OSHA Hazard Information Bulletins
Chemical Exposures from Industrial Valve and Piping Systems

May 14, 1996

Hazard Information Bulletin - Chemical Exposures from Industrial Valve and Piping Systems

The purpose of this Hazard Information Bulletin is to heighten public awareness of the potential for death, physical injury, and/or illness resulting from the unexpected release of chemicals during refinery and other chemical process operations. OSHA recognizes that non-compliance with existing requirements is the exception, rather than the rule, in these industries. This bulletin is intended to bring to the attention of employers, employees, and OSHA field personnel fatal accidents that have occurred in industrial operations, and the methods that can be employed to reduce the risk of such accidents. In addition, this bulletin is intended to alert OSHA's field compliance personnel to such hazards so that the scope of future inspections adequately addresses these risks. This document is not intended to impose additional compliance requirements on affected employers.

Fundamentally, employers and employees must be alert to the fact that working with a "closed system" does not always ensure safety. Operations involving the opening of valves or pumps on otherwise closed systems or working on such equipment that is not isolated or locked/tagged out are particular sources of danger. When a normally closed system is opened, the potential exists for releasing hazardous chemicals into the workplace in unknown concentrations.

Examples of Accidents:

The Agency reviewed previous fatality inspections involving the opening of valves or piping systems and found numerous incidents where one or more workers had died. Some examples of these types of accidents included:

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.

Common Factors and Problems

A common theme running through these fatalities is that they involved situations where a closed industrial system was opened through a valve or pump either to perform maintenance work, vent by-products, or remove condensate. The hazards inherent in these operations should be addressed by one or more of the following measures:

  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.

While the risk of accidents cannot be entirely eliminated, these procedures and practices will reduce the potential for an accidental exposure to a hazardous chemical(s).

Applicable Control Measures:

Engineering Controls: Plant systems containing hazardous chemicals must be completely assessed to assure that valves capable of releasing the toxic agent to the atmosphere are permitted to be opened only when absolutely necessary and are then vented using appropriate safety precautions. The valves must also be capable of being locked/tagged out.

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.

Monitoring and Detection Equipment: Operators working on units where there is potential exposure to hazardous chemicals may need to be supplied with personal monitoring equipment. Alternatively, stationary monitors could be installed. Personal or stationary monitors must be capable of sounding an audible alarm or warning.

Training: All current and new employees should receive training in standard operating procedures covering all aspects of the job, with emphasis on safe work practices. Where appropriate, training should also include field observations (on-the-job training) by qualified supervisory personnel, including verification that workers have satisfied the training requirements.

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.

Respiratory Protection: Respirators must be provided by the employer when effective engineering controls are not feasible, or while they are being instituted, when such equipment is necessary to protect the health of the worker. The employer must provide respirators that are applicable for the purpose intended.

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.

Applicable Standards:

The following standards may apply according to the nature of the process.

  • 29 CFR 1910.119 - Process Safety Management
  • 29 CFR 1910.120 - Hazardous Waste and Emergency Response
  • 29 CFR 1910.132 - Personal Protective Equipment
  • 29 CFR 1910.134 - Respiratory Protection
  • 29 CFR 1910.146 - Confined Spaces
  • 29 CFR 1910.147 - Lock Out and Tag Out
  • 29 CFR 1910.1000 - Permissible Exposure Limits for Hazardous Chemicals
  • 29 CFR 1910.119) and a serious hazard is determined to exist, the general duty clause - Section 5(a)(1) of the OSH Act may apply and require a process hazard analysis to be conducted. If use of the general duty clause is anticipated as a result of similar circumstances to those described in this Bulletin, compliance officers are reminded to refer to the Field Inspection Reference Manual (FIRM) for guidance.


    For more information contact Ray Donnelly, Director for the Office of General Industry Compliance at (202) 219-8031.