Air Scrubbers are NOT like Dehumidifiers So WHAT?!...Vacuuming floors, carpets, woodwork, etc. in...

1William M. Vaughan is President and Principal Scientist of Nauset Environmental Services, Inc.

(East Orleans, MA). Correspondence should be directed to [email protected].

Air Scrubbers are NOT like Dehumidifiers – So WHAT?! William Vaughan, PhD, QEP, CIEC

1

Prepared for IAQA 16th

Annual Meeting

(Orlando – February 2013)

SUMMARY & INTRODUCTION A common topic of discussion amongst mold remediators is “How long do you operate your air

scrubbers after HEPA vacuuming?” Such a question was raised during an open discussion

session at a Chapter meeting that indicates that boxy air scrubbers and boxy dehumidifiers are

considered similar devices operating under the same principles.

This presentation will provide the basis of the differences between the operation/effectiveness of

these devices. Then it will explain how to take advantage of the basic difference to improve the

assessment of Condition 2 (settled spores) as called for in ANSI/IICRC S520-2008 – “The

Professional Mold Remediation Standard and Reference Guide.” Once the potential Condition 2

contamination is identified using paired air samples - quiet and fan-disturbed - the talk will focus

on effective cleaning of these settled spores. Following thorough HEPA vacuuming in a space, a

combination of aggressive air disturbance with strong fans/leaf blowers and several oscillating

fans in combination with air scrubber(s), a process we at Nauset Environmental Services, Inc.

(NES) have worked on since 2004 and call “Air Polishing”, one can remove most of the settled

spores. The paper will show examples of these techniques in several settings and include videos

showing the techniques in action.

[NOTE: This presentation is based on the author’s experience and the laws of physics.]

HARDWARE

Air scrubbers are basically enclosures with powerful fans that draw air through a coarse pre-filter

and then a large HEPA filter at rates of about 150 CFM to 900 CFM. The recycling of the air

through the HEPA filter removes suspended particles from the air:

Examples of air scrubbers (Abatement Technologies)

Air Scrubbers are like NOT Dehumidifiers- SO WHAT?! Orlando ’13

Dehumidifiers also move the air but at slightly lower flow rates 400 CFM. However in the air

pathway are chilled metal fins that are kept below the dew point temperature of a typical room

air. When the room air contacts these fins, moisture condenses out of the air and is pumped to a

suitable drain achieving water removal rates of 150 pints/day water removal and up to 300 pints

per day.

Examples of dehumidifiers (Abatement Technologies)

Comparison

While these devices have a similar appearance and move air with powerful fans, they have

different operating principles:

Air scrubbers remove particles by trapping them in the HEPA filters for

removal/disposal. However, the particles must be in the air first.

Dehumidifiers remove water vapor from the air by condensing it out against refrigerated

fins. The water vapor is in the air since it a gas.

The difference is both subtle and significant:

• One can dry a room/carpet with a combination of dehumidifier(s) and circulating fan(s)

BECAUSE liquid water has vapor pressure and can evaporate, becoming a gas!

• Vapor pressure means that individual water molecules change state and become a

gaseous vapor, moving into the air, where they can diffuse or are circulated toward the

chilled plates in the dehumidifier. By moving into the air as seen in the following

schematic THAT EVAPORATION PROCESS dries the room/carpet.


Initial “wet conditions”

After some evaporation

Nearly dry


• The role of the dehumidifier is to provide the chilled plates on which dew point

condensation occurs thus removing the water molecules (vapor) from the air and, in the

process, reducing the vapor concentration in the area so more water molecules can

evaporate from the room’s/carpet’s surfaces, thus drying the space. A dehumidifier

merely speeds a natural process.

Since particles/spores are solids and have no vapor pressure, once settled they just lay there!

They need physical forces - strong drafts – to “kick” them back into the air.

No change over hours-days without strong drafts

HOW LONG DOES IT TAKE FOR SPORES TO SETTLE OUT?? It depends on their size.

This graphic from the CDCP (Center for Disease Control and Prevention) shows that mold

spores are in the general size range of about 0.8-20 µ (microns, or millionths of a meter).


Particles/spores settle out of the air over time in turbulent air as seen on the right side of this

CDCP graphic.

The settling rate varies with spore size. The half-life for smaller spores near 1 µ to settle out in a


typical eight foot room is about 12 hours and for slight larger spores near 3 µ, a more common

spore size, the half-life is only 1.5 hours. Even larger spores settle out faster as shown.

BOTTOM LINE: In light of the above information, even if you operate an air scrubber for

many hours to a couple of days, most of the particles that were initially suspended have either

been scrubbed out of the air or settled to surfaces in the room before the first day is over and you

have missed the opportunity to filter them out. Longer operation of air scrubbers alone will

not improve the removal of the spores from the room. That fact of life poses a problem for the

remediator since those un-removed settles spores are Condition 2 Contamination that

professional mold remediators are supposed to address and remove according to the consensus

industry standard (ANSI/IICRC S520-2008 “Professional mold Remediation Standard and

Guideline).

SOLUTION TO THIS SETTLED SPORE DILEMMA AND

APPROACH TO IMPROVED DETECTION AND CLEANING

When one realizes that spores are not visible to the human eye and settle out, continuing to

contribute to Condition 2, settled spore contamination, one needs a different approach to both

identify the settled spores in the first place AND THEN to clean them better than methods

depending solely on stand-alone air scrubbers.

HISTORY

In December 2003, IICRC issued S520 established that Condition 3 contamination (actual

mold growth) and Condition 2 contamination (settled spores) needed to be addressed by

physical removal. When it was revised and became and industry consensus standard,

ANSI/IICRC S520-2008 the guidance calling for cleaning up Condition 3 and Condition 2 were

retained. Thus one must still address the issues of identifying potential Condition 2

contamination and how to focus cleaning on these settled spores by “physical removal” as

spelled out in S520.

This paper describes an approach developed to characterize settled spores via paired air samples

- quiet and fan-disturbed - using a common 12” fan. The 12” fan stirs up the settled spores from

a suspect area and mixes/integrates them so they can be sampled. If comparison of the results

from the paired samples shows a statistically significant difference, one can approach the

remediation as a Condition 2 issue.

As has been described above, since settled mold spores are NOT REMOVED by the methods

many mitigators have used, the method that NES has developed of “air polishing” is presented,

based on the disturbed sampling approach to investigating for the presence of settled spores.

Following thorough HEPA vacuuming in a space, “air polishing” involves a combination of

aggressive air disturbance with strong fans/leaf blowers and several oscillating fans in

combination with air scrubber(s) to suspend and remove most of the settled spores. The paper

proceeds with examples of these sampling and cleaning techniques in several settings. In


addition there is a comparison of the disturbed sampling approach using spore traps with the

sampling for viable spores under quiet conditions.

LOOKING FOR INVISIBLE SETTLED SPORES An initial typical air sample can show low spore levels and the place “looks” great – yet it may

still be contaminated by settled spores. They are not measured/characterized by the typical

(quiet) air sampling effort – setting up a tripod with a spore trap or culture plate and drawing air

into/onto the collection medium. That “quiet” approach measures those spores that have not yet

settled and can be quite misleading. We have encountered many situations where “visual

inspection” and quiet sampling has led the mitigator to conclude that things “are pretty good”

and his/her initial HEPA vacuuming has been sufficient.

Visual inspection is totally inadequate for determining settled spores since they are below the

resolution limit of the human eye, about 50μ (microns). Settled spores have been a critical

element in IICRC’s approach to mold cleanup since 2003, spurred by knowledge of the health

impact of molds and the fact that mold spores are biological organisms, capable of

recontaminating a space! [REMEMBER: If you were to remove 99.9% of oil, PCB or lead

contamination after an area was impacted by a release you would have only 0.1% of the original

contamination. If you remove 99.9% of mold spores and another leak recurred, there is a good

chance that the area will be re-contaminated, since molds spores can grow and reproduce,

increasing their numbers.]

Finding settled spores - HOW DO YOU KNOW THAT THERE ARE SETTLED SPORES

PRESENT INITIALLY or LEFT BEHIND FOLLOWING HEPA CLEANING?

Some professionals recommend taking tape lift or swab samples to determine the presence of

settled spores, Condition 2 contamination, as part of an initial baseline assessment or post-

remediation verification (PRV) sampling; but where do you take those samples??

Floors? Walls? Easy to reach places? Every stud bay? Every fifth stud bay?

Also how many samples do you need from each lift/wipe location? It has been

suggested that upwards of 50 to 100 samples (perhaps 10% of the surface area) may be call for to

have improved scientific confidence in adequately characterizing a space. Will the

pressure for scientific confidence be severely compromised by real-world budget constraints?

One approach to these assessment dilemmas, both pre and post-remediation, is to take

“disturbed” air samples that are paired with “quiet” (typical) air samples. We at NES have been

utilizing disturbed air sampling since 2004 and find it definitive and very cost effective in

addressing Condition 2 mold contamination. We use common 12” table fans for this activity

since they might be found and used in a home.

The advantage of disturbing the air disturbs the settled spores from many surfaces in a

room/area, including rafters in cathedral ceilings, nooks and crannies in awkward corners,

baseboard heat exchanger fins, etc. can be impelled into the air and mixed so that they can be

sampled in a traditional way. The disturbance integrates settled spores from many possible

locations in a room/area. The disturbance simulates, to some extent, human activities that could


remobilize the settled spores to travel to uncontaminated areas after containment barriers are

removed. Those activities might include:

Cooling occupants or providing general ventilation using table fans or floor fans

Laying carpet during which effort rolls of carpet and padding are dropped onto the

subflooring and rolled out creating sudden strong puffs of air

Opening windows or operating attic fans that simulate outdoor drafts through the

windows

Remodeling activities that involve dropping supplies or material, like dry wall panels,

onto the floor

Vacuuming floors, carpets, woodwork, etc. in the normal course of house maintenance

During these “normal” human activities, settled spores present or left behind can be kicked into

the air by drafts and then slowly settle onto the new/cleaned surfaces in a room/area after

refurbishing. NES’s idea has been to simulate those occupant activities with drafts from a

typical 12” table fan while there is still a chance to make sure the cleaning activity to date has

been reasonably effective and, if not, suggest further “air polishing” of the room/area to reduce

the settled spores even more.

Disturbing the surfaces - HOW CAN YOU DISTURB THE AIR WITHOUT BEING NON-

REPRESENTATIVE?

At first NES adopted the guidance for the asbestos abatement industry where leaf blowers are

operated and moved about within containment areas for extended periods of time before and

during air sampling. These aggressive “clearance” samples are called for under standard

industry protocol and must result in very low fiber counts on filter samples before an area is

declared clean enough to be re-opened for occupancy.

NES was criticized for this approach, even though it did point out areas where additional

remediation activities were required. The criticism was that those extremely strong drafts were

not “typical” for “lived in” spaces and resulted in too stringent a cleanup challenge in light of the

absence of firm clean-up guidance.

NES then switched to using 12” household fans, either table or floor styles. These are the type

and size fans purchased to provide ventilation and cooling all over the country. That lighter level

of disturbance was considered acceptable in a living space and not extreme, as the leaf blowers

were. The technician disturbs the air by holding the fan and directing it around the space being

sure to blow back and forth across the floor in a regular grid pattern, across moldings and

horizontal ledges, into baseboard fins, into corners, and any place one can imagine where spores

could have settled in a room. Two to three minutes of waving the fan is usually sufficient to

cover most surfaces, obviously longer for larger rooms/areas.


Example of disturbance patterns that are combined

NES does not take a “disturbed” air sample by itself to determine Condition 2 contamination,

but pairs it with a traditional “quiet” air sample to see how much the airborne spore levels

change when the settled spores are mobilized into the air. In this way two samples, usually spore

trap samples, give a fairly thorough, integrated picture of mold spore contamination in a

room/area. By using the total spore number, NES focuses on the health impact for occupants,

since both viable and non-viable spores can cause allergic reactions in sensitized individuals.

(Of course there is often, but not always, one outdoor air sample during these efforts in order to

compare the mix of spores outdoors with those indoors to demonstrate any water-induced mold

amplification. Since our focus in these paired sampling efforts is on Condition 2 in a given

space we are not nearly as concerned regarding possible outside sources, especially in indoor

investigations of moisture intrusion situations.)

Here are some example of what NES’s paired samples have found and how they have been used:

EXAMPLE 1 [Post-remediation] - Failure of two baseboard heaters led to damage from direct

water as well as condensation. Four separate areas in the house were contained and remediated

by HEPA vacuuming and wiping down. Air scrubbers were operated for nearly 48 hours as part

of the normal remediation. NES was brought in for post-remediation verification (PRV)

sampling at a time when the outdoor total spore level was 2,650 S/m3.


Chart 1

Chart 1 shows the initial post-remediation air sample pairs (quiet and disturbed) in each of the

four areas. In Areas A and C, disturbing the air with the 12” fan stirred up few additional spores.

In Area B, near one of the leaks, the total spores were initially at 1,222 S/m3, a seemingly

acceptable level compared to the 2,640 S/m3 in the outdoor air. However, the total spores

increased 18-fold after the fan’s drafts suspended them, but, within those samples, the

Aspergillus-Penicillium (Asp-Pen –like) spores (“A-P” in the chart) increased 24-fold! That is a

statistically significant difference (i.e. well over an order of magnitude) indicating a reservoir of

settled spores persisting after the traditional remediation.

In Area D, on the floor below the other leak, the difference in levels induced by the fan’s drafts

is much more dramatic. The initial quiet conditions at 944 S/m3 again seem to be quite

acceptable. However, the total spore levels increased some 41-fold under the influence of the

drafts with Asp-Pen like spores increasing some 120-fold!

Other examples will be cited later in this paper where NES has used this disturbed air technique

to reveal extensive Condition 2 contamination. The bottom line is that the additional

information from a “disturbed” air sample can point to the need for initial or further remediation

to reduce Condition 2 contamination and it is more cost-effect and has less sampling bias than

subjective selected tape or wipe samples from somewhat arbitrary locations.


EXAMPLE 2 [Initial investigation] - Rental apartment with leak in bathroom above kitchen.

A handyman had removed part of the kitchen ceiling. A plumber fixed leak. The tenant wanted

air sampling to confirm conditions were safe.

The kitchen looked clean (see Figure). There was no VMG and no moldy odor.

Apartment kitchen after repair of bathroom leak above kitchen corner cabinet

Paired air sampling revealed a serious situation (see Chart 2):

- Under quiet sampling -

Total Spores were less than 400 S/m3 with only 267 S/m

3 being the leak

indicator Asp-Pen like spores.

There were no Stachybotrys spores detected.

- Under disturbed sampling -

Total spores increased to almost 30,000 S/m3 with Asp-Pen like spores at

nearly 14,000 S/m3.

Nearly 4,400 S/m3 of Stachybotrys spores were detected!


Kitchen Spore Levels -

Quiet & Disturbed

0

5,000

10,000

15,000

20,000

25,000

30,000

Sp

ore

s/s

tru

ctu

res

/m

^3

Stachy 0 4,356

Asp-Pen 267 13,900

Other 122 11,666

Kitchen - Q Kitchen - D

Chart 2

The paired sampling approach clearly revealed extensive Condition 2, settled spore

contamination that was not initially obvious with the additional concern for excessive

Stachybotrys spores.

In this case visual inspection was not sufficient. Quiet air sampling was not sufficient. Only

paired sampling revealed the extent of serious contamination.

EXAMPLE 3 Cross-contamination] - There was an intermittent leak from a pressure relief

valve on a basement water heater. Paneling in the basement was heavily impacted by mold (see

photo below). Carpet and paneling were removed from the lower level by a mold remediator.

The question was whether there was cross-contamination of the floor above (see photo below).

Paired sampling revealed Asp-Pen like spore levels in the living room about 6-fold higher than

the initial low values from the quiet sample - 260 S/m3 under quiet conditions and 1,950 S/m

3

under disturbed conditions.

This comparison indicated a slight amount of cross contamination that could probably be

reduced by routing use of a residential HEPA vacuum on the hardwood floors.


Mold on basement paneling Living room at top of basement stairs

Chart 3

EXAMPLE 4 [Residual settled spores] - A basement water heater failed. Some wet building

materials were removed from the in the initial response (see photo). There was no formal

remediation. There was no visible mold growth (VMG) reported and there was no moldy odor

indicating active mold growth. The question was whether further mold remediation was

warranted.


Basement Baseline Spore Levels -

Quiet & Disturbed

0

100,000

200,000

300,000

400,000

500,000

600,000

Sp

ore

s/s

tru

ctu

res

/m

^3

Stachy 0 190

Asp-Pen 2,100 550,000

Other 2,900 950

Baseline - Q Baseline - D

Basement storage area with lower drywall removed on left

Baseline mold sampling (Chart 4) revealed somewhat elevated total spores at about 5,000 S/m3

with moisture/leak indicator Asp-Pen like spores comprising about 40% of the mix at

2,100 S/m3. Following fan disturbance the total spore levels rose about 1,100 fold to

550,000 S/m3 with essentially all now being Asp-Pen like spores, a definite indication of

Condition 2, settled spore contamination, calling for professional mold remediation.

Chart 4


EXAMPLE 5 [Initial investigation] - A second floor apartment in a 19th

century building

developed extensive mold growth on the walls during the tenants’ second fall-winter of

occupancy. A 3-year old resident became ill and developed asthmatic conditions. The previous

summer an aquarium shop had opened on the opposite side of the ground floor, NOT under the

apartment. After the parents wiped the walls and cleaned as best they could (see photo below),

the question was whether the apartment was suitable for reoccupancy.

Master bedroom

The NES paired data for total spores appear in Chart 5 below.

In addition to an investigation by NES, about 6 days later with no intervening remediation

activity, an experienced mycologist was called on to carry out an investigation in the same

apartment using a different approach.

The mycologist did quiet sampling for viable spores and found:

- Master bedroom - 380 CFU/m3 consisting of:

Penicillium at 300 CFU/m3

Cladosporium at 69 CFU/m3

Aspergillus glaucus at 11 CFU/m3

Those CFU data appear in Chart 6 below with the vertical scale expanded 1,500-fold.


M Bedroom Spore Levels -

Quiet & Disturbed

0

250,000

500,000

750,000

1,000,000

1,250,000

1,500,000

Sp

ore

s/s

tru

ctu

res

/m

^3

Stachy 0 0

Asp-Pen 4,900 1,500,000

Other 2,200 0

M Bedroom - Q M Bedroom - D

M Bedroom CFU Levels - Quiet[Vertical scale expanded 1,500x]

0

500

1,000

CF

U/m

^3

Asp-Pen 311

Other 68

M Bedroom CFU

Chart 5

Chart 6 with vertical scale magnified

It is obvious that the paired sampling

revealed significant Condition 2

contamination above the already elevated

quiet total spore counts. The viable spore

sampling significantly underestimated the

degree of contamination calling for

professional mold remediation.

Cleaning up Condition 2 settled spores -

HOW DO YOU CLEAN UP CONDITION 2 SETTLED SPORES? One must realize that

settled spores have eluded the traditional carpet fan/air mover and air scrubber approaches to

remediation. They do that because mold spores are solid objects and cannot “jump” into the air

on their own. They need drafts. BUT not any draft will do.


If you are trying to remove leaves from a driveway, you sweep the leaf blower back and forth

across the surface and gradually corral/move the leaves into the pile you want. You know that if

you just set up the leaf blower in the driveway and walked away, you would move the leaves off

the surface only in the direct path of the exhaust while leaves on either side would just lay there

even though the leaf blower’s blast is very strong. Similarly, on a much smaller scale, a

carpet/snail fan that is blowing in one direction without being redirected can mobilize only those

spores in its direct draft, not those to the side, much less those in the room behind it.

NES’s approach to reduce settled spore levels is to direct remediators to follow an “Air

Polishing” protocol AFTER the traditional approach following the general guidance Section 12

and Chapter 11 of ANSI/IICRC S520-2008. [NOTE that the concept of “air washing” has been

mentioned in the industry for some time, but usually involves just extended operation of air

scrubbers, NOT active, multiple disturbances with high velocity air combined with on-going

disturbance from oscillating fans.] The “air polishing” protocol involves maintaining the

containment with worker’s still wearing protective gear, then:

Ensure that air scrubbers being used are cleaned and evaluated for proper

performance. [NOTE - Guidance was developed for the Portable High Efficiency Air

Filtration Device Field Testing and Validation (“PHEAF”) Standard that is

temporarily suspended by the Indoor Environmental Standard’s Organization

(IESO).]

Set up at least one air scrubber in each of the areas or rooms remediated (depending

on size), as opposed to operating in the negative air mode under which spores outside

the containment could be drawn into the newly “cleaned” space. Set up 4-6 or more

oscillating fans (similar to those used to disturb the air in the above discussion) in the

same area/room to minimize stagnant air zones. [Several air polishing systems can be

operated at the same time in various areas of the building or in one large area.] Be

creative with aiming oscillating fans since they are not there for the comfort of

inhabitants in the center of the room, rather for minimizing the quiet areas where

spores can settle at the edges/corners of a room. One can use stand-type oscillating

fans aimed up to rafters, exposed beams, shelves, etc. to stir up spores on those

surfaces.

If there are several gutted rooms with a common small air space, bounded by studs

and incomplete partitions, a single air scrubber can still work. Use multiple smaller

oscillating fans in the smaller areas to keep nooks, crannies and corners disturbed and

add one or more carpet fans to develop a circulation pattern to direct the suspended

spores to the central air scrubber.

Periodically, 2-3 times a day, use a strong fan or leaf blower to stir up the settled

spores left over after the remediation activities so that they can eventually be moved

to the air scrubbers on drafts from the fans and be filtered out of the air. Direct the

leaf blower to all corners of the room and elevated surfaces that are difficult to reach.

In addition, reposition and/or redirect the air scrubber(s) exhaust as well so that it hits

a new corner or quiet zone after each visit. Be sure to direct drafts to any baseboard

fins in the room. [The high velocity of a leaf blower ensures better mobilization of

settled spores!]

Operate the oscillating fans and air scrubber(s) for at least 36-48 hours in each

area/room after the traditional cleanup is completed, periodically revisiting the

room/area for leaf blower mixing and ALSO repositioning the smaller fans after each


leaf blower visit. Repositioning the oscillating fans reduces the dead zones where

spores can settle out and collect.

To indicate the effectiveness of “air polishing” alone with no additional HEPA vacuuming in

Example 1 above look at the data in Chart 7 from our first example with four impacted areas

(plotted in Chart 1 above and reproduced here for easier comparison).

Chart 1 repeated

=====================================================

Chart 7 with 20-fold expanded vertical scale compared to Chart 1


In Area B the quiet spore levels have been reduced to under 600 s/m3 and the disturbed spore

levels only increased by less than 3-fold under fan disturbance, compared to 18-fold before “air

polishing,” and Asp-Pen levels increased by less than 6-fold, compared to over 22-fold before

“air polishing.”

In Area D the effect of “air polishing” is more dramatic. The quiet air sample now has total

spore levels just over 2,100 S/m3, down some 88%. When the surfaces were disturbed by the

fan, the total spore readings now increased just over 5-fold, compared to over 410-fold earlier.

Following fan disturbance Asp-Pen like spores increased just over 4-fold to only 244 S/m3,

compared to the 120-fold increase to nearly 39,000 S/m3 initially.

CONCLUSION: Over the last eight years the air polishing technique has been demonstrated to

successfully reduce the level of total spores in areas with demonstrated Condition 2

contamination (like areas B & D in this house), without any additional HEPA vacuuming.

The use of strong leaf blowers at the air polishing stage, NOT at the initial, pre-remediation,

baseline investigation stage, aims at aggressively moving any settled spores into the air. Several

oscillating fans minimize the quiet zones and keep the spores airborne longer for filtration by the

air scrubbers. There are likely to be fewer settled spores left over following this approach,

resulting in a higher likelihood of a successful PRV evaluation and fewer return trips that extend

the remediation – saving money for the client and shortening the overall remediation effort to

achieve documented success. NES believes that this is a very valid approach to achieving the

“physical removal” of settled mold spore contamination called for in S520.

NOTE: Several mold remediators in the southeastern Massachusetts area (and others NES has

heard from at these IAQA meetings) have stated that they are now happily and successfully

using this “Air Polishing” technique!

William M Vaughan, PhD, QEP, CIEC

Nauset Environmental Services, Inc.

508-247-9167

[email protected]

www.NausetEnvironmental.com

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