United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/S2-91/004 May 1991
Project Summary
Asbestos Fiber Reentrainment
During Dry Vacuuming
and Wet Cleaning of
Asbestos-Contaminated Carpet
John R. Kominsky and Ronald W. Freyberg
A study was conducted to evaluate
the potential for asbestos fiber
reentrainment during cleaning of car-
pet contaminated with asbestos. Two
types of carpet cleaning equipment
were evaluated at two carpet contami-
nation levels. Airborne asbestos con-
centrations were determined before and
during carpet cleaning to evaluate the
effect of the cleaning method and
contamination loading on fiber
reentrainment during carpet cleaning.
Overall, airborne asbestos concentra-
tions during carpet cleaning were two
to four times greater than concentra-
tions prior to cleaning. The level of
asbestos contamination and the type
of cleaning method used had no statis-
tically significant effect on the relative
increase of airborne asbestos concen-
trations during carpet cleaning.
This Project Summary was developed
by EPA's Risk Reduction Engineering
Laboratory, Cincinnati, OH, to announce
key findings of the research project
that is fully documented In a separate
report of the same title (see Project
Report ordering information at back).
Introduction
Buildings that contain friable asbestos-
containing materials (ACM) may present
unique exposure problems for custodial
workers. Under certain conditions, asbes-
tos fibers can be released from fireproofing,
acoustical plaster, and other surfacing
material. The release of asbestos by aging
and deteriorating ACM is known to be
episodic and relates to a myriad of fac-
tors, such as the condition and amount of
asbestos present, the accessibility of the
material, activity within the area, vibration,
temperature, humidity, airflow, use pat-
terns, etc. A major concern is the extent
to which carpet and furnishings may serve
as reservoirs of asbestos fibers and what
happens to these fibers during normal
custodial cleaning operations.
The U.S. Environmental Protection
Agency (EPA) performed a series of con-
trolled experiments in an unoccupied
building 1) to evaluate the effectiveness
of a high-efficiency particulate air (HEPA)-
filtered vacuum cleaner and a HEPA-fil-
tered hot-water extraction cleaner in the
removal of asbestos from carpet, and 2)
to evaluate the potential for reentrainment
of asbestos fibers during carpet-cleaning
activities. The study was designed to
compare carpet asbestos concentrations
before and after cleaning with each
cleaning method at two known contami-
nation levels. Concentrations of airborne
asbestos in the work area before and
during carpet cleaning were also com-
pared.
The report summarized here presents
only the air monitoring results from the dry
vacuuming and wet cleaning of the as-
bestos-contaminated carpet to evaluate the
Printed on Recycled Paper
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potential for fiber reentrainment during
cleaning. The results of the carpet sample
analyses and the effectiveness of two
cleaning methods in removing asbestos
fibers from contaminated carpet are pre-
sented in a separate report.
Study Design
Test Facility
This study was conducted in an unoc-
cupied building at Wright-Patterson Air
Force Base in Dayton, OH. Two rooms,
each containing approximately 500 ft2 of
floor space, were constructed in a large
bay of the building. The rooms were con-
structed of 2- x 4-in. lumber with studs
spaced on 24-in. centers and 3/4-in. ply-
wood floors. The inside of the rooms (the
ceiling, floor, and walls) was double-cov-
ered with 6-mil polyethylene sheeting. (The
interior layer of polyethylene sheeting was
encapsulated and replaced after each ex-
periment.) Where the joining of separate
sheets of polyethylene was necessary, the
sheets were overlapped at least 12 in.
and joined with an unbroken line of adhe-
sive to prohibit air movement. Three-in.-
wide tape was then used to seal the joint
further on both the inside and outside of
the plastic sheeting.
Entry from one room to another was
through a double-curtained doorway con-
sisting of two overlapping sheets of 6-mil
polyethylene placed over a framed door-
way. Each sheet was secured along the
top of the doorway; the vertical edge of
one sheet was secured along one vertical
side of the doorway and the vertical edge
of the other sheet was secured along the
opposite vertical side of the doorway.
Room size (approximately 29 x 17 x 7.5
ft) was based on the minimum amount of
time required to vacuum or wet-clean the
room arid to attain an adequate volume of
sample air to achieve a specified analyti-
cal sensitivity. A 52-in., ceiling-mounted,
axial-flow, propeller fan was installed in
each room to facilitate air movement and
to minimize temperature stratification.
Separate decontamination facilities for
workers and waste materials were con-
nected to the experimental areas. The
worker decontamination facility consisted
of three totally enclosed chambers as fol-
lows:
1) An equipment change room with
double-curtained doorways, one to the
work area and one to the shower room.
2) A shower room with double-cur-
tained doorways, one to the equipment
change room and one to the clean change
room. The one shower installed in this
room was constructed so that all water
was collected and pumped through a three-
stage filtration system. The three-stage
filtration system consisted of a 400-u.m
nylon-mesh, filter-bag prefilter; a 50-u.m
filter-bag second-stage filter; and a 5-u.m
final-stage filter. Filtrate was disposed of
as asbestos-contaminated waste. Water
was drained from the filtration system exit
into a sanitary sewage system.
3) A clean change room with double-
curtained doorways, one to the shower
room and one to the noncontaminated
areas of the building.
Air Filtration
After each experiment, the airborne as-
bestos concentrations were reduced to
background levels by HEPA filtration sys-
tems. These units were operated during
both preparation and decontamination of
the test rooms; they were not intended to
be operated during the carpet cleaning
phase of each experiment.
One HEPA filtration system was dedi-
cated to each test room. Each unit pro-
vided approximately 8 air changes per
every 15-min period. The negative pres-
sure inside the test rooms ranged from
-0.08 to -0.06 in. of water. All exhaust air
passed through a HEPA filter and was
discharged to the outdoors (i.e., outside
the building). All makeup air was obtained
from outside the building through a win-
dow located on the opposite side of the
building from the exhaust for the HEPA
filtration systems.
Experimental Design
Two carpet cleaning methods, dry
vacuuming with a HEPA-filtered vacuum
and wet cleaning with a HEPA-filtered hot-
water extraction cleaner, were evaluated
on carpet artificially contaminated at two
levels, with approximately 100 million and
with 1 billion asbestos structures per
square foot (s/ft2). Each combination of
cleaning method and contamination level
was replicated four times.
Four different (same model) HEPA-fil-
tered vacuums and four different (same
model) HEPA-filtered hot-water extraction
units were used in this study so that the
results would not be influenced by the
peculiarities of a single unit. Each machine
was used only once per combination of
cleaning method and contamination level.
This experimental design yielded a total
of 16 experiments. Three work-area air
samples were collected before carpet
cleaning and three work-area air samples
were collected during carpet cleaning for
each of the 16 experiments.
Two experiments were conducted each
day of the study. Each combination of
cleaning method and contamination level
was tested twice in each test room. A
single experiment consisted of contami-
nating a new piece of carpet (approxi-
mately 500 ft2) with asbestos fibers, col-
lecting work-area air samples, dry vacu-
uming or wet cleaning the carpet while
concurrently collecting a second set of
work area air samples, removing the car-
pet, and decontaminating the test room.
Each test room was decontaminated by
encapsulating the polyethylene sheeting
on the ceiling, walls, and carpet before
their removal. These materials were re-
placed after each experiment.
Materials and Methods
A survey was made of 14 General Ser-
vice Administration (GSA) field offices in
11 States distributed across the United
States to determine the most prevalent
types of carpet, HEPA-filtered vacuum
cleaner unit, and HEPA-filtered hot-water
extraction unit to use in this study. Building
managers were asked to identify 1)the
specific type and manufacturer of carpet,
2) the manufacturer and model of HEPA-
filtered vacuum cleaner, and 3) the manu-
facturer and model of HEPA-filtered hot-
water extraction cleaners routinely used in
their GSA buildings.
None of the GSA offices routinely wet-
cleaned their carpet. When wet-cleaning
was necessary, contractors were hired to
perform the work. Therefore, six trade as-
sociations were surveyed to obtain their
recommendations on a HEPA-filtered hot-
water extraction cleaner.
Selection of Carpet
Eight of the fourteen GSA offices indi-
cated a preference for the same manufac-
turer and type of carpet. The selected
carpet was first-grade, 100% nylon, with
0.25-in. cut pile, 28 oz of yarn per square
foot, and dual vinyl backing. The carpet
was manufactured in roll sizes of 4.5 by
90ft.
Selection of Carpet Cleaning
Equipment
HEPA-Filtered Vacuum
The HEPA-filtered vacuum selected for
this study was the model most frequently
mentioned in the GSA survey. The unit
had an airflow capacity of 87 ft3/min and a
suction power of 200 watts. This unit was
also equipped with a motor-driven carpet
nozzle with a rotating brush.
Hot-Water Extraction Cleaner
Three of the trade associations surveyed
recommended the same hot-water extrac-
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tion unit. The selected cleaner was
equipped with a HEPA-filtered power head
with a moisture-proof, continuous-duty, 2-
horsepower vacuum motor that develops
a 100-in. waterlift. This unit was also
equipped with an extractor tool that uses
a motor-driven 4-in.-diameter by 14-in.-
tong cylindrical nylon-bristle brush to agi-
tate and scrub the carpet during the ex-
traction process.
Sampling Methodology
Air samples were collected on open-
face, 25-mm-diameter, 0.45-p.m pore-size,
mixed cellulose ester membrane filters with
a 5-u.m pore-size, mixed cellulose ester
backup diffusing filter and cellulose ester
support pad contained in a three-piece
cassette. The filter cassettes were posi-
tioned approximately 5 ft above the floor
with the filter face at approximately a 45°
angle toward the floor. The filter assembly
was attached to an electric-powered
vacuum pump operating at a flow rate of
approximately 10 L/min. In each test room,
the air samplers were positioned in a tri-
angular pattern. Air samples were collected
for a minimum of 65 min before and again
during carpet cleaning to achieve a mini-
mum air volume of approximately 650 L.
The sampling pumps were calibrated both
before and after sampling with a precision
rotameter.
Analytical Methodology
The mixed cellulose ester filters were
analyzed by transmission electron micros-
copy (TEM). These filters were prepared
and analyzed in accordance with the
nonmandatory TEM method as described
in the Asbestos Hazard Emergency Re-
sponse Act (AHERA) final rule (52 CFR
41821).
Statistical Analysis
Airborne asbestos concentrations were
determined before and during carpet
cleaning to study the effect of the clean-
ing method and contamination loading on
fiber reentrainment during the carpet
cleaning. Three work-area samples were
collected before and during the carpet
cleaning for each experiment. A single
estimate of the airborne asbestos con-
centrations before and during cleaning was
then determined by averaging the three
respective work-area samples. As a mea-
sure of relative change in airborne asbes-
tos concentration, the ratio of the concen-
tration during cleaning to the concentra-
tion before cleaning was computed. The
natural bg of this ratio was then analyzed
by using a two-factor analysis of variance
(ANOVA) with the cleaning method and
contamination level as the main factors.
The two-factor interaction term was also
included in the model. This analysis is
equivalent to assuming a kxjnormal distri-
bution for airborne asbestos measure-
ments and analyzing the log-transformed
data for differences between airborne as-
bestos concentration before and during
cleaning. The lognormal distribution is com-
monly assumed for measurements of as-
bestos and other air contaminants. Sum-
mary statistics (arithmetic mean and stan-
dard deviation) were calculated according
to cleaning method and contamination
level.
Carpet Contamination
Selected levels of carpet contamination
for this study were based on reported
field data. These data indicated that as-
bestos concentrations in contaminated car-
pet ranging from approximately 8,000 to 2
billion s/ft2 had been detected by use of a
microvac technique. Bulk sample sonica-
tion of the samples had revealed levels
ranging from 30 million to 4 billion s/ft2.
Based on these reported results, the two
target experimental asbestos contamina-
tion levels of approximately 100 million
and 1 billion s/ft2 were believed to repre-
sent carpet contamination likely to be
present in buildings where asbestos-con-
taining materials are present.
For this project, the decision was made
to prepare sealed ampules of fiber dis-
persions so that the contents of one am-
pule dispersed in 6 L of freshly distilled
water would provide the concentration of
suspension required for artificial contami-
nation of one 500-ft2 sample of carpet.
Calculations of the amount of chrysotile
required were based on the assumption
that all of the fibers needed to contaminate
one carpet sample would be contained in
a volume of 50 ml sealed in one ampule.
Application of Dispersion to
Carpet
A meticulously cleaned, hand-pumped,
garden sprayer was used to apply the
asbestos dispersion to the carpet. A fixed
number of pumps was used for each batch
to provide consistent spray pressure. The
desired controlled spray was experimen-
tally determined by trial and error before
the tests with asbestos began. The pres-
sure was kept within the desired range by
adding a fixed number of pump strokes
after each fixed area was sprayed in a
predetermined pattern by following a grid
work of string placed over the carpet before
the beginning of each experiment. The
tank was periodically agitated to help keep
the asbestos fibers suspended. Dehu-
midifiers were placed in the room over-
night to aid in drying the carpet. The fol-
lowing day, a 200-lb steel lawn roller was
rolled over the carpet surfaces to simulate
the effects of normal foot traffic in working
the asbestos into the carpet.
To ensure no bacterial growth had oc-
curred in the sprayer between uses, the
inside of the sprayer and the outlet pipe
were treated with a 10% to 15% solution
of Ctorox* to remove any bacteria and
their byproducts. Any bacterial growth
would scavenge fibers from the suspen-
sion and cause fibers to become attached
to the wall of the container. The container
and outlet pipe were then rinsed with iso-
propyl alcohol.
Carpet Cleaning Technique
The carpet was vacuumed or wet-
cleaned for a period of approximately 65
min to allow the collection of a sufficient
volume of air to attain an analytical sensi-
tivity of 0.005 s/cm3 of air. The carpet was
cleaned in two directions, the second di-
rection at a 90° angle to the first.
Quality Assurance
TEM Analyses
Specific quality assurance procedures
for ensuring the accuracy and precision of
the TEM analyses of air samples included
the use of lot, laboratory, and field blanks
and replicate and duplicate analyses.
Filter lot blanks consisted of unused
fillers selected at random and submitted
for prescreening analysis for background
asbestos contamination before the start of
field work to determine the integrity of the
entire lot of filters purchased for EPA re-
search studies. One hundred lot blanks
were submitted for TEM analysis. No as-
bestos structures were detected in the
1000 grid openings analyzed. The lot of
filters was subsequently considered ac-
ceptable for use.
During the setup of the air sampling
pumps, preloaded filter cassettes were la-
beled and handled in a manner similar to
that for the actual sample filters, but they
were never attached to the pump. One
field blank was collected for each of the
16 experiments. Two of the 16 filters each
contained one asbestos structure. Also,
before each of the 16 experiments, one
sample cassette was selected from the
filter inventory to be used as a laboratory
blank. These samples were sealed and
submitted for use by the analytical labo-
ratory to ensure against any blank inter-
"Mention of trade names or commercial products does
not constitute endorsement or recommendation for use.
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ference during the analytical procedure;;.
Two of the 16 sealed blanks each con-
tained two asbestos structures. Analysis
of the field and laboratory blanks demon-
strated that filter contamination was com-
parable to background levels of asbestos
on filters; these background levels are de-
fined as 70 s/mm2 in the AHERA final rule
(October 30, 1987; 52 CFR 41826).
Duplicate sample analysis provides a
means of quantifying intralaboratory preci-
sion and refers to the analysis of the same
grid preparation by a second microscc-
pist. Five samples were randomly selected
for duplicate analysis. Replicate sample
analysis provides a means of quantifying
any analytical variability introduced by the
filter preparation procedure and refers to
the analysis of a second grid preparation
from the original filter. Five samples were
randomly selected for replicate analysis.
The coefficient of variations associated
with the duplicate and replicate sample
analyses were 22% and 32%, respectively.
Since the replicate analyses used differ-
ent filter preparations, a higher coefficient
of variation is expected.
Spray-Application Techniques
To confirm the validity of the spraying
technique, an additional experiment was
conducted using a pesticide sprayer iden-
tical to those used to apply the chrysotile
to the carpet samples. An ampule of low-
concentration suspension was diluted to
500 ml, and then further diluted to 6L in
the pesticide sprayer, using freshly dis-
tilled water. The sprayer was thoroughly
shaken and the contents were sprayed!
out into several containers. Three 500-mL
samples of the spray were collected, one
at the beginning of spraying, one when
approximately 50% of the contents had
been discharged, and one just before the
T»bh 1. Summary Statistics for Airborne Asbestos Concentrations Before and During Carpet Cleaning
Approximate
Contamination
Loading, s/ft*
100 million
Before
cleaning
HEPA-
Filtered
Cleaner
Hot-water
extraction
Airborne Asbestos
Concentration, s/cm3
Number pf
Data Points* Average Standard Deviation
3 0.0673 0.0874
During
cleaning
Dry-vacuum
Hot-water
extraction
Dry-vacuum
0.0571
0.1639
0.2531
0.0315
0.0911
0.1655
1 billion
Before
cleaning
Hot-water 4 0 0761
extraction
0.0471
During
cleaning
Dry-Vacuum
Hot-water
extraction
Dry-vacuum
0.1424
0.1577
0.2248
0.1235
0.0690
0.1499
•Each data point is the average of three work-area samples.
end of spraying. These three samples were
analyzed to determine if the concentration
and size distribution of the fibers changed
during the period of spraying. The aver-
age asbestos structure concentration for
these three samples was 2.33, 2.18, and
2.38 s/L, respectively. These results indi-
cate no significant loss of fibers during the
transfer of the diluted liquid suspension
through the sprayer's hose and nozzle.
Similarly, no significant change in fiber
size distribution was evident during the
transfer of the diluted liquid suspensions.
Wet Clean Dry Vacuum Wet Clean Dry Vacuum
Low Contamination High Contamination
Figure 1. Average airborne asbestos concentrations before and during carpet cleaning.
Results and Discussion
Figure 1 presents the average airborne
asbestos concentrations measured before
and during cleaning for each cleaning
method and carpet contamination loading.
The samples collected before cleaning
were obtained after the carpet was con-
taminated to determine the baseline con-
centration in the test room. Table 1 pre-
sents the summary statistics (arithmetic
average and standard deviation).
Air sampling results from 2 of the 16
experiments showed that the average air-
borne asbestos concentrations decreased
during both wet cleaning and dry vacuum-
ing of the carpet. The explanation for this
anomaly is that the HEPA filtration system
used to ventilate the test rooms was inad-
vertently operating during the carpet
cleaning phase of these two experiments.
Therefore, these results were omitted from
the statistical analysis of the data.
There was no statistically significant in-
teraction between cleaning method and
contamination level (p«0.8901); that is, the
effect of the cleaning method on airborne
asbestos did not vary significantly with
contamination level. No statistically signifi-
cant difference was evident between clean-
ing methods with respect to fiber
reentrainment (p-0.5847); that is, the mean
relative increase in airborne asbestos con-
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Tibk 2. Structure Morphology Distribution for Air Samples Collected Before and During Carpet Cleaning
Structure
Type
Chrysolite
Amphibole
Ambiguous
Total
Number of
Bundles
30
0
2
32
Number of
Clusters
7
2
0
9
Number of
Fibers
2,661
5
70
2,736
Number of
Matrices
59
1
2
62
Total
2,757
8
74
2,839
centration during carpet cleaning with a
dry vacuum was not significantly different
from that found during wet cleaning.
Similarly, no statistically significant dif-
ference was evident between carpet con-
tamination loadings with respect to fiber
reentrainment (p-0.0857); that is the mean
relative increase in airborne asbestos con-
centrations during carpet cleaning when
the carpet contamination level was 100
million s/ft2 was not significantly different
from that found when the carpet contami-
nation leading was 1 billion s/Tt2.
The ANOVA results do, however,
indicate that, overall, the mean airborne
asbestos concentration was significantly
higher during carpet cleaning than just
before cleaning (p=0.0001). Specifically,
a 95% confidence interval for the mean
airborne asbestos concentration during
% of Fibers
carpet cleaning as a proportion of the air-
borne concentration before cleaning
showed that the mean airborne asbestos
concentration was between two and four
times greater during carpet cleaning.
Airborne Asbestos Fiber
Distribution
The TEM analysis of the 95 work-area
samples before and during cleaning yielded
a total of 2839 structures. Of these, 2757
(97.1%) were chrysotile, 8 (0.03%) were
amphibole, and 74 (2.6%) were ambigu-
ous. The structure morphology distributbn
is summarized in Table 2.
These data indicate that the original
chrysotile fibers used to prepare the di-
luted asbestos suspension remained in-
tact as fibers. There appeared to be no
significant tendency for the fibers to clump
Low Carpet Contamination,
100 millions/ft*
Asbestos Suspension
Dry Vacuuming
I I Wet Cleaning
>2.3
Fiber Length, jim
High Carpet Contamination,
1 billion s/ft2
Asbestos Suspension
Dry Vacuuming
r~1 Wet Cleaning
together as a result of the suspension
preparation, the carpet contamination, or
the cleaning technique.
The presence of amphibole asbestos
fibers in the air was probably due to con-
ditions existing before the experiment.
Prestudy air monitoring identified two am-
phibole asbestos fibers in seven air
samples collected.
Eighty-four percent of the chrysotile
structures identified were 1 u.m or less in
length. Only nine particles were identified
with lengths greater than 5 u,m. Figure 2
compares the fiber sizes of airborne as-
bestos during carpet cleaning with fibers
in the low- and high-concentration asbes-
tos suspensions. For example, approxi-
mately 60% of the asbestos fibers used to
contaminate the carpet with 100 million
s/ft2 were greater than 1.1 u.m. Less than
15% of the fibers observed in the air dur-
ing carpet cleaning were greater than
1.1 urn. These data suggest that the larger
asbestos particles either remained in the
carpet or were prevented from escaping
into the air by the carpet cleaning activity.
Conclusions
Both dry vacuuming and wet cleaning
of carpet artificially contaminated with as-
bestos fibers resulted in a statistically sig-
nificant increase in airborne asbestos
concentrations. The increase did not vary
significantly with the type of cleaning
method (wet or dry) or with the two levels
of asbestos contamination applied to the
carpet.
Although this research revealed signifi-
cant increases in airborne asbestos con-
centrations during cleaning activities in a
controlled study under artificial, simulated
conditions, it is not known if such increases
occur in real-world custodial operations.
Obviously, this possibility is a concern.
Recommendations
This research suggests that normal cus-
todial cleaning of asbestos-contaminated
carpet may result in elevated airborne as-
bestos concentrations. Further research is
needed to determine actual exposure risk
to custodial workers performing these ac-
tivities in buildings containing friable as-
bestos-containing materials.
The full report was submitted in fulfill-
ment of Contract No. 68-03-4006 by PEI
Associates, Inc., under the sponsorship of
the U.S. Environmental Protection Agency.
>3.4
>5.0
>7.3
>10.8
>.5 >.7 >1.1 >1.6 >2.3
Fiber Length, jim
Figun 2, Comparative plot of cumulative percentages of airborne asbestos fibers during dry vacuuming and wet
cleaning of carpet with asbestos fibers in the low and high concentration suspensions.
. GOVERNMENT PRINTING OFFICE: IWI - 548-028/40008
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J.R. Kominsky and R. W. Freyberg are with PEI Associates, Inc., Cincinnati, OH 45246
W.C. Cain and T.J. Powers are the EPA Project Officers (see below).
The complete report, entitled "Asbestos Fiber Reentrainment During Dry Vacuuming
and Wet Cleaning of Asbestos-Contaminated Carpet," (Order No. PB91-161695AS;
Cost: $17.00, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Risk Reduction Engineering Laboratory
U.S. Environmental Pmtection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati, OH 45268
BULK RATE
POSTAGE & FEES PAID
EPA PERMIT NO. G-35
Official Business
Penalty for Private Use $300
EPA/600/S2-91/004
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