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 25, 1989

MEMORANDUM FOR:          Michael G. Connors
                         Regional Administrator

THROUGH:                 Leo J. Carey, Director Office of Field Programs

FROM:                    Thomas J. Shepich, Director Directorate of
                         Compliance Programs

SUBJECT:                 Respiratory Protection Requirements for Sour Crude
                         Oil Tank Gauging Operations

This is in response to your letter of January 5, concerning the subject captioned above. We have responded to your questions in the order of which they were presented.

1) 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.

2) Generally, yes. See 1) above.

3) Based on an approximate correlation of 50:l of vapor phase to liquid phase concentrations of H(2)S and the new PEL for H(2)S of 10 ppm, concentrations of H(2)S of 0.2 ppm or greater in the sour crude oil can result in concentrations in air of 10 ppm or greater.

4) If air monitoring is not performed prior to gauging and there is a significant concentration of H(2)S present in the crude oil, than the atmosphere surrounding the hatch opening must be assumed to be IDLH.

5) SCBA or air-line with escape provisions is required while the monitoring is performed.

6) Yes. The standby personnel required by [29 CFR 1910.134(g)(3)(i)-(vi)] must be present.

7) Yes.

8) Yes.

9) No. If there is remote monitoring of the sour crude oil tank, which can accurately assess the worst case conditions of exposure at the hatch opening, then the employer has met the requirements of [29 CFR 1910.134(g)(2)(i)]. [29 CFR 1910.134(g)(2)(i)] should be cited in conjunction with 29 CFR 1910.134(a)(2) in the situation described in question 8.

10) Yes.

[This document was edited on 03/29/99 to strike information that no longer reflects current OSHA policy.]

11) It would be better to cite [29 CFR 1910.134(c)(1)] in situations where there is not a high potential for concentrations of H(2)S to reach 300 ppm or greater. In situations where a strong case can be made that there is a potential for airborne concentrations of H(2)S to reach or exceed 300 ppm, [29 CFR 1910.134(d)(2)(i-iii) and (g)(3)(i-vi)] should be cited where applicable.

DATE:               January 5, 1989

MEMORANDUM FOR:     Thomas J. Shepich, Director
                    Directorate of Compliance Programs

THROUGH:            Leo Carey, Director Office of Field Programs

FROM:               Michael G. Connors Regional Administrator Region V

SUBJECT:            Request for Interpretation of Applicable Respiratory 
                    Protection Requirements for "Sour" Crude Oil Tank Gauging 

The potential for release of life threatening concentrations of hydrogen sulfide gas into the atmosphere where "sour" oil and gas operations are conducted is well known in the petroleum drilling, transporting and refining industries. Employers involved in transporting "sour" crude oils from production well sites to pipelines are required to manually gauge storage tanks before and after each transfer in accordance with industry established (i.e. American Petroleum Institute) procedures. As these storage tanks are located outside at remote locations, a single employee is dispatched to perform the necessary gauging on a regular basis (gauging schedules vary depending on when transfers are made from individual storage tanks). Tank gauging requires an employee to climb to the top of the storage tank, open a thief hatch, and determine the tank level by means of a plumb bob. Crude oil temperature and specific gravity readings may also be taken at this time, which would involve taking a sample from the tank and/or reading a gauge. Normally, the entire procedure takes approximately five to ten minutes.

Hydrogen sulfide exposure during the gauging operation occurs when the thief hatch is opened. The vapor space in these storage tanks can have vapor phase hydrogen sulfide concentrations up to hundreds of parts per million. A recent technical article on this subject (see enclosure A) states: "Liquid phase hydrogen sulfide concentrations above 8 ppm by weight can produce atmospheres immediately dangerous to life or health (IDLH) in residual fuel oil storage tanks and ship and barge holds." Thus employees opening these thief hatches, without appropriate personal protective equipment, can be exposed to life threatening concentrations of hydrogen sulfide gas which is released through the hatch into the employees' breathing zone. The concentration of hydrogen sulfide gas released through the hatch depends on many factors: the concentration of "sour" components in the crude oil; the level of liquid crude oil in the tank; the temperature of the crude oil in the tank, any pressure differential between the vapor space in the tank and the outside atmosphere; the size of the hatch opening; and local environmental conditions (i.e. ambient temperature, wind speed, wind direction, etc.) at the time the gauging is being performed.

Region V's current interest in the hazards associated with gauging tanks containing sour crude oils stems from a fatality which occurred in Michigan in March of 1988. While attempting to gauge a tank containing sour crude oil, hydrogen sulfide rich vapors from the head space of the tank were released into the breathing zone of an employee immediately rendering him unconscious with death following shortly thereafter. As a result of the investigation of this fatality, the Michigan Division of Occupational Health, Bureau of Environmental and Occupational Health issued citations to both the employer and to a crude oil transport company in a related investigation. Both companies were cited under Michigan Occupational Health Standard No. R3302- 2 (see enclosure B), which contains wording identical to federal standard [29 CFR 1910.134(g)(3)(i-vi)] (see enclosure). These citations were subsequently contested by both employers.

On December 13, 1988, I met with representatives of Total Crude Oil Transport, Inc. (one of the cited companies) and the Michigan Oil and Gas Association at their request. The applicability of the cites standard and feasibility of compliance were discussed.

These representatives stated that tank gauging operations are performed in a variety of different ways in this industry. Some companies allow the gauging to be performed by a single employee, regardless of the sour component concentration in the crude oil, provided he/she is equipped with appropriate respiratory and air monitoring equipment. Other companies, including Total, assign a stand-by person when the vapor head space of the storage tank is likely to exceed 300 ppm hydrogen sulfide (e.g. the NIOSH IDLH limit). However, respiratory protection equipment is generally not worn while air sampling is being conducted. Instead, employees rely on work practice controls (i.e. standing up wind; noting temperature of oil in tank; cracking thief hatch slightly to take air readings). Some employees wear badge type hydrogen sulfide monitors which either alarm, or change color, to warn them of exposures to high hydrogen sulfide concentrations. It is also common for employees to carry canister masks (negative pressure respirators) for evacuation purposes.

Yet these representatives are not aware of any situations where an employee, wearing an SCBA, goes to monitor and gauge a tank supported by at least two stand-by men as stipulated in [29 CFR 1910.134(g)(3)(i-vi)]. Requiring the industry to adopt this practice would have a severe economic impact on their operations. Furthermore, various safety issues concerning employees climbing ladders and transversing catwalks with this type of respiratory protection were brought up.

Regarding potential engineering controls which could be used to eliminate and/or reduce the hazards involved with the manual gauging, the Michigan Oil and Gas Association has been investigating eight different types of automatic gauges. Yet estimate for installation and continued maintenance run up to $10,000 per tank. There are significant corrosion problems with sour crude oils and API will not currently accept automatic gauging as it is not as accurate as manual gauging. Installation of pet cocks on storage tank to aid manual gauging was found to be feasible, but these items are also expensive to retrofit.

In addition, copies of an interpretation of [29 CFR 1910.134(d)(2)(i-iii) and (g)(3)(i-vi)] by Region VI were given to me at this time (see enclosure C). In short, these representatives felt that this standard is not applicable to this particular situation. At the conclusion of the meeting, the above representatives stated that they would be contacting you under the auspices of the API for a formal OSHA interpretation on the above matters.

Further research into this subject by members of my Technical Support staff revealed a May 30, 1984 interpretation letter from John B. Miles, Jr. to Ms. Gayla McCluskey of Sun Exploration and Production Co., and API Recommended Practice 55 which also discuss these hazards (see enclosures D and E). Calls placed to Technical Support sections in Regions VI and VIII revealed that it is common industry practice to allow tank gauging operations to be performed by a single employee provided with appropriate respiratory and air monitoring equipment. Region V has also heard reports that there have been several fatalities nationwide where employees have been overcome by hydrogen sulfide during tank gauging operations. Flint Watt, Chief, Michigan Division of Occupation Health, states that his people have investigated four fatal incidents due to this case. Both Region VI and Region VIII are also aware of fatalities, but could not provide specific examples. However, we contacted Joe Ashley, Office of General Industry Compliance Assistance, and after checking the federal OSHA fatality reports, he could not locate a single case of this type for the past several years.

As this hazard involves operations in more than one Region; the interpretations issued thus far appear to be vague or inconsistent; and the methods by which the hazard is to be abated will involve a significant number of well sites (estimated to be approximately 100,000) and may have significant economic impact on the industry, Region V is asking for guidance in determining how the provisions of the respirator standard are to be applied. Therefore, I ask you to provide us with answers to the following questions so that we can determine the appropriate enforcement stance on this issue:

1) [29 CFR 1910.134(g)(2)(i)] requires that: "appropriate surveillance of work area conditions and degree of employee exposure or stress shall be maintained." Where gauging of sour crude oil tanks is concerned, how often must air monitoring be performed to assess employee exposure?

2) As the concentration of hydrogen sulfide in the vapor space of the storage tank will depend on a variety of factors (i.e. sour component percentage in crude oil; crude oil level in the tank; temperature of crude oil; local environmental conditions; size of hatch opening, etc.) is air monitoring required prior to each gauging operation?

3) Is there a weight percentage of hydrogen sulfide in liquid crude oil where air monitoring would not be required?

4) If air monitoring is not performed prior to gauging, can the air space around the hatch opening be classified as IDLH assuming the tank contains a high percentage (i.e. over 8%) of sour crude oil?

5) If air monitoring is required prior to gauging, and it can't be done without exposing the employee doing the monitoring to the hazard, what level of respiratory protection must be provided?

6) If full protection (i.e. SCBA or air-line with escape provisions) is required while air monitoring is performed, do the appropriate stand-by personnel have to be present as required in [29 CFR 1910.134(g)(3)(i-vi)]?

7) If the vapor head space of a closed storage tank is monitored by remote methods without exposing employees to the hazard, can this reading be used as a worst case in determining the extent of respiratory protection needed when gauging is to be performed?

8) 29 CFR 1910.134(a)(2) states, in part: "Respirators shall be provided by the employer when such equipment is necessary to protect the health of the employee. The employer shall provide the respirators which are applicable and suitable for the purpose intended." Is it appropriate to cite this standard if employee(s) are found to be gauging storage tanks which contain sour crude oils without respiratory protection and no air monitoring has been conducted to evaluate the hazard?

9) Should [29 CFR 1910.134(g)(2)(i)] be cited in conjunction with 1910.134(a)(2) if the situation in question 8 exists?

10) 29 CFR 1910.134(e)(3) state[d], in part: "Written procedures shall be prepared covering safe use of respirators in dangerous atmospheres that might be encountered in normal operations or in emergencies. Personnel shall be familiar with these procedures and available respirators." Is it appropriate to cite this standard if no written procedures have been developed for gauging operation involving storage tanks containing sour crudes?

11) Would it be better to cite [29 CFR 1910.134(c)(1)] for the situation posed in question 10 instead of [29 CFR 1910.134(d)(2)(i-iii) and (g)(3)(i-vi)]?

If you require additional information on this subject, please feel free to contact Mark Kaszniak, a safety engineer in my Technical Support Section at FTS 886 - 6288.