occupational health Engineer and HSE
Aromatic Isocyanate Surface Contamination 
Sampling and Evaluation Techniques


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).
 
Wipe Sampling for Screening
 
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..

Wipe Sampling for Laboratory Analysis

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.

Monitoring Inside Protective Equipment (gloves, suits).

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.
Evaluating PPE for Dry Chemicals

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

Prepared by: Richard Lawrence, Chemis
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