introduction
As required under the AHERA of 1986,
the EPA has promulgated a final rule re-
garding inspections, abatement, and man-
agement of asbestos-containing materials
(ACM) in schools (40 CFR Part 763). The
rule describes procedures for determining
when critical containment barriers can be
removed.
After the abatement work site has
passed a thorough visual inspection, clear-
ance air monitoring is conducted. Before
the air monitoring is begun, floors, walls,
and ceilings should be swept with the
exhaust of a 1-hp (minimum) leaf blower.
Stationary fans, with the air directed to-
wards the ceiling, must be used to pro-
vide continuous air circulation in the work-
place. In most cases, air monitoring
samples are analyzed by transmission
electron microscopy (TEM). Air samples
must be collected on 25-mm diameter fil-
ters either 0.4-u,m (or smaller) pore-size
polycarbonate or 0.45-jim (or smaller)
pore-size mixed cellulose ester membrane
filters contained in a three-piece cassette.
For 25-mm filters, sampling rates between
1 and 10 L/min must be used to achieve a
recommended air volume of 1200 to 1800
L. Under certain circumstances (depend-
ing on the size and nature of the abate-
ment project), a site may be cleared by
having the air samples analyzed by phase
contrast microscopy (PCM).
The AHERA TEM clearance criterion is
primarily comparative in nature; i.e., it is
based on a comparison of airborne as-
bestos concentrations inside the abate-
ment work area with those outside the
abatement work area but not necessarily
with concentrations from outside of the
building. Outdoor samples are normally
recommended, however, because they are
less likely than indoor air samples to be
affected by work practices that might con-
taminate other areas inside the building.
The AHERA clearance test requires the
Printed on Recycled Paper

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collection of at  least five samples inside
the abatement area and five samples out-
side of the area. A statistical test (the Z-
test) is then used to determine if the aver-
age concentration inside the  abatement
area is higher than the average concen-
tration  outside the abatement area.  If the
Z statistic is less than or equal to 1.65,
the site passes  the clearance test and is
considered acceptable for reoccupancy.
  The  AHERA Z-test is  preceded by an
initial screening  test and  a blank contami-
nation test.  The initial screening test com-
pares the average filter  concentration of
the five samples collected inside the abate-
ment area against a value of 70 struc-
tures per mm2  (s/mm2).   If the average
filter concentration is less than or equal to
70 s/mm2, the work area passes the clear-
ance test without analysis of the outside
samples being required.  If the work area
samples do not pass the  screening test, a
minimum of  three blanks (filters through
which  no air has been drawn) are ana-
lyzed to check for the possibility of filter
contamination that would distort the test
results.
  A joint research effort by the EPA Of-
fice of  Research and Development's Risk
Reduction Engineering Laboratory (RREL)
and the  NJDOH  was conducted  during
the summer of 1988  to document AHERA
clearance air-sampling practices and clear-
ance concentrations  of airborne asbestos
at 20  asbestos-abatement sites  in New
Jersey. Each abatement took place  in a
school  building  and  involved  removal of
surfacing material, thermal system insula-
tion, or suspended ceiling tiles.

Study Design and Methods

Site Selection
  Although selection of the 20 asbestos-
abatement projects was based largely on
availability, each site also met the follow-
ing criteria:

  (1)  Each abatement project  was in a
     school  building.
  (2)  The abatement project involved re-
     moval of one or more of the follow-
     ing: (a) sprayed- or troweled-on sur-
     facing material; (b) thermal system
     insulation  from mechanical  equip-
     ment (i.e.,  boilers,  tanks, heat ex-
     changers,  pipes, etc.); or (c) sus-
     pended ceiling  panels.
  (3)  The abatement project was governed
     by written  specifications prepared in
     compliance with the minimum  re-
     quirements of the State of New Jer-
     sey Asbestos  Hazard Abatement
     Subcode (N.J.A.C. 4:23-8) and EPA
     guidance for work practices and pro-
     cedures to be  used in  performing
     asbestos-abatement projects.
  (4) The abatement project was cleared
     in accordance with the sampling pro-
     tocol specified in the AHERA  final
     rule (40 CFR Part 763).

Site Documentation
  At each  site,  background  information
describing the abatement area and the
ACM abated and other miscellaneous in-
formation were obtained  by  interviewing
an asbestos safety technician (AST) certi-
fied  by  the  New Jersey Department  of
Community Affairs and employed by an
ASCM firm.  The ASCM firm was  em-
ployed by the School District or Local Edu-
cation Agency.  The AST continuously
monitored and  inspected  the  asbestos-
abatement project in accordance with the
Asbestos  Hazard Abatement Subcode
(N.J.A.C. 5:23-8).  The AST must be on
the job site continuously during the abate-
ment project  to ensure that  the  work is
performed in accordance with the regula-
tions  specified  in the Asbestos  Hazard
Abatement Subcode.
  The following information was gathered
to document  the  AHERA clearance air-
sampling practices  used by the  ASCM
firm at each site:

  (1) conditions of sampling, i.e.,  aggres-
     sive versus nonaggressive sampling
     and the use of  circulating  fans  to
     maintain air circulation during clear-
     ance sampling,
  (2) air sampling methods, i.e., filter me-
     dium, type of filter  cassette, sam-
     pling rate, sample volume, and loca-
     tion of air samplers;  and
  (3) asbestos safety technician's project
     report on the onsrte supervision and
     AHERA clearance air monitoring.

Air Sampling Strategy
  As part of this present  study, NJDOH/
EPA collected preabatement air samples
(1) in the perimeter area (i.e., outside the
intended work area but inside the build-
ing) before the containment barriers were
constructed and (2) outdoors to determine
whether the abatement action significantly
affected the airborne asbestos concentra-
tions in  these areas.  The preabatement
sampling was conducted under static con-
ditions (i.e., activity in  the area was mini-
mal,  and the heating, ventilation, and air-
conditioning  system was  not  operating).
Preabatement sampling was possible  at
only  nine sites because of difficulties en-
countered in identifying sites that  met the
selection criteria.   At eight of the  nine
sites, five samples were collected both in
the perimeter of the intended abatement
work  area and outdoors.  At one site,
three samples were collected in the abate-
ment work area, two samples in the pe-
rimeter, and five samples outdoors.  The
configuration of the building and the areas
specified for abatement necessitated col-
lecting samples in the intended abatement
area at this site.
  Postabatement air samples were col-
lected  at the 20  abatement sites.   Five
area air samples were collected in  each
of three areas: the abatement work area,
the perimeter, and outdoors. The samples
were collected at approximately the same
time and location (within a radius of 5 ft)
as those collected by the AST for AHERA
clearance of the site.  In the abatement
work area, samples were collected  under
the sampling conditions that existed dur-
ing the final-clearance air sampling.  The
perimeter area samples  were  collected
under static conditions.
  in  addition  to  analyses   of  the
postabatement air samples collected  by
NJDOH/ EPA, analyses were also obtained
of  the postabatement  clearance air
samples collected by the  ASCM  firms.
Clearance  of each abatement  site was
based on the results of the latter analy-
ses.

Sampling Methodology
  NJDOH/EPA air samples were collected
on  open-face,  25-mm-diameter, 0.45-n.m
pore-size, mixed cellulose ester membrane
filters with a 5-ju.m pore-size, mixed cellu-
lose ester, backup diffusing filter and cel-
lulose  support pad contained in a three-
piece cassette.  The filter cassettes  were
positioned approximately 5 ft above the
floor on tripods, with the filter face at ap-
proximately a 45° angle toward  the floor.
The filter assembly was attached to a 1/6-
hp  electric-powered vacuum pump oper-
ating at a flow rate of approximately 9 !_/
min. The sampling pumps were calibrated
with a precision rotameter both before and
after sampling. A primary calibration stan-
dard was used to calibrate the  precision
rotameter in the field.

Analytical Methodology
  The NJDOH/EPA mixed cellulose ester
filters were prepared and analyzed  in ac-
cordance  with the nonmandatory  TEM
method, as described in the AHERA final
rule (40 CFR 763). A sufficient number of
grid openings were analyzed for  each
sample to ensure a sensitivity (the con-
centration represented by a single  struc-
ture) of no greater than 0.005  asbestos s/
cm3 of air sampled.  The  specific length
and width  of each structure were  also

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 measured  and recorded.  The Public
 Health and Environmental Laboratories of
 the NJDOH performed the TEM analyses
 on  the field samples under a separate
 cooperative agreement with  EPA's RREL
 in Cincinnati.

 Statistical Analysis
  The Wilcoxon Signed  Rank test was
 used  to evaluate  differences in. airborne
 asbestos concentrations before and after
 abatement. This nonparametric statistical
 procedure analyzes the relative ranks and
 magnitudes of  the differences between
 paired data rather than analyzing the ac-
 tual data  values,  and it  requires fewer
 assumptions regarding the underlying sta-
 tistical distribution  of the data.
  The AHERA  Z-test was used to com-
 pare the final-clearance samples collected
 inside the  abatement  area  with the
 samples collected  outside the  abatement
 work  area  (inside the building and out-
 doors).

 Results and Discussion

 Site  Descriptions
  Sixteen of the  abatement projects in-
 volved general  occupancy areas (class-
 rooms, offices,  recreational  rooms, corri-
 dors,  etc.); three  involved  boiler rooms
 and mechanical equipment  rooms; and
 one involved both of these types of areas.
 At 13  of the project sites, the abated ACM
 consisted of surfacing material  (acoustical
 plaster or fireproof ing); at 3 sites,  both
 surfacing material  and thermal  system in-
 sulation; and at 2 sites, suspended ceiling
 tiles.   At  17 sites, the ACM  contained
 chrysoltile asbestos (from  2% to 93%); at
 2 sites, amosite asbestos  (from 2%  to
 10%); and at 1 site, both chrysoltile (from
 10% to 75%) and  amosite (from 30% to
 40%).
  The abatement projects  involved 11 dif-
 ferent  abatement  contractors,  8  ASCM
 firms,  and 5 TEM analytical laboratories.

 Observed AHERA Clearance
 Practices

 Aggressive Sampling
  A 24-hour drying time is recommended
 before postabatement clearance air moni-
toring.  Postabatement  air monitoring
 should be  conducted  under aggressive
 sampling conditions. The abatement area
floors,  walls,  ledges,  ceiling,  and other
surfaces  should be swept with  the ex-
 haust  from  forced-air  equipment (e.g., a
 minimum 1-hp  leaf blower)  to dislodge
any remaining  dust, and  stationary fans
should be used to  keep fibers suspended
during  sampling.  Current guidance on
asbestos-abatement work practices  and
procedures recommends aggressive air-
sweeping  of the abatement  area  for at
least 5 min per 1000 ft2 floor area.  The
AHERA rule recommends the use of at
least one  stationary fan per 10,000 ft3 of
workspace, with the air directed toward
the ceiling to  keep the asbestos fibers
suspended during sampling.
  At 8  of the  20  abatement sites,  the
ASCM firms allowed less than the EPA-
recommended  drying time of 24 hr after
the completion of final cleaning before fi-
nal clearance air monitoring  was begun.
The drying times  for these eight sites
ranged from 2 to 18 hr.
  At 19 of the 20  abatement sites,  ag-
gressive sampling techniques were used.
At 14 of these 19 sites, the recommended
aggressive air-sweeping rate of at least 5
min per 1000  ft2 of  floor area was not
achieved.
  At only  12 of the  20 sites were station-
ary air fans used to maintain air circula-
tion during clearance air sampling. Box-
type fans were  used at nine of these sites,
and pedestal-type fans were used at three
sites.   At  15 of the observed sites,  the
ASCM firm failed to  use the number of
fans per given  volume of workspace re-
quired by AHERA.

Filter Types
  The ASCM firms  used mixed cellulose
ester  membrane filters to  collect  clear-
ance air samples at  14 of the 20 observed
abatement sites.   Polycarbonate  mem-
brane filters were used at six sites. The
AHERA rule permits the use of either filter
type; however,  the pore-size must be less
than or equal to 0.45jim for mixed cellu-
lose ester  filters and 0.4 u.m  for polycar-
bonate filters. At three sites, 0.8-u,m pore-
size mixed cellulose ester membrane fil-
ters were  used to  collect  clearance air
samples;  this  did  not comply  with  the
AHERA regulations.  All filters used for
clearance  air monitoring were 25 mm in
diameter and were contained in three-piece
cassettes with a 50-mm extension cowl.

Flow Rates and  Air Volumes
  Each filter assembly was attached to an
electric-powered pump operating at a
specified airflow rate.  The air samples
were generally  collected for a set length
of time to  achieve a certain minimum air
volume.  The AHERA rule states that pump
flow rates  between  1 and 10 L/min may
be used for 25-mm-diameter filters.  The
ASCM firms practiced this at 18 of the 20
sites observed.  At two sites, air samples
were collected  at flow rates greater than
10 L/min.  Air volumes ranged from 1320
to  4161  L for the postabatement  air
samples collected inside and outside the
abatement area at the observed sites. The
AHERA rule  recommends sampling be-
tween 1200 and 1300 L of air for 25-mm-
diameter filters.

Analytical Methods
  At 18 of the  20 observed sites, the
laboratory reports indicated that the ASCM
firms' final  clearance air samples  were
analyzed by TEM in  accordance with  ei-
ther the mandatory or nonmandatory TEM
methods described  in AHERA.   At two
sites, PCM  was used to analyze the clear-
ance air samples. Although the  samples
were reportedly analyzed in accordance
with NIOSH Method  7400 at these two
sites, improper filters (for this method) were
used to collect the clearance samples (0.4-
u.m pore-size  polycarbonate filters instead
of the  0.8-u.m pore-size mixed  cellulose
ester filters specified in NIOSH Method
7400).

AHERA Clearance Tests
  Two sets of data were collected:   (1)
data collected and analyzed by the ASCM
firms and their contract laboratories (which
were used to declare the site clean and to
release  the abatement contractor); and
(2)  data collected and analyzed  indepen-
dently by NJDOH/EPA.

ASCM Sample Analyses
  Two of the 20 sites were cleared as the
result of ASCM-firm data analyzed  by
PCM.  During the period  when the  TEM
analyses were being phased in, AHERA
permitted the use of PCM for clearance of
removals involving 3000 ft2 or less of ACM.
At least five samples were required inside
the  abatement area, and the fiber concen-
tration of each had to be below the limit of
reliable quantrtation (0.01 f/cm3 for NIOSH
Method 7400) to pass the clearance crite-
rion.  Clearance as  the  result  of PCM
analyses was permitted at one  site be-
cause the removal involved approximately
2200 ft2 of ACM;  however, the single
sample  used  to  clear the site  was not
sufficient. AHERA requires a minimum of
five samples for clearance with the use of
PCM.  One site, which involved the  re-
moval of approximately 5300 ft2  of ACM,
was cleared as the result of PCM  analysis
of two samples even though TEM clear-
ance was required.   The  other  18  sites
were cleared based on the results of the
initial screening test.

NJDOH/EPA Sample Analyses
  Table 1 summarizes the results of the
AHERA initial screening test and the
AHERA Z-test for each abatement  site,
based  on  the  NJDOH/EPA samples.

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Tabl01. Summary ofAHERA Initial Screening Test and AHERA Z-Test Results From Samples Collected by the New Jersey
        Department of Heahh/U.S. Environmental Protection Agency

                Moan Concentration,  a/cm1

Site
A
B
C
D
E
F
G
H
1
J
K
L
M
N
O
P
Q
R
S
T
/if aai
Abatement
Area
0.002
0.016
0.060
0.079
0
0.024
0.007
0.016
0
0.004
0.063
0.118
0.322
0.100
0.004
0.005
0.099
0.002
0.012
0.049
met tea}
Perimeter
0.001
0.008
0.002
0.062
0
0.002
0.010
0.062
0
0.001
0.008
0.066
0.002
0.003
0.003
0.007
0.055
0
0.003
0.030

Outdoor
0
0.001
0.004
0.052
0
0.001
0
0.003
0.006
0.001
0
0.004
0.002
0.004
0.001
0.003
0.007
0
0
0.015
AHERA
Initial
Screening
Pass
Fail
Fail
Fail
Pass
Fail
Pass
Fail
Pass
Pass
Fail
Fail
Fail
Fail
Pass
Pass
Fail
Pass
Fail
Fail

Z-Test
with
Perimeter
Pass
Pass
Fail
Pass
Pass
Fail
Pass
Pass
Pass
Pass
Fail
Fail
Fail
Fail
Pass
Pass
Fail
Pass
Pass
Fail
Z-Test
with
Outdoor
Pass
Fail
Fail
Pass
Pass
Fail
Pass
Pass
Pass
Pass
Fail
Fail
Fail
Fail
Pass
Pass
Fail
Pass
Fail
Fail
Twelve of the 20 sites would have failed
the initial screening test had the samples
collected by NJDOH/EPA been  used.  (In
contrast, all 18 sites for which TEM analy-
sis was used by the ASCM firms for clear-
ance passed the initial screening test and
were cleared for reoccupancy.)  Ten of
the 12 sites that would have  failed the
initial screening  test had the NJDOH/EPA
data been used  would have subsequently
failed the  AHERA Z-test based on com-
parison  with outdoor air samples.   The
other two sites  would have  passed the
AHERA Z-test,  primarily because of el-
evated levels of asbestos in  the outdoor
and perimeter air.  The remaining eight
sites would have passed both  the initial
screening test and  the  Z-test regardless
of whether outdoor or perimeter levels
were used in the Z-test comparison.
  Choosing the perimeter area outside the
work area but inside the building or the
outdoor air as the "outside" reference point
in the AHERA Z-test would have affected
the outcome of the clearance comparison
two sites.  In each case, the site would
have passed  the Z-test  if the  perimeter
values had been used in the comparison
and failed if the outdoor levels  had been
used.   The perimeter area  outside  the
work area can be compromised by work
practices that may contaminate other ar-
eas inside the building, by a breach in the
critical barriers surrounding the work area,
by the  air-filtration systems  (e.g.,  torn
ductwork passing through adjacent build-
ing areas), or by preexisting ACM in the
area.  Outdoor samples are less likely to
be affected by these conditions, and their
use in the clearance comparison would
generally provide  a more stringent com-
parison.

Asbestos Concentrations
Before and After Abatement
  Preabatement samples were collected
in the perimeter area and outdoors at nine
sites.   Overall,  the trend toward higher
concentrations of airborne asbestos after
abatement was significant in both the pe-
rimeter and outdoor air  (p <0.05).   The
cause of elevated asbestos concentrations
in  the perimeter and outdoor air is un-
known; however, conditions such as  torn
ductwork,  improper seals on  air filtration
units,  and breached containment were ob-
served at several sites.

Conclusions
  The principal  conclusion  during  this
study  is  that consultants who  conduct
clearance air monitoring often do not com-

                   4
pletely understand and follow the AHERA
sampling and analytical requirements and
recommendations.
  Discrepancies existed between AHERA
clearance concentration results of sample
analyses reported by the ASCM firms em-
ployed by the building  owner and those
reported independently by NJDOH/EPA.
  Making the  choice between perimeter
or outdoor  samples as the "outside val-
ues" in the AHERA Z-test is critical  in
determining if  an area  is acceptable for
occupancy.  Analyses of  NJDOH/EPA
samples showed that two sites would have
passed the AHERA Z-test  if  perimeter
samples  had been used as the "outside
values" but  would have failed had outdoor
samples been  used.
  Although  the general  trend was toward
statistically  significant increases in asbes-
tos concentrations after abatement (com-
pared  with  preabatement concentrations
at nine sites), only three  of the  seven
apparent increases were statistically sig-
nificant-on an individual basis.

Recommendations
  This study points up the need to de-
velop a comprehensive guidance docu-
ment that addresses the procedures and
protocols of AHERA air monitoring.  Im-

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proper final clearance air monitoring re-
sulted in part from a lack of understanding
of AH ERA air monitoring procedures. The
contractors expressed concern that the
current EPA-recommended protocols are
contained in more than one document,
which makes them difficult to understand
completely. A single guidance document
containing both procedures and protocols
for proper AHERA. clearance air monitor-
ing could supplement existing EPA guid-
ance (Guidelines for Conducting the
AHERA TEM Clearance Test to Deter-
mine Completion of an Asbestos Abate-
ment Project—EPA 560/5-89-001), which
emphasizes interpretation of AHERA clear-
ance results.
The inconsistent AHERA clearance sam-
pling and analysis results obtained by
monitoring firms and TEM laboratories
should be investigated further in the con-
text of the new training and National Vol-
untary Laboratory Accreditation Program
(NVLAP) certification requirements to de-
termine if additional corrective measures
are needed. This problem is being ad-
dressed by EPA's Office of Toxic Sub-
stances; however, in the interim, compli-
ance with the AHERA sampling and ana-
lytical methods should be strongly encour-
aged.
The persistent elevated asbestos con-
centrations found in perimeter and out-
door areas require further definition to de-
termine the sources and to identify the
appropriate corrective measures. Re-
search proposed by RREL for FY '91 in-
cludes assessing methods of field-testing
the high-efficiency particulate air (HEPA)
filtration units. In the interim, the need for
strict adherence to containment practices
prescribed in the AHERA regulations
should be emphasized.
The full report was submitted in fulfill-
ment of Contract Nos. 68-03-4006 and
68-CO-0016 by PEI Associates, Inc., un-
der the sponsorship of the U.S. Environ-
mental Protection Agency.
£l).S. GOVERNMENT PRINTING OFFICE: 1991 - 548-028/40065

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   J.R. Kominsky and R. W. Freyberg are with PEI Associates, Inc., Cincinnati,  OH
     45246. J.A. Brownlee and D.R. Gerb&r are with the New Jersey Department of
     Health, Trenton, NJ 08625.
   T.J. Powers is the EPA Project Officer (see below).
   The complete report, entitled "AH ERA Clearance at Twenty Abatement Sites," (Order
     No. PB91-217398AS; 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 Protection 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/S2-91/028

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