Negative-pressure respirators for isocyanate paint spray

NOTICE: This is an OSHA Archive Document, and may no longer represent OSHA Policy. It is presented here as historical content, for research and review purposes only.

January 25, 1985

Dr. Bruce Karrh
Vice President
Safety, Health and Environmental Affairs
E.I. duPont de Nemours and Company
[Recipient address omitted]
Dear Dr. Karrh:

This is in response to your recent request concerning the use of negative-pressure air-purifying respirators for protection against paint spray containing isocyanates.

Our technical staff has reviewed the respirator cartridge breakthrough studies on isocyanate containing paint spray as well as the respirator field performance studies on asbestos and lead which duPont has submitted. We agree with the conclusions made in the duPont cartridge study that the preferential breakthrough of solvent over the isocyanates can only be applied to a specific enamel formulation. As we stated in a letter to you previously, it is infeasible to test the preferential breakthrough of all different combinations of solvents, isocyanates and thinners used in spray painting. Our staff has found that there are no data to indicate that the painters would smell the odors of solvents or the isocyanates in the workplace while other odorous substances may be present.

~~Mine Safety and Health Administration/~~National Institute for Occupational Safety and Health (~~MSHA/~~NIOSH) have not approved negative-pressure air-purifying respirators for protection against isocyanates since these compounds do not have adequate odor warning properties. Additionally, the respirator wearers could be exposed, without knowing it, to isocyanates through leakage at the facepiece seal of a negative pressure respirator.

[This document was edited on 03/24/99 to strike information that no longer reflects current OSHA policy.]

Since the isocyanates are among the most toxic substances on OSHA's permissible exposure limit table and they cause irreversible damage to overexposed employees, the negative-pressure air-purifying respirator is not acceptable for protection against isocyanates containing paint spray because it does not provide a sufficient margin of safety.

Sincerely,

John B. Miles, Jr.
Director
Directorate of Field Operations

[Company correspondence reproduced on OSHA page; omitted here.]

The data in the enclosed reports do indicate a long service life for both solvents and isocyanates under the stated test conditions. However, these studies do not encompass the wide temperature and humidity variations which may be present in paint spraying operations. For example, the DuPont studies were run at relative humidities below 61%. There was no indication of % RH in the Mobay study. Ernest Moyer and I reviewed the two studies. Our specific comments are as follows:

DuPont Study

Reference
Comment
--------- -------------------------------------------------------- Page 4 This should read "NIOSH utilizes this flowrate in Par. 2 their paint spray testing for certification." The last line reference quoted does not state a recommendation that this is a heavy breathing rate.

Page 6 An initial 15 minute exposure setting may not be Par. 1 indicative of the particulate level throughout the test.
Mobay's result indicate that this can vary throughout the test.

Page 16 There is no collection time given for the impinger last par. samples.

Page 12 This data does reflect the true downstream par. 1 concentration for this sample period. This data supports Mobay's conclusion that cartridges should be discarded after each work shift.

Page 12 This statement may not be entirely true. Depending on Par. 2 the loading of the cartridge, a worker may be exposed to a long period of solvent vapor breakthrough.

Page 12 There was no data or reference given to support the line 18 statement that this is a representative concentration.
If the concentration of HDI used in the test are representative (ie. Table III levels) this point should be made more strongly since many of the exposure levels shown in your testing are below the ceiling level.

Table I, Only one long term study with paint was done on the MSA III, IV cartridge. This does not represent much data on which to base conclusions.

Table II, V The upstream concentration of the vapors is relatively
low. Is this in agreement with the field survey of the body shop?

Table II 100 ppm of cellosolve acetate. What does this mean?
Was the upstream concentration a little above 100 ppm or could it have been over 1000 ppm?

Mobay Study

Reference Comment --------- ------------------------------------------------------ Page 1 Page 1 was missing. Table 1 The HDI and solvent levels are low (upstream). In fact the HDI is below the NIOSH recommended ceiling of 20 ppm. Table 1, 3, There is no indication of the relative humidity. and 4

Overall, both of these studies are interesting. Both studies indicated that for the conditions of the test (concentration, humidity, temperature, paint type) that the solvents breakthrough before HDI. However, further studies need to be performed to show that this remains true over a wide variety of conditions. The data used to determine what the representative work concentration is critical. If indeed the workplace concentrations of HDI is as low as the upstream concentrations in your tests, then OSHA may consider the use of APR for Imron, Centari, and Desmodur N based on the fact that the concentrations are normally below the ceiling.

It is difficult for us to comment on the MAK document. Only three test subjects were used in their determination of warning properties. The data on the effects of individuals with several years of exposure is restricted since workers were exposed to other toxic substances.

The question of determining adequate warning properties is a complicated one. The test methods used to determine physiological responses widely vary. Thus, the data cited in the literature must be carefully evaluated. The NIOSH report on isocyanates indicates that they do not have good warning properties. The lack of warning properties will eliminate the possibility of NIOSH approval for APR. This may be unfortunate since APR are so widely accepted.

We hope you will find our comments useful. We found the studies very interesting. It is good to know that others are also concerned over respiratory protection.

If I can be of any further assistance, please feel free to contact me.

Sincerely yours,

Nancy J. Bollinger Assistant Chief
Testing and Certification Branch
Division of Safety Research