Standard Interpretations - Table of Contents
• Standard Number: 1910.134

April 14, 1993

Mr. LeRoy H. Ernst
Managing Director
North Dakota Motor Carriers Association, Inc.
1031 East Interstate Avenue
Post Office Box 874
Bismarck, North Dakota 58502

Dear Mr. Ernst:

This is in response to your request for an interpretation of the Occupational Safety and Health Administration (OSHA) Respiratory Protection Standard, 29 CFR 1910.134, as it relates to oil fields. Your specific questions concerned respiratory protection for employee exposures to hydrogen sulfide (H(2)S) released from tank hatches. We will answer your questions in the order presented in your correspondence.

1. If periodic testing for hydrogen sulfide in the atmosphere at crude oil/production water storage tank thief hatches does not indicate the presence of hydrogen sulfide (H(2)S), is respiratory protection required to be worn by employees engaged in tank gauging activities or other operations such as the opening of covers, valves, etc. at those tanks?

2. If periodic testing for hydrogen sulfide in the atmosphere at crude oil/production water storage tank thief hatches indicates hydrogen sulfide in concentration less than the permissible exposure limit, is respiratory protection required to be worn by employees engaged in tank gauging activities at those tanks?

Response to Questions 1 and 2

According to 29 CFR 1910.1000, Air Contaminants, respiratory protection would be required to be provided to employees, if periodic testing indicates employee exposures to H(2)S at concentrations above the permissible exposure limits (PEL). As indicated in Table Z-2 of the standard, the PEL for H(2)S is a ceiling standard of 20 ppm. A maximum peak exposure of 50 ppm is permissible for 10 minutes but only if no other measurable exposure occurs during the workshift. The employer would be responsible for performing an exposure determination for all types of employee activity. This determination could be based on results of periodic testing, if that data accurately characterizes employee exposure.