Effective Local Exhaust Ventilation for ControllingFormaldehyde Exposures in a Gross Anatomy Laboratory

F.R. Demer\ R.A. Notary and J.C. Rosen'Departments of Risk Management & Safety1 and Facilities Design & Construction"

The University of Arizona, Tucson, Arizona, 85721

Poster Presentation at the 1996 American industrial Hygiene Conference & ExpositionWashington Convention Center, Washington, D.C.

ABSTRACT

Overexposure to formaldehyde and related health complaints have long been associated with dissection of embalmed human

cadavers. Previous studies have shown exposure levels exceeding current occupational health criteria and standards. However,

published reports regarding proven effective control methods and technologies are limited. Given this shortage of information,

various methods to control formaldehyde exposure at a medical school gross anatomy laboratory were evaluated through personal

exposure measurements. Several interim controls were sequentially implemented, including increased dilution ventilation, general

and local filtration with treated charcoal, and modified embalming methods. All were found to be inadequate. Special local exhaust

work tables and a controlled supply air system were ultimately installed. Standard dissection tables were modified with slot exhausts

on both sides, providing up to 1200 cfm exhaust per table. Air is supplied in a fairly laminar flow from above the tables. The system

includes simple controls which reduce system energy consumption in unoccupied times and encourage system use. The laboratory

accommodates 35 cadavers and is used by approximately 100 students and instructors. Personal samples collected before the final

system installation, showed TWA formaldehyde exposures ranging from 0.01 ppm to 4.0 ppm, with an average of 1.1 ± 0.8 (n = 56).

STEL exposures ranged from 0.4 ppm to 6.7 ppm, with an average of 2.6 ± 1.8 (n = 40). After the system was operational,

formaldehyde exposures were reduced to, and in most cases less than, the analytical limit of detection, which is more than an order

of magnitude less than the current ceiling value of 003 ppm recommended by ACGIH. User involvement ensured the necessary

system flexibility and operational and ergonomic requirements. Acceptance is high. Further system testing and adjustments are

needed to optimize energy efficiency while maintaining adequate exposure control.

INTRODUCTION

FORMALDEHYDE, an irritant gas and suspect human carcinogen 1, is widely used as a component of embalming agents used in

gross anatomy laboratories for cadaver preservation. Acute symptoms of formaldehyde exposure are prevalent among workers in

such laboratories and levels often exceed current occupational health criteria and standards.i"

Various approaches have been suggested to control exposure, including: good work practices, alternative embalming

agents/formulations, personal protective equipment, dilution ventilation and local exhaust. 6-12 Of the methods proposed, only local

exhaust ventilation combined with good work practices have shown promise in adequately controlling formaldehyde exposures while

allowing normal laboratory function. Several designs, based either on standard industry ventilation for open tanks (slot tables) or

grinding tables (down draft tables)." have been discussed and tested as prototypes.P'":":" Few reports exist regarding actual field

use and performance of such designs.9,14

This presentation outlines the University of Arizona's efforts to control formaldehyde exposures in a medical school gross anatomy

laboratory. The development of a local exhaust system, its novel features, and performance testing, are described.

THE PROBLEM

The gross anatomy laboratory at the University of Arizona College of Medicine was a large L-shaped room (approximately

35,000 fe ) housing 25 stainless steel cadaver dissecting worktables, each serving four students (see Figures 1 and 2). Five

instructors were also assigned to the laboratory which is located on a third floor exterior corner of a health science complex built in

1968. Cadaver use is approximately 200 hours per year, including 3 hours, twice a week during class, in addition to independent

study and class preparation.

The laboratory had general ventilation with a flow rate of 5400 cfm. Air was supplied by several ceiling vents evenly spaced

throughout the laboratory and exhausted from one primary ceiling location, with additional small perimeter returns. The laboratory

was positive in pressure relative to adjacent areas. At the air handler, return air from the laboratory and other building areas was

mixed with approximately 10% fresh outside air, filtered through two large banks of treated, activated charcoal, and supplied back to

building areas.

In 1992, concern arose regarding formaldehyde exposures to medical students and other building occupants. This resulted in

extensive exposure monitoring and systematic efforts to reduce exposures through various means. In response to increased indoor

air quality complaints, the treated, activated charcoal beds in the air handler were replaced. This action had no effect on

formaldehyde exposures in the laboratory or indoor air quality complaints. Soon after, return air vents in the lab were blocked off and

the laboratory's exhaust and supply were increased by approximately 25% and balanced to keep the room negative in pressure with

respect to surrounding areas. This eliminated indoor air quality complaints but due to the close proximity of lab occupants to

formaldehyde sources during dissection, no significant reduction in lab exposures were noted.

Between use, the cadavers were wrapped in embalming fluid-soaked cloth and enclosed in plastic bags. Embalming fluid drippings

were collected in open buckets located under each table drain. To reduce formaldehyde emission with better source enclosure, the

body bags and buckets were replaced with cadaver storage units (custom-made, plastic bins with elastic-rimmed plastic covers).

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Only the part of the body being dissected was exposed and fluid drippings which collected in the body trays were periodically

removed with kitchen basters for disposal.

The formalin concentration in the primary embalming solution was reduced to 5 - 6% - as low as possible without compromising

cadaver preservation. Total elimination of formaldehyde was not practical with current embalming technology. Experiments with

ceiling fans to better mix the room air were conducted. While exposures under the fan were reduced, exposures nearby were

increased. Respirators were suggested but were not feasible because they would severely limit anatomists' vision, communication

and perspective.

After two semesters of attempted controls and subsequent personal exposure monitoring, formaldehyde exposures were still a

concern. Personal samples collected and analyzed by either ASTM Method 05014-89 or OSHA Method 52 showed time-weighted

average (TWA) exposures during three-hour classes between 0.01 ppm to 4.0 ppm, with an average of 1.1 ~ 0.8 (n = 56). The

OSHA action limit of 0.5 ppm (8-hr TWA) was exceeded in 29% of samples and the OSHA PEL of 0.75 ppm (8-hr TWA) was

exceeded in 9% of samples. Fifteen-minute average exposure (or STELs) ranged from 0.4 ppm to 6.7 ppm, with an average of 2.6

~ 1.8 (n = 40). The OSHA STEL of 2 ppm was exceeded in 58% of the samples (see Figure 3).

Local exhaust was finally considered necessary for exposure control. For energy conservation purposes, use of a recirculating,

filtered exhaust table was first explored. A prototype exhaust table was constructed by adding slots to both sides of a standard

cadaver table and a fan and two treated charcoal filters in series to the underside. This system reduced formaldehyde

concentrations, but the idea was abandoned primarily because of the cost and short usable life of the filters (100 hours) and the lack

of a filter breakthrough indicator. User complaints of noise, cleaning difficulties and ergonomic concerns were also factors.

Following this prototype, efforts focused on a total exhaust system.

100% ., IExposure Limits (ppm)NIOSH REL 0.016 8-hr TWA

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Figure 3. Breathing zone formaldehyde levels in a gross anatomy laboratorybefore and after local exhaust ventilation.

THE SOLUTION

A multidisciplinary team was formed to design a local exhaust system. The main design criteria included: reducing formaldehyde

levels, ease of access and work with cadavers (i.e. ergonomics), specimen preservation (temperature control and minimize

desiccation), ease of cleaning, utilize existing dissection tables, and minimize operating and installation costs. Other ancillary criteria

sought to improve lighting, minimize noise and improve aesthetics, in conjunction with expanding the laboratory. A conceptual

approach satisfying these criteria was a modification of slotted exhaust tables previously reported in the literature.":":":" The design

team closely collaborated throughout the design process.

The design, which was ultimately developed, tested and installed in the anatomy teaching laboratory of the medical school is shown

and described in Figures 4 through 16. This final model, preceded by two prototypes (which were used to identify and correct

ergonomic concerns), is a slotted plenum connected to a standard dissection table. The table surface forms the top of the plenum.

Two removable sides with slots are added, as are the bottom of the plenum and two end collars. The end collars allow connection to

either a removable end piece or a removable flanged exhaust duct connection. The table is connected to a vertical duct via a flexible

duct connection, and then to a plenum above the ceiling that is maintained at -0.7" w.c. Air is supplied via a pressurized plenum

through diffuser ceiling tiles from above the table.

Exhaust and supply air flows are variable and controlled by the user through an electric timer switch (0 - 2 hours) which operates a

motorized, two-position damper in the vertical exhaust duct and a task light above the table. For energy conservation, exhaust flow

through the table is always a minimum of 100 cfm when the cadaver is covered and formaldehyde emissions are low. During

cadaver use, the user actuates the electric timer to use the task light. This opens the damper to increase table exhaust flow to 1200

cfm. The timer ensures that the system returns to minimum air flows should the user forget to turn off the system. The supply is

maintained at a percentage of exhaust ensuring that the laboratory is always at negative pressure to surrounding areas (see Figure

17 for an explanation of the sequence of operation).

NOVEL FEATURES

1) Exhaust connected to manifold exhaust plenum with constantly maintained -0.7" w.c. (see Figure 17 for a description of thesystem operation).

2) Diffuser ceiling tiles distribute supply air from pressurized ceiling plenum over the tables at a low velocity (see Figure 5).

3) Motorized, 2-position exhaust damper with minimum setting conserves energy during times of non-use - 1200 cfm/100 cfmare maximum/minimum air flows (see Figure 6).

4) Electric timer controlling exhaust damper and task light - promotes system use and conserves energy (see Figure 7).

5) Flexible duct connection to reduce vibration transmission and adaption to various table placements (see Figure 8).

6) Flanged duct transition for noise reduction and connectability to either end of table (see Figure 9).

7) Retrofit of existing cadaver table with new exhaust collection system - all stainless steel construction of table components (seeFigure 10).

8) Removable end connection to allow 1800 table rotation and ease of cleaning (see Figures 11 and 12) - quick release pawlfasteners allow easy removal.

9) Removable side panels for ease of cleaning (see Figures 13 and 14) - pin fasteners are cabled to table to avoid beingmisplaced during cleaning.

10) Table holds molded plastic cadaver storage unit with elastic-rimmed, impermeable cover - limits cadaver desiccation andformaldehyde emissions between use (see Figure 15).

11) Low profile, thin, slotted plenum with contoured edge - promotes ergonomic table function (see Figure 16). Slot velocity =2000 fpm, plenum velocity = 500 to 1,000 fpm.

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AIR FLOW DIAGRAM

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1) Two position, motorized damper opens when individual table control timer switch is enabled. Switch also energizes tasklighting at each table.

2) As more tables are energized, exhaust duct static pressure falls below set point, thus signaling exhaust fan variable frequencydrives (VFDs) to increase fan speed.

3) Supply fan VFDs modulate to ensure that supply airflow is at a constant proportion of exhaust airflow as measured in eachduct main.

4) Exhaust and supply fans are staged as needed to match flow requirements. Only one exhaust fan and one supply fanoperate during low use periods.

The laboratory which was expanded with the ventilation modifications now accommodates up to 35 cadavers (approximate room

volume is 33,000 fe), each on an exhausted dissection table (see Figure 18). The system has been in operation for one semester.

Since the ventilation modifications, formaldehyde exposures have been reduced to, and in most cases less than, the analytical limit

of detection, which is more than ten times less than the current ceiling value of 0.3 ppm recommended by ACGIH. Exposure levels,

which were re-evaluated during activities and by methods representative of previous sampling, are now close to 100 times less than

pre-ventilation levels (see Figure 3).

Subjective feedback from the users has been very positive with regard to all of the initially stated design criteria. Specimen

preservation is accomplished by keeping the laboratory at 65°F, using the covered, cadaver storage units, and by regular use of a

wetting solution (a mixture of mostly methanol, methoxypropanol, phenoxyethanol, and methyl salicylate).

CONCLUSION

1. The slot table design is effective in controlling formaldehyde exposures in a gross anatomy laboratory to less than currentoccupational health criteria and standards.

2. User involvement ensured the necessary system flexibility and operational and ergonomic requirements. User acceptance ishigh.

3. The exhaust system can be adapted to standard dissection tables. Therefore, the added cost of substituting presently usedtables with new ones does not discourage system installation.

4. The system includes simple controls which reduce system energy consumption in unoccupied times and encourage systemuse.

5. Further system testing and adjustments are needed to optimize energy efficiency while maintaining adequate exposurecontrol. Tracer gas testing to ascertain capture efficiencies, and air flow and pressure monitoring to tract system air volumecontrol, are planned. The installation of visual flow indicators may be considered.

ACKNOWLEDGEMENTS

We would like to acknowledge Henry Johnstone of GLHN Architects & Engineers, Inc. ( Tucson, AZ), the consulting design engineeron this project. We would also like to recognize others who contributed to the success of this project including: Drs. RobertMcCuskey and Dan Burns and Grant Dahmer, from the UA Department of Cell Biology and Anatomy, Ann Libecap from the UACollege of Medicine Administration, Steven Holland from the UA Department of Risk Management and Safety, and Steve Mikitishand Richard Knott from the UA Department of Facilities Management. Also worth recognizing is TA CAID Industrial Inc. (Tucson,AZ) for their superb stainless steel fabrication work. Lastly, we would like to thank Ruben Dominguez for developing the illustrationsfor this presentation.

REFERENCES

1. Documentation of the Threshold Limit Values and Biological Exposure Indices, American Conference of GovernmentalIndustrial Hygienists, Sixth Edition, 664-688, 1991.

2. Skisak, C.M., Formaldehyde Vapor Exposures in Anatomy Laboratories, Am. Ind. Hyg. Assoc. J., 44(12), 948-950, 1983.

3. Perkins, J.L., and Kimbrough, J.D., Formaldehyde Exposures in a Gross Anatomy Laboratory, J. Occ. Med., 27(11), 813-815,1985.

4. Fleisher, J.M., Medical Students' Exposure to Formaldehyde in Gross Anatomy Laboratories, NY State J. Med., 87:385-388,1987.

5. Uba, G., Pachorek, D., Berstein, H., Garabrant, D.H., Balmes, J.R, Wright, W.E., Amar, RB., Prospective Study ofRespiratory Effects of Formaldehyde Among Health and Asthmatic Medical Students, Am. J. Ind. Med., 15:91-101,1989.

6. Boiano, J.M.,Health Hazard Evaluation Report No. HETA-084-098-1497, Univ. of Pennsylvania Medical Education Building,NIOSH, 1984.

7. Cia, S.E., Ong, C.N., Foo, S.C., and Lee, H.P., Medical Students' Exposure to Formaldehyde in a Gross Anatomy DissectionLaboratory, J. Amer. College Health, 41: 115-119, 1992.

8. Akbar-Khanzadeh, F., Vaquerano, M.U., Akbar-Khanzadeh, M. and Bisesi, M.S., Formaldehyde Exposure, AcutePulmonary Response, and Exposure Control Options in a Gross Anatomy Laboratory, Amer. J. Ind. Med., 26:61-75,1994.

9. Grafstein, 0., Tirosh, Z., Shraiber, L.C., Bar-On, M., Dissection Tables with Local Exhaust Ventilation in an AnatomyLaboratory, 41st Annual International Conference on Campus Safety, NSC, Monograph No. 57, 265- 271, 1994.

10. Pabst, R, Exposure to Formaldehyde in Anatomy: An Occupational Health Hazard?, The Anatomical Record, 219:109-112,1987.

11. Feigley, C.E., Kennedy, R.J., Dwiggins, G.A., Local Exhaust Ventilation of a Dissection Table, Appl. Ind. Hyg., 4(12), 309-312,1989.

12. Gressel, M.G., Hughes, R., Effective Local Exhaust Ventilation for Controlling Formaldehyde Exposures During Embalming,Appl. Occup. Environ. Hyg., 7(12), 840-845, 1992.

13. Industrial Ventilation - A Manual of Recommended Practices, American Conference of Governmental Hygienists, 22thEdition, 1995.

14. Korczynski, R.E., Effectiveness of Downdraft Ventilation in Morgues, Appl. Occup. Environ. Hyg., 11(1), 5-8, 1996.