The OSHA Technical Center in Salt Lake City received a
request for assistance at a facility that uses methylene
bisphenyl isocyanate (MDI, CAS no. 101-68-8) in their
production process . It was decided that an inspection
would include screening and sampling for possible MDI
surface contamination (as well as air sampling for MDI).
The following surface monitoring techniques were evaluated
in preparation for that inspection.
(The information in this paragraph is for information
only and should not be taken as a basis for OSHA policy.)
A route of workplace exposure to chemicals with low vapor
pressures, such as aromatic isocyanates, may be through
skin contact with contaminated solvents or surfaces (1,2).
Aromatic isocyanates present a respiratory sensitization
hazard (1,2). Laboratory studies with animals have
indicated that respiratory sensitization to both TDI (3,4)
and MDI (5) can be induced by dermal contact alone. The
ability to determine surface contamination may be useful
in evaluating the effectiveness of housekeeping,
decontamination and chemical protective equipment.
Direct reading indicators, such as commercially
prepared pads that change color when they come in contact
with specific chemicals (or classes of chemicals), are
available for aromatic isocyanates. These types of
indicators may be used as a screening tool, when assessing
the extent of surface contamination, because they are
inexpensive and the results are immediate. If an indicator
wipe yields a positive result, a wipe sample can then be
taken and sent to a laboratory for confirmation.
The mention of the commercial products does not
constitute an endorsement.
The use of direct reading instruments and indicators
can be effective in helping employers to comply with the
OSHA personal protective equipment standard, 29 CFR
1910.132 (d)(1)(I) and (f)(1)(iii) and (iv).
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Wipe Sampling for Screening
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| Materials: |
At the time of the
inspection, the OSHA Salt Lake Technical Center
had an aromatic isocyanate indicator wipe kit in
stock called a Swype® kit (6). This kit consists
of indicator wipes called Swype®, a spray bottle
of a developer solution that contains a chemical
which activates the Swype® and indicator patches
that are worn under PPE, such as gloves, to test
the effectiveness. The kit also contains a spray
bottle of decontamination solution and a skin
cleaner. The effectiveness of the skin cleaner and
decontamination solution was not investigated.
1. Gloves and other personal protective
equipment must be worn during testing, as
appropriate. "Best" style 727 nitrile
gloves should provide protection to the
hygienist's hands for the time required to perform
the screening.
2. Gloves must be changed after a positive
result to avoid cross contamination of any
subsequent tests.
3. Spray the area to be sampled lightly with
the Developer Solution. Use as little as needed to
ensure that the surface is wet. Excess solution
will dilute contamination, possibly below the
detection limit. When testing a vertical surface
or knob, some of the solution may begin to
"run-off" or drip. This
"run-off" should be captured onto the
pad to ensure that any contaminant present has not
been lost. The Developer Solution contains a
proprietary component which activates the Swype®
pad.
4. Wait approximately 30 seconds for any
aromatic isocyanate to dissolve, then wipe the
surface with a surface Swype® pad.
5. Allow 2 to 3 minutes for the color to
develop. A pastel red-orange or pink color
indicates aromatic isocyanate contamination. The
color varies depending on the type of isocyanate
present. The surface Swype® detection limit is
approximately 3-5 µg.
6. Record appropriate information as needed.
7. If the surface Swype® tests indicate a
positive for contamination, the hygienist may want
to take corresponding surface wipe samples for
laboratory quantitation and confirmation in key
samples..
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Wipe Sampling for Laboratory Analysis
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| Materials: |
Glass fiber filters,
scintillation vials and a derivatizing solution
are required for this sampling procedure.
1. Gloves and other personal protective
equipment must be worn during sampling, as
appropriate. "Best" style 878 butyl
gloves provide protection to the hygienist's hands
for the time required to perform the sampling.
2. Gloves must be changed after obtaining each
sample to avoid cross contamination of any
subsequent samples.
3. A solution of 10.0 mg 1-(2-pyridyl)
piperazine per milliliter acetonitrile is
prepared. The 1-(2-pyridyl) piperazine is a
derivatizing agent that stabilizes the isocyanate.
The derivatives also allow a greater sensitivity
during the analysis.
4. Estimate the number of samples that will be
taken. An over estimate might be better. Prepare
vials by adding 1.0 milliliter of the
1-(2-pyridyl) piperazine solution to each vial. It
is recommended that the solution be pipetted into
the vials in a controlled environment, before
sampling, to eliminate any chance for
contamination.
5. Untreated glass fiber filters are the
appropriate wipe media.
6. Reagent grade acetonitrile is used to wet
the filter. The acetonitrile acts as a solvent to
dissolve and extract any contaminant present.
7. Using a dropper, wet the filter until almost
dripping.
8. Select an area immediately adjacent to the
area where the Swype® yielded a positive test
result.
9. Using the filter, wipe an area about 100 cm2
rubbing the entire area side to side, then up and
down. In many instances such as knobs and levers
it may not be possible to wipe 100 cm2
.
10. Place the filter in a scintillation vial
containing the derivatizing solution, label the
vial, and record appropriate information.
11. The samples are ready to be analyzed by a
laboratory. The OSHA Salt Lake Technical Center
uses OSHA method 47 for analysis of MDI, and OSHA
method 42 for analysis of 2,6-TDI and 2,4-TDI.
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Monitoring Inside Protective
Equipment (gloves, suits).
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Studies have shown that solvents containing chemicals
may act as a vehicle allowing the chemicals to permeate
gloves and protective clothing (7). The Permea-Tec®
aromatic isocyanates detection system may be used for work
site evaluation of chemical protective PPE. For example, a
negative result (no color change) of the Permea-Tec®,
after being worn under a glove for a time period, in a
work environment known to have contaminants present,
demonstrates that the glove protection was effective for
that time period, in those working conditions. The Permea-Tec®
is an indicating pad is attached to a band-aid like
adhesive strip.
1. Place one or more Permea-Tec® patches (pad side
out) on the fingers, palms, wrist, lower arm (near
cuff of glove), wherever there is likely to be
permeation or contamination.
2. Worker then don their PPE and work for a time
period as they normally would. (If the worker normally
change gloves every two hours then the time period is
two hours, for example).
3. After the shift, allow the workers to doff the
gloves as they normally would, then collect, identify,
and note the color of the pads.
4. In most cases the Permea-Tec® pad should not
need any further treatment. If solvent (containing
isocyanates) permeation has occurred, then this
solvent should be sufficient to activate the pad.
5. If permeation or penetration of the PPE by the
solvent containing aromatic isocyanates has occurred,
a reaction turns the pad a pastel red-orange to pink.
It is a reliable indicator to a detection limit of 3-5
µg aromatic isocyanates.
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Evaluating PPE for Dry Chemicals
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1. There may be situations where the Industrial
Hygienist may want to use Permea-Tec® pads for dry
chemicals. (For example: unprotected handling of
components that are assumed to be totally cured.) In
this case, after the pads have been collected, 3 drops
of solvent (methanol works well) needs to be placed
directly onto the pad. Again gloves must be worn
during sampling and solvent dispensing.
2. The methanol (or other solvent) wicks into the
pad and enables a reaction that turns the pad a pastel
red-orange to pink if aromatic isocyanate
contamination is present. It is a reliable indicator
to a detection limit of 3-5 µg
References
1. "Preventing Asthma and Death from Diisocyanate
Exposure", Department of Health , Education and
Welfare, NIOSH, ALERT, Cincinnati, OH, March, 1996, DHHS (NIOSH)
Publication No. 96-111, 2-3.
2. Material Safety Data Sheet for MDI, DOW Chemical
Company, Midland, MI, 1995, MSD002334, 1.
3. Bickis, U. Investigation of dermally induced airway
hyperreactivity to toluene diisocyanate in guinea pigs.
Ph.D. thesis, Department of Pharmacology and Toxicology,
Queen's University, Kingston, Canada. November, 1994.
4. Karol, M. H., Hauth, B. A., Riley, E. J., and
Magreni, C. M. Dermal contact with toluene diisocyanate (TDI)
produced respiratory tract hypersensitivity in guinea
pigs. Toxicol. Appl. Pharmacol, 1981, 58, 221-230.
5. Rattray, N. J., Botham, P. A., Hext, P. M.,
Woodcock, D. R., Fielding, I., Dearman, R. J., and Kimber,
I. Induction of respiratory hypersensitivity to
diphenylmethane-4,4'-diisocyanate (MDI) in guinea pigs.
Influence of route of exposure. Toxicology, 1994, 88,
15-30.
6. CLI, Colormetric Laboratories, Inc. 1261A Rand Road,
Des Plaines, IL, 60016-3402, Telephone: (847) 803-3737.
7. Gunderson, E. C., Kingsley, B. A., Witham,C. L. and
Bromberg, D.C. A Practical Study in Laboratory and
Workplace Permeation Testing. Appl. Ind. Hyg., 1989, Vol.
4, 12, 324-329
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| Prepared by: Richard
Lawrence, Chemist |
Date:
August 21, 1997 |
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