OSHA requirements are set by statute, standards and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations. This letter constitutes OSHA's interpretation of the requirements discussed. Note that our enforcement guidance may be affected by changes to OSHA rules. Also, from time to time we update our guidance in response to new information. To keep apprised of such developments, you can consult OSHA's website at https://www.osha.gov.

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.

However, where the gauging of sour crude oil tanks is concerned, air monitoring must be performed prior to each gauging operation, unless the weight percentage of H(2)S in the liquid crude is low enough that there is no potential for exposure above the PEL.

If air monitoring is not performed prior to gauging and there is a significant or unknown concentration of H(2)S present in the crude oil, then the atmosphere surrounding the hatch opening must be assumed to be immediately dangerous to life and health (IDLH), so that self contained breathing apparatus (SCBA) or air-line with escape provision is required while the gauging is performed, and the other requirements of [29 CFR 1910.134(d)(2) and (g)(3)] must be met. This determination was made by the Agency in 1989 as the result of reported fatalities during tank gauging operations and subsequent inspections.

3. If periodic testing is not acceptable, must an employee who has an H(2)S monitor, which will trigger a warning alarm, on his/her person wear respiratory protection while engaged in activities as described in Items 1 and 2.

4. Is periodic testing required? If so, what is the acceptable time frame for such testing (i.e., daily, weekly, monthly, etc.)?

Response to Questions 3 and 4

Since OSHA has no specific monitoring requirements for H(2)S, the employer is responsible for determining what type and frequency of monitoring is appropriate to determine employee exposures, based on the nature of the hazard. As noted above, the employee would not be required to wear respiratory protection unless his or her exposure exceeded the PEL or unless there was the potential for an emergency. There is no specific requirement that respirators be worn while monitors are in use, or vice versa. It is the employer's responsibility to determine what engineering controls, work practices and protective equipment are appropriate to comply with the standard. See also answer to Question 1 and 2 above for specific requirements for tank gauging.

5. If respiratory protection is required to be worn while an employee is engaged in those activities as described in Items 1 and 2, must the employee have an H(2)S monitor on his/her person while at the tank site?

Response to Question 5

As noted above, an employee would only be required to wear a respirator when the activities caused an employee to be exposed above the PEL. If an employee were wearing a respirator, then, in accordance with [29 CFR 1910.134(g)(2)(i)], appropriate surveillance of work area conditions must be conducted. An H(2)S monitor can be used for this purpose, but the employer may determine whether other measures may be appropriate. Please note that if the employee is wearing the respirator in a dangerous atmosphere, then the requirements of [29 CFR 1910.134(d)(2) and (g)(3)] must be met, including communications capability and an appropriately equipped standby person (or persons). This requirement cannot be met solely by use of a monitor or warning alarm.

Please note that, if there is a potential for an uncontrolled release of H(2)S, the situation could represent an emergency. Such an emergency release would be covered under 29 CFR 1910.120, the Hazardous Waste and Emergency Response (HAZWOPER) standard, unless it were an incidental release, as defined in the standard, 29 CFR 1910.120(a)(3), where there is no potential safety or health hazard. Paragraph (q) of 29 CFR 1910.120 covers emergency responses regardless of location. If sections of the oil field were considered treatment, storage and disposal facilities or hazardous waste clean-up operations, other sections of 29 CFR 1910.120 would also apply.

The HAZWOPER standard directs employers to develop an emergency response plan which includes appropriate safety and health measures, such as monitors, alarms and a written personal protective equipment (PPE) program. Since respirators may be needed during an emergency response to an uncontrolled release of H(2)S, the written PPE program developed in compliance with HAZWOPER must address the selection, limitations, maintenance, storage, training, fitting, and donning and doffing procedures for respirators in addition to other PPE. In addition, all the requirements of CFR 1910.134, including paragraph [(g)] must be met when employees are required to use respirators to meet HAZWOPER requirements.

The complete answer to the several questions which you raise would depend on whether the potential for H(2)S exposure represented an emergency and what would constitute an appropriate emergency response plan to address that exposure. These are determinations which must be made by the employer, based on the actual worksite conditions. We are enclosing information on the HAZWOPER standard which you may find useful.

We hope this information is responsive to your concerns. Thank you for your interest in worker safety and health.


Roger A. Clark, Director
Directorate of Compliance Programs