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In 1988, two workers were operating a sodium turnstate purification system. One worker attempted to pump a sodium sulfhydrate solution into a tank and accidentally opened the valve to another tank which contained an acidic solution (pH 2.9). The mixture of the two compounds generated and released hydrogen sulfide gas to which the deceased was exposed.

In 1988, a refinery employee received a fatal exposure to hydrogen sulfide gas while draining the contents of a knockout drum to an oily water sewer, rather than activating a closed system to pump out the drum. The worker failed to observe procedures calling for the use of a closed system, and the valve to the sewer was not locked out.

In 1993, employees were working in a coker unit that thermally cracks heavy residual feed through a process called delayed coking. The workers were preparing to switch the feed to the core drum, which necessitated opening and closing a number of valves. Three workers were involved with opening and closing the valves, each working at a different location. As the operation was proceeding, a loud noise was heard and a vapor cloud was observed in the vicinity of the pumps feeding the process. The vapor cloud ignited, fatally burning two of the workers.

In 1993, workers were draining refrigerant oil from collection traps on an anhydrous ammonia refrigeration system. The employees were using hand tools to open the valves and drain off the oil when they were severely exposed to anhydrous ammonia, resulting in two fatalities.

In 1994, an employee was killed when disconnecting a line from an ammonia valve. The line had not been adequately isolated, causing the release of liquid ammonia which struck the worker's face and body.

In 1994, one worker was killed and one worker was injured while attending to pumps in a muriatic acid unit. While working on the pumps, an over-pressurization of one of the process tanks occurred, causing a rupture which sprayed the workers with muriatic acid.

In 1994, a tragic fatality apparently caused by exposure to hydrogen sulfide was reported by the Billings, Montana, Area Office. The accident was associated with opening a valve to a sewer cup during the draining of a fuel gas knockout drum in a hydro treating unit of a petroleum refinery. Normal work procedures included periodically opening a valve that carried a water-gas mixture to a separator which removed and vented hydrocarbon gases to a flare. During the preceding winter, the piping to the separator froze, and the drum was temporarily drained to the sewer. The Agency believes that due to unclear procedures, the temporary practice of draining some of the water-gas mixture to the sewer in some instances may have been continued, or was incorporated by some workers into the normal draining procedures. The deceased is thought to have opened the valve to the sewer believing it to be part of the draining procedure, resulting in the release of toxic amounts of hydrogen sulfide that killed the worker.

1. Performing a process hazard analysis to address the hazards of the process and engineering and other control measures to ensure worker safety, including a complete evaluation and assessment of process systems handling waste products, by-products, and/or unreacted process components. Recommendations made by the PHA team, including recommended engineering changes, should be promptly implemented unless the employer justifiably rejects the recommendation pursuant to the guidelines contained in OSHA Instruction CPL 2-2.45A CH-1, "29 CFR 1910.1 19, Process Safety Management of Highly Hazardous Chemicals -- Compliance Guidelines and Enforcement Procedures," (September 13, 1994), Pages B-21 and B-22;

2. Assuring a system is under lockout/tagout, including draining and purging of lines and equipment, prior to working on the system;

3. Assuring that written procedures are clear and provide complete instructions for the safe performance of work activities;

4. Assuring that employees, including contract employees, are trained in applicable procedures and safe work practices, and that the employees understand and adhere to the current operating procedures of the process.

Sewer systems for draining tanks or drums which present a potential exposure to hazardous chemicals should be constructed so that they are closed, vented to a safe location, or not open to the atmosphere. Alternatively, appropriate respiratory protection should be worn before these systems are used.

A valve configuration on an industrial process should be such that only the valves used for routine use as part of the normal process are readily capable of being opened. If the valves are required to be opened only for occasional shutdown operations, they must be locked/tagged in the closed position to preclude erroneous opening during routine plant operations. Valves that must remain available for immediate use in emergency operations should be clearly labeled as such so that they are not accidentally opened during routine process or maintenance operations.

Training must include proper procedures for working near areas of potential exposure to hazardous chemicals and address the hazards of exposure. While labeling of pipes cannot be required, the hazard communication standard does require that the employer address the hazards of unlabeled piping systems in a written hazard communication program and that the information be provided through training to workers.

Written procedures must be developed for the safe use of respirators during the performance of operations presenting a potential exposure to a hazardous chemical(s).

Under circumstances where individuals may be exposed to an unknown concentration of hydrogen sulfide or some other hazardous chemical, back-up personnel with appropriate respirators and emergency equipment must be present.