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 http://www.osha.gov.

May 2, 2014

Mr. Paul Crook
Safety and Health Manager
Fluoro-Seal International, L.P.
16360 Park Ten Place
Suite 325
Houston, TX 77084

Dear Mr. Crook:

Thank you for your letter to the Occupational Safety and Health Administration's (OSHA's) Directorate of Enforcement Programs (DEP). Our OSHA Region VII Office forwarded your letter to me. We apologize for the delay in our response. This letter constitutes OSHA's interpretation only of the requirements referenced herein and may not be applicable to any question not detailed within your original correspondence. Your inquiry is related to the application of OSHA's standard, Process Safety Management (PSM) of Highly Hazardous Chemicals, 29 CFR 1910.119, to cylinders of highly hazardous chemicals.

Scenario: You state the following regarding the use and storage of anhydrous hydrogen fluoride (AHF) at your facilities:

  1. Fluoro-Seal uses AHF at its facilities to treat plastic bottles;
  2. Fluoro-Seal conducts its AHF operations in single story, open-warehouse type buildings;
  3. The warehouse buildings are sprinkler-protected;
  4. AHF is contained in U.S. Department of Transportation (DOT) 3AA-2400 cylinders. Each cylinder contains 80 pounds of liquid AHF;
  5. Fluoro-Seal at times connects two full AHF cylinders (160 pounds total) in the barrier treatment area (BTA);
  6. Some Fluoro-Seal facilities have two adjacent BTAs that contain an aggregate amount of either 160 or 320 pounds of AHF;
  7. Each Fluoro-Seal facility has two AHF cylinder storage racks located within a warehouse building that contain 24 cylinders (12 cylinders per rack) for a total AHF rack inventory of 1920 pounds;
  8. AHF cylinder locations include:
    1. two cylinder storage racks on opposite sides of the warehouse building at least 120 feet apart; and
    2. the two cylinder storage racks are at least 120 feet from the BTA(s); and
  9. In some cases there are partial racks of full cylinders located near the BTA(s). The AHF quantity in the partial racks and the BTA(s) do not exceed the PSM threshold quantity (TQ) for AHF.

Question 1: Where conditions (forces) that would be created by an anticipated event are the same or less than the forces which the DOT standard 3AA-2400 requires a cylinder to withstand (e.g., heat, pressure, impact, corrosion, etc.), can the DOT-rated cylinder itself be an effective barrier such that each independent and unconnected cylinder of anhydrous hydrogen fluoride (AHF) constitutes a separate process for purposes of PSM, regardless of proximity to any one or more other DOT 3AA-2400 rated cylinders containing AHF?

Response: To determine if cylinder design constitutes an effective barrier for the non-interconnected equipment and to determine whether the cylinders are part of a PSM-covered process, you must first consider the definition of process at 29 CFR 1910.119(b):

"Process" means any activity involving a highly hazardous chemical including any use, storage, manufacturing, handling, or the on-site movement of such chemicals, or combination of these activities. For purposes of this definition, any group of vessels which are interconnected and separate vessels which are located such that a highly hazardous chemical could be involved in a potential release [emphasis added] shall be considered a single process.

For co-located equipment to be considered a PSM-covered process, there must be a reasonable probability that an event such as an explosion would affect unconnected vessels which contain quantities of the chemical that when added together would exceed the threshold quantity and provide a potential for a catastrophic release. In general, unconnected vessels must be evaluated by the employer to determine if they would interact during an incident, and if such a reasonable condition exists these vessels would be included in the process.

In some cases, physical barriers can effectively separate unconnected vessels to the extent that the potential for a chemical release is adequately controlled. For example, where a dike is used around a liquid storage vessel to fully contain released material and prevent it from interacting with another vessel outside the dike, and neither vessel by itself contains the threshold quantity, then this physical barrier would be considered acceptable in making the two vessels remote from each other. In addition, OSHA has previously stated that employers can use passive controls1 depending on the hazard to achieve adequate separation of vessels. Conversely, OSHA has also stated that other engineering controls (e.g., sprinkler systems, automatic-closing fire doors, etc.), and administrative controls (e.g., operating procedures, mechanical integrity procedures, and training) used to prevent and mitigate a catastrophic release of a covered HHC may not be used to determine the extent of a process as defined in paragraph 1910.119(b). As you have mentioned the presence of sprinklers in your facility, please note that building sprinklers are not a consideration for determining the boundaries of the covered process because they are an active engineering control.

In your facilities, Fluoro-Seal stores all the non-interconnected cylinders in an open warehouse. Should a fire occur that envelops the warehouse, it is expected, based on a U.S. EPA contractor's evaluation2 that the cylinders would catastrophically fail and release their AHF contents. Based on the EPA evaluation: 1) OSHA does not consider the cylinder design to be an effective barrier that distinguishes the boundaries of a process; and 2) the PSM standard requires you to aggregate the amounts of AHF in the cylinders at each of these sites to determine if the AHF TQ is exceeded. If the aggregate amount of AHF exceeds 1,000 pounds at any of your facilities, those facilities with greater than the TQ have a PSM-covered process.

Question 2: If you do not concur with the company's determination that the DOT-rated cylinder itself constitutes an effective barrier, is storage of all cylinders in one building or under the same roof, regardless of the distance between storage areas, a single PSM-covered process? If not, would the separation of the rack storage areas by 120 feet be sufficient to constitute multiple processes, or is the appropriate distance for facility management determination? If it is for management determination, what factors should be the basis for management's determination of the distance needed to establish a separate process?

Response: For storage and use of cylinders of AHF inside an open warehouse as described in the scenario above, separation distance is likely not a determinate factor for establishing the boundaries of the covered process. As noted in the response above, if there is a reasonable probability that an event such as an explosion would affect any nearby unconnected vessels, the PSM standard requires an employer to take steps to minimize the hazard of an uncontrolled release of an HHC. Based on the description you provided, there are no barriers to segregate or protect the cylinders in the event that a fire or explosion envelops the warehouse and its contents. Because AHF cylinders on their own are not designed to withstand a building-wide fire, the entire contents of all the AHF cylinders could be released. As a result, if a threshold quantity of AHF is present in the co-located cylinders, the PSM standard would apply.

Question 3: If you do not concur with the company's determination that the DOT-rated cylinder itself constitutes an effective barrier, would the storage racks constitute separate processes if each rack were located in the same building, but each rack were located behind a separate concrete block wall that is a minimum of eight feet high?

Response: To adequately segregate the AHF cylinder storage racks in your warehouse such that no PSM-covered process exists, the PSM standard requires consideration of the adequacy of any barriers you might construct to segregate the storage of your AHF cylinders. The barriers must be constructed in a manner that mitigates any fire or explosion hazards to the degree that a release of HHC in one storage area will not lead to the release of HHC in the other area. In your specific situation, if you were to adequately segregate the storage of the AHF into two or more areas such that no one area contains greater than 1,000 pounds of AHF, then OSHA would consider the storage of AHF cylinders in your warehouse to be a non-covered process.

More specifically to your question about the use of 8 foot concrete walls. OSHA believes that an effective barrier in your situation is a wall that both provides complete separation (e.g. to the ceiling) between your two AHF storage racks, and is constructed to an appropriate fire resistant rating.

For more information about recognized and generally accepted good engineering practices (RAGAGEP) and other safe practices related to the storage, handling, and use of AHF cylinders and other corrosive and toxic gas materials, see:

  • NFPA 1 - 2012, Fire Code, including Chapter 60, Hazardous Materials;
  • NFPA 5000 - 2012, Building Construction and Safety Code, including Chapter 34 High Hazard Contents;
  • NFPA 400 - 2012, Hazardous Materials Code, including Chapter 21, Storage, Use, and Handling of Compressed Gases and Cryogenic Fluids in Portable and Stationary Containers, Cylinders, and Tanks, in particular see Section 21.3.9, Toxic and Highly Toxic Gases; and
  • NFPA 55 - 2010, Compressed Gases and Cryogenic Fluids Code, including Chapter 7, Compressed Gases which contains Section 7.9, Toxic and Highly Toxic Gases.

Question 4: Our analysis of an event that could cause a release has considered improbable events such as a building collapse (whether due to fire or other cause), it has excluded occurrences such as a nuclear bomb which, of course, is not an "impossible" eventuality. Must the likelihood of release be evaluated based on some reasonably anticipated eventuality, or must it be established that the release is "impossible" or "could not possibly" result under any circumstances?

Response: Because your process contains co-located equipment, to determine the boundaries of your process you must consider hazards that could reasonably be expected to cause a release from your process. In your case, there appears to be a reasonable probability that a fire in your AHF storage warehouse(s) could result in the release of HHC contained in the separate cylinders. Therefore, any evaluation you conduct to determine the extent of the boundaries of your process should at a minimum take into account the impact of a full warehouse fire.

For more information about different causes of chemical releases, see Guidelines for Vapor Release Mitigation, Appendix A: Loss-of-Containment Causes in the Chemical Industry.3 Note that this publication lists fire as one of the many causes of loss-of-containment events.

Thank you for your interest in occupational safety and health. We hope you find this information helpful. 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 http://www.osha.gov. If you have any further questions, please feel free to contact the Office of Chemical Process Safety and Enforcement Initiatives at (202) 693-1850.

Sincerely,

Thomas Galassi, Director
Directorate of Enforcement Programs


1 Passive mitigation protection for separate equipment includes protections where actions/interventions are not required. Passive engineering controls include, but are not limited to: 1) separation by distance; 2) blast resistant construction; 3) dikes, etc. When determining if separate equipment is part of a covered process, the employer's evaluation may take credit for well designed and reliable passive mitigation systems that effectively prevents the separate equipment under consideration from affecting a release. In other words, if the employer's evaluation determines that a storage tank is adequately separate from a process under consideration based on its separation distance or the construction of a blast resistant wall, the storage tank would not be considered part of the process under consideration. Conversely, if the separation distance or the wall is inadequate to prevent the process from affecting a release from the storage tank or vice-versa, then the process and the separate storage tank would be considered one covered process.

2 Memorandum from ERG to U.S. EPA, Subject - ERG-1-4(CE) Technical Direction 8 - Fluoro-Seal CAA §112(r) Compliance Review, December 5, 2011

3 AIChE - Center for Chemical Process Safety (CCPS), 1988