Sampling hydrogen sulfide ceiling and peak exposures

September 28, 1995

Mr. Robert J. Smith
Vice President, Operations
Courtaulds Fibers, Inc.
[Recipient address omitted]
Dear Mr. Smith:

This is in response to your letter of August 1, to Lana Graves, Area Director of the Occupational Safety and Health Administration's (OSHA) Mobile Area Office. That letter was forwarded to our office for response. In that letter, you requested the appropriate method for assessing hydrogen sulfide peak exposure levels.

In your letter, you mentioned that your were using both the instantaneous and 10 minute time period sampling techniques. You stated that you felt the appropriate method for measuring hydrogen sulfide was the 10 minute sampling period method alone.

In answering your question, please refer to 29 CFR 1910.1000(b)(2) which requires that an employee's exposure to any substance listed in Table Z-2 shall not exceed at any time the acceptable ceiling concentration limit, except for a time period and up to a concentration not exceeding the maximum duration and concentration allowed in the acceptable maximum peak column. The example given in 1910.1000(b)(3) states that "...an employee may be exposed to a concentration of Substance A (with a 10 ppm TWA, 25 ppm ceiling and 50 ppm peak) above 25 ppm (but never above 50 ppm) only for a maximum period of 10 minutes."

Hydrogen sulfide can be a severe acute hazard, and in reviewing the USA Standard Z 37.2-1966 it was noted that hydrogen sulfide is an extremely toxic and irritating gas and a significant property of the gas is it's temporary paralytic effect on the olfactory nerve. High concentrations can result in severe consequences before the odor is detected. Sampling methods are currently available and should be used for measuring both the 10 minute and instantaneous levels of hydrogen sulfide in the workplace. For these reasons, it is felt that your current policy of measuring both the 10 minute and instantaneous levels of this gas is appropriate.

Thank you for your interest in occupational safety and health. If you have any further questions, please contact OSHA's Office of Health Compliance at [(202) 693-2190].

Sincerely,

Ruth McCully, Director
Office of Health Compliance Assistance

[Earlier OSHA routing memo, requester letter, and supporting material reproduced on OSHA page; omitted here.]