OSHA Hazard Information Bulletins1
Use of Hydrofluoric Acid in the Petroleum Refining Alkylation Process

November 19, 1993




  • Director
  • Office of Field Programs


  • Director
  • Directorate of Technical Support


  • Hazard Information Bulletin1: Use of Hydrofluoric Acid in the Petroleum Refining Alkylation Process

The purpose of this bulletin is to alert field personnel to the potential safety and health risks posed by hydrofluoric acid (HF) used in HF alkylation units and to present the control measures implemented by industry to reduce workers' exposure, and pertinent OSHA requirements.

In recent years the petroleum refining industry has placed an increasing emphasis on the safety of the use of HF in petroleum refineries. Refineries use the acid in a manufacturing process called "alkylation," which is increasingly important in producing a high-quality gasoline. Hydrofluoric acid is hazardous and corrosive and, if accidently released, can form a vapor cloud. If the vapor cloud is concentrated enough it can be toxic until sufficiently dispersed. In the past five years, there have been a number of accidental releases of this acid from alkylation units at major petroleum refineries in the United States.

Pure hydrogen fluoride is a clear, colorless, corrosive liquid that has roughly the same weight as water (comparing equal volumes). It boils at 67 degrees Fahrenheit and, depending on the release conditions, can form a vapor cloud if released to the atmosphere. It has a sharp, penetrating odor that human beings can detect at very low concentrations (0.04-0.13 ppm2), in the air. It is completely soluble in water, in which it forms HF, which, in concentrated solutions, vaporizes in air to form a noticeable cloud.

To protect against adverse effects from exposure to hydrofluoric acid in the workplace, the Occupational Safety and Health Administration has established a permissible exposure limit (PEL) of 3 ppm averaged over an eight-hour workshift. The National Institute for Occupational Safety and Health immediately dangerous to life or health (IDLH) concentration for HF is 30 ppm3.

Any contact with HF liquid or vapor can produce serious, painful chemical burns, sometimes with delayed onset and hypocalcemia. The vapor can be extremely irritating to the eyes, skin and respiratory tract. Short-term exposure at high concentrations can cause serious health effects or death due to extensive respiratory damage.

Because of the chemical burn hazard present with HF, refineries have incorporated many or all of the following engineering controls at HF alkylation units:

  • Construction of concrete containment curbs around reactor and HF storage vessels.
  • Installation of segregated sewer systems designed to contain spills and runoff from HF acid areas. Effluent is treated for HF neutralization and removal before release to refinery main sewers.
  • Routing all vents from the unit to a soda ash scrubber to neutralize HF.
  • Installation of soda ash solution vats for neutralizing equipment that is to be removed from the unit for maintenance or disposal.
  • Installation of feed drying and HF acid regeneration systems to keep moisture content of acid less than 4 percent to prevent corrosion of equipment.
  • Potassium hydroxide scrubbing of light products leaving unit to neutralize trace amounts of HF that may present.
  • Incineration of HF acid sludge in process heaters.

The above controls are designed to contain HF inside the unit area, thereby minimizing exposure potential to workers outside the alkylation unit.

In addition, several OSHA regulations provide for the safe handling of hazardous chemicals. Refineries that handle HF must meet many requirements. For example, they must do the following:

  • Develop and implement a process safety management program in accordance with OSHA standard 29 CFR 1910.119, if they meet threshold quantities.
  • Monitor the site to determine the appropriate level of employee respiratory protection (29 CFR 1910.134).
  • Provide information and training, including first-aid training, to employees about the hazardous chemicals to which they are exposed by implementing a hazard communication program, (29 CFR 1910.1200).
  • Implement a program of engineering controls, work practices and personal protective equipment to control exposure (29 CFR 1910.134(b)(6), 29 CFR 1910.1000)
  • Develop and implement an emergency response plan, including emergency procedures and training of personnel (29 CFR 1910.120, 29 CFR 1910.38)

As with most refinery processes, the primary exposure control method used in HF alkylation units is the containment of all process substances within the unit equipment (i.e, vessels, piping, and pumps). Greatest exposure potential occurs:

  • During process stream sampling;
  • During unloading of HF from trucks;
  • Due to process leaks (fugitive emissions);
  • Due to equipment failures (e.g., pump seals); and
  • During equipment maintenance.

In June 1992, the American Petroleum Institute issued Recommended Practice 751, Safe Operation of Hydrofluoric Acid Alkylation Units. Due to the severe hazard potential of HF, compliance officers should familiarize themselves with this document prior to making an inspection involving HF.

Please disseminate this bulletin to all Area Offices, State Plan States, Consultation Project Officers and appropriate local labor and trade organizations.

1 The Directorate of Technical Support issues Hazard Information Bulletins (HIB) in accordance with OSHA Instruction CPL 2.65 to provide relevant information regarding unrecognized or misunderstood health hazards, inadequacies of materials, devices techniques, and safety engineering controls. HIBs are initiated based on information provided by the field staff, studies, reports and concerns expressed by safety and health professionals, employers, and the public. Information is compiled based on a thorough evaluation of available facts and in coordination with appropriate parties.

2 American Industrial Hygiene Association, Emergency Response Planning Guidelines, AIHA Emergency Response Planning Guideline committee, Akron, Ohio, 1988.

3 U.S. Department of Health and Human Services, NIOSH Pocket Guide to Chemical Hazards, Publication No. 90-117, Cincinnati, Ohio, June 1990.