control contractors) should be conductedand appropriate corrective actions taken. If the problems havecome from changes in the pattern of occupancy in the areathat the system serves, modifications may be needed in the de-sign of the system.

Proactive maintenance. Proactive maintenance is far-reach-ing; it includes inspection for cleanliness and operations,cleaning, and filter replacement. Some procedures should becarried out seasonally and others annually. Property ownersshould arrange for periodic in-house or contracted mainte-nance service for HVAC systems.

HVAC system correction during commercial maintenanceprocedures. The previous section outlined typical inspectionprocesses and the steps usually needed to determine if HVACsystems are functioning properly. Perfunctory maintenanceand inspection processes, usually performed for the sake ofeconomy, may not reveal latent indoor air quality problems,and almost always fail to assure the comfort of building occu-pants. The maintenance process requires diagnosis, planning,documentation, and communication with building manage-ment to assure achievement of adequate IAQ.

The qualified maintenance technician should be able toidentify defects in design or installation and also to diagnoseand correct items that reflect mechanical or electrical faileduses. Attempts should be made to initiate elements of “predic-tive” maintenance. Examples include vibration measurementof rotating devices, insulation resistance integrity of HVACsystem motors (including compressors), and periodic overallairflow and water-flow measurement. Failure of HVAC sys-tems, although sometimes instant and possibly catastrophic, isoften gradual and predictable. Actual repair and remediationtechniques are well documented (1 I) and will not be detailedhere.

Preserving IAQ during building renovation. A high poten-tial for compromising IAQ exists during building renovations,as the renovations may generate pollutants and alter ventila-tion. These problems may be minimized by conducting IAQdesign and procedural reviews with a specific IAQ controlagenda and by retaining a qualified IAQ industrial hygienistwith engineering experience, or a consulting engineer with in-dustrial hygiene and IAQ experience, to review design andimplementation plans. Building personnel should be informed,and an IAQ industrial hygienist could be appointed to admin-ister the IAQ plan. Further steps to reduce IAQ problems in-clude renovating in off-hours, sealing off construction spaces,and ensuring that particles and gases are satisfactorily con-trolled. Some renovations may necessitate removing person-nel from the area being renovated and the surrounding areas.

IAQ correction during renovation or remodeling opera-tions. During renovations and remodeling operations, occu-pant exposures can occur; therefore a decision is neededbefore the process begins on whether occupancy should con-tinue. The three critical steps in the detection and remediationprocess, should harmful agents be liberated, are communica-tion, evaluation, and remediation.

1. Communication. The communication process begins withimmediately alerting the administrator of the IAQ re-sponse plan that an incident has occurred. The report mayoriginate with the party causing the incident or from facility


2.

.3.

occupants. In the communication process, delay in notifica-tion should be minimized, regardless of concerns about cul-pability. The plan should emphasize that reports of possi-ble incidents should be taken seriously and action shouldbe immediate.Evaluation. Upon notification of an IAQ incident duringbuilding renovation, it is imperative that the administratorof the IAQ response plan evaluate options rapidly and con-servatively. All options, ranging from containment, vacat-ing the area, and requests for third party assistance (i.e.,local HAZMAT forces), should be considered and imple-mented on a timely basis.Remediation. After communication, evaluation, termina-tion, and containment, potentially harmful sources shouldbe pursued vigorously and completely. Entry of particles,fumes, or vapors should be ended by use of approved di-rect contact measures (i.e., cleaning, vacuuming, etc.), orconcentrations reduced by appropriate approved ventila-tion measures. All contaminants should be mitigated with-out transferring the problem from the area undergoingrenovation to another area. Professional third-party reviewof these measures is encouraged to assure that completeand correct measures are undertaken.

Competent and trained staffi The healthy building has acompetent and trained staff that is cognizant of the IAQ im-plications of HVAC maintenance. Even a well-designed build-ing can have poor IAQ if maintained poorly. Modern HVACequipment such as boilers, chillers, fans, and pumps, can bequite sophisticated, often incorporating sensitive electroniccomponents. The equipment may be integrated with a varietyof controls, including pneumatic, electronic, and direct digitalcontrol (DDC) devices. In larger buildings, and even in somemedium-size buildings, these controls may be managed with acomputerized and automated system. Thus, without extensiveand continuous hands-on training, maintenance staff may beunable to operate the building properly. Appropriate hands-ontraining and complete operations and maintenance manualsshould be provided.

Current Residential Design and Construction Practices:Description and Deficiencies

Design and delivery. Designing and building small residentialbuildings, especially single-family houses, contrasts markedlywith the process for other types of buildings. Houses are “de-signed” once and built many times, in different locations, ondifferent types of foundations, and with diverse modifications.The use of stock plans from plan books is widespread, whereascustom homes designed by an architect and incorporating sys-tems designed by engineers arc a small minority. Typically,the “design team” is a single person. The builder may alsobe the developer and may use employees to perform someservices that would ordinarily be subcontracted. Expertise inidentifying and avoiding potential IAQ problems may belacking.

Builders of speculative housing build for an anonymousbuyer whose tastes are assumed based on overall perceptionsabout buyers and experience with previous buyers. There arealways exceptions, but few home builders see upgrading IAQas a significant marketing opportunity, nor do they see failureto incorporate IAQ upgrades as leading to buyer complaintsor call-backs. As a result, IAQ upgrades are likely to be incor-porated voluntarily in new homes only where their incremen-tal cost is very small, the measures are prescriptive in natureand understandable to the nonspecialist, and/or the changes

539

are beneficial and marketable for reasons aside from their im-pact on IAQ.

Design and delivery of combustion equipment. The design/delivery phase can have significant influence on the exposuresto combustion emissions in residential structures. All combus-tion devices should be ventilated effectively, and major com-bustion devices such as furnaces should be isolated from theinterior space. In designing venting systems, one should con-sider the interactions of all the devices acting on the houseairflow system. Vented appliances are designed to have com-bustion emissions released to the outdoors when operatednormally. Back-drafting may bring combustion products intothe house because of a malfunctioning venting condition.

Radon control. New homes built in areas with high radonpotential should be designed and constructed to facilitate re-mediation if elevated radon levels are found after occupancy.Radon-resistant construction features include a permeablelayer underneath the basement floor slab or slab-on-grade; apolyethylene membrane above the subslab layer prior topouring the floor slab; a vent stack extending from below thefloor to above the roof, and electrical wiring to facilitate in-stallation and activation of a fan to depressurize the layer be-low the slab. A set of prescriptive requirements for radon con-trol along these lines has been added to the 1995 Council ofAmerican Building Officials (CABO) One and Two FamilyDwelling Code, so this type of construction should becomemore common (12).

Surface drainage. It is standard practice to slope the groundaway from foundation walls to provide positive drainage ofsurface water and discharge from downspouts. However, asthis soil must be placed after the foundation wall is poured orerected, proper compaction of the fill is critical if the finalgrade is to be maintained. If the fill is not fully compacted, itwill settle around the foundation wall and eliminate positivedrainage away from the home. In that event, the likelihood ofa damp basement or crawl space, or even of major leaks at thebasement floor level, is greatly increased, facilitating growthof microorganisms and subsequent IAQ and other problems.

Multifamily buildings. Multifamily buildings representnearly a quarter of new housing construction stock and 18%of the new residential construction since 1990 (13) in theUnited States. As building types, they fall between other resi-dential and commercial construction. The population in thishousing stock has a higher proportion than single family hous-ing of renters, lower income, and minority group members,but not-as popularly perceived-elderly residents. The twomain issues relating to indoor air quality and the design andconstruction of apartment buildings are the provision of me-chanical ventilation systems and the lack of attention to de-tails to prevent moisture penetration.

Ventilation systems are typically required in large apart-ment buildings to exhaust air from kitchens and bathrooms.Outdoor air is typically supplied through the corridors, whereit enters the apartments through the gap under the door. How-ever, because of noise complaints from the tenants on the topfloors, the roof exhaust fans are often shut down.

New apartments are often required by code to have directsupply and exhaust at each apartment. There is no evidencefrom the field on the efficacy of these systems. Because of theconflicts over reducing energy costs and the provision of venti-lation air, ventilation systems in multifamily buildings are of-ten run intermittently, if at all. Apartment building managersand owners may not perceive ventilation as critical, and it maybe given low priority in the maintenance and operation of thebuilding, unless tenant complaints-usually regarding cookingsmells from other apartments-are frequent. Unlike single-

540 AMERICAN JOURNAL OF RESPIRATORY AND CRITICAL CARE MEDICINE VOL. 156 1997

family housing whcrc infiltration and natural ventilation havebeen used to provide adequate air entry, the patterns of airflow in multifamily buildings are quite complex; depending onthe height of the unit and the wind direction, some apartmentsmay not receive any natural infiltration.

Moisture inspection und repair. Moisture is a major prob-lem in multifamily buildings, because of the configuration ofunits. Balconies are prime locations for rain penetration, andflat roofs may be ineffective in preventing water entry. Cou-pled with the frequent lack of maintenance, moisture entry inapartments can lead to water-damaged materials. Anothersource of moisture in apartments is the use of unvented gasstoves and ranges for space heating. In large multifamilybuildings, tenants are often billed directly for their electricspace heat, but the gas stove is typically metered centrally andthe tenants are not billed for their individual consumption.The tenant realizes the economic benefit of using the “free”gas heat, but the unvented stoves produce a great deal ofmoisture-in addition to the combustion gases-that fre-quently results in condensation on walls and other surfaces.

Entry mechanisms. (I) External leakage. There are two en-try paths through which moisture can enter the residential en-vironment. The first is leakage through the building shell, ei-ther through the roof, walls, windows, doors, or other buildingstructures and components. The second is through paths be-low grade slabs and walls. (2) Internal leakage. Another causeof water presence within the home is internal leakage or over-flow (i.e., pipes, basins, tubs, appliances) or condensation ofinternal moisture on cold surfaces. Moisture condenses at atemperature known as dew point. Expressed in units of tem-perature (degrees), the dew point varies with the temperatureand the relative humidity within a space. For example, if ahome environment is kept at 7.5” F and 50% relative humidity,any surface lower in temperature than 5.5” F will cause con-densation to occur. Thus, cold window surfaces can promotecondensation with subsequent water damage and mold growthat window sashes within and on the surface of adjacent walls.This problem is most likely with single-pane windows or ther-mally unbroken window frames in cold climates. Installationof furnaces directly onto concrete floors may also promotemold growth as dew-point condensation occurs during the

TABLE 2

EXTERNAL LEAKAGE

Yearly

l Inspect chimney for cracksor damage

l Inspect all roof flashingsfor integrity and soundness

l Inspect attic spaces from below forsites of leakage,either after

Seasonally

l Inspect all roof gutters forpitch and drainage

l Inspect all leaders for conductingwater away from the building

rainstorms or during snow meltsl Inspect roof surface for missing

or damaged shingles or roofingl Inspect soffits for adequate

seal at roof and wall surfacesl Inspect pitch of all exterior grade

surfaces so that water leads awayfrom the building

l Inspect attics for adequateventilation to outdoors toavoid condensation

l Inspect all glazing and window anddoor frames for adequate sealingand caulking

l Inspect all building walls andabove-grade foundation walls forcracks and spalling if concrete

summer. Leaving a small gap between furnace and floor cansolve this problem. The manufacturer’s installation instruc-tions should be consulted for more information.

Preventive maintenance and inspection checklist. The work-shop participants’ recommendations for homeowners’ check-lists for periodic inspection and repair as required, to preventleakage and sources of condensed moisture within the homeare shown in Tables 2 and 3.

Moisture control in the home. Remediation is generally atwo-step process undertaken once the presence of water hasbeen detected. The first and obvious step is to prevent furtherdamage by correcting structural defects, repairing leaks, cor-recting drainage, and managing internal sources.

The second step involves repairing the damage. Mechani-cal deterioration, spalling, rot, component separation, anddelamination generally require the conventional correctiontechniques of removal, patching, and/or replacement. Hiddensurfaces should be fully exposed to examine moisture entry ordeposition sites for signs of mold or bacterial growth. Thesecontaminants are usually readily identifiable by color, texture,or odor, and, once identified, they need to be removed.

Inspection and maintenance of residential HVAC systems.HVAC systems that are poorly operated or maintained cancause significant indoor air quality problems by not providingproper environmental conditions of temperature or humidity,or by contaminating living areas through malfunction. MostHVAC systems in homes are not designed to clean air byremoving particles-other than very large particles-andgases. A list of tasks designed to prevent operating and main-tenance problems is given in Table 4.

HVAC remediation in the home. This section deals with re-medial procedures to be employed once signs of HVAC mal-function are detected.

Remediation is again effected in two steps. First is the de-termination of a design or installation deficiency, or a mainte-nance problem such as improper heating system flue sizing,

TABLE 3

INTERNAL MOISTURE

Yearly

l Inspect all crawl spaces forsigns of liquid moisture.Examine the insulation andwood framing for mold andmildew discoloration

l Check for proper venting ofall supplementary homeheating and water heatingappliances

l Check all exposed pipes forsigns of present or pastleakage (mineral deposits)

l Inspect, when possible,exposed pipes leadingupward to concealed wallspaces

l Check for proper venting tooutdoors of bathroom fans andclothes dryers

l Examine “Floating Floor”trenches for signs of moldor moisture

l Look for signs of moisture onfloors of attic spaces

l Look for water stains at windowsash, on exposed walls, andceilings

Seasonally

l Check all basement wall and floorsurfaces for signs of leakage or moldgrowth. If there is a strong mold odorthere is a problem, and the source ofthe problem must be eliminated

l Limit home humidifier settings (ifused) to the lowest possible settingduring dry winter conditions

l Utilize dehumidifiers for allbelow-grade surfaces suspectedof containing recurrent moisture

l Check the pitch of air conditioningcondensate lines and drainage at exitpoint of building

American Thoracic Society 541

TABLE 4

PREVENTIVE MAINTENANCE CHECKLIST FOR HOMEOWNERS

Yearly

l If possible, install inspection doorin supply and return ductworkmains for visual duct inspection.Ducts can be checked fromregrsters with a mirror and aflashlight

l Consider installation of carbonmonoxide detector(s) in thehome

l Inspect all supply and returnregisters for correct operation andcleanliness

l Check all heating and hot waterflues for pitch and integrity

l Check all refrigerant lines forproper insulation to prevent watercondensation

Seasonally

l If suspect, have local utilitycheck furnaces, heaters, orappliances for gas leaks orimproper conditions

l Inspect the outside of thehouse during heavy rain toobserve the performance ofgutters and drainage

l Vacuum all heat exchangesurfaces, filters, racks, andblowers at filter changes

l Examine air conditioningdrain pans for pitch, absenceof organic material, andproper condensed water flow

l Inspect and cleanhumidifiers on biweeklybasis during humidificationseason

l Replace heating/coolingfilters at least seasonally

installation, or slope. Common deficiencies also include im-proper pitch of the air conditioning condensate pan with inad-equate drainage and inadequate disposal of collected air con-ditioning condensate (e.g., piping condensate to the spaceunder a basement or crawl space floor slab). Improper filtersize installation permits bypass of dust particles and their rein-troduction into the house. Once a deficiency is identified, thenthe second step-repairing the damage-should take place.

HVAC muintenance issues. Low airflow, odors, and dis-comfort can result from blocked filters or obstructed or closedair ducts. Humidifiers require frequent cleaning during the hu-midification season, and can themselves be significant sourcesof microorganisms. In combustion appliances, fuel-air ratioscan be incorrect, resulting in incomplete combustion, andleading to a release of carbon monoxide or carbon particles. Inolder systems, heat exchange surfaces may deteriorate or be-come punctured, liberating products of combustion into thespace. A preseason service contractor or utility checkup of aheating system should identify many of these defects.

Control of residential renovation processes. To assure thatoccupants will not be adversely affected by renovations gener-ating dust, particulates, or vapors, the space under construc-tion should be physically isolated from the rest of the resi-dence, and air from the isolated space should be exhausted.The supply and return ducts of the heating and air condition-ing system that serve this area should be sealed with 6-mlpolyethylene sheeting and the ducts kept clean during con-struction. If the existing HVAC system will be reconnected tothe renovated or remodeled space, the capacity of the systemmust be adequate to provide the required/desired thermal andair quality control throughout the residence (14, 15).

Other IAQ Problem-Solving IssuesEmission tests. To eventually establish emission guidelines, ar-chitects, purchasing agents, and general consumers will re-quire both accurate emissions testing and an understanding ofthe health effects of emissions. Emissions from a great varietyof materials have been measured using controlled chambertests. American Society for Testing and Materials (ASTM)Standards for chamber testing have been established and

emission rates are usually reported as “steady state” in mass(microgram or milligram) per square meter per hour. Thesestudies have been conducted at national and private facilitiesin North America and Europe. Results depend on the testcondition’s temperature, humidity, and volume flow rate.Emission rates are shown to depend on material preparation,preconditioning, and age. For example, emissions from paintsvary with drying rates, number of layers, and composition.

We know substantially less about the emission rates of ma-terials under conditions of actual use. Only recently has a stan-dardized method for in situ testing of emission become avail-able (16,17). Although “as used” conditions are more relevantfrom the point of view of the occupant, tests of this type willnot provide a readily useful way to discriminate among com-ponents. Standardized laboratory testing, along with modelingand health evaluation, does provide an objective evaluationscheme to compare among products.

Product labeling. Modern building materials and productsmay have complex chemical formulations and release volatileorganic compounds (VOCs). There is a substantial body of lit-erature and genera1 experience that associate elevated mix-tures of VOCs with symptoms (18). Products are often usedon a daily basis in homes and offices, and population expo-sures are ubiquitous. Aging of materials and/or reactions withgases (i.e., ozone) may continue the release of VOCs or alde-hydes. Emission rates and composition vary among specificproducts and sometimes among batch productions.

In the long-term, it may be cost effective to reduce emis-sions from building materials and equipment. Reduction is ac-complished by product/component reformulation and process/production controls. Removal or reduction of these and othersources avoids total reliance on ventilation to achieve a safeindoor air quality. Broader societal gains potentially includeconservation of petroleum chemical stocks, reduction of pho-tochemical compounds, and conserving of energy.

A study of the olfactory properties can also be helpful inunderstanding the sensory emission of building materials (19).Recently, Jensen and coworkers (20) compared the perceived(relative) odor intensities with chemical emission data from 13linoleum products. Multivariate analysis of the data revealedthat two principal factors could explain 68% of the odor inten-sity variation. The factors were aliphatic Ch-Cx acids and Cs,C,, and C,,, unsaturated aldehydes, respectively. The CC/sniff-ing analysis of emissions and the above approach appear to bea powerful combination to identify odorous VOCs.

The Danish indoor climate labeling system. Denmark uses alabeling system that rates VOC emission from building mate-rials according to impact on comfort and health (21). The sys-tem unifies chemical emission testing over time (months) (in-cluding a standard room and mathematical modeling of theemission profile, when necessary), and health evaluation. TheDanish system focuses on comfort and includes odor annoy-ance and mucous membrane irritation, with plans to add othermaterial characteristics (e.g., fiber release). Two design crite-ria were set: the labeling system shall be easily comprehensi-ble, and, at the same time, operational and dynamic. The pa-rameter used for labeling is the time value t(C,,,) required foremissions to decay to a point at which room concentrationswould be below the indoor relevant values, C,i of VOC,, pres-ently based on either odor detection thresholds or mucousmembrane irritation thresholds. The time value, t(C,), is ameasure of the duration during which new building materialmay increase exposure, as well as the probability of indoor airquality problems. Odor thresholds are used because they gen-erally are at least one order of magnitude lower than mucousmembrane irritation thresholds. The system may also be used


for single VOCs when a specific health end point has been re-ported. In addition, the system has a built-in safety procedurefor sensory testing over time, thus providing sensory emissionprofiles (intensity and acceptability) by the use of a specialchamber and a panel of judges (22). The evaluation should beperformed at approximately the same time as the chemicallydetermined time value. Several building products have nowbeen labeled by this process.

The Canadian experience. To help builders, architects, andsensitive persons who are intending to build and renovate, theCanada Mortgage and Housing Corporation has compiled areference guide on building materials (23). Product listings forresidential construction materials were gathered that containinformation on health effects from two sources: existing orpublished health information and experiential informationbased on the experiences of perceived environmentally hyper-sensitive persons on exposure to these materials.

It should be noted that incentives to protect the environ-ment such as recycling materials may not be compatible withefforts to improve indoor air quality. The incorporation of re-cycled materials can introduce new pollutants into the indoorenvironment, e.g., recycling rubber tires. Although the landfillburden is reduced, using them in such products as carpet un-derpads results in an increase of emissions from rubber insidebuildings. The applications of recycled materials must be care-fully selected. Recycled cellulose-primarily newsprint-isused in chemically treated slurry for insulation in residentialconstruction. In hot and humid climates, this can provide a mi-crobial growth site, as the composite is closed in with gypsumprior to complete dryout. There is also potential outgassingfrom the chemical fire retardants used in the slurry to meetfire code restrictions

Strategies to encourage product labeling. For labeling to beuseful to decision-makers, including consumers, architects, in-terior designers, engineers, and building owners, it must berelevant to design-condition parameters and also must identifythe classes of contaminants of concern. For target products toreduce VOCs, labeling should probably be kept to a very sim-ple pass/fail standard. Behind this label, additional standard-ized, independently tested information should be availableto those charged with special construction of low-emissionsbuildings for sensitive populations or for specific climate con-ditions. Information on the VOC emission rate should show asimple quantitative analysis tool that relates square feet of in-stallation to cubic loads. Any quantitative standard relating tothe performance calculation method should recognize the in-herent difficulties in assessing total surface areas of all materi-als specified for buildings and the relatively limited practicalapplication of this method for most types of construction. Ifthe quantitative analysis standard is simplified, it is morelikely to be used in ventilation load calculation.

Supply-type strategies for reducing VOC emissions frombuilding materials can complement demand-type strategiessuch as product labcling. One approach is to provide an incen-tive to reformulate or modify products by, for example, revis-ing the current system for reporting and regulating emissionsat the point of manufacture so that downstream emissions arealso considered, thereby regulating total emissions instead.Under this approach, manufacturers who could demonstratereduced emissions at the point of end-use could take credit foremissions reductions in their Toxic Release Inventory filingsand pollution prevention strategies. This could shift the emis-sions from locations where effective ventilation is problematicto locations where exhaust systems designed to eliminate largeamounts of emissions are present, and reduce the overall bur-den of dealing with released chemicals while effecting greater

reductions of population exposures. A variation of this ap-proach would be to foster development of voluntary industrystandards for VOC release on a product-by-product basis. Al-though this approach has some appeal and follows the currentcooperative trends, results to date have been mixed. Substan-tial improvements in woodstove performance have been made.However, labeling for carpets lack specificity and sensitivityand consequently has limited usefulness for architects andconsumers.

RecommendationsThe problems in indoor air quality resulting from the commonpractices of building design, construction, commissioning, andmaintenance/operation are not likely to improve withoutinvolvement of other stakeholders. A potentially importantplayer in the solution of indoor air quality problems is the in-surance industry. Not only is the insurance industry a majorholder of commercial building investment property but itsbusiness encompasses workers’ compensation and tort liabilitycoverages. To date, workers’ compensation claims for building-related illness are limited by physicians’ inability to identifybuilding-related etiologies for asthma and hypersensitivitypneumonitis in individual patients; lack of familiarity of infec-tious disease physicians of the workers’ compensation cover-age for Legionella pneumonia among employees; and infre-quent claims of financially significant, permanent impairmentfor sick-building syndrome. Nevertheless, the financial incen-tives for insurance companies may increase as a function ofpublic and medical professional recognition and the shift fromworkers’ compensation to third party liability claims againstmanufacturers, building owners, and ventilation contractors.

In a climate of litigation, another opportunity for interven-tion/prevention regarding indoor air quality is during lease ne-gotiation, which could include specifying building performancefor indoor air quality. In the short run, marketing of indoor airquality performance may provide a competitive advantage forbuilding owners and a health/productivity advantage for ten-ants/buyers seeking commercial or residential property. Incommercial property transfers, financial interests could in-clude indoor air quality inspections both for system design andpostdesign performance. Such inspection is routine for termiteinfestation in some parts of the country, for asbestos in someolder commercial properties, and for radon in residentialproperty in some locations. Thus, extension of due diligencewith respect to broader indoor air quality concerns is perhapsfeasible in order to increase incentives to address indoor airquality by building owners.

Several professional organizations show substantial activityregarding indoor air quality because of membership involve-ment in problem-solving or prevention. The leading group inimpact is ASHRAE, as its standards become the basis ofbuilding codes in many localities. However, the process bywhich standards evolve is driven by consensus among variousinterested parties, and public health is not necessarily the driv-ing principal. Other professional groups with substantial edu-cational or standard setting activities include the BuildingOwners and Managers Association (BOMA), InternationalFacility Management Association (IFMA), American Instituteof Architects (AIA), American Industrial Hygiene Associa-tion (AIHA), and the American Conference of GovernmentalIndustrial Hygienists (ACGIH). The ACGIH BioaerosolsCommittee does not believe that quantitative standards withrespect to bioaerosols are feasible given current measurementmethods for most bioaerosols and the dearth of exposure-response relationship information.

Several trade associations may develop or have developed

American Thoracic Society s43

.

an interest in indoor air quality because such concerns are crit-ical to their business and protection from liability. These in-clude the North American Insulation Manufacturers Associa-tion, the Air-Conditioning and Refrigeration Institute, theNorth American Duct Cleaners Association, the National AirFiltration Association, the National Association of HomeBuilders, and the Association of Home Appliance Manufac-turers. These trade associations should have a substantial in-terest in needed research on etiologies of indoor air qualitycomplaints, along with their resolution, and prevention. Cer-tainly, individual companies have occasionally taken aggres-sive roles in IAQ investigation teams because of attribution ofIAQ problems to their products.

Employee representatives have taken a role in motivatingattention to indoor air quality for specific groups of employ-ees. Examples include service, teacher, and government em-ployee unions. With the absence of accountability for indoorair quality, the role of an educated public in motivating changeis important. Approaches are needed for informing the public,possibly beginning with school curricula.

Finally, government at federal, state, and local levels is animportant stakeholder regarding indoor air quality. Govern-ment buildings account for a significant number of officebuildings in the United States, and government workers areamong the major groups affected by poor indoor air quality.Aside from productivity concerns in an era of governmentdownsizing, the government has substantial agency commit-ment pertinent to indoor air quality regulation, investigation,and research. The obvious federal agencies include the Gen-eral Services Administration (GSA), the Occupational Safetyand Health Administration (OSHA), the National Institutefor Safety and Health (NIOSH), the Centers for Disease Con-trol and Prevention (CDC), the Department of Defense(DOD), the Department of Housing and Urban Development(HUD) and the Department of Energy (DOE). State and lo-cal governments also have the burden of governmental em-ployee complaints and the responsibility for public health in-vestigation of complaints from nongovernmental workers,including the substantial source of problems in schools. Thereis perhaps room for an educational partnership between gov-ernment agencies and trade associations that can lead to fa-vorable changes for indoor air quality. In this regard, NIOSHand CDC-with respect to communicable disease in hospitals,schools, and other community facilities-may be able to takeleading roles as nonregulatory agencies.

SOURCE CONTROL

Source control is essential to achieving healthy indoor airquality. The methods used for source control vary accordingto the pollutants and range from complex and costly solutions(e.g., earth removal in the case of severe radium contamina-tion) to relatively simple remedies (e.g., not smoking in thehome). This section includes recommendations for the generalpopulation and some recommendations for special popula-tions. APPENDIX A provides a list of recommendations for re-ducing the number of particles in the indoor environment tominimize the negative health effects of indoor air pollution.As possible, statements in this section are referenced to the lit-erature, but some recommendations are based on professionaljudgment, absent published data. The pollutant sources ad-dressed include moisture, building materials and products thatemit VOCs, pesticides, household products, and other pointsources and particulates. Specific sources well-covered else-where in the literature and in the previous workshop such asenvironmental tobacco smoke, radon, asbestos and lead paint,

did not receive extensive consideration by this working group(24,25). For radon, asbestos, and lead paint, the Environmen-tal Protection Agency offers guidance (26-29).

Moisture

Moisture underlies some of the most common indoor air qual-ity problems. For example, high relative humidity allowshouse dust mite infestation to occur, and water damage andwater reservoirs facilitate proliferation of microbes. Water in-cursion can also lead to structural degradation of building andventilation system components, which can result in further in-door air quality problems.

Associations between moisture problems and health effects.Moisture-related health problems are diverse, including aller-gic diseases, infection, and complaints of musty odors. The al-lergic diseases affected by moisture include allergic rhinitisand asthma, with house dust mites and building-associatedfungi as possible moisture-related triggers for those diseases.Hypersensitivity pneumonitis, a less commonly recognized im-munologic lung disease, has occurred in endemic form inbuildings with contaminated spray water humidification, wa-ter-damaged materials, and visible bacterial or mold growth.Apart from physician diagnoses of asthma and hypersensitiv-ity pneumonitis, epidemiologic studies document that indica-tors of residential dampness are associated with respiratorysymptoms in children (30).

Contaminated reservoirs from which water is entrainedinto indoor air can produce bacterial infection, with Legionellapneumonia as the prototype. Legionellosis has been attributedto diverse sources, including cooling towers, hot water heaters,shower heads, and whirlpools. Pontiac fever, a febrile syn-drome, is also associated with exposure to aerosolized Le-gionella bacteria. Immunocompromised persons are at risk forfungal infection from saprophytic fungi in indoor air (31).

Sources of moisture. The primary source of moisture-related problems is usually in the building envelope-in thewalls, roof, and foundation of the structure. A major area ofconcern is the failure of the water-proof roof membrane. Leakstypically occur at the junction of the roof and the wall parapet.Any opening in the exterior envelope (e.g., vents. flashings,skylights, doors, windows) is a potential site for the entry ofmoisture. As mentioned previously, balconies and overhangsare also well-documented areas of moisture entry. Deteriora-tion and ultimate failure of scaling materials such as grout,caulking, and other sealants can lead to moisture entry. Thelocation and the installation of the vapor barrier in the build-ing envelope are critical in preventing future moisture dam-age, particularly moisture condensation in the walls. Sub-grade leakage from rain, irrigation, and ground water allspeak to the need for careful design and construction of base-ment walls and foundation drainage.

In addition to moisture introduced from outside the build-ing, there are also numerous indoor sources of moisture, in-cluding unvented combustion equipment, as well as activitiessuch as showering and cooking. Good design should provideventilation for areas where indoor moisture levels can be high.People, pets, and plants are sources of indoor moisture, as areindoor pools, spas, and fountains.

HVAC equipment is a frequent source of moisture prob-lems because of inadequate disposal of condensate from con-densation on pipes and ducts and from cooling coil condensatedrainage and carry-over. Standing water in humidifiers, evap-orative coolers, cooling towers, condensers, and air washers maybecome a source of contamination. Water damage, whethercaused by flooding from broken pipes or natural flooding, mayalso lead to moisture damage of materials.


Moisture mitigution strategies. Drying affected areas andmaterials is a first step in tackling moisture-damaged areas.Identifying the sources of recurrent moisture can help deter-mine strategies for remediation, whereas repairing the dam-aged area may not address the underlying reasons for themoisture. In the case of moisture damage, all water-damagedporous materials such as carpets, insulation, acoustic materi-als, and ceiling tiles, should be removed and replaced.

lnadeyuate dehumidification capacity of HVAC systemsmay lead to moisture problems as well. HVAC equipmentshould be designed and installed so that reservoirs of stagnantwater can drain as intended; for example, drain pans and sumppumps should be sloped to drain. A critical design require-ment is that all systems have easy accessibility to allow forroutine inspection and maintenance; individual interior com-ponents of systems must be easily accessible as well.

Building MaterialsBuilding materials that are potential sources of indoor pollut-ants include particleboard, adhesives, glues, sealants, wall cov-erings, paints, stains and varnishes, cabinets, tile grout, plas-ters and cements, furniture, draperies, carpeting, and plasticlaminates. The principal pollutants from these materials arevolatile organic compounds (VOCs) and semivolatile organiccompounds (SVOCs). Emissions from building materials aretypically maximal at the time of installation and retrofitting,and outgassing decays over a period of weeks or months.Thus, building materials are more likely to be sources of prob-lems during initial occupancy.

Associations of exposure to VOCs with health effects. VOCsare ubiquitous in indoor air, although they are also found out-doors. They can be characterized by their indoor/outdoor con-centration ratios. For typical indoor-related VOCs, the ratio islarger than I. Concentrations of indoor VOCs may be charac-terized by substantial variation both in time and in space, de-pending on the source dynamics and the building attributes.Indoor concentrations are typically below Threshold LimitValues (TLV) levels and airway irritation thresholds, but of-ten above odor thresholds.

Links between VOC concentrations and complaints aboutindoor air quality and symptoms have been postulated. How-ever, the etiology of complaints and symptoms is likely com-plex and multifactorial, and characterizing the contributionsof VOCs may bc difficult. Effects of VOCs might follow di-rectly from inhalation of gases, but VOCs may also have ef-fects by binding to particles. Particles, in particular, floor dust,can act as carriers of VOCs and SVOCs. Exposures to VOCsand SVOCs might thus occur through deposition of particleson the skin, as well as by inhaling the compounds themselves.

Mechanistic hypotheses have been advanced that ascribe arole to VOCs in causing symptoms in building occupants.Thus, responses have been proposed as consequent to: (I) to-tal exposure to VOCs-additivity of individual VOCs is pro-posed so that a mixture might have adverse consequenceseven though individual VOCs are present at concentrationswell below TLV values; (2) specific irritants, e.g., formalde-hyde or acrolein. underlie the effect; (3) VOCs in combinationwith other pollutants (particles) or other elements of the workenvironment combine to produce adverse effects; (4) physico-chemical propertics of the VOCs such as acidity, basicity, oreffects on surface tension of the eyes tear film are responsible;(5) odors trigger symptoms; (6) reactive species formed bychemical reactions in indoor air are responsible.

Furthermore, in most indoor environments, pollutantsother than VOCs are present, such as ozone, nitrogen oxides,

and particles with VOCs adsorbed on their surfaces. In addi-tion, other factors affecting responses to air pollutants such asthermal climate and psychosocial dynamics of the workplaceshould be considered in a holistic manner (18).

The VOCs emitted from building materials may originatefrom different types of pollutant sources. Primary pollutantsources emit free (nonbound) VOCs. The primary VOC pol-lutants are generally of low molecular weight. Chemically orphysically bound VOCs may also be relevant to health. Hy-drolytic decomposition may also result in release of VOCs, asmay oxidative degradation and reemission of adsorbed VOCs.

Specific Building MaterialsCarpets. The benefits of carpets include acoustic control, softsurface, protection against trauma, thermal insulation, dura-bility, attractiveness, and resilience. However, carpets can bereservoirs for allergens and growth environments for housedust mites and molds. To date, these concerns about carpetshave related to their uses in homes, offices, and schools, andparticularly to their being sources of biologic particulate anti-gens. Carpet underlays may also be VOC emitters, and the ad-hesives used for commercial installations to subsurface have apotential to release VOCs. There is also concern that carpetcleaning can be a source for indoor pollutants, as can fumiga-tion of carpets.

The issues below relate primarily to special populations(32).

1.

2.

3.

4.

Reservoir for allergens. House dust mites are unavoidablein climates of high and moderate humidity. The carpet isnot the primary means of exposure but provides a reservoirfor infestation of bedding in homes and for the generationof airborne particulates with vacuuming and human activ-ity. For animal dander from household pets, carpeting isthe major reservoir from which particulate antigen can begenerated by human activity. Approximately 30% ofAmerican homes have one or more cats and 40% have oneor more dogs, with more than 60% having one or bothtypes of animal (33).Growth environment for house dust mites and molds. Dirtaccumulates over time, rendering the carpet a favorablemedium for the growth of molds. Carpets in basements,bathrooms, and other areas prone to moisture are likelysources of molds. Carpets laid on concrete slab-on-gradeare also subject to trapping of moisture below the carpet,which is a potential source of microbial contamination.Cleaning and fumigation. Carpet steam injection cleaning isless likely to leave large amounts of residual moisture thancarpet shampooing, but it may leave carpets damp, contrib-uting to mite and mold growth. Both methods may leaveresidual chemicals, so products should be carefully se-lected. Waterless processes are chemically based, and moreinformation on the potential health effects of these prod-ucts is needed. Vacuuming can contribute to the load of re-spirable particles in the air. This loading can be avoided byusing equipment that is directly exhausted outside (i.e.,central vacuum systems), with a HEPA filter or a doubleelectrostatic bag.Chemical emissions. Numerous VOCs, including 4-PC(4.phenyl cyclohexene), toluene, and styrene, have beenidentified as released from carpets. These emissions origi-nate from the latex backing and the numerous chemicaltreatments applied to the carpet fibers such as those for soiland stain repellency, antistatic, and pest resistance. Chemi-cal emissions are higher when the carpet is newly installed,


and then diminish with time: it may be prudent, therefore,to increase ventilation at the time of installation. As car-pets age, the reservoir effects in No. 1 above predominate.

5. Odors. Carpets act as efficient sinks for odors generatedfrom human activities such as cigarette smoking and cook-ing. Solvent emissions from painting and other mainte-nance activities can be adsorbed by the carpet fibers andreemitted.

6. Carpet underpads and adhesives. Carpet underpad materi-als also contribute VOCs. The underpad also serves as areservoir for dirt from the top or moisture from belowwhen laid on concrete. Underpads deteriorate in time,turning brittle and becoming sources of particulates. Theunderpad selected should be stable and have minimal emis-sions. Commercial installations typically use adhesives.Mechanical installations using tacks or fasteners on softsubfloor surfaces or Velcro-type tapes on concrete or hardsurfaces are preferable. Water-based adhesives have feweremissions than solvent-based adhesives.

Wall vinyls. These materials are VOC emitters, as may bethe adhesives used to mount them. If a durable wall surface isneeded and a latex-based paint is not acceptable, a water-based commercial grade coating should be used instead of vinylwall covering.

Paints, stains, and varnishes. Interior water-based paintscan substitute for oil-based paints as their VOC emissionstend to be lower, although emission decay may be muchslower. In cases where water-based paints are not appropriate,special durable, washable paints have been developed for themarket. There are numerous labeling and manufacturer’s in-formation sheets available for guiding the consumer. In someinstances, odorless stains and varnishes are available. Storedpaints in enclosed spaces such as garages may affect indoor airquality and should be recycled rather than stored or disposedof improperly.

Drywall. Drywall is a fairly inert substrate and an accept-able finish material from the IAQ perspective. Installationand finishing generates particles. When drywall is being tapedand sanded in occupied buildings, all ventilation ducts shouldbe sealed, as should openings to occupied areas.

Ceiling tiles. Suspended ceiling tile systems may form theunderside of the return airflow in an institutional or commer-cial building. The top surface of the ceiling tile is typically cov-ered with one coating of sealant to offset the potential for fineparticulate dusting. Sample tiles should be examined carefullyto assure that the sealant coat is effective. Where the returnair plenum has an exposed steel structure sprayed with fire re-tardant materials, care should be taken to ensure that thespray-on material has enough cementitious content to main-tain proper binding and prevent contamination of the returnair plenum. Fully ducted return air systems using sheet metalducts are preferable to using ceiling cavities as the air plenum.

Cabinets and other uses o,f particleboard. Cabinets made ofparticleboard or medium-density fiber board (MDF) manu-factured from urea-formaldehyde resin can be sources offormaldehyde and other organic compounds. Emissions are ofless concern if solid hardwood is used, but higher costs are in-volved. If particleboard or MDF are used, all surfaces andedges should be laminated to encapsulate the emissions. Al-ternatively, several coatings of a low-odor acrylic sealant canbe used. Composite wood in substrate applications such asflooring system reinforcement is a potential source of formal-dehyde and other VOCs; carpet over pressed wood subfloorwill still allow the emissions to pass through. Other subfloorssuch as construction-grade plywood, manufactured with phe-

nol-formaldehyde resin, have lower formaldehyde emissionsthan does particleboard or MDF, and should be selected.

Adhesives, glues, and sealants. These can be sources of ali-phatic hydrocarbons, aromatic hydrocarbons, chlorinated hy-drocarbons, ketones, and esters. Exposures should be mini-mized by vacating the premises and increasing ventilationduring and after application. Use of these products may be re-duced by mechanical connections and cementitious groutcompounds. Alternatively, low emissions products are avail-able and consumers should use manufacturers’ product infor-mation in making their selections.

Plastic laminates. Plastic laminates are typically used in thefinishing of counter tops, cabinetry, elevator cab interiors,door surfaces, and washroom partitions. Laminates are un-likely sources of emissions; they can, as stated previously, sealthe emissions from the substrate (usually particleboard orMDF). Emissions, however, will escape from unlaminated sur-faces-the undersides, backs, edges, and holes for adjustableshelving. All surfaces should be laminated or sealed, or alter-nates for application should be considered. Solid wood prod-ucts could be used for cabinetry and doors, whereas metal par-titions are recommended for washrooms, mirrored glass andfabric installations for elevators, and ceramic tile, stainlesssteel, or natural stone for counter tops.

Furniture. Furniture made of composite wood can be asource of formaldehyde and other emissions. Upholstered fur-niture can also be a source of formaldehyde emissions. Theemissions can come from the fabric covering, chemical finishon the fabric, the foam upholstery, or composite wood base. Itcan also support mite growth and be a reservoir for mite andanimal dander allergens. For persons prone to or having aller-gic diseases or asthma, it may be prudent to consider limitingthe amount of upholstered furniture in their home.

Pesticides Used In or Around the Home

All pesticides-whether herbicides, insecticides, or fungicides,depending on their target-are intended to control pests. Theactive ingredients are semivolatile, whereas inert ingredientsand carrier solvents may have varying volatility and content.The inert ingredients may themselves be as or more toxic thanthe active ingredients. Of the many pesticides that are in usetoday, we know the acute and chronic health effects of only asmall fraction.

Herbicides applied on lawns and termidicides appliedaround foundations can enter the house in soil gas, in the samemanner that radon enters the house. These chemicals there-fore potentially can contaminate indoor air of homes. The ter-midicides used have been the persistent organochlorine insec-ticides such as chlordane, and contamination of some houseshas been demonstrated (34). Direct application indoors ex-poses the occupants to the volatile ingredients and residues.Exposure may occur through inhalation of particles on whichthese semivolatiles are adsorbed.

Homeowners may want to explore methods of controllingpests without the use of pesticides. Some pests, notably silver-fish and carpenter ants, are bioindicators of moisture in thehouse. The first line of control of these insects is to controlmoisture. Cockroaches can be baited or trapped, and, whencombined with meticulous sealing of entry points, disruptionof food supply and cleaning offer effective control. Sticky ormechanical traps can help to control other common pests. Fortermite control, a successful method not employing largeamounts of pesticides is to prepare baits containing a gram ofa chitin inhibitor; this can control colonies of termites occupy-ing several hectares (35). Fewer chemicals are used, and they


are targeted to the pests with less potential harm to the envi-ronment and the occupants.

Household Products, Office Products, and Other Point Sources

Among the many different products used inside homes, offices,and other nonindustrial buildings, those that may introducecontaminants into indoor air include cleaning agents, polishes,paints, deodorizers, and even pens and marking pens. Otherpotential sources are personal care products, moth balls (pes-ticides), and adhesives. These sources are ubiquitous and arefrequently used in large quantity. A 1986 Danish databasestudy shows that more than 60,000 tons (12 kg/person) peryear of cleaning and maintenance products for hard floor cov-ering and furniture alone were used from more than 700 dif-ferent products in Denmark. Some of these products are usedon a regular and long-term basis and others only episodically.Many household and office products have a large number ofchemical constituents, including VOCs, SVOCs, surfactants,and polymers. Some products have perfumes added, either tomask other odors or to indicate their use. Some of these per-fume constituents such as limonene are themselves VOCs.Laboratory testing has shown that substantial concentrationsof VOCs can result from cleaning agents during their use.However, there are only sparse data on the contribution ofthese products to typical ambient levels of VOCs and otherchemicals in homes and offices.

Despite the lack of data establishing that these productscause particular health symptoms, minimizing exposures topotentially harmful constituents is recommended. This may beachieved by substitution of different products or product se-lection by the consumer, elimination of perfumes from prod-ucts, and the provision of information on appropriate use con-ditions. The voluntary product labeling used in Denmark anddiscussed in the previous section is an example of this last ap-proach; it is intended to (I) improve indoor air quality inbuildings, (2) provide a tool to stimulate the development ofproducts believed to be more friendly in the indoor environ-ment, and (3) provide manufacturers and users with compre-hensible information about the products they manufactureand buy.

Other Point Sources in Homes and OfficesMaterials used in crafts and hobbies can be significant sourcesof indoor air pollution, including solvents in glues and paints,adhesive components (acrylates), heavy metals (lead in solderand stained glass), isocyanates (polyurethane varnishes), andwood dusts and methylene chloride (furniture refinishing ma-terials). Product labeling usually provides information on haz-ardous contents and appropriate precautions. In the home,exposures from crafts can be reduced by using materials inwell-ventilated spaces. For dusts generated from hobbies,housekeeping practices are critical. Exhaust ventilation to theoutdoors should be considered for using pottery kilns in thehome, since glazes can contain toxins such as lead and sensitiz-ing metals.

Equipment used in homes and offices includes copiers,printers, facsimile machines, blueprint machines, binding ma-chines, cables, and VDTs. Such equipment may emit VOCs,including formaldehyde and particles, ozone, and NO,. Emis-sions may depend on activity and can have concentrations thattypically decline with distance from the machine. Some of thisequipment is directly vented to the outdoors, but often it isnot. Ozone and NOx, can react with other substances in theair, producing reactive species such as aldehydes. Processedpaper itself emits both particles and VOCs, as do carbon pa-

per and carbonless copy paper. Emissions from these sourcesmay be minimized by direct venting, segregation of equipmentto isolate it from workers, and selection of lower-emittingproducts.

Control of pollution sources is incomplete if the odors fromthe occupants are not minimized. Perfumes are among themost difficult to control since they are perceived by their usersas pleasurable. Personal rights and preferences for perfumedproducts must be evaluated against the discomfort that scentscause for some people. The odoriferous materials are highlyvolatile synthetic chemicals; in effect, they contribute to thetotal VOCs. Scented personal products are not limited to per-fumes; they include residual scents on clothing from deter-gents and fabric softeners, soaps, shampoos, deodorants, skinlotions, and cosmetics. The only successful method of controlis to eliminate these odors, either by avoiding their use, aswith perfumes, or by using unscented products.

Design for Source Control

Several issues should be addressed in the design and retrofit ofbuildings to ensure good indoor air quality. Some of the dis-cussion below was introduced previously; strategies are rec-ommended here as initial methods of controlling sources of in-door air pollution.

Site characteristics. For all building types site characteristicsshould include a clean, well-drained soil. Soils should be ex-amined for contaminants and, if present, cleaned or replacedprior to construction. Soils that are damp or subject to lique-faction should be drained, and surfaces under slab areasshould have a gravel or well-draining sand sub-base.

Climate. A major consideration in the control of indoor airquality is climate. Buildings in regions with high relative hu-midity are subject to mold and mildew in envelope assemblies.The dew point in the wall should be reached on the cool sideof the vapor barrier in a material or air space not subject tomoisture degradation. Rainy climates require special attentionto detailing at joints, connections, and roof parapet mem-branes so that they are continuous. Hot, dry climates with highair conditioning requirements should receive careful attentionto potential moisture in drip pans caused by condensation. Ina number of states, there are known areas of elevated soil ra-don levels. In such areas, basements and crawl spaces shouldhave radon control systems installed or at least “roughed in”to facilitate mitigation in the event that high levels of radonare found in the building.

Building age. The age of the building may affect the type ofproblems encountered. Some new buildings have IAQ prob-lems associated with emissions from the materials. Occasion-ally, microbial contamination may be a problem in a newbuilding because of building envelope failure. In older build-ings, asbestos may be present in building materials and venti-lation systems may be inadequate or performance may havebeen compromised by changes in occupancy patterns. Newconstruction in old buildings should be undertaken with careto ensure that airflow patterns will be either maintained or im-proved, local point sources of contamination are identified,and construction waste and dust are controlled.

Building construction. This may be a source of residualcontaminants that continues to cause problems for the ventila-tion system during use. Construction sequencing should en-sure that materials having high emissions are installed underwell-ventilated conditions to limit absorption by adjacent softmaterials. Dusty installations should not contaminate ventila-tion systems or lead to the collection of dust in plenum areas.

Building maintenance. Building maintenance should be di-


rected at the products, materials, and systems specific to thebuilding. Performance may suffer from poor operations andmaintenance procedures that have a significant effect on ven-tilation rates, control of mold and mildews, and control of par-ticulates, with a subsequent effect on IAQ.

Outdoor air quality. Outdoor air quality may have a signifi-cant effect on indoor air quality. ASHRAE Standard 62 (8)references consideration of outdoor air quality to standards ofthe Environmental Protection Agency. Cleaning of outdoor airmay be needed for nonresidential buildings in polluted areas.

Building envelope integrity. This is a significant control fac-tor in the maintenance of IAQ. The envelope should ade-quately control and restrict the airflow into the building. Theenvelope should also control moisture infiltration by a contin-uous vapor barrier on the warm side of the insulation system.The envelope integrity should include the roof, walls, andfloor or slab system. The building should be operated at aslight positive pressure, if possible.

VENTILATION

Ventilation has been a long-standing cornerstone of the engi-neering approach to managing indoor air quality. When con-sidered within the context set by the mass-balance formula-tion, pollutant concentrations depend on the strengths of thesources and the sinks within the building, the rate of removalof pollutants from the air, and the rate of dilution. Ventilationair affects dilution.

Standard 62 of the American Society of Heating, Refriger-ating, and Air Conditioning Engineers (ASHRAE) (8) definesventilation air as “air delivered to a space to dilute airbornecontaminants; the use of outdoor (makeup) air and appropri-ately cleaned recirculated air.” (36) Whereas source controlshould be the first step in controlling indoor air pollution,sources can never be fully eliminated, and dilution by ventila-tion is an inescapably needed approach to managing indoor airpollution. By generally affecting concentrations of indoor air,ventilation inherently offers a solution to the multiplicity ofpollutant sources and contaminants within a building.

Recommendations have been made for more than 100years on the amount of ventilation needed for indoor environ-ments (37). The basis for these recommendations has variedover time (Figure 2). The initial concerns that drove thechoice of numbers related to control of infection-subse-quently, the work of Yaglou and coworkers (38)-shifted thebasis to maintaining odors from occupants at an acceptablelevel. More recently, the general rationale for selection ofoverall ventilation rates has shifted to assurance of health. Thepublic expects that indoor environments should be healthfuland assumes that residential and nonresidential buildings in-herently pose no threat to health. There is now an attempt onthe part of ASHRAE to provide ventilation standards that doprovide healthy indoor air quality. Thus, Standard 62 ofASHRAE includes both comfort and health within its scopeand purpose (8). However, other concepls of ventilation maybe held by other professional groups and the general public asthey respond to indoor environments. Notions of thermalcomfort as well as access to direct entry of outside air throughwindows may also be included within the public’s criteria forjudging the acceptability of indoor air.

Control of InfectionControl of airborne infections, especially tuberculosis, washistorically important in the setting of ventilation standards.Recently, because of outbreaks of tuberculosis in institutionalsettings, CDC/NIOSH issued official recommendations for

ventilation rates in high-risk areas well above rates recom-mended for comfort (39). Because source control through caseidentification and treatment will never be fully effective inhealth-care institutions, exposures to the mycobacterium thatcauses tuberculosis will continue to occur in isolation roomshousing known or suspected cases, but, perhaps more impor-tantly, from unsuspected cases housed throughout healthcarefacilities. General levels of ventilation have limited value forreducing transmission of tuberculosis. High-risk exposure ar-eas vary among institutions, but they include hospital isolationrooms, rooms where high-risk procedures such as bronchos-copy are performed, and common areas such as emergencywards and clinic waiting areas where persons with undiagnosedand contagious infections may expose others.

The economic consequences of controls for transmission oftuberculosis in health care facilities are substantial. The poten-tial caseload varies by geographic location and type of facility.Institutions have reported the need to isolate as few as sevenand as many as 93 suspected cases for every true case of tuber-culosis; thus, a 200-bed hospital can be estimated to require asmany as 75 isolation rooms, each providing six to 12 room-airchanges per hour, exhausted directly to outside, and imposinga substantial energy penalty. For waiting areas and other largecommon places, high levels of ventilation may not be techni-cally achievable in existing structures. Because we lack experi-mental or epidemiologic studies demonstrating that any par-ticular ventilation rate provides effective protection againstinfectious diseases, mathematical modeling has been used toestimate the protection of various ventilation rates relative toexposures of varying intensity and duration (40). Models oftransmission using data from epidemiologic investigations oftuberculosis outbreaks suggest that the protection reached bypractically achievable ventilation rates is likely to be incom-plete. It is necessary to supplement ventilation by other meansof air disinfection such as filtration and upper room germicidalirradiation. A reasonable approach to environmental controlof airborne infection would be maintaining a baseline level ofventilation and supplementing with additional disinfection ofair throughout high-risk facilities.

For other infectious agents, there are limited epidemiologicdata associating lower ventilation rates with higher prevalenceof symptoms and illnesses in occupants of buildings (41). Onestudy suggested higher rates of transmission of infectious pul-monary disease in more tightly constructed military barracks(42). Another recent study of pneumococcal infection showedincreased transmission in jail areas with the lowest ventilationrates (43). It is thus plausible that lower ventilation rates in of-fices, schools, and other indoor environments may allow in-creased transmission of common infectious respiratory dis-eases such as influenza or colds.

Odor Control and Comfort

Historically, ventilation rate guidelines have been based oncontrol of odors and comfort, and these remain the primarybases for the current guidelines. Prior to the era when com-plex effluents such as the odors from human bodies could beanalyzed into their chemical constituents, the nose served asthe best available detector. The presence of a notable amountof odor served as the criterion for insufficient ventilation.Now, although complex effluents can be analyzed chemically,the relationship between integrated odor as perceived by aperson and the isolation and quantification of the odor-rele-vant ingredients in such effluents has proved a formidablechallenge, as yet unmet. Over the decades, however, concernwith odor as merely a source of discomfort has been replacedwith concern for odor as a potential indicator of an unhealthy


environment. Although ASHRAE has not explicitly justifiedits ventilation recommendations on the basis of odor control,those recommendations have resembled the requirements forcontrol of occupancy odor derived from chamber studies inwhich judges rated the odor of persons who occupied a cham-ber. The data on control of occupancy odor and expert judg-ment together have been the foundation for ASHRAE’s rec-ommendations. The recommended rates also consider specificlocations, offering higher values for such locations. ASHRAErecommendations reflect consensus of committees composedof HVAC engineers and other professionals, including healthprofessionals.

In the past, when entry of outdoor air came principally fromopening windows, one could argue that ventilation and ther-mal control (generally cooling) were almost inseparable andthe relative contributions of the perception of freshness fromdilution of indoor contaminants and of achieving comfortabletemperature could not be identified. Chemosensory and ther-mosensory sensations interact, and cool spaces seem to engen-der fewer complaints than do warm spaces. While in a spacethat is too warm, a person may be more responsive to othernoxious sensory input such as, for example, from an air pollut-ant. Thus, both thermal and atmospheric environments mayaffect ventilation requirements. In the modern era, buildingsoften provide comfortable thermal environments with or with-out the delivery of a given amount of outside air. However,occupants may be unable to specify whether lack of comforthas thermal or sensory origins.

The interaction between chemosensory and thermosensorystimuli may hold as strongly for irritation and warmth-cold asfor odor and warmth-cold. Dryness-wetness should also be con-sidered. In a warm environment, people may report dry eyes.Whether the feeling of dryness arises from actual loss of eyemoisture, from sorption of chemicals onto the eyes, fromwarmth, or from dryness may not be known to the affected per-son, who may misattribute the source. The complexity of com-fort responses to various dimensions of the environment shouldbe considcrcd in building operations and problem diagnosis.

Standards for comfort, regardless of how the dimensions ofcomfort are defined, should promote one or more of threegoals: (I) “transparency” of the environment, so that the occu-pant takes no notice of warmth or cold, of the presence of anyodors, of the occurrence of intrusive noise, and of other char-acteristics of the environment; (2) facilitation of human func-tioning, c.g., reading efficiently with unirritated eyes; (3) anacceptable trade-off between subjective costs and benefits; forexample, the noise from a window fan-coil unit should seeman acceptable penalty for desired functioning along anotherdimension such as clearance of contaminants or control oftemperature.

The health impact of the recommendations of ASHRAEStandard 62 has not been formally tracked, although energyimpacts have been reported. However, experience over recentdecades indicates that complaints about odor and sensorycomfort are reasonably controlled with the current standard,absent strong and objectionable sources. Field experience in-dicates that ventilation at the specified rates also limits thetransmission of airborne infection indoors. Of course, there issubstantial variation in expectations and in willingness to payfor achieving acceptable indoor air quality, and expectationsmay change over time. In an environment with clean air, theintroduction of even a level of minor contamination may proveless acceptable than in an environment with less clean air.

Health AssuranceThere has been little awareness of ventilation practices andstandards by the health community and of the implications of

these practices and standards for the public’s health. AlthoughASHRAE has had input from health professionals in develop-ing Standard 62, the process leading to the standard does notinvolve formal cross-institutional or cross-discipline interac-tions to assure full engagement of the many relevant disci-plines concerned with indoor air quality and health. In fact, nosingle organization or entity holds jurisdiction over indoor airquality. ASHRAE uses a committee process to develop itsstandard, and, in order to conform to the organization’s con-sensus process requirements, committee membership includesa broad set of interests, particularly from the economic sectorsmost affected by the standard. However, there is no “con-sumer” or “public” representation on the committee. Cur-rently, there are several health scientists and indoor air qualityresearchers and experts on the committee, as well as mechani-cal engineers, representatives of the heating, ventilation andair conditioning (HVAC) industry, building code officials,contractors, protobacco and antitobacco smoking interests,building products manufacturers, and others.

A consensus among such diverse interests tends to producecompromise and suppress innovation and major change fromone version of the standard to the next. The imperative forASHRAE 62, the ventilation standard, derives from the exi-gencies of engineering practice. Engineers need targets as theydesign the HVAC systems for buildings. In addition to healthand comfort considerations, the engineer is faced with issuesof cost and liability. ASHRAE’s SSPC 62 reviews the basis forthe standard and periodically revises it. The most recent ver-sion, 62-89, was released in 1989, and the process of revision isnow underway. The recommendations for nonresidential build-ings have been codified, but they have not been applied to theresidential environment.

Paradoxically, the engineering community sets the onlyindoor air quality standard addressing healthy indoor air.ASHRAE uses a consensus approach in setting the ventilationstandards, offering tables of recommended ventilation ratesfor various environments. Ideally, the choice of numbers shouldbe based on an understanding of the full range of adversehealth and comfort effects associated with indoor air contami-nants. Information on exposure-response relationships wouldbe used to identify “safe” or acceptable concentrations and,together, source control, air cleaning, and ventilation wouldbe used to reach these concentrations. Of course, the requisiteinformation is lacking for most indoor pollutants, and the au-thors of ASHRAE’s SSPC 62 have drawn heavily on field ex-perience and the evidence on odor in setting the standards.Uncertainties are evident and acknowledged but practicingengineers need this consensus judgment to have a target valuefor design.

Ventilation RatesVentilation capacity is typically set as a building is designed.However, it may be impossible to anticipate all future usesand the spectrum of susceptibility of occupants. Moreover, ca-pacity is not synonymous with performance as the building isused and ages. Building uses and occupancy patterns maydiverge from those originally intended, and inadequate main-tenance may compromise performance. Consequently, thehealth impact of ventilation depends not only on the originaldesign capacity but also on system operation and maintenance.

Ventilation rates are usually specified as cubic feet of out-door air per minute per person (cfm/p). They may also bespecified as cubic feet of outdoor air per minute per squarefoot of building area (cfm/sf), or as air exchange rate, usuallygiven in air changes per hour (ach). Finally, total supply air,


including both thermally treated outdoor air and recirculatedair, is usually referred to as the supply air rate.

4

We lack the data necessary to specify ventilation rates usingthe mass-balance approach. We cannot identify health-basedtarget concentrations for exposure to many indoor pollutants,and source strengths are known for only a small portion of themany pollutant sources typically found indoors. Sources mayalso change significantly over time in their emissions, and sim-ilar sources from different manufacturers may vary considerablyin their emission rates. Even the same product from the samemanufacturer may vary in emissions among production batches.For many chemicals, we lack information on toxicity, and wehave little understanding of interactions among pollutants.

Numbers such as ventilation rates imply a degree of cer-tainty that may be unwarranted. In fact, the range of numbersconsidered and adopted in recent decades varies more nar-rowly than the range of source strengths that can be found inindoor environments and the likely range of susceptibilities ofthe potential occupants. Because of the variation in pollutantsand their source strengths, and in occupant populations, rely-ing on ventilation rates alone in standards or in guidelines maynot provide adequate indoor air quality for all buildings or forall occupant populations.

In reality, the ventilation rates most commonly used for de-sign in the United States come from building codes and fromthe ASHRAE ventilation standards. There are variations inthe codes throughout the country, and there are differencesamong the various versions of the ASHRAE standards. There-fore, depending on where and when a building is built, it mayhave been designed to a range of ventilation rates. Generally,these rates have ranged from 5 to 20 cubic feet per minute perperson of outside air during the past 60 years (Figure 2).ASHRAE 62.Xc) specifies a minimum outside air ventilationrate of 15 cubic feet per minute per person (cfm/p). Certaintypes of spaces require more ventilation based on occupantactivities or other factors than would be predicted by the na-ture and strength of the expected sources.

The federal government has not promulgated ventilationrate standards. To some degree, perhaps, the existence of theASHRAE standards has reduced the need for the governmentto participate more actively in setting ventilation standards.During the previous two decades, wider recognition and ac-ceptance of indoor air concerns have coincided with a trend

Billings Flugge1895

Tredgold1836l-l ASHRAE 62-8 1-

I I I I I I I1825 1850 1875 1900 1925 1950 1975 2000

Figure 2. Historical ventilation guidelines (see Reference 57) (Usedwith permission).

toward deregulation, and the current climate is not favorablefor national regulatory initiatives that would address indoorair pollution. However, some states such as California andMassachusetts have developed their own regulations regard-ing indoor air quality and ventilation. In California, the Occu-pational Safety and Health Agency has adopted a rule requiringoperation of ventilation systems and creation of maintenancerecords (44). These records must be accessible to employeeswho request them.

Although much of the general information on ventilationapplies to all buildings, the residential setting presents a sepa-rate, unique set of issues. There is essentially no purposefulventilation in most residential structures in the United States;i.e., there is no structural or mechanical means designed intothe structure for the explicit purpose of exchanging indoorand outdoor air. Rather, residential ventilation is provided byunintentional leakage, the goings and comings of occupants,and intentional opening of windows and doors for ventilation.Forced air heating and cooling systems-the predominanttype of space conditioning systems used in United States resi-dences-are often misconstrued as ventilation systems by thepublic. These systems run only periodically and are not typi-cally connected directly to outside air, and therefore they can-not be counted on to provide for general ventilation needs andexpectations. Similarly, local ventilation equipment such askitchen and bathroom exhaust ventilators, although beneficialand now required amenities, cannot be counted on to satisfythe general ventilation needs for one entire structure. To date,ASHRAE has only addressed the residential ventilation issuein a cursory fashion: the 62-1989 Standard requires 0.35 airchanges per hour or 15 cfm per person, whichever is higher.However, a note in the standard allows for windows and natu-ral ventilation to satisfy this requirement, and consequentlymechanical ventilation in residences is usually limited.

Is there a single “right” number for ventilation rate? Thenecessary ventilation could be calculated if one knew the rele-vant contaminants, their rates of generation, their concentra-tions in incoming air, their stability, and the acceptable maxi-mal concentrations. In the absence of information on thesefundamental components of the mass-balance equation, anygenera1 recommendation must be modeled and then used withappreciation of its uncertainty. The need to control for humanoccupants and their activities provides one basis for ventila-tion values per occupant in the space. This approach assumesthat one person emits odors in the same way as another, thathuman occupants generate largely unique odors of strictly in-door origin, and that we can “measure” these odors qua odorspsychophysically. From studies performed in chambers duringthe many previous decades, it appears that a ventilation rateof 15 to 20 cfm per sedentary, nonsmoking occupant will sat-isfy the aesthetic criteria of the large majority of visitors fromnonpolluted spaces (37). Conceptually, this approach fits intothe mass-balance model.

The odor-based approach, however, requires knowledge ofthe number of persons who will occupy a space. It also typi-cally ignores levels of contaminants generated independentlyof occupants. Further, as typically used, it sets requirementsbased on impressions of unadapted visitors to a space; thus, itmay lead to total ventilation rates for some densely occupiedspaces such as theaters that seem too high and too energy-intensive and even too unachievable in certain geographic lo-cations such as those having hot, humid climates. However,lowering rates in congregate settings such as theaters may pre-dispose to increase person to person airborne infection unlessalternate methods of air disinfection are added.

Ventilation is limited in maintaining a quality of indoor air

sso AMERICAN JOURNAL OF RESPIRATORY AND CRITICAL CARE MEDICINE VOL. 156 1997

that will be healthy and comfortable for everyone. There areranges of expectations and potential susceptibility across thepopulation; these ranges imply that one or a few recom-mended ventilation levels cannot provide health and comfortfor all. In fact, the current ASHRAE standard 62-89 promisescomfort for only a substantial majority (interpreted as 80%)of building occupants, recognizing that comfort cannot rea-sonably be assured for all occupants. The spectrum of sensitiv-ity to pollutants implies that some persons may not toleratereasonably achievable exposures, and for some pollutants, i.e.,carcinogens, there may be no level of exposure that is not as-sociated with some projected risk. Additionally, any ventilat-ing system can have only limited flexibility and all future usesand associated needs for ventilation cannot be anticipated.

There are constraints on the amount of ventilation that canbe used. Construction and energy costs mount with increasingventilation rates. Additionally, the relationship between venti-lation rate and health and comfort consequences may not belinear, and specifying higher ventilation rates may not havethe intended consequences. Further, higher ventilation ratesmay lead to difficulty with moisture control, both with regardto excessive dryness that may affect occupant comfort and ex-cessive moisture that may foster microbial growth.

Technology

Although questions remain about how much ventilation tosupply, there are many proven ventilation technologies thatcan deliver adequate ventilation air for the maintenance ofboth contaminant control and comfort. These technologies areaffordable for most types of nonresidential projects. The tech-nologies can best be categorized as features that should beconsidered in the HVAC system design. APPENDIX B providesa listing and descriptions.

Maintenance

Even a well-designed ventilation system may perform inade-quately if allowed to degrade over time. From initial operationand throughout its lifetime, the system must be inspected reg-ularly and tested to assure continued proper operation. Beforeinitial occupancy and after any remodeling, the system perfor-mance should be verified through a commissioning process asin conformance with the original design. The ventilation sys-tem in most commercial buildings is usually controlled by thetemperature control system. Therefore, the temperature con-trol operation should be verified in conjunction with commis-sioning the entire mechanical system. The outside air quantityand the airflow at each supply air diffuser should be measuredby an independent test and air balance (TAB) contractor. Thecommissioning process must also include the provision of com-plete mechanical system documentation, including mechanicalsystem drawings, control system diagrams, and the TAB reportand maintenance manuals. Guidance for commissioning is pro-vided in ASHRAE commissioning guideline No. 1 (10).

Proper ventilation system operation and maintenance(O&M) are critical for continued satisfactory performance.These activities must start with thorough training of the build-ing maintenance staff as part of the original commissioning.HVAC systems can be very complex, especially in larger com-mercial buildings with sophisticated electronic controls inter-facing with computerized building management systems; there-fore, extensive hands-on training is necessary.

Maintenance needs to be performed according to a preven-tive maintenance schedule. The schedule should include fre-quent inspections that follow the manufacturer’s recommen-

dations. Although this schedule must include items such asregular filter changing, it must go farther and include “system”maintenance of the entire HVAC system.

Proper maintenance and regular calibration of an air econ-omizer ventilation system are especially important. As de-scribed in APPENDIX B, an air economizer cools the build-up ofinternal heat in commercial office buildings by flushing thebuilding with large amounts of cooler outside air. Inadequateventilation is a clear signal that the economizer is operating in-correctly and needs maintenance.

If the economizer ventilation system is maintained cor-rectly but the temperature control system allows the buildingto overheat, perceived inadequate ventilation with complaintsof stale and stuffy air may occur even when commercial officebuildings are operating with generous amounts of outside air.This is most common in the spring and fall in commercialbuildings located in temperate climates that are operating withair economizer cooling; then the economizer will be supplyingmaximal outside air (in the range of 50 to 100 cfm/person).

A pattern often exists to the temperatures in these build-ings. At the start of the day, temperatures are in the range of67 to 70” F, and then gradually rise to overheated conditions of75 to 80” F by 5:00 P.M. At the higher temperatures, the rela-tively dry air of the spring and fall can be perceived as staleand stuffy (45). To detect this swing of temperature, it may benecessary to measure the indoor air temperatures continu-ously for a week when the outside temperature is changing.The solution is a comprehensive ventilation and temperaturecontrols system tune-up. A well-documented explanation ofthe maintenance required is provided in “Ventilation SystemO&M: A First Step for Improving IAQ” (46).

The costs of high-quality preventive maintenance for me-chanical systems can be readily justified. Preventive mainte-nance protects and extends the life of the equipment; avoidscrisis-causing breakdowns and expensive unplanned repairs;provides for better budgeting of building maintenance ex-penses; increases employee comfort by assuring proper venti-lation system operation. Although HVAC system initial con-struction costs can be on the order of $12 per square foot(one-time cost), and personnel costs are on the order of $100to $400 per square foot annually, HVAC operation costs areon the order of $2 per square foot annually.

General Recommendations for Ventilation of Buildings

The institutional process that leads to the setting of ventila-tion standards does not include a sufficiently broad rangeof organizations and professionals. ASHRAE has re-sponded to the needs of engineers in its Standard 62. How-ever, the scope and purpose of Standard 62 have extendedinto the health domain, challenging the expertise and expe-rience of an organization of engineers. Interactions amongrelevant organizations are needed to engage health, engi-neering, architectural, and other relevant groups in devel-oping ventilation standards.Airborne disease transmission should be given more con-sideration in HVAC design. Items of specific concern in-clude general air turnover rates, high efficiency filtration,and pressure relationships for isolation of air flow.In general, accountability of a building’s indoor air qualityand HVAC performance should be improved.There is a critical need to improve general knowledge forcontractors, builders, and operators regarding the practicalaspects of indoor air pollution control. Better approachesto identify sources of pollutants and to find solutions forcontrolling them are needed.


AIR CLEANING AND TREATMENT

Overview on Air Cleaning Devices

Air cleaning is a general term referring to the removal of par-ticles and gases from the air by mechanical devices that mayfilter particles and/or chemically remove gases. (A technicalappendix to this workshop report contains more detailed cov-erage of air cleaning and filtration. APPENDIX C was written af-ter the workshop in order to provide additional backgroundon air cleaners.) Portable devices are manufactured to cleanair within rooms, whether in homes or offices. Large buildingstypically have HVAC systems that remove some large parti-cles from supply air; they may have additional systems to cleanthe air flowing through the system.

Air cleaning devices for rooms include a fan to move airthrough the apparatus; typically the devices contain elementsto remove particles and gases, although some simple devicesmay only be intended to remove particles. The technologiesfor removing particles incorporated into the devices includemechanical filters; electrostatic precipitators, which chargeparticles and then collect them onto a surface with the oppo-site charge; and ion generators, which charge particles andthereby facilitate their deposition. There are several types ofmechanical filters: flat panel filters, pleated filters, and high ef-ficiency particulate air (HEPA) filters. Some small devicesmay contain a flat panel particulate filter, which is not efficientin removing particles. HEPA filters are highly efficient in re-moving particles of a wide range of sizes, and the acronymoriginally referred to High Efficiency Particulate Arrestor.Gases are not removed by the filters directed at particles, ex-cept for those gases and vapors that have been sorbed on toparticulate matter. Charcoal or other sorbent materials maybe incorporated into the device to remove gases and vapors.Such sorbents can become saturated and need to be replacedor reconditioned periodically to maintain performance and toassure that collected gases and vapors do not revolatilize tothe air.

For persons with lung disease, air cleaning has particularappeal. Portable devices can be moved from room to room,possibly creating a more healthful environment for the aller-gen- or smoke-sensitive person. Centrally located devicescarry the same potential appeal and possible benefits and af-ford the possibility of residence-wide air cleaning. Other typesof cleaning such as duct and surface cleaning have also beenproposed as beneficial to health.

Among the target sources for air cleaning in residences arecigarette smoking, airborne allergens, and volatile organiccompounds (VOCs) from household products and materials.The major allergen sources indoors include dust mites in bed-ding, furniture, and carpets; fungi or bacteria growing onmoist surfaces; cats, dogs, and other pets kept in houses; cock-roaches; and outdoor allergens that have entered the home.

The potential benefits of air cleaners might be demonstratedindirectly by showing that their use reduces concentrations ofpollutants and personal exposures or directly by showing healthbenefits; however, there is surprisingly little evidence for eitherindirect or direct benefits. Review of this evidence was thestarting point for the evaluation of air cleaners by the workinggroup. The group also considered the technical challenge ofcleaning air in the presence of strong sources.

Consider the simplest of cases where a portable air filterappliance is used in a closed room that is not mechanicallysupplied with air. Mixing efficiency for the space will be ig-nored for this illustration. The percentage reduction in pollut-ant concentrations in a well-mixed room affected by using aircleaners is given by:

551

% Reduction = 100 x (&)

where N = air changed per hour (l/h), V = room volume (cuft), E = fractional efficiency of the cleaner to remove particlesin a specific size range, Q = flow through cleaner (cu ft/h).

Thus, the effectiveness of an air-cleaning device dependson the size and ventilation of the room where it is used, the ef-ficiency of the cleaner, and the volume of air flow through thecleaner. For a substantial reduction of particle concentration,a very efficient and high airflow device is required. As an ex-ample, consider a room 20 by 12 ft and 8 ft high that has 10 airchanges per hour. If a 90% reduction in airborne concentra-tion of particulate matter present in the incoming air is de-sired, then a device with an airflow of 3,200 cu ft/min and a90% efficient particle filter could be specified to meet thisgoal. For allergens, virtually complete removal may beneeded, particularly for the most sensitive persons. Let us saythat 99% removal was required for this small room. Closingwindows and doors and running the air conditioner on recircu-lation (assume no additional removal) might reduce the air ex-change rate to somewhere between 0.1 and 0.5 per hour. At0.5 h-’ air exchange rates, the air cleaning device would needa flow rate of more than 1,500 cfm and a high efficiency filter(0.99) to clean to the desired level. At lower air exchangerates, only 350 cfm would be needed along with a moderatelyefficient filter (0.9) to meet the desired levels of airborne par-ticles. These trade-offs between airflow and filter efficiency aswell as the conditions of the intended space indicate the chal-lenge faced by manufacturers and users of portable air cleaners.

Given this challenge, perhaps not surprisingly a review ofthe literature does not provide strong evidence for benefits ofair cleaners. Few adequately designed controlled studies of por-table air cleaners have been reported. These studies have hadsmall sample sizes, which tempers their interpretation. Theyare further limited by their diverse locations-and hence theheterogeneity of exposure addressed-and by their partici-pants’ heterogeneity.

Other groups have also considered this evidence, includingan ad hoc committee of allergists who met at the request ofthe Food and Drug Administration and the participants in theprevious ATS/ALA workshop. The report of the allergists(47) comprehensively reviewed the literature through 1987.That group could not find sufficient sound evidence to supporta firm recommendation for the use of air cleaners. Participantsin the 1988 ATS/ALA workshop did not find new, major con-tributions to the literature that would provide a rationale fordeparting from the earlier view of the committee of allergists.

Since these earlier reports, some additional studies havebeen published, but these are still subject to the limitation ofsample size as well as to other methodologic problems.

Recommendations on Air Cleaning Devices

Based on review of the earlier and most recent literature, theworking group was in agreement with the 1988 statement ofthe American Academy of Allergy, Asthma and Immunology(47): “Absence of adequate data on the clinical relevance ofindoor ambient allergen levels, as well as the effect of air-cleaning devices on these levels, plus a general lack of healtheffects by these devices in published double-blind studies pre-cluded any firm recommendations for their use. It was clear,however, that use of room air-cleaning devices in the absenceof other forms of environmental control was not reasonable.”The evidence accumulated over approximately a decade hasnot been sufficiently abundant or conclusive to support an af-firmative recommendation for use of the devices for control of

s52 AMERICAN JOURNAL OF RESPIRATORY AND CRITICAL CARE MEDICINE VOL. 156 1997

allergen exposures. The National Asthma Education Pro-gram’s Guidelines fiw the Diagnosis and Management ofAsthma, and the NHLBFWHO Workshop Report: GlobalStrategy for Asthma Management and Prevention (48,49) statethat environmental control measures should be the first mea-sure for the treatment of asthma; physicians should instructtheir patients in the appropriate hierarchy of control, begin-ning with primary source reduction. Health care providersshould not prescribe, endorse, or tacitly accept use of aircleaners alone as an effective environmental control strategy.

These recommendations reflect the limited number of ap-propriately designed clinical trials on the efficacy of air clean-ing devices for those with asthma and allergic diseases, as wellas for other groups who might potentially benefit, e.g., personswith cystic fibrosis or chronic obstructive pulmonary disease(COPD). The group noted that the database for evaluating aircleaners had changed little since the publication in 1988 of thestatement by the American Academy of Allergy, Asthma andImmunology. In addition to the obvious need for more clinicaltrials, the group recommended additional indoor air studies tocharacterize concentrations and size distributions for airborneallergens. Information is also needed on exposure patternsand the factors influencing exposures. Until research has fur-ther addressed indoor allergens and demonstrated clinicalbenefits, manufacturers should not imply that the devices havehealth benefits.

We conclude then, that if allergen sources are present inthe space, commercially available portable air cleaners willnot be 100% effective for all situations in reducing airborneallergen-containing particles to levels where effects will notoccur. Strong intermittent sources are particularly problem-atic. Cats, for example, might shed allergens periodically and/or in areas where portable air cleaning devices might not beable to respond adequately. Furthermore, deposited antigensare not affected by air cleaners. Mites excrete allergens aslarger particles on to surfaces (i.e., within carpet or bedding).These allergen-bearing particles become airborne sporadicallyby mechanical disruption. The relevant exposures may takeplace at times of close proximity to the source, e.g., lying on acouch or contact with bedding. Thus, transient conditions mayproduce short-lived exposures that evoke responses, whereasin the long-term, room or house-wide average airborne levelscould be reduced by air filtration. Therefore, source controlshould always be the first choice for allergen control in resi-dences.

The well-designed electronic air cleaner generates only asmall amount of ozone. When the fan is off, the ionizer shouldgo off as well. Electronic air cleaners will not present prob-lems in homes or offices where air exchange rates are typicallybetween 0.2 to 2 h- ‘. The group expressed general concernthat any electronic air cleaner, ionizer, ozone generator, officeequipment, or motor should not generate ozone above theFDA limit of SO ppb (50) in any occupied space. The groupalso considered removal of gases and vapors from indoor air.Sorption beds, with materials such as activated charcoal andpermanganate/alumina, are widely used in removing organiccompounds from recycled air.

Reactive catalytic materials that are effective in removingozone, nitrogen dioxide, and carbon monoxide from ambientair at room temperature are under development. These reac-tors might also prove effective for aldehydes and ketones aswell because these compounds contain the carbonyl grouppresent in carbon monoxide. These catalysts may be useful forcleaning intake air in areas where ambient air quality stan-dards are not being met. An unsolved problem with sorptionor reactive beds is the lack of reliable means to determine the

effective residual capacity while they are in use. The grouprecommended the development of an appropriate test method,perhaps by the American Society for Testing and Materials(ASTM).

Filtration in Residences and Large Buildings

Filters are usually part of residential forced air heating andcooling systems. Less expensive furnace filters are designed tocapture dirt particles that might soil the mechanical equip-ment. The use of pleated filters that are 60% efficient for3.0+m particles (with an ASHRAE-rated efficiency of 95%)would significantly reduce particle accumulation within thebuilding ventilation system. Higher performance filters arecommercially available, and specifying that filters be capableof removing a minimum of 50% of the 0.3~pm size particles isreasonable. Figure C.4 in APPENDIX C shows the particle sizefractional efficiency for pleated filters having different ASH-RAE performance ratings. Note that minimal efficiency forthese and most filters occurs between 0.1 and 0.5 pm.

For homes, residents should be aware of the followingchecklist, which might be asked of a furnace maintenance con-tractor.

1.

2.3.

4.

5.6.7.

8.

Is the filter holder sealed and does it cover the furnace/airconditioner intake?Do the air supply ducts leak into unoccupied spaces?Are the return air ducts tight so they draw air from occu-pied spaces?What is the efficiency of the pleated filter? Should you con-sider a more efficient filter?Is the condensation drain clogged?Is there mold growth on the walls of the air handler?Is there visible dirt and/or mold growth on the ductwork?Does the air smell moldy, particularly at times when thebasement or garage is damp?If the filter or fibrous insulation has become wet, will it beremoved?

Research needs include studying the effectiveness of differ-ent filtration modes on health end points; the particle charac-teristics of allergen-bearing particles, emission rates, expo-sure, and exposure/response relationships; and the efficiencyof filters at the very low concentrations of particles that arecharacteristic of buildings.

Duct Cleaning in Residences

Duct cleaning is usually performed by one of three methods:(I) commercial-type vacuum cleaners that vacuum the surfaceof the ducts; (2) an air washing or air sweeping method using acompressed air hose upstream and a vacuum device down-stream to dislodge and remove debris from the ducts; (3) amechanical brush, often along with a compressed air driver ro-tary device, which moves down the duct dislodging debris,with HEPA negative air equipment placed downstream. Thenumber of duct cleaning services has increased substantially.Although health claims are often made, no studies documentany health benefit from duct cleaning. Case studies have, how-ever, documented that ductwork can be cleaned and, in somecases, the cleaning has lowered fungal spore counts for longperiods (51, 52). Anecdotal data support both positive andnegative health impacts.

Clearly, ducts that are so filled with debris that airflow isrestricted should be cleaned. Such soiling is likely to occuronly on the return air end of the system if the supply system isprotected adequately by filtration. Fungal growth in ductwork


with fibrous lining is an indication that the lining should be re-placed, not cleaned. Such growth is likely to occur in ductworkthat is not adequately protected by filtration and where mois-ture control is ineffective.

Without additional research, we cannot recommend the ef-ficacy of one method of duct cleaning versus another or spec-ify the periodicity of preventive cleaning. In addition, the useof biocides in residential ductwork is not warranted. Sealingmicrobial growth within ductwork is also not advisable, espe-cially where moisture problems are continuing. If a consumerdoes elect to have ducts cleaned professionally, the processshould always include cleaning of the furnace blower bladesand cabinet, and all furnace components of an air conditioningsystem, if present. If duct debris is contaminated with biologicgrowth, duct surfaces should be free of all dust after cleaningto avoid dispersal of potentially irritating particulates upon re-activation of the system. Professional duct cleaning for officebuildings is expensive and lacking in performance standards.When contracting for cleaning surfaces, a wipe test of residualdust value should be specified (see Table Cl in APPENDIX Cfor guidance).

Other Methods Proposed for Indoor Air Cleaning

The cffectivcness of vacuum cleaning in removing settled ortracked-in dirt from surfaces varies by type of surface, charac-teristics of the dirt, and by the equipment and methods used.Currently there are no standard methods that inform consum-ers about vacuum cleaner effectiveness. Limited laboratorytests show substantial variation among vacuum cleaners in re-tention of a cat allergen charge placed in a bag. If possible,doubling the vacuum cleaner bag can improve retention of catallergen. Other studies show that aggressive cleaning of rugsand carpet with a rotary brush generates substantial quantitiesof coarse size particles. Some vacuum cleaners have superiorperformance and HEPA-like bag filtration. Some methods ofsurface cleaning (steam injection, wet mopping) are likely togenerate less suspended particulate matter than dry surfacemethods.

The scientific data are insufficient to support claims thatplants improve or degrade indoor air quality. Plants can raisehumidity levels and serve as reservoirs and supply nutrientsfor fungal growth. Although some plants have been shown toremove some organic vapors, it is unlikely that plants by them-selves could be an effective control strategy.

POTENTIALLY SUSCEPTIBLE POPULATIONS

Overview

The general population is heterogeneous on a number of char-acteristics, such as atopy, bronchial responsiveness, and sus-ceptibility to infection, that are determinants of susceptibilityto the adverse effects of indoor air pollution. Whether thesecharacteristics have a genetic basis or are acquired, their pres-ence may affect the risk of disease in persons exposed to envi-ronmental agents. The diversity of the factors determiningsusceptibility and the myriad environmental exposures of con-cern imply that the population of potentially susceptible per-sons is large. Concerns about the effects of indoor air pollu-tion on thcsc special, susceptible populations have increasedin recent years. The rising number of persons with a diagnosisof asthma, for example, has drawn attention to the possiblymounting exposures of allergic persons to indoor allergens.

For susceptible persons, there are abundant opportunitiesfor exposure to potentially hazardous indoor air pollutants.Inhalable particulate allergens derived from pollens, dust

mites, and fungal spores are of sufficiently small size to passinto the respiratory tract where the antigen-antibody reactionoccurs. Additionally, exposures to some agents may also takeplace through ingestion and skin contact. For example, expo-sure to allergens may occur through ingestion of certain foods(e.g., milk, eggs, peanuts), and skin contact with certain sub-stances (e.g., latex).

A seemingly increasing number of persons report being af-fected by odors. Organic solvents such as benzene and toluene,which are released by a variety of building materials (paints,finishes, and adhesives, for example), have characteristic odors.These and numerous other gaseous chemicals of increasingmolecular complexity comprise the VOCs measured in indoorair. Some compounds such as mercaptans that arc added tonatural gas and perfumes are strong odorants (i.e., they havelow odor thresholds). There has been speculation that low con-centrations of odorant pollutants may have adverse effects, al-though only speculative hypotheses can be advanced concern-ing potentially involved mechanisms of pathenogenesis.

The Nature of Susceptible Populations

Susceptibility is multidimensional and can result from manyfactors, including disease status (Table .5), sociodcmographiccharacteristics (age, sex, and socioeconomic status), genotype,and environmental exposures. Thus, occupational agents cancause increased bronchial responsiveness and asthma, and en-vironmental tobacco smoke (ETS) increases risk for lowerrespiratory infections in young children. The distribution ofsusceptibility in a population is continuous for many factors,covering a broad range that extends from the most resistantand healthy persons to the susceptible, impaired, and diseased.Thus, a spectrum of resistance to infection exists with healthypersons at the most resistant end and immunocompromisedpersons (e.g., those with AIDS) at the most vulnerable; evenamong persons with ATDS, there is a wide range of impair-ment of host defenses against infection. For example, thecounts of helper lymphocytes (CD4 cells) in persons withAIDS extend from normal levels to virtual absence.

Disease States

Decrements in immune system function range from minimal,as in most recipients of usual doses of oral steroid treatmentfor asthma, to severe, such as the lack of function of compo-nents of the immune system in AIDS. Along this continuum,persons with AIDS develop increasing susceptibility to infec-tious agents and become at risk from a broadening array ofpathogens. For example, invasive aspergillosis occurs only inthe severely immunocompromised. Immunocompromised pa-tients are of special concern in hospitals, both because themost severely infected are congregated in hospitals, and be-cause exposures to some infectious agents may be more likelyin hospitals than elsewhere. Atopic persons make up anotherlarge, susceptible population, at risk for asthma and allergic

TABLE 5

’ SOME DISEASES THAT INCREASE SUSCEPTIBILITY TOINDOOR AIR POLLUTANTS

Disease

Cystic fibrosisAIDSOther immune deficiency diseasesAsthmaAllergic rhinitis

Susceptible to:

Infectious agentsInfectious agentsInfectious agentsAllergens, irritantsAllergens, irritants~_ ~


rhinitis. Atopy has a genetic basis, but atopy-associated diseasesare presumed to result from gene-environment interactions.

Some evidence indicates that allergen exposure in atopicpeople is a risk factor for the development of allergic diseases,although we lack evidence of reduced disease occurrences af-ter implementation of environmental control measures. How-ever, it is prudent for parents with a history of atopy to prac-tice allergen control with the expectation of reducing theirchildren’s risks for allergic diseases.

Potentially Susceptible Populations: Persons withAsthma and Allergies

Primary prevention. Our knowledge of risk factors for asthmain susceptible infants and children is now sufficient to justifystrategies for reducing exposures of those at high risk. A his-tory of asthma and allergy in parents and siblings is stronglypredictive of childhood asthma; a genetic basis for this associa-tion is assumed and is under intensive investigation. Allergenexposure has been shown to increase the risk for earlier onsetof asthma.

Although controlled data on exposure avoidance andasthma risk are limited, recommendations for exposure con-trol should be made for persons at high risk for asthma and toparents whose children are at high risk. Such persons shouldseek housing with characteristics associated with lower levelsof allergen and irritant exposure. The following recommenda-tions are considered most important by the working groupparticipants.

1

2.

3.

4.

5.

Houses should have low levels of indoor humidity. In gen-eral, this is accomplished by using central air conditioningand avoiding evaporative coolers and humidifiers. In someclimates additional use of dehumidifiers may be necessaryto achieve the optimal relative humidity, levels of less than50%, which do not support mite and mold growth. Reach-ing these levels may not be feasible in humid sections of thecountry.Recognized reservoirs for house dust mites should be re-duced. Carpets should not be placed directly on cementslabs or in the child’s bedroom; mattresses and box springsshould be encased with a mite-proof encasing, and pillowsshould either be covered or washed, as should bedding, inwater at 130” F on a regular basis, preferably weekly. Blan-kets can be washed monthly in a similar manner. Water-bed coverings can become moldy because moisture cancondense on them if they are not continuously heated.There should be no warm-blooded pets kept in the home.It may be prudent to learn if recent occupants have hadpets, particularly cats: it may be appropriate to avoid homesin which the previous inhabitants had warm-blooded pets.Cockroach infestations should be eliminated and controlmaintained.Exposure of a child to tobacco smoke should be avoided.Smoking by the mother appears to carry the highest risk.

Control of house dust mites. In addition to the general rec-ommendation for low humidity (Item no. 1) and the specificrecommendations for mite control given above (Item no. 2)other modalities may also assist in control of mite levels. Sec-ondary measures to reduce exposure include control of mitesin carpets and upholstered furniture, which are the other ma-jor sources of mite allergen. These measures include removingcarpets and upholstered furniture from rooms and reducingpotential dust-collecting items from the bedroom, which is themajor site of exposure to mite allergens for most persons;avoiding lying on upholstered furniture; covering upholstered

furniture with impermeable covering; and avoiding vacuumingwith an unmodified vacuum cleaner, or being present in theroom during such vacuuming.

Acaricides can be employed to reduce the mite populationin carpets, and tannic acid can be applied to carpets to dena-ture the residual mite allergen. These chemical treatments areonly partially effective and the effect persists only for a fewmonths, making repeated treatment necessary. In some stud-ies, acaricide treatment has been shown to reduce mite aller-gen levels, whereas in others this treatment has been ineffec-tive (53).

Controlling other indoor allergens. Animal dander andcockroach allergen are the other principal indoor allergensthat have been implicated in causing allergic disease. Animaldander is shed by the animal and on to the reservoirs affordedby carpets, upholstered furniture, and bedding from which itbecomes reentrained in the air through the effects of humanactivity. Cockroach allergen is present predominantly in innercity homes and homes in the warmer parts of the UnitedStates. The greatest concentration of cockroach allergen isfound in the kitchen. The importance of indoor mold exposureis less clearly established for conditions of ordinary exposure,but it may be important where unusually high moisture ispresent, as in some basements or where flooding or leakagehas occurred previously.

Of course, animal danders are best limited by not havingpets in the home and cleaning thoroughly if animals werepresent in the past. Less effective is to limit the range of thepets in the house, particularly excluding them from the sensi-tive person’s bedroom. Neither measure eliminates the reser-voirs of dander, which have been shown to continue contami-nating the environment for as long as six months. Tannic acidand injection steam carpet cleaning can be used to denature orremove residual allergen after pet removal, but the effects ofboth are limited. Because animal dander allergen is associatedwith particles that may remain airborne for prolonged periods,the allergen can travel throughout the house by movement ofair, inside and outside of the HVAC system. Therefore, thebedroom door and heating vents should stay closed through-out the day. Opening windows in the bedroom will dilute theallergen and partially reduce the level of small respirable par-ticles containing animal allergens that are in the air.

Cockroaches can be controlled by thorough cleaning, re-ducing the presence of food, paying careful attention to seal-ing the insects’ entry points, and by trapping or using poisonedbaits. In apartment buildings, cockroaches can move from oneunit to another, and all possible entry points must be sealed. Itmay be prudent to avoid chemical pest control, if possible, be-cause of potential exposure to fumes from pesticide applica-tions and to residual pesticide in the indoor environment.Cockroaches are known to develop resistance to pesticides overtime, making repeated use less effective.

Mold control is accomplished by reducing humidity, asmolds, like house dust mites, thrive on high humidity. Re-moval of soft material that has become contaminated withmold growth may also be necessary.

Although there have not been prospective controlled stud-ies that demonstrate the health benefits of reducing exposuresto these allergens, there is little reason to doubt the effective-ness of reduction of exposures to animal dander or dust mites.For sensitive persons, benefits are also expected from reduc-tion of cockroach and mold exposure.

Air cleaning devices can be effective only against allergensthat are suspended in the air. Both mite and cockroach aller-gens are associated with large particles, which tend to fall rap-idly from the air; therefore, air cleaners can contribute little to


this natural clearing secondary to gravity. Air cleaners can re-move fungal spores and animal dander allergens. However,the quantity of these allergens in reservoirs in carpets and up-holstered furniture far exceeds the amount in the air. Further-more, the allergen is readily reentrained from these reservoirsby human activity. Use of air cleaners should be consideredonly after sources of allergen exposures have been addressed.

Environmentul tobucco smoke and other irritants. Patientswith asthma have airways that are hyperresponsive to irritantstimuli. Exposure to environmental tobacco smoke (ETS) hasbeen shown to exacerbate the status of children with asthmaand possibly to increase risk for asthma (54). It has also beenshown to increase symptoms in adults with asthma. It is pru-dent to recommend elimination of ETS exposures in the homefor children and adults with asthma. Patients with asthma alsoreport symptoms from other exposures of irritants in the homeenvironment, and perfume is frequently reported to cause symp-toms. Some asthmatics may also be adversely affected by othersources of irritants such as cleaners and polishes.

Potentially Susceptible Populations: Persons Affected bySick Building Syndrome

In any building, there will be a range of susceptibilities amongoccupants to indoor air pollution exposures or other adverseconditions rather than a sharp distinction between susceptibleand nonsusceptible persons. Thus, only a proportion of work-ers in an office building-those for whom exposures have ex-ceeded a threshold of physiologic tolerance-would be ex-pected to have physiologic responses to low level adverseexposures. As the distribution of human responsiveness to theresponsible agents is likely to be a continuum, it is probablethat, at higher exposure levels, a greater proportion of the ex-posed population would respond adversely. As an example, itis well recognized that generally less than 5% of those actuallyexposed to sensitizing microbiologic materials in indoor envi-ronments develop hypersensitivity pneumonitis, a recognizedbuilding-related illness, or complaints. The human response tothermal environments is so diverse that at any given tempera-ture, a minimum of 20% of building occupants, and generallymore, find thermal conditions to be unacceptable. Adversehealth responses in buildings may involve parameters docu-mented to cause building-related illness or thermal discomfort,including chemical (e.g., carbon monoxide or formaldehyde),biologic (e.g., fungi or dust mites), or physical (e.g., tempera-ture, humidity, or air movement) factors. APPENDIX D pro-vides a detailed account of an investigation of workers withpossible building-related illnesses.

Symptoms that are apparently work-related should not bedismissed solely because etiologic factors cannot be identified.Levels of various environmental parameters currently consid-ered acceptable may in fact not be. For instance, multiplestudies have demonstrated that even within the indoor tem-perature range long considered acceptable, higher tempera-tures are associated with increased symptom prevalence. Be-cause not all contaminants or conditions with adverse humaneffects are known or recognized (e.g., specific etiologic agentseven for clearly documented outbreaks of hypersensitivitypneumonitis often cannot be identified), worker symptomsmay result from exposures or conditions not yet causally im-plicated in building-related illnesses. These exposures or con-ditions, though quite plausibly causing adverse effects, maynot yet be widely measured (e.g., endotoxins, various single orcombined VOCs), or measurement methods may not be readilyavailable (e.g., many mycotoxins).

Is there a relationship between occupants who reportsymptoms in buildings where adverse exposures or conditions

555

cannot be identified, and those with multiple chemical sensi-tivity? Known as MCS, multiple chemical sensitivity is definedas long-lasting intolerance to chemicals and odors in the in-door environment. (See the next section.) As “problem”buildings are among the few environments that have producedsimultaneous multiple claims of MCS development, sick-building syndrome (SBS) is considered by some to be synony-mous with MCS. This is not the case, considering the verycommon occurrence of work-related symptoms among officeworkers in all buildings studied, compared with the relativelyinfrequent occurrences of MCS. There are also relativelysmall proportions of claimed MCS development even in se-vere “problem” buildings with very high proportions of work-ers having work-related symptoms.

Potentially Susceptible Populations: Persons with MultipleChemical Sensitivity or Idiopathic Environmental Intolerance

Persons with this entity, generally termed multiple chemicalsensitivity, or MCS, and recently relabeled as Idiopathic Envi-ronmental Intolerance by the World Health Organization(55) are usually self-described as hypersensitive to more thanone, but not necessarily all, chemicals. Generally, such pa-tients report more than one symptom, usually associated withmultiple agents. Symptoms may include a burning sensation inthe eyes or throat, cough, dyspnea, fatigue, headache, rashes,weakness, feelings of anxiety, panic, inability to think clearly,and related neurologic complaints. After a person’s perceivedexposure to an inciting agent, the symptoms may last for abrief time or for hours or even for days. An individual may be-come symptomatic and even debilitated by symptoms from al-leged exposures even at levels generally considered inoffen-sive or innocuous to most people. The perceived cause-effectrelationship between chemical exposure and symptoms iscommonly defined by the patient based on perception of anodor or on perception of irritation. The person with MCS maybelieve that his or her own olfactory sensitivity exceeds that ofthe normal person.

The particular agents to which persons with MCS allege hy-persensitivity vary from person to person, with the agents towhich any patient claims susceptibility frequently varying overtime, and possibly including substances such as fine fragrancesthat others may find desirable and pleasurable. The naturalhistory of MCS has not been described. Anecdotal reports in-dicate that over long periods of removal from exposure to of-fending chemicals, persons with MCS may gradually return tonormal. The role of avoidance in the condition has not beenwell-characterized.

The mechanisms leading to MCS remain uncertain, and ex-posure reduction may be the only relief from symptoms formany MCS sufferers. Control measures to improve indoor airquality for the population generally would also apply to thisgroup of people. Specific approaches for home environmentsof persons with MCS would be person-specific and require in-dividual guidance. Persons with MCS have formed their ownsupport networks for exchange of information on managingsymptoms by physical control of the environment. Typically,the home environments of many patients with MCS aresparsely furnished, and rigid dust control is maintained; aswell, there is an absence of chemical products and of fleecymaterials. Because of the ambiguous nature of MCS and thechanging spectrum of substances to which the patient withMCS exhibits symptoms, there is little to make in the way ofspecific recommendations for exposures to particular agents.Systematic research using sound methods has been recom-mended to define and manage this poorly understood condition.


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44. State of California, Department of Industrial Relations, Division of Oc-cupational Safety and Health. 1002. Mechanically Driven Heating andVentilating and Air Conditionmg (HVAC) Systems for MinimumBuilding Ventilation. General Industry Safety Qrdcrs. CaliforniaCode of Regulations, Sacramento, CA. Section 51422514X.

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47. Nelson, H. S.. S. R. Hirsch, J. L. Ohman. T. A. E. Platts-Mills. C. E.Reed, and W. R. Solomon. 1088. Recommendations for the use of res-idential air-cleaning devices in the treatment of allergic respiratorydiseases. .I. Allergy Clin. Immunol. X2:661-66Y.

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(EPA). Consumer Product Safety Commission (CPSC), and Ameri-can Medical Association. lYY4. Indoor Air Pollution. An Introductionfor Health Professionals. IJ.S. Government Printing Office, Washing-1on. DC. 523-2 I718 1.722.

51. Ahmad. I., B.. ‘Tanacl, and J. D. Mitrani. 1904. Effectiveness of HVACSanitalion Processes in Improving Indoor Air Quality. Florida Inter-national liniversity. Department of Construction Management, Mi-ami, FL. Technical Publication No. 11.3.

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5.1. Woodlolk. .1. A., M. L. Hayden, N. Couture, and T. A. E. Platts-Mills.199.5. Chemical treatment of carpets to reduce allergen: comparison ofthe effects of tannic acid and other treatments on proteins derivedfrom du\l mites and cats. J. Allrrgy C/in. Immunol. 96:325-333.

54. (J.S. Environmental Protection Agency (EPA) and Indoor Air Division.lYY2. (‘urrent Federal Indoor Air Quality Activities. U.S. Govern-ment Printing Office, Washington, DC.

5.5. LINEI’-ILO-WHO, 01 trl. lYY6. Conclusions and recommendations of aworkshop on multiple chemical sensitivities (MCS). Rrgul. Toxicol.Plrrrnrcru~l 24:s I XX-S1 X9.

56. Thatcher. 1‘. L., and D. W. Layton. 1095. Deposition, resuspension, andpenetration of particles within a residence. Armos. Environ. 29:14X7-1497.

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APPENDIX A

Particle Reduction Strategies

The following is a list of recommendations for reducing particles inthe indoor environment, and thereby reducing problems caused by in-door air pollution.

Ambient Pnrticlesl llpgradc filters to > 50% at 0.5 pm with target to improve

removal efficiency.l Relocate air intakes away from obvious sources.

n11sr. Clean exterior and entrance sites.l Conduct high efficient particle removal by use of washable

rugs and other surfaces at entranceway.l Ensure enhanced cleaning of all internal surfaces.l Reduce the USC of textile covered surfaces, i.e., partitions/

wall covcringsiwall-to-wall carpeting.l Advance development and application of cleaning perfor-

mance standards.

l Encapsulate, seal, and/or isolate all potentially friable sur-faces.

l Direct duct supply and return air (i.e., do not use open ceil-ing plenum space).

l

EquipmentI s o l a t e / z o n e v e n t i l a t i o n w h e r e e m i s s i o n s c a n b e i d e n t i f i e dand efficiently captured.

l Site exhaust f i l t r a t i o n w h e n i t c a n b e d e m o n s t r a t e d t h a tsource m i t i g a t i o n i s m o r e c o s t - e f f e c t i v e s t r a t e g y

concentration, d u s t b u r d e n , o r o c c u p a n t e x p o s u r e .

General ffumun ActivityImprove e f f i c i e n c y o f v a c u u m s t o reduce

l

l lJpgradc

l

557

APPENDIX 6

Ventilation Technology

Proven, affordable ventilation technologies that can deliver adequateventilation air for the maintenance of both contaminant control andcomfort should be considered in the HVAC system design. A listingand descriptions are below.

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

Air Economizer. This type of ventilation system offers a signifi-cant advantage for increased outdoor air ventilation over systemsusing a fixed minimum amount of outside air. In commercialbuildings, heat from lights and people must be dissipated from theinterior core year-round. With an air economizer, this is done byflushing with large amounts of outside air. For commercial build-ings located in temperate climates, there will he generousamounts of outside air for the majority of hours of the year (in therange of 30 to 100 cfm/person), especially in the spring and fall.Therefore, economizers are much more forgiving to design inade-quacies and building use changes. Occasionally, they arc rejectedbecause of the space needed for ductwork. However, with presentemphasis on indoor air quality, an air economizer system may ac-tually be more cost effective than alternatives.Direct Digital Control with Simple Graphic Intetfbce. ManyHVAC systems have been controlled by computers in recentyears. However, graphic interfaces now simplify the lcvcl ofknowledge required to operate the HVAC system and drasticallyimprove the likelihood of the system being operated correctly. Allcomputer-controlled HVAC systems need periodic audits to as-sure that erroneous messages are not being given.Variuhle Air Volume (VA\/) with Outdoor Air Injection. Thesesystems deliver variable airflow to spaces, depending on require-ments. VAV systems can contribute to indoor air quality com-plaints if the airflow restriction is too great. Advances in cquip-ment design and software controls now allow the amount ofoutdoor air delivered to the occupants to be maintained, eventhough the total supply of air is decreased to save on electricalconsumption.Demand Control Ventilation and Reliable Carbon Dioxide Sen-sors. We now have affordable sensors that can serve as indicatorsof the level of occupancy and thus be used to increase ventilationair delivery in proportion to the occupancy. thereby saving en-ergy. When demand control ventilation is utilized, some baselinelevel of outdoor air ventilation is needed regardless of the carbondioxide controller.Indoor Air Quality Air Conditioning Condensare Drain Pans.Many companies are now marketing IAQ drain pans and IAQ airhandling units. These systems arc typically designed to avoid thebuild-up of stagnant water in the air handling system and to facili-tate its hygiene.Low Pressure Drop High Efficiency Air Fibers. Recently, manyair filter manufacturers have made available a selection of ex-tended surface pleated air filters that allow much higher air filtra-tion to be utilized without a significant increase in fan horsepower.Outdoor Air Preconditioning C/nits. Until recently, removing thehumidity from outdoor air in a hot and humid climate was veryenergy-demanding. Now, there are proven technologies for re-moving humidity before the outdoor air is brought into the build-ing that are much less energy intensive. This type of system ispreferable in any climate that is considered hot and humid, oreven temperate and humid.Tight Building Envelopes and Air Conveyance Ducts. Researchersin Florida and California have recently shown that tightening airducts in both homes and commercial buildings, and reducingbuilding shell leakage, can have a dramatic effect on both improv-ing air quality control and reducing air conditioning energy bills.Unlined Air Conveyance Ducts and Nonpermeuhle DWI Liners.Many designers have altered their design practice to eliminate po-rous duct liners from the HVAC ductwork because of the poten-tial for accumulation of dirt and dampness to lcad to moldgrowth. Some manufacturers have begun to make available non-porous duct liner.Return Plenum Design. Because of difficulties encountered i ncleaning ceiling plenums and maintaining adequate pressure con-


11.

12.

trol between different HVAC zones, some designers have elimi-nated the use of return air plenums. In general, when a return ple-num is used, it is very important for the architect, engineers, andcontractors to ensure that the perimeter of the plenum above theceiling is very carefully sealed to prevent movement of unwantedairflow and air contaminants from one zone to the next.Verticul Displacement Ventilution Technology. Although used inparts of Europe for many years, vertical displacement air supplyhas only been incorporated recently by designers in the UnitedStates to enhance the natural movement of air within a room.This type of system can reduce drafts, enhance air quality, and re-duce energy consumption by fans. Often this type of system isused with a 100% outdoor air design and heat recovery, therebypreventing movement of contaminated air from one part of abuilding to another while achieving good energy efficiency. Thepotential electrical energy savings with this type of system are sig-nificant. Alternately, the electrical savings from reduced fanhorsepower can be utilized to provide improved climate controlwith dehumidification and air conditioning in areas that may nothave been previously air conditioned or dehumidified.Personal Work Stution Control of HVAC Systems. Some manu-facturers have made available systems for personal control of air-flow and temperature control at workstations. This approach mayoffer enhanced occupant comfort. Inherent in this approach is theneed to maintain more dispersed HVAC equipment and controls.It is also important that the personal control equipment be acces-sible for preventive maintenance.

APPENDIX C

Air Cleaning and Filtration

Concepts and Definitions

The term “filtration” refers to processes in which individual sus-pended solid particles are separated from a fluid (vapor or liquid)phase, and collected on or inside a “filter.” The filter is a medium thatinteracts with or exerts a force on particles dispersed in a fluid, at-tracts them to its surface, and retains them. The performance or effi-ciency of a filter or of a filtration process can be measured by theweight fraction of particles removed; that is, the percentage by weightof particles removed from the air. This term can be ambiguous andeven misleading from the health perspective. Efficiency that is basedon the weight fraction collected tends to emphasize disproportion-ately the removal of large particles, which are frequently not those ofmost concern for health. Other definitions of efficiency are based onthe number of particles collected, or on the weight fraction of particles

collected within a narrow size range. The passing of a fluid through afilter is also associated with consumption of energy; thus, another fea-sible efficiency concept may be that of energy expended per numberor unit weight of particle collected.

The degree of air cleaned by filtration reflects a complex set of pa-rameters including the chemical and physical properties of the parti-cles, the filtering medium, flow rate, turbulence, mass loading on thefilter, and other factors. A single term like “efficiency” is generally in-adequate to describe the performance of a filtration process, unlessqualified by numerous conditions. Solid particles vary widely in size,shape, and composition. Volume, number, and surface area of sus-pended particles have been characterized (see Figure C.l). Particlemass is typically bimodal, with two fractions characterized by coarsefraction and fine fraction. In Figure C.2, the bimodal distributionfound in indoor atmospheres with the predominant constituents ineach fraction are shown.

Sources of Particles

Sources of indoor air particles include penetration of outdoor air con-taining particles, resuspension of settled dust, cooking, combustionappliances, aerosol sprays and powders, cigarettes, vacuuming, mo-tors, recondensed vapors from sources such as candles, oils, and lubri-cants, and copy machines. Biologic spores, pollens, dander, skin flakes,and mite allergens are typically larger than 1 urn in size and hencemore easily removed by filtration. Nonviable fragments of cells, acti-nomycetes, viruses, and strains of DNA may very well be less than 0.1wrn in size (although viruses are quite small, they are often present inthe air as a constituent of a droplet and therefore might be a few mi-crons or so). The expected sizes for common indoor particles and thetime required to fall 1 m or about half the height of a typical room aregiven in Table C.l.

Recent studies using sophisticated particle-size analyzers haveshown that combustion events in the home produce abundant quanti-ties of ultrafine particles (< 0.1 pm), which are carried by convectivecurrents and disperse quickly as room air mixes and is displaced. Verysmall but high in number, the particles grow by agglomeration, diffuseto surfaces, or are removed from the indoors by air exchange. How-ever, like all particles less than a few microns in size (5 urn), they set-tle out very slowly. Disturbing surface dust creates clouds of particles.Studies have shown that vigorous house cleaning resuspends particlesgreater than 5 p,m in size. Even walking across a carpet will greatly in-crease particles 5 to 25 )*rn in size. Small sizes are not as likely to beresuspended (56). Although particles 100 pm in size or greater willsettle quickly, convective currents and agitation by people and petswill keep many coarse-size particles suspended in the indoor air.

- 1.2- 6

2- l.O- 5

O-0.1 1

ParoWe diamebr (pm)

Figure C. 7. Plots illustrating the relationship of particle number, surface area, and volume distribution as afunction of particle size (Source: Whitby, K. T. 1975. Modeling of atmospheric aerosol particle size distri-butions: a progress report on EPA research grant No. R800971, “sampling and analysis of atmosphericaerosols.” Minneapolis, MN: University of Minnesota, Mechanical Engineering Department: p.lll-21; parti-cle technology laboratory publication no. 253).


AMMONIUM. NITRATES,CARBON. LEAD, ANDSOME TRACE CONSTITUENTS

/ CRUSTAL MATERIAL(SILICON COMPOUNDS.IRON, AWMINUM), SEA \SALT, PLANT PARTICLES \

\

0.1 1 .o 10.0

PARTICLE DIAMETER,flm

Figure C.Z. Idealized representation of typical fine- and coarse-particle mass and chemical compositiondistribution in an urban aerosol. (Source: U.S. Environmental Protection Agency, EPA-600/8-82-029a, De-cember 1992).

When activities in the home cease at night, particle measurementshave clearly shown that PMlo concentrations decrease substantially.

Filtration of Particles

Different filtration media rely on different interaction mechanisms forthe separation and collection of particles and have distinct efficienciesfor particles of varying sizes and/or shapes; the collection efficiency offilters changes with time and is also affected by the flow rate of thefluid through the filter. Commonly, filtration processes are designedfor collecting primarily one type or size-range of particles. The dust-holding capacity of (he filter and the operating cost for the filtrationsystem-energy requirements for moving the fluid phase through thefilter and filter replacement costs-arc also important parameters forthe consumer. Thus, a single efficiency value, commonly cited in com-mercial literature to charactcrixe the performance of a filter, may nothe sufficiently informative for consumers.

The purpose of filters. even in general ventilation applications,may differ from case to case, and with it the performance criteria ofprincipal interest. We return to the example of air filtration removingallergens (pollens, house dust mites, spores, etc.) from a home.

It should now he readily apparent that the actual effectiveness ofany air cleaning dcvicc will depend on the proximity to the source,capture efficiency, filtration efficiency, air exchange rate, volume ofthe setting, and location of persons, among other factors. It is under-standahle that demonstrated health benefits of air cleaning are still

TABLE C.l

APPROXIMATE PARTICLE SIZES AND TIME TO

Type

Diameter

(cLm)

Human hair

Skin flakes

Observable dust in air

Common pollens

Mite allergen

Common spores

Bacteria

Cat dander

Tobacco smoke

Metal and organic fumes

Ceil debris

Viruses

100-l 50

20-40

> 10

1 s-25

1 O-20

2 - 1 0

l - 5

1 -+ 0.5

0 . 1 - l

<0.1-l

0 . 0 1 - l

< 0.1

SElTLE 1 METER*

Time

5s

5 min

10h

10d

elusive given the inherent difficulties in quantifying exposures. Manu-facturers as well as users report favorable results, hut an appropriatelydesigned clinical trial on the efficacy of air cleaning devices for asthmaand allergic diseases, as well as other groups who might potentiallybenefit, has not been conducted.

Filter testing methods. It follows from the gcncral considerationsabove that the expected performance of a filter cannot he describedwithout attention to many technical details. Accurate comparisons ofdifferent air cleaners (filters) can be made only on the basis of dataobtained by standardized test methods. Unfortunately, testing by ex-isting standards (e.g.. ANSI/ASHRAE 52.1-1992) is not equally appli-cable to all filtration devices. For example, ANSI/ASHRAE 52.1specifies as the material for challenge in its arrestance test a standarddust mixture that simulates typical dusts encountered in HVAC sys-tems. However, this standard test dust contains graphite particles thatwill cause electrostatic (or “electronic”) filters to malfunction in ar-restance tests. Test dust is specified at 72% (wt) Arizona road dust,23% powdered carbon, and 5% cotton lint. Performance based on thistest dust says little about how the filters might remove particles in therespirable size fraction.

The ASHRAE 52.1-92 (or its previous version, ASHRAE 52-76)procedure tests filters in several important ways.

1. The weight arrestance test measures the collection efficiency forcoarse particulates (those associated with HVAC system fouling)and is more appropriate for low efficiency filters (10 to 30%) suchas those found on home furnaces and commercial HVAC systems.

PERCENT ARRESTANCE (ASHRAE Standard521 TEST METHOD)

50 60 70 80 90 92 97 90 99I I I I I I I

% ATMOS. DUST-SPORT EFFICIENCY (ASHRAE Standard 52.1

GROUP I 20 30 40 50 60 70 80 9 0 9 5 9 8I I I I I II I

4 b % DOP EFFICIENCY (MIL-STD-282)GROUP II 10 20 30 4 0 5 0 6 0 8 0

I I I I I I I I

4GROUP III

w

GROUPIV +W

figure C.3. Comparison of filter performance ratings. (Reprintedby permission of the American Society of Heating, Refrigeratingand Air-Conditioning Engineers, Atlanta, Georgia. From the 1996ASHRAE Handbook: Systems and Equipment.)


TABLE C.2

EXPECTED FILTER PERFORMANCE RATINGS FOR DIFFERENT FILTER TYPES*

Filter Type

Panel-type filter

Pleated panel-type filter

Extended surface-typesupported or nonsupported

Extended-area pleatedHEPA-type filters

Atmospheric DustWeight Arrestance Spot Efficiency DOP Efficiency

Filter Media w (%) w

Spun-glass, open cell foam, 50-90expanded metals and screen,synthetics, textile denier wovenand nonwoven, or animal hair

Fine denier nonwoven synthetic 85-95 15-30and synthetic-natural fiber blends,or all natural fiber

Fine glass fibers, fine electretsynthetic fibers, or wet-laid paperof cellulose glass, synthetic, or all-glass fibers

95-99.7 30-98 80

Wet-laid ultafine glass fiber paper 99.99 > 98 99.97-99.999

l Reorinted bv oermission of the American Societv of Heatino. Refrigerating, and Air Conditionmg Engineers (ASHRAE). 1996. ASHRAEHanddook: Syst&s and Equipment. ASHRAE, Inc., Atlanta, GA.“’

The dust-holding capacity test measures the expected life of the fil-ter under given operating conditions.The dust spot efficiency test is a semiquantitative measure of thefilter’s collection efficiency for fine particles-those associatedwith the smudging of the interior surfaces of buildings. The test isappropriate for medium cfficicnt filters (20 to 98%). Upstream anddownstream paper target filters collect particles and the opacity ismeasured (light transmission).The mcasurcment of resistance versus airflow is related to the en-ergy required to operate a filter.

ASHRAE 52.1-92 fails, however, to address two important issuesrelated to indoor air quality: the filter collection efficiency for “respi-rable particles” (those in the 0.01 to IO km size range) and the effi-ciency of removal of biologic materials (spores, fungi, bacteria, andviruses). To address the issue of rating filter efficiencies for respirable-sized particles relevant to the nuclear industry and for personal pro-tective masks, another test was developed. Heating liquid dioctylphtha-late (DOP) and then cooling it carefully can produce a uniform-sizedaerosol. The DOP test uses 0.3 pm condensed droplets and light-scattering detectors for dctcrmining the particle retention propertiesof higher performance filters. Applications in microelectronics manu-facturing now require filter efficiencies of 99.9995% in the DOP test.It can he seen in Figure C.3 how these three tests compare. To inter-pret the reported efficiencies of manufactured filters, it is important tonote the reference test. A cheap furnace filter might state 90% effi-

100

9 0

8 0

70

60

50

40

30

20

10

00.1 1

Particle Diameter (microns)

10 0 250 Pa

0 I , I I I I,,, I I I111#11 , 1 v VIII'0.01 0.1 1 10

Particle Diameter (microns)

Figure C.4. Fractional filtration efficiency of four pleated filters Figure C.5. Fractional filtration efficiency of a pleated-paper filterhaving ASHRAE efficiencies ranging from 40 to 95% (Source: Han- (65% ASHRAE efficiency) for clean and dust-loaded conditionsley, et al. 1993. Fractional aerosol filtration efficiency of air clean- (Source: Hanley, et al. 1993. Fractional aerosol filtration efficiencyers. Proceedings of Indoor Air 1993: Sixth International Confer- of air cleaners. Proceedings of indoor Air 1993: Sixth Internationalence on Indoor Air Quality and Climate, Munksgaard International Conference on Indoor Air Quality and Climate, Munksgaard Inter-Publishers, Copenhagen, Denmark). national Publishers, Copenhagen, Denmark).

ciency when it is really less than 20% effective by the AtmosphericDust Spot Efficiency test. (See Table C.2 for comparison of methods.)

A test procedure (ASHRAE 67 1 -RP) recently developed by RTIunder contract to ASHRAE utilizes fractional efficiency testing-“penetration measurements” on artificially generated aerosols-tocharacterize the efficiency of filters for the removal of particulates inthe size range of 0.3 to 10 pm. This research was specifically commis-sioned for the purpose of developing a consensus standard method oftesting (MOT), and this work is nearing conclusion. Standard 52.2(M&hod of Testing General Ventilation Air Cleaning Devices for Re-moval Efficiency by Particle Size) is currently out for its second publicreview and is likely to be published by mid-1997. This new test proce-dure, if adopted as a standard, will provide a reproducible (? 2%)methodology for testing the particle removal efficiency of filters usedfor general ventilation. It is technically feasible to extend the frac-tional efficiency test to particle sizes less than 0.3 pm to include mostviruses and combustion sources that vaporize oils, fats, and proteins infood to generating ultrafine aerosol.

The performance of four pleated filters is shown in Figure C.4 forparticle sizes ranging from 0.01 to 3 pm in diameter. These pleated fil-ters were rated by the ASHRAE Percent Weight Arrestance test as95,85,&j, and 40% efficient. The filter efficiencies for 0.1 km size par-ticles ranged from N 1 to 50%, which illustrates the importance ofspecifying particle size or at least test conditions when reporting effi-ciencies. It can be seen in Figure C.5 how the overall efficiency of a fil-ter increases as it collects more dust. Dust loading increases the pres-

100

90

6 0

70

60

0 40 Pa: (clean)

1

American Thoracic Society S61

sure drop, measured as Pascals,,, across the filter and hence the fanpower requirements. Another important parameter for comparing fil-ters is the total recommended maximum mass loadings. New standardtest methods will most likely require performance curves for differentparticle sizes over a filter’s expected life. Other more sophisticatedbut not standardized filter tests have emerged as the result of needs inspecialized industries (e.g., semiconductor manufacture and con-trolled hospital environments). The results of such tests, conductedwith specific types of particles, may be misleading if extended to moretypical environments. These and many other tests have been used andmisused to characterize filter performance and to underpin claims thatmay be misleading when quoted out of context.

have carbon and glass fibers woven together and can be no more thanl/4-inch thick. They are effective for limited periods of time. Not allorganic vapors or gases have the same adhering affinity, so careful at-tention to specific applications is advised. Air temperature will affectadsorption efficiency, and there is a potential for release of vapors.

APPENDIX D

Investigation of Workers with PossibleBuilding-Related Illness(es)

Introduction

Elecfronic uir cleanerx Electronic air cleaners (EACs) use electro-static precipitators to remove particles from the air by giving them anelectric charge. Units used in forced air systems in residences andcommercial settings usually have two stages. A high voltage low cur-rent is supplied to wires that spew off positive or negative ions thatquickly attach to particles. The second stage has oppositely chargedcollection plates that attract and hold the particles. Well-designed andwell-operated EACs arc quite efficient, usually achieving 95% re-moval of DOP 0.3 p,m particles. Poor maintenance and loss of electricfield potential in the EACs have been linked to secondary particleproduction. Also, ozone is formed when wires produce corona dis-charge. However, improved design lowers ozone generation so levelsinside homes and offices are usually barely detectable, though oneshould bc aware that operating some electronic air cleaners in smallsealed rooms can result in unhealthful levels of ozone.

Investigations of illness among workers that may bc related to the in-door environment in the building where they work have been initiatedtraditionally by two different mechanisms.

Building management receives “complaints” from occupants.These complaints may include symptoms (headache, mucosal irri-tation, etc.) that are attributed by the worker 10 the building envi-ronment, or perceptions of adverse conditions (“too dry,” “staleand stuffy”).One or more workers seek medical attention for evaluation ofsymptoms that occur at work. After evaluation the physician at-tributes the health problems lo the building in which the patientworks.

Sorhenfsfi~r venfilufion uir. To remove gaseous contaminants, a va-riety of sorbent materials arc used. Activated carbon, which is madefrom sieved coconut-shell carbon, removes many gases and vaporsfrom an airstream by adsorption. The carbon granules have an enor-mous surface area per mass. Gas molecules diffuse to the surfacewhere they arc retained. Sorbent “filters” (charcoal, permanganateialumina, or other malerials) are typically available for HVACs in re-fillable 1 to 1 and l/&inch refillable panels. Depending on the packingand mesh size, sorbcnt panels can be 90 to 95% effective in removingmost organic compounds.

Although this difference may appear unimportant, the process andoutcomes of evaluation will be different because the focus ot the n-vestigation, and the training, experience, and perspective of those in-volved, will be very different. Building management has traditionallycalled upon engineers, architects, and, increasingly “IAQ consultants”-an emerging profession. These professionals take the perspectivethat the building is “sick.” Therefore the building, particularly theHVAC system, is evaluated to identify conditions that could createoccupant discomfort, dissatisfaction, or symptoms.

There are several solid-phase sorbents available today. All sor-bents have limitations that affect their performance and operatingtime; eventually the surface becomes saturated with vapors. Unlikeparticle filters, there is no direct way to know if adsorbing filters haveexceeded their useful life. Water vapor competes for surfaces and willdecrease performance. Charcoal-packed beds or panels that are lessthan l/4-inch thick will not be effective. New matrix web fabric filters

In the second mechanism, when a worker consults a physician, theevaluation is based on the premise that the worker is sick. The pri-mary physician may call upon occupational or public health physiciansor industrial hygienists in an effort to identify the specific illness andthe causative exposure(s).

From the mid-1970s until now, the conceptualization, definition.and majority of investigations of this problem have been from the firstperspective, i.e., problem-solving for buildings. Symptoms or otherstated problems have often been considered as indicators of “problembuildings,” and not directly evaluated. Cause and effect relationships

STEP 1 DISTI2

GUISH SYMPTOMS FROM ERCEPTIONSL

Symptom (e.g headache) Perceptions (e g ‘loo hot/cold7refer t MD

9

refer to building

\r

management

STEP 2A - IS symptom consistently work-related0- r

NO Yes

other STEP 3A Evidence of othermedIcal medical problem (e.g. hypertension)problem

Ye6 ho

STEP 28 - Do other workers have same

Y complaints7 4NO YBS

suspect localized Suspect more wadespreadproblem, e.g. HVAC.problemoutdoor au Intake, outdoorpollution

STEP 4A Treat problem medically,do s;ztoms re;olve?

No Poswble building-related health problem

9 “G

5A-Are others in b Ming affected?STE

NO Y=

suspect lxal~zed problem STEP 6B -are affectedand/or increase susceptibilw workers located in one area

4or throughout the building?

STEP 6A - Move worker local edto another floor, another site i

-&red

SU* locaked suspect WAC- outdoor aw Intakeproblem. contaminant - outdoor air pollutionsource. venblabon problem -centralized or wdespread

microbial wntammahon

figure D. 7. Possible building-related discomfort, dissatisfaction, or symptom (directed to building man-agement or personal physician) (Source: R. M. Menzies. Used with permission).


between health effects and environmental parameters have not beensought specifically. Instead, deficiencies in building operation andmaintenance have been sought, and corrected if found. If remedial ac-tions resulted in resolution or reduction of the workers’ problems (asexpressed in “complaints” to building management), then a cause andeffect relationship was often concluded post-hoc.

Principles of Investigation of PossibleBuilding-Related Illness(es)

Investigation of workers’ discomfort, dissatisfaction, and/or symptomswould be improved by adopting a unified approach incorporating as-pects of both perspectives (see Figure D.1). The following generalprinciples are derived from experience of these two perspectives.

1. “Complaints” or problems identified by workers should be distin-guished as symptoms (headache, chest tightness, wheezing, fa-tigue) versus perceptions (“too hot,” “stale and stuffy”). Symp-toms may indicate a health problem and these should be referredto a physician for evaluation no matter who is consulted first. Forexample, it is important to ensure that headaches are not indica-tive of a medical problem such as hypertension. On the otherhand, perceptions of environmental problems should be directedto building management rather than to health professionals.The symptoms should be categorized as work-related or notwork-related. In occupational medicine the classic definition ofwork-related symptoms are those that begin after arrival at workand resolve upon leaving work. Occasionally, symptoms may be-gin many hours later. For example, hypersensitivity pneumonitiscan manifest I2 to 24 h after exposure. Symptoms usually resolverapidly, cvcn within minutes after lcaving work, but they may per-sist for weeks after a single exposure in those most severely af-fccted. In more severely affected persons, work-related symptomsshould resolve on weekends, vacations, or with other prolongedabsences from the work environment.The symptoms typically reported by workers in office buildingsinclude headache, fatigue, difficulty concentrating, and mucosalirritative symptoms-none of which can be measured objectively.It is axiomatic that health professionals as well as building man-agement accept that the symptoms experienced by the workersare real. Failure to identify a clear cause does not mean that thesymptoms can be dismissed as psychologic. Such an attitude is po-tentially harmful because it denigrates the workers and reducesthe likelihood of detecting and solving problems. In the long runthis will worsen communication and exacerbate tensions betweenworkers and building management.Workers and their advocates should remain open to the possibil-ity that work-related symptoms are not necessarily related to thebuilding environment or to indoor air quality. Symptoms may bedue to job stress, anxiety, or physical or ergonomic factors.Evaluation of possible building-related illnesses requires exper-tise in architecture, engineering, and industrial hygiene as well asin medicine, and few persons have expertise in all these domains.Therefore, a team approach with good communication betweenpersons with different expertise is essential. It is in everyone’sbest interest to evaluate and resolve symptoms among workers.Building managcmcnt should be open to the possibility thatsymptoms among workers arc related to the building environ-ment and to solutions proposed by physicians on behalf of per-sons or groups of workers. Physicians should work with buildingmanagement to review possible causes and solutions, and publichealth departments should provide assistance, including expertiseand industrial hygiene mcasurcments.The symptoms considered typical of sick building syndrome areusually very heterogeneous. Therefore, if the symptoms reportedby several workers are more homogeneous, the possibility of asingle causative agent should be considered. In outbreaks ofbuilding-related illness caused by microbial contamination, manyworkers presented with similar respiratory symptoms, raising thesuspicion of alert clinicians.When the symptomatology of a group of workers is homoge-neous, the nature of the symptoms reported may provide some in-

8.

9

10.

11.

12.

13.

dication of the likely problem. However, much of our current un-derstanding of exposure response relationships in the officeenvironment is derived from case series or from cross-sectionalstudies. Consistent relationships with symptoms have been de-tected for only a few of the possible causative agents in the officeenvironment. Other parameters have been recognized to causesymptoms on the basis of studies in the home or outdoor environ-ments.The number and spatial distribution of symptomatic workers mayprovide important clues to the cause. For example, if a group ofaffected workers are all located on a single floor or in one section,a localized problem such as a strong contaminant source or venti-lation malfunction should be suspected. On the other hand, ifworkers in many different parts of a large building report similarsymptoms, this may indicate a generalized problem such as con-tamination of the HVAC system supplying these different areas.The temporal distribution of symptoms may provide furtherclues. Seasonal variations suggest problems related to tempcra-ture or humidity, outdoor pollutants if outdoor air supply variesseasonally, or house dust mite or fungal allcrgcn exposure, whichmay increase during seasons with higher humidity. Other prob-lems may be specific to certain times of the week. For example,symptoms that occur each Monday morning may reflect accumu-lation of indoor contaminants over the weekend if ventilation sys-tems are shut down during these unoccupied periods.The traditional definition of “sick building syndrome” has encom-passed many symptoms, including headache, fatigue, difficultyconcentrating, irritation of the skin, eyes, nose, and throat, lowerrespiratory symptoms, and others. There is no cvidcncc that thesediverse symptoms represent a single disorder or syndrome. Onthe contrary, it seems quite plausible that “SBS” is made up ofmany different disorders, each with specific symptoms and caus-ative agents.Symptoms may be related to temperature, humidity, and air movc-ment-the so-called comfort parameters. These parameters canvary significantly from building to building, hut they also can varysubstantially within a single building, from floor to floor or evenfrom worksite to worksite. The spatial and temporal variationsdetected have, in turn, been associated with variation in symp-toms reported by workers in a number of epidemiologic studies.Therefore it is important to investigate the “comfort parameters”first, as they may account for a significant proportion of all symp-toms, and they are the most amenable to corrective action. Theseparameters should be measured directly at the worksite of af-fected workers, on repeated occasions. Fortunately they can bemeasured relatively easily and rapidly with direct reading instru-ments, allowing more accurate characterization of workers’ expo-sure.Measurement of many indoor air quality parameters, such as car-bon monoxide, formaldehyde, volatile compounds, fungal spores,or respirable dust, is complex and expensive. It is not possible tomeasure all these parameters at the workstations of all symptom-atic workers, so exposure must be estimated on the basis of mea-surements at a sample of sites. Because these parameters alsoshow substantial spatial and temporal variation, workers’ true ex-posure may be inaccurately measured. The difficulties of obtain-ing accurate environmental measurements may, in part, explainthe failure to detect consistent associations between these param-eters and workers’ symptoms.For a specific exposure, workers will develop symptoms, or otherhealth effects, if they are susceptible to that level of exposure. Atlow levels of exposure only a few highly susccptiblc persons maydevelop symptoms. As the concentration of a contaminant in-creases, the number of persons affected may also increase. It ispossible that a few workers may develop symptoms when exposedto contaminants at concentrations that the vast majority of workerscan tolerate. Therefore, when a person has work-related symptomsfor which the cause cannot be identified, changing worksites mayresolve the problem. However this does not necessarily mean thatthe workers who move into this same site will develop symptomsbecause they may be less susceptible to the same, albeit unknown,exposure.


List of Participants:

EMIL J. BARDANA, JR., M.D.

Oregon Health Science University, Dept. of Medicine

REBEC‘C.A BASCOM, M.D., M.P.H.

University of Maryland, Pulmonary Division

HARRIET BLJRC;E, PH.D.

Harvard School of Public Health

H. E. BARNEY BLJRR~~~HS

Building Wellness Consultancy

TERESA C~ADY

Bunting Coady Architects

DAVID D~c.ou~sro

National Association of Home Builders Research Center

THAD Golxsti, PH.D.

Ball Slate University, Dept. of Natural Resources andEnvironmental Manugement

LEE HATHoN, M.S.

OSHA Response Team

LAWRENCE S. KIRS~H, ESQ.

Cadwalader. Wickersham & Taft

KAI‘HLEEN KREISS, M.D.

National Jewish Center, Occupational Medicine Division

HAL LEVIN

Hal Levin and Associates

RI~HAKII LO(.KEY, M.D.

American Academy of Allergy and Immunology

JEFFREY C. MAY, M.S.

J. May Home Inspections, Inc.

MARK J. MENDI-LL, Pl1.D.

NIOSH/IWSB

RICHARU MENZIES, M.D., M.Sr.

Montreal Chest Hosptial

SWIRLI:Y MURPHY, M.D.

American Academy of Pediatrics

EUWARU A. NARDELL, M.D.

Cambridge Hvsptial

HAROLI) S. NELSON, M.D.

NaGonul Heart, Lung, and Blood Institute

VIRGINIA SALARES, PH.D.

Canada Mortgage and Housing Corporation

GENE SAXI-IIIIKT., P.E.

Monsen Engineering Company

THOMAS S(.HNEII)ER, M.Sc.

Nutional Institute of Occupational Health (Denmark)

JOHN A. TALIX~I., M.S.

U.S. Department of Energy

STEVEN T. TAXOR

Taylor Engineering

WILLJAM A. TURNER, P.E.

The Turner Group

DWJGHT W. UNDERHILL, Sc.D., CIH

University of South Carolina School of Public Health

JOSEPH A. VENTRESCA, M.S.

City of Columbus, Facility Management Division

PEDER WOLKOFF , PH.D.

National Institute of Occupational Health (Denmark)

JAMES E. WOODS, PH.D.

Virginia Polytechnic Institute

Organizing Committee:

Workshop Co-chair

JONATHAN M. SAMET, M.D., M.S.

Johns Hopkins UniversitySchool of Hygiene and Public Health

Workshop Co-chair

JOHN D. SPEN~LER, PH.D.

Harvard School of Public Health

WILLIAM S. CAIN, PH.D.

University of California, San Diego

RICHARD C. DIAMOND, PH.D.

Lawrence Berkeley Laboratory

LEYLA ERK MCCURDY, M.S.

A LA Indoor Air Programs

RONALD WHITE, M.S.T.

ALA Environmental Health Programs

Staff

RUTH NEWLIN, M.P.H.

ALA Indoor Air Programs

Workshop Staff

ALLYN ARNOLD , M.P.H.

Johns Hopkins UniversitySchool of Hygiene and Public Health

MARION GRANICIAN

A LA Indoor Air Programs

LEE FERNANDO

University of New Mexico

Co-Sponsors

AMERICAN ACADEMY OF ALLERGY AND IMMUNOLOGYAMERICAN ACADEMY OF PEDJATRICSA MERICAN SOCIETY FOR HEATING, REFRIGERA’I‘INC~ AND

AIR CONDJTIONING ENGINEERS

CENTERS FOR DJSEASE CONTROL AND PREVENTJON

EPA, INDOOR ENVJRONMENTS DJVISI~NNAIIONAL ASSOCIATJON OF HOME BUILDERS

RESEARCH CENTERNATJONAL INSTITUTE FOR OCCUPATJONAL SAFETY

AND HEALTH

S64

Bibliography

AMERICAN JOURNAL OF RESPIRATORY AND CRITICAL CARE MEDICINE VOL. 156 1997

Banks. D. E., and D. N. Weissman. editors. 1994. Immunology and AllergyClinics of North America. Indoor Air Pollution: An Allergy Perspective.W.B. Saunders, Philadelphia, PA.

Burge, H. A.. editor. IYYS. Bioaerosols. Indoor Air Research Series. LewisPublishers-CRC Press, Boca Raton, FL.

Gammage, R. B., and B. A. Berven, editors. lYY6. Indoor Air and HumanHealth, 2nd ed. Lewis Publishers-CRC Press, Boca Raton, FL.

Godish, T. lYY.5. Sick Buildings. Definition, Diagnosis and Mitigation. LewisPublishers-CRC Press, Boca Raton, FL.

Husman, T. IYYh. Health Effects of Indoor-air Microorganisms. (Review).Sctmtl. .I. Work Environ. Hwlth 225-13.

Ledford, D., and R. Locky, editors. 1994. Building- and home-related com-plaints and illnesses: “Sick Building Syndrome.” J. Allerfiy Clin. Immrnol.Suppl. Y4:(2, Pt. 2).

Maroni, M., B. Seifert, and T. Lindvall, editors. 1995. Indoor Air Quality. AComprehensive Reference Book: Air Quality Monographs, Vol. 3.Elsevier; Amsterdam, The Netherlands.

Samet, J. M., and J. D. Spengler, editors. 1991. Indoor Air Pollution: AHealth Perspective. Johns Hopkins University Press, Baltimore. MD.

Seltzer, J. M., editor. 1995. Occupational Medicine: Effects of the Indoor En-vironment on Health. Hanley and Belfus, Inc., Philadelphia, PA.

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