United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-89/004 July 1989
&EPA Project Summary
A Method to Measure Protective
Clothing Permeation Under
Intermittent Chemical Contact
Conditions
Rosemary Goydan, Todd R. Carroll, Arthur D. Schwope, and Robert C. Reid
A preliminary method was devel-
oped to measure chemical permea-
tion of protective clothing under
intermittent chemical contact condi-
tions. The test presently used ASTM
Method F739-85, measures per-
meation when the clothing material is
in continuous contact with the
chemical during the test, These
ASTM results may overestimate the
permeation resulting from intermit-
tent chemical contacts typical in the
manufacturing environment. The
preliminary method summarized here
was developed for the U.S. Environ-
mental Protection Agency's Office of
Toxic Substances (OTS). By using the
method, OTS could assess the ability
of protective clothing to reduce
dermal exposure risks during the
manufacture and use of new chem-
icals.
The proposed method involves
repeated contact cycles of duration
tcycle: the chemical contacts the
material for a short duration, denoted
as ton, the chemical is removed, and
air sweeps the material surface for
the remainder of the cycle. Tests
were conducted using nitrile rubber/
acetone, natural rubber/tetrachloro-
ethylene, and various ton/tcycie ratios.
The results indicate that lower
levels of chemical permeation would
be measured using the proposed
method than those using ASTM F739.
The measured breakthrough times
were comparable but the permeation
rates were greatly reduced. Following
detection of breakthrough, the per-
meation rates oscillate with a period
equal to tcycie. Although only a
limited number of experiments were
performed, the method appears to
generate reproducible results that
agree fairly well with mathematical
model predictions derived from Pick's
laws of diffusion. Further investiga-
tion of the applicability and limita-
tions of the method is recommended.
This Project Summary was devel-
oped by EPA's Risk Reduction Engi-
neering 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
Section 5 of the Toxic Substances
Control Act (Public Law 94-469) requires
prospective manufacturers to submit
Premanufacture Notifications (PMNs).
Approximately 2,500 PMNs are submitted
annually. OTS must review these PMNs
within 90 days of their submission before
new chemicals are manufactured or
imported. The primary objective of the
review is to assess the potential risks to
human health that could result from
contacts during the manufacture,
processing, and end use of the PMN
substance. Many PMNs are not
subjected to all aspects of the review
process; those that are judged to pose
health or environmental risks, however,
require detailed assessments of the
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potential for releases and exposures. If
sufficient concerns are raised to warrant
regulation, engineering controls, work
practice restrictions, or protective
clothing and equipment are investigated
as ways to reduce those risks.
Because the PMN submitter often
recommends protective clothing as a
way to minimize dermal exposures, OTS
needs to be able to assess protective
clothing performance; specifically its
performance in limiting dermal exposures
under realistic use conditions. One OTS
option is to request that PMN submitters
test the clothing materials and submit the
resultant data. If testing is to be
requested, however, OTS must then be
able to specify relevant test methods and
data reporting requirements.
At present, the recommended test
method for measuring the permeation
properties of protective clothing materials
is ASTM Method F739-85. Because
ASTM F739 specifies continuous chem-
ical contact, however, exposure esti-
mates based on these permeation data
may overestimate actual exposures in
the manufacturing environment. Often
these contacts are infrequent and of
short duration.
This study investigated the feasibility
of developing a test method to measure
permeation under chemical contact
conditions thought to be more repre-
sentative of actual workplace contacts.
Several researchers have investigated
methods to measure permeation under
intermittent or "splash" conditions and
each has defined the contact differently.
Most of these studies focused only on
the measurement of breakthrough times.
In this study a preliminary method was
evaluated for measuring breakthrough
times, permeation rates, and cumulative
permeation under conditions of inter-
mittent chemical contact. The procedure
involves repeated cycles of short-
duration chemical contact. The approach
was selected because it could be well
controlled, would use the same ap-
paratus as ASTM F739, should be
broadly applicable and reproducible, and
may be a realistic simulation of inter-
mittent chemical contacts. Also, this
controlled intermittent contact procedure
can be modeled mathematically with the
use of Pick's laws of diffusion.
Experimental [Methods and
Procedures
Materials
The experimental program was con-
ducted using two combinations of
chemicals and protective clothing
materials. In the first combination, nitrile
rubber was the clothing material and
acetone the challenge chemical. This
combination was selected because
acetone readily! permeates nitrile rubber
under conditions of continuous chemical
contact. In the second combination,
natural rubber j/vas the clothing material
and tetrachloroethylene the chemical.
This second combination was selected to
explore the usefulness and reproduci-
bility of the proposed method for a less
volatile/more viscous chemical.
i
Analytical Methods
A Miran 8t)A Infrared Spectro-
photometer (Foxboro Company, Foxboro,
MA)* was employed to detect the con-
centration of the chemical' in the col-
lection medium. The spectrophotometer
was calibrated [prior to testing each day
tests were run. j
Permeation Tiest Procedures
Except for the modification to the
chemical cotntact procedure, all
permeation tests were conducted in
accordance with ASTM Method F739-
85. All tests were performed in the
open-loop mode in which the collection
medium, air, ^s continuously passed
through the collection chamber of the
test cell where| it collects any permeant
and carries it to the detector, from which
it is exhausted. The collection air flow
rate was set at llO liters/min (Lpm) for the
test duration. |
The permeation tests were performed
at 20°C and jvere continued until the
permeation rates reached a steady state.
Replicate tes^s were performed to
investigate reproducibility. Permeation
tests were conducted using the standard
continuous co[ntact procedure and sev-
eral variations of the intermittent contact
procedure for each chemical/material
pair.
ASTM F739 Continuous Contact Tests
- Permeation tests were performed using
the ASTM F739 continuous contact pro-
cedure as the basis for comparison with
the intermittent chemical contact results.
The challenge chamber of the test cell
was filled with the challenge chemical for
the duration of the test.
Intermittent Chemical Contact Tests -
The intermittent chemical contact pro-
cedure is defined as a cyclic process
with each cycle having a duration equal
to tcyc|e. Each cycle began with an initial,
full surface contact of the challenge
chemical with the clothing material
specimen for a short duration defined as
ton- At the end of t0n. the chemical was
quickly drained (approximately 15 sec)
from the challenge chamber of the test
cell. The challenge chamber was then
swept by a fresh air stream for a set
period defined as tpurge to complete the
contact cycle. The purge air flow was set
at 2.5 Lpm.
ton and tpurge define the contact cycle:
tcycle = ^n + tpurge 0)
These cycles of short duration
chemical contact/long duration air sweep
were repeated for the duration of the
permeation test. Three variations of
chemical contact time and contact cycle
time were studied:
* Mention of trade names or commercial products
does not constitute endorsement or recommen-
dation for use. i
• ton = 1 m'n anQl tcycle = 1
• ton = 5 m'n ancl tcycle = 15 min' anc)
• ton = 10 min and tcyc|e = 60 min.
Results and Discussion
Experimental Results
The results for the series of continuous
and intermittent contact tests are
reported for nitrile rubber/acetone (Table
1) and for natural rubber/tetrachloro-
ethylene (Table 2). The results are
summarized in terms of breakthrough
times, steady-state permeation rates,
and the cumulative amounts permeated
at 1 hr.
Under continuous chemical contact,
permeation of the acetone through the
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Table 1. Continuous and Intermittent Contact Permeation Test Results for Acetone and Nitrite Rubber at20"C
Contact
Condition
Continuous
5 min/15 min
10 min/ 60 min
1 min/15 min
Ratio
ton
'cycte
1.0
0.33
0.17
0.07
Thickness*
(cm)
0.056
0.054
0.053
0.050
0.047
0.052
0.052
0.046
rj.045
Breakthrough
Time (min)
18
16
16
21
18
16
18
43
46
Steady-state
Permeation Rate
(pg/cm2-min)
1770
1830
1880
-t
760
260
250
280
-t
Cumulative
Perm, at 1 hr
(lig/cm2 x 10-3)
77.5
72.5
63.8
23.0
28.8
2.4
2.5
1.5
1.2
Exp.
No.
1
2
3
6
7
8
9
4
5
"Nitrile rubber specimens were cut from commercially available gloves (Pioneer Stansolv A-14, 0.05 cm nominal thickness).
tPeriodic oscillation in permeation rate did not reach a stable cycle.
Table 2. Continuous and Intermittent Contact Permeation Test Results for Tetrachloroethylene and Natural Rubber at 20"C
Ratio
Contact
Condition
Continuous
5 mini 15 min
1 min/15 min
ton
tcvcia
1.0
0.33
0.07
Thickness'
(cm)
0.042
0.040
0.043
0.040
0.042
0.040
Breakthrough
Time (min)
5.3
4.6
4.9
4.6
9.0
6.0
Steady-state
Permeation Rate
(ltg/cm2-min)
6170
7400
-t
3750
1720
1650
Cumulative
Perm, at 1 hr
(uglcm2 x 10-3)
370.7
304.9
-t
175.0
64.9
65.0
Exp.
No.
10
11
14
15
12
13
"Natural rubber specimens were cut from commercially available gloves (Edmont Fab-tek 26-668, 0.04 cm nominal thickness).
t Sample degraded after approximately 30 min.
nitrile rubber specimen was detected
after an average of 17 min. An average
steady-state permeation rate of 1,820
lig/cm2-min. In comparison, the inter-
mittent contact tests demonstrate that the
acetone permeation through the nitrile
specimen is reduced relative to that for
continuous contact. The reduction is
mainly in permeation rates; breakthrough
times generally remained unchanged.
changed. Similarly for natural rubber/
tetrachloroethylene (Tabl.e 2), the
permeation measured under intermittent
contact conditions is reduced when
compared with that measured under
continuous contact conditions.
More specifically, the intermittent
contact method produces a dramatic
change in the permeation rate as a
function of time. In all cases, a strong,
periodic oscillation develops with a
period equal to the cycle time, tcyc|e.
Eventually, a stable or steady cycling is
reached (Figures 1 and 2). Note that this
steady-state value, calculated as the
integrated average value once the rates
have reached a steady oscillation, appear
to be reduced approximately by the ratio
of (t0rA)ycle) fram that of the continuous
contact case. This reduction was some-
what smaller for natural rubber/tetra-
chloroethylene and may be attributed to
the lower vapor pressure of the
tetrachloroethylene. Also note the good
reproducibility between the replicate
experiments.
Comparison with the Results of
Other Investigators
The results generated in this study
are consistent with the behavior meas-
ured by other researchers for related
intermittent contact or splash tests. The
other studies, however, focused on
measurement of break-through times
only.
Sansone and Jonas (1981) found
that the breakthrough times measured for
permeation of a chemical droplet were
comparable to those measured for
continuous liquid contact with the
clothing material. Benzene and carbon
tetrachloride permeation through several
protective clothing elastomers were
studied. In all cases, the droplet was free
to evaporate as well as to permeate the
clothing material. The authors reported
that 70% to 90% of the deposited droplet
evaporated and did not permeate the
material.
Man et at. (1987) investigated a
method involving cyclic contact: short
duration liquid contacts followed by
periods of continuous vapor contact. The
procedure used the ASTM cell with a
small volume of liquid chemical sealed in
the challenge chamber; liquid splashes
(achieved by tilting the cell so that the
chemical/material contact occurred) were
alternated with periods of vapor contact
(during which the sealed cell was rotated
so no liquid contacted the material
surface). The authors studied the effect
of varying the frequency of a 2-sec
liquid splash on the breakthrough time
and reported two modes of behavior for
the chemicals tested. For chlorinated
polyethylene, breakthrough times gen-
erally were longer as the frequency of the
splashes was decreased. For a Viton/
nylon/chlorobutyl laminate, breakthrough
times did not change with splash
frequency and agreed with the results for
the continuous contact method. They
attributed these differ-ences to the
wettability of material by the chemical.
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7 min/15 min
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Figure 1 .
20
40 60
Time (min)
80
100
Permeation of acetone through nitrite rubber at20°C for continuous contact,
1 min/15 min intermittent contact cycle and 5 min/15 min intermittent contact
cycle. \
ouu
-
Permeation Rate (fjg/cm2-mln)
% S §
5 O O O
L I 1 I I I 1
C
,p""*
S* \ Continuous
/ _ -
//•
/ ^ + £xp. M>. ?0
' • ; • £XA /Vo. / /
//' — *T 5min/15min + Exp. No. 12
!* ,% /\ / \ * Exp. No. 13
±i T' \ / v r v x E*p- No- 14
ii tV \ J \ ! \ • *E*'-N°-15
fa. II \ i ^
« V^x N^V f\. /V ^ \,
) 20 40 60 80 10
r Time (min)
Figure 2. Permeation of tetrachloroethylene through natural rubber at 20°C for continuous
contact, 1 min/15 min intermittent contact cycle and 5 min/15 min intermittent
contact cycle. \
For the nitrile/acetone and natural
rubber/letrachloroethylene systems
studied here, the chemicals appeared to
readily wet and be absorbed by the
clothing materials; however, no direct
measurements of wettability were made.
Thus, the behavior observed by Man et
a/., for the wetted chemical/material case,
might also be expected in this study, i.e.,
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essentially no variation in breakthrough
time with contact frequency or duration.
Comparison with Mathematical
Model Predictions
To aid interpreting and understanding
the experimental results, a mathematical
model of the intermittent contact scenario
was developed. The model is based on
Pick's law of diffusion-a mathematical
relationship describing the diffusion of a
species through a membrane for a
specific set of boundary conditions. For
this application, however, separate (but
related) equations are required to
describe the permeation behavior.
The intermittent contact permeation
equations were derived from the general
heat transfer solution of Carslaw and
Jaeger (1973). The model assumes:
• A constant diffusion coefficient;
• No swelling of the membrane;
• No external mass transfer resistances;
and
• That chemical contact begins instan-
taneously at the start of t0n and ends,
also instantaneously at the end of ton
(defined also as the start of tpurge).
The Pick's law equations predict that:
• The permeation rates develop
periodic oscillations with the period
equal to tcyC|e.
• Breakthrough times for the intermittent
contact case will equal those
measured for continuous chemical
contact for the systems and ton/tcyC|e
ratios studied here.
(Note: Breakthrough time is defined as
the time at which the permeation rate
or cumulative permeation exceeds the
lower detectable limit defined by the
instrument sensitivity, collection
medium flow rate, and surface area
contacted. Differences in breakthrough
time may be predicted for other
systems, e.g., shorter ton segments,
less sensitive detection limits.)
• Eventually, the permeation rate-time
curves will reach a steady or stable
cycling with the same rates obtained at
comparable fractions of a cycle. The
number of cycles required to reach
this stable oscillation period should be
proportional to (L2/DtcyC|e) where L is
the material thickness and D, the
diffusion coefficient.
At this stable cycling state, the
integrated average value of the
permeation rate, P, during a contact
cycle will vary as:
where Pc is the steady-state rate
measured for continuous chemical
contact.
In general, the test results are
consistent with the model predictions
given the simplifying assumptions that
were used in developing the model. As
reported in Tables 1 and 2, the
breakthrough times are comparable with
those for the continuous contact case. In
one case, the 1 min/15 min intermittent
contact for the nitrile/acetone, a sig-
nificantly longer breakthrough time was
measured. This result is not predicted by
the model. One possible explanation is
that some of the simplifying assumptions
are not appropriate for very short
duration intermittent contact scenarios.
The permeation rate results are also
generally consistent with the model
predictions. The periodic oscillations
track fairly close with tcyc|e, and the
average 'permeation rates during the
stable cycling period for the intermittent
contact cases are reduced approximately
by the ratio of ton/tcyc|e. The results for
natural rubber/tetrachloroethylene are,
however, reduced by a smaller ratio.
Conclusions and
Recommendations
A test method was developed to
measure protective clothing permeation
under conditions of intermittent chemical
contact that may simulate workplace
contacts better than those of ASTM
F739. The proposed method uses the
ASTM F739 permeation cell and a
straightforward modification to the ASTM
F739 chemical contact procedure. The
intermittent contact method could be
incorporated as an optional procedure in
that method. Breakthrough time, per-
meation rate, and cumulative permeation
results from this feasibility study show
good reproducibility; however, only two
polymer/chemical combinations were
tested, nitrile rubber/acetone and natural
rubber/tetrachloroethylene.
Although the results of this preliminary
study are promising, further evaluation is
required to better define the repro-
ducibility, applicability, and limitations of
the proposed intermittent contact per-
meation test. We recommend additional
testing be performed using chemical and
polymer combinations that cover a range
of physical properties (e.g., viscosity,
volatility, and surface wetting) and
permeation properties (e.g., short and
long breakthrough times, high and low
permeation rates). We recommend
investigating a broader range of chemical
contact times, ton, and contact cycle
times, tcyc|e, to better understand the
effect of these variables on the measured
permeation data. This could be achieved
by an inter-laboratory evaluation of the
method coordinated through the ASTM.
In the long term, this procedure can be
useful as a standard method for assess-
ing protective clothing permeation under
more realistic contact conditions. One
goal should be to define a standard set of
intermittent contact conditions as a
baseline to compare results for various
chemical and material combinations. This
method is recommended as a possible
way for OTS to improve their exposure
assessment capabilities required for the
thorough review of PMNs. The method
could be specified by OTS in cases when,
permeation data are to be generated by
the PMN submitter to demonstrate that
the PMN substance can be safely
handled using protective clothing.
Specific intermittent contact conditions
for testing could be recommended. The
permeation rates or cumulative amount
permeated should be reported as a
function of time for the given ton and
tcycle conditions. Also, OTS should
require reporting of the breakthrough
time, clothing material thickness and
surface area, the analytical method
sensitivity, the collection medium flow
rate (open-loop systems) or volume
(closed-loop systems), and tempera-
ture.
The mathematical model for the
intermittent contact case could possibly
be used by OTS to estimate the
permeation that may occur during the
handling of PMN substances. Although
the model presently involves several
simplifying assumptions, it is believed
that the predicted results are repre-
sentative and provide a satisfactory
technique to estimate the effect of
intermittent chemical contact as com-
pared to continuous contacts.
The intermittent contact test method
and mathematical model could also be
applied to the study of protective clothing
decontamination procedures. Modification
of the method to include a surface
washing/air drying step would enable one
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to study the effect of surface decon-
tamination on residual chemical per-
meation during subsequent clothing use
and chemical contact.
The full report was submitted in
fulfillment of Contract No. 68-03-3293 by
Arthur D. Little, Inc., under the
sponsorship of the U.S. Environmental
Protection Agency.
Rosemary Goydan, Todd R. Carroll, and Arthur D. Schtyope are with Arthur D.
Little, Inc., Cambridge, MA 02140-2390; and Robert C. Reid is with
Massachusetts Institute of Technology, Cambridge, MA 02139.
Esperanzo P. Renard is the EPA Project Officer (see below).
The complete report, entitled, "A Method to Measure Protective Clothing
Permeation Under Intermittent Chemical Contact Conditions," (Order No. PB 89-
161 509IAS; Cost: $21.95, 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:
Superfund Technology Demonstration Division
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
Edison, NJ 08837-3679
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