United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/S2-91/059 Feb. 1992
EPA Project Summary
Improvement of PMN Review
Procedures to Estimate
Protective Clothing Performance;
Executive Summary Report
Rosemary Goydan, Arthur D. Schwope, Todd R. Carroll, and Thomas J. Stolki
Through a five-year program per-
formed with the EPA Office of Research
and Development, the Chemical Engi-
neering Branch (CEB) of the EPA Of-
fice of Toxic Substances (OTS) has de-
veloped state-of-the-art tools for as-
sessing the effectiveness of rubber and
plastic protective clothing materials as
barriers to chemicals. These tools were
developed for use by CEB to conduct
more thorough assessments of the po-
tential for occupational exposures to
new chemicals as required in the
Premanufacture Notification (PMN) re-
view process. The tools include:
a computerized model for pre-
dicting the permeation of chemi-
cals through common clothing
materials using Fickian diffusion
theory and the physical property
data typically available from a
PMN submission,
guidelines for specifying perme-
ation testing and interpreting the
results of such tests, including
development of a new, intermit-
tent chemical contact permeation
test method, and
- a manual that guides the assess-
ment of protective clothing per-
meation on the basis of pub-
lished data, data from CEB-pre-
scribed testing, and the output
of the predictive model.
The report summarized here de-
scribes the development of these tools
and lists the products delivered under
this project from October 1985 through
September 1990.
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
Section 5 of the Toxic Substances Con-
trol Act (Public Law 94-469) requires pro-
spective manufacturers or importers of new
chemicals to submit PMNs, which are re-
viewed by OTS, before the chemicals are
manufactured or imported. Although many
substances are not subjected to all as-
pects of the review process, those that
are judged to pose health or environmen-
tal risks require detailed assessments of
the potential for releases or exposures
during manufacture, processing, and end
use. When the PMN submitter recom-
mends the use of protective clothing to
limit dermal exposures, OTS needs a rapid
and well-substantiated approach to assess
the ability of protective clothing to act as a
barrier to the PMN chemical.
The approach developed in this pro-
gram centers on assessing the effective-
ness of protective clothing materials as a
barrier to chemical permeation. Perme-
ation resistance is an important measure
of the effectiveness of protective clothing
in reducing or limiting dermal exposures.
As illustrated in Figure 1, however, the
performance of protective clothing as a
chemical barrier is only one of many im-
portant considerations required for the
proper specification of protective clothing.
Proper selection and, as importantly,
proper use of protective clothing requires
multiple considerations starting with the
definition of the hazard and ending with
disposal of the used clothing.
The main objectives of this program
were to develop a computer model for
predicting permeation one that would
Printed on Recycled! Paper
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Task
Duration
Frequency
Chemical State
Degree of Control _
DataBase
Testing
Experience
Models
Figure 1. Selection and use of protective clothing.
meet OTS' needs and operational re-
quirements and to develop an inte-
grated system for assessing the perme-
ation resistance of protective clothing ma-
terials one that would be part of the
PMN review process. To guide in devel-
oping the computer model, OTS estab-
lished the following criteria: the model
should:
be easy to use,
be applicable to a wide range of
chemicals and protective clothing
materials,
be applicable to chemicals not used
to develop the model,
not require data other than those
typically supplied in PMN submis-
sions or readily estimated using es-
tablished techniques,
predict the cumulative mass of
chemical that permeates the cloth-
ing material as a function of time,
and
enable the prediction of break-
through times at specified perme-
ation rates or cumulative amounts
permeated.
Accuracy requirements for the model
outputs were not specifically defined. The
criteria for evaluating chemical resistance
test methods included the types of data
that are generated, cost to perform the
tests, skill level required to run the tests,
and the limitations of the tests.
To assess the resistance of protective
clothing materials to chemical permeation,
four integrated approaches were devel-
oped to estimate permeation which in-
volve a predictive model, test specifica-
tion, and test data review. The three tools
developed from this program a perme-
ation model, guidelines for specifying test
methods and interpreting data, and a user
manual are discussed below.
Permeation Prediction Model
Theory and Initial Development
The permeation prediction model was
developed using diffusion theory and Pick's
law mathematical relationships to estimate
the permeation rate and cumulative
amount of chemical that permeates a
polymeric material at any time following
the initiation of the chemical contact. The
relationships require two fundamental pa-
rameters: the diffusion coefficient, O, and
the solubility, S, of the permeant in the
polymer of interest. The Pick's law ap-
proach was selected because it was
judged to provide the best opportunity to
satisfy OTS' criteria. Although other
methods (e.g., statistical correlation meth-
ods) may be more accurate in some cases,
such methods often cannot predict per-
meation behavior as a function of time
and lack sufficient theoretical basis for
extrapolation to new chemicals.
A prototype model was developed in
1988. The prototype estimated the per-
meation of pure chemicals through five
clothing materials: butyl rubber, LDPE,
natural rubber, neoprene, and nitrile rub-
ber. Two approaches to estimate S were
developed: one using a group contribu-
tion approach, UNIFAP S, and the second
using an equation of state approach, EOS
S. One approach to estimate D, CORR
D, was developed. The model was de-
signed to run on a personal computer,
was easy to use, required minimal data
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inputs, and predicted permeation behav-
ior as a function of time including break-
through times. The validation of the pro-
totype was limited by the availability of
reliable data that described permeation as
a function of time. It was concluded that
further testing of the modej was required
and that the approach to estimate diffu-
sion coefficients should be refined.
Permeation Model Refinement
The permeation model was refined
through the analysis of an additional, larger
set of permeation data that became avail-
able in 1989. The data set included
breakthrough time and steady-state per-
meation rate data for approximately 200
chemical/material combinations, although
few data pertained to LDPE. The effort to
refine the permeation estimation model
focussed on improving the procedure to
estimate diffusion coefficients. The effort
was twofold: to undertake a preliminary
investigation of the importance of the con-
centration dependence of D and to improve
the estimation of constant D values.
Concentration Dependent
Diffusion Coefficients
The investigation of concentration de-
pendent diffusion coefficients used nu-
merical methods to calculate permeation-
time profiles for general cases of concen-
tration dependent behavior. A finite differ-
ence numerical analysis technique was
developed, and for 15 of 31 chemical/
polymer combinations analyzed, the per-
meation-time data could be more accu-
rately described using a concentration de-
pendent D. The permeation-time data set
was too small, however, to develop pre-
dictive correlations for D. Consequently,
the permeation estimation model still uses
the assumption of a constant D. The
correlation equations, initially developed
to estimate constant D values, were re-
fined by analyzing the larger set of "aver-
age" D values now available.
Prediction Accuracy
To test the accuracy of the revised
model, the model predictions were com-
pared with the available permeation data.
Overall, the accuracy of the model is fair
for predicting the permeation of organic
chemicals through butyl rubber, natural
rubber, neoprene, and nitrite rubber. The
model predicts the permeation behavior
within an order of magnitude for 70% to
80% of the chemical/polymer combina-
tions evaluated, which is often within the
range of experimental values reported in
the literature. The UNIFAP S/CORR D
was found to be more accurate than the
EOS S/CORR D approach, which tends
to underestimate the permeation behav-
ior. The UNIFAP S/CORR D approach
cannot be applied in all cases, however,
because required input parameters are
not available for several chemical func-
tional groups.
Computer System
The permeation estimation model was
coded in FORTRAN to run on IBM^or
compatible personal computers. The data
input requirements depend upon the
method selected to estimate S:
UNIFAP S/CORR D
-structure defined using UNIFAP
group designations,
-molecular weight (daltons), and
-liquid density (g/cm3)
EOS S/CORR D
-molecular weight (daltons),
-liquid density (g/cm3), and
-vapor pressure (mm Hg)
On-screen instructions are provided for
the selection of menu options and the
input of the required data. The perme-
ation model output is automatically directed
to the computer screen. Options are pro-
vided to print, plot, or save the results to a
disk file.
External Peer Review
The permeation prediction model was
externally peer reviewed in June 1989 for
ease of use, clarity, utility of output, and
accuracy of predictions compared with ex-
perimental data. In general, their review
comments were positive, particularly re-
garding ease of use and utility of output.
In some cases, the reviewers believed
that the prediction accuracy warranted im-
provement, particularly regarding the pre-
diction of breakthrough times.
Guidelines for Specifying Test
Methods and Interpreting Data
Review of Test Methods
In developing test methods and data
analysis procedures, the applicability and
limitations of existing chemical resistance
test methods were reviewed: methods for
measuring permeation resistance, degra-
dation resistance, liquid immersion weight
change, and chemical sorption/desorption
of protective clothing materials. Although
physical property test methods were also
reviewed, they were not pursued in this
project. The ASTM Method F739 perme-
ation test method was recommended as
the best method for assessing the barrier
effectiveness of protective clothing materi-
als to liquids, gases, and multicomponent
solutions.
ASTM F739 Reporting
Requirements
ASTM F739 was reviewed in detail to
identify limitations of the data generated
and to develop specific guidelines for data
interpretation. Although the permeation
test is straightforward in concept, a range
of results can be obtained under different
testing conditions for the same chemical/
material combination. Breakthrough de-
tection time is often reported as the mea-
sured parameter by which to characterize
barrier effectiveness. Breakthrough de-
tection time, however, is not an intrinsic
property of the chemical/material pair and
can be strongly affected by the experi-
mental parameters.
Permeation data measured and reported
as a function of time are recommended
as most useful to the exposure assess-
ments required in the PMN review pro-
cess. Revised reporting requirements
were recommended to the ASTM F23
Committee in 1987. As a result, the data
reporting section of ASTM F739 was re-
vised and the ASTM F23 Committee pro-
mulgated the ASTM F1194 Standard
Guide for Documenting the Results of
Chemical Permeation Testing on Protective
Clothing Materials in 1989.
Intermittent Contact Permeation
Test Method
A preliminary method was developed in
1988 to measure chemical permeation
under intermittent chemical contact condi-
tions. Because the ASTM F739 method
specifies continuous chemical contact, the
results may overestimate permeation re-
sulting from "splash" or intermittent chemi-
cal contacts typical in the manufacturing
environment. The proposed method in-
volves repeated cycles in which the cloth-:
ing material is alternately exposed to the
chemical and then to a stream of air.
Measured breakthrough detection times
were comparable with those measured by
the ASTM F739 method, but permeation
rates were greatly reduced and oscillated
with the exposure cycle. The intermittent
contact permeation method was the sub-
ject of an ASTM inter-laboratory evalua-
tion in 1989, and the results were posi-
tive. Efforts are now in progress to pro-
mulgate this method as an ASTM stan-
dard method.
Permeation of Multifunctional
Acrylates
In 1989, OTS' specific need for perme-
ation data for the general class of com-
pounds known as multifunctional acrylates
was addressed. Performing permeation
tests for these compounds is not routine,
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however, because of their low vapor pres-
sure and low water solubility. Silicone
rubber sheeting was selected as the col-
lection medium for the ASTM F739 Method
because of its favorable performance in
other projects performed under this con-
tract. Permeation tests were conducted
with trimethylolpropane triacrylate
(TMPTA), 1,6-hexanediol diacrylate
(HDDA), and two mixtures of 1,6-
hexanediol diacrylate with 2-ethylhexyl
acrylate (EHA) at 20°C with butyl, n'rtrile,
and natural rubber glove materials. None
of the acrylate compounds nor the mix-
tures were detected to permeate the butyl
or n'rtrile rubber at the conditions and sen-
sitivity of the method. Pure HDDA, a 50%
HDDA/50% EHA mixture, and a 25%
HDDA/75% EHA mixture permeated the
natural rubber material. TMPTA perme-
ation through the natural rubber was also
detected but only in one of the triplicate
tests after 360 min. Comparison of these
results with those reported in the literature
shows that the multifunctional acrylates
permeate the glove materials (in this case
natural rubber) at much lower rates than
those measured for simple, low molecular
weight acrylate compounds.
User Manual
A User Manual was prepared in
1990 to document the integrated ap-
proach recommended for using the
procedures developed to assess pro-
tective clothing material permeation
in an instructive and concise format.
The manual was prepared as a
supplement to the CEB Manual for the
Preparation of Engineering Assess-
ments. The user manual outlines four
approaches to assess the permeation
of chemicals through protective cloth-
ing materials based on the technical
developments described above:
* review existing permeation data
for the PMN chemical
review existing permeation data for
structural analogues of the PMN
chemical
» use the permeation prediction
model
specify permeation testing
Selecting the approach, or approaches,
depends on the types of information avail-
able for the chemical under review and
the desired accuracy of the assessment.
No one approach Is recommended and
using multiple approaches may be appro-
priate. The types of permeation estimates
range from specific estimates of potential
dermal exposure due to permeation, to
materials recommendation for further test-
ing, to the identification of materials not
suitable for use.
Conclusions
In a five-year program, the OTS/CEB
developed state-of-the-art tools for as-
sessing chemical permeation of rubber and
plastic protective clothing materials. OTS
developed these tools to conduct more
thorough assessments of the potential for
occupational exposure to new chemicals
as required in the PMN review process.
The tools include:
a computerized model for predict-
ing the permeation of chemicals
through common clothing materi-
als,
guidelines for specifying permeation
testing and interpreting the results
of such tests, and
a user manual that guides the as-
sessment of protective clothing per-
meation on the basis of published
data, data from CEB-prescribed
testing, and the permeation model
predictions.
Consequently, OTS now has a docu-
mented and substantiated approach to
assess the potential for protective clothing
permeation by PMN chemicals, one of
several important factors to consider in
the overall assessment of dermal expo-
sures. This capability will enable more
thorough assessments of occupational
exposures in the PMN review process and
better compliance with the mandate of
Section 5 of TSCA.
Recommendations
The primary recommendation is that
OTS incorporate the permeation assess-
ment procedures into its standard dermal
exposure assessment process. Not only
will this result in more thorough assess-
ments, but the procedures can be vali-
dated and areas requiring further devel-
opment can be identified through applica-
tion to actual PMN cases. Recommenda-
tions regarding further refinement of the
tools reported here follow.
Permeation Prediction Model
Before further efforts are undertaken to
refine or extend the predictive model, OTS
should reevaluate its requirements, spe-
cifically those regarding prediction accu-
racy. Acceptable model accuracy must
be defined and prioritized relative to broad
applicability, ease of use, and cost of de-
velopment. At present, the model is use-
ful for order of magnitude estimates. No
efforts to improve this accuracy can be
undertaken until a larger set of well docu-
mented, permeation-time data is obtained.
If such data are obtained, specific rec-
ommendations are:
to further test the accuracy and ap-
plicability of the present model for
LDPE and consider expanding the
model to other clothing materials,
in particular the newer, multilayer
plastic materials,
to pursue approaches to predict the
concentration dependence of the
diffusion coefficient and to expand
the applicability of the UNIFAP
group contribution approach to pre-
dict S.
to develop a model to estimate
chemical mixture permeation.
Guidelines for Specifying Test
Methods and Interpreting Data
OTS should continue its involvement
with the efforts of ASTM Committee F23
on Protective Clothing. To date, this in-
volvement has improved and better de-
fined permeation test methods for specifi-
cation. Also, OTS should support the
continued development of the EPA Guide-
lines for the Selection of Chemical Protec-
tive Clothing manual and chemical resis-
tance database, the use of which is an
integral part of the assessment procedures
developed here. Specific recommenda-
tions are:
to pursue the promulgation of the
intermittent contact permeation test
method as an ASTM method.
to maintain an awareness of devel-
opments by the AStM and other
EPA program offices regarding test
methods for measuring the physi-
cal properties and the participate
penetration of clothing areas that
may warrant the development of
assessment procedures.
Integration of Procedures into
PMN Review Process
When applicable, the permeation as-
sessment methods developed in this
project should be incorporated as part of
the standard procedure for assessing der-
mal exposures. OTS should also con-
sider other important aspects of clothing
selection and use (i.e., physical perfor-
mance of clothing, effect on job perfor-
mance, clothing reuse, and disposal is-
sues, etc.) and judge whether these areas
warrant development of assessment pro-
cedures.
The full report was submitted in fulfill-
ment of Contract No. 68-C9-0037, Work
Assignment 0-10, by Arthur D. Little, Inc.,
under sponsorship of the U.S. Environ-
mental Protection Agency.
itU.S. GOVERNMENT PRINTING OFFICE: 1992 - 648-080/40158
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R. Goydan, AD. Schwope, T.R. Carroll and T.J. Stolkiare with Arthur D. Little,
Inc., Cambridge, MA 02140-2390
Esperanza P. Renard is the EPA Project Officer (see below).
The complete report, entitled "Improvement ofPMN Review Procedures to
Estimate Protective Clothing Performance; Executive Summary Report,"
(Order No. PB92-105 691AS; 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 Off her can be contacted at:
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
Edison, New Jersey 08837-3679
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/S2-91/059
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