Archive Notice - OSHA Archive

NOTICE: This is an OSHA Archive Document, and may no longer represent OSHA Policy. It is presented here as historical content, for research and review purposes only.

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

September 9, 1993

Ms. Charlotte Uram
Landels, Ripley & Diamond Attorneys
Hills Plaza 350 Steuart Street
San Francisco, CA 94105-1250

Dear Ms. Uram:

This is in response to your November 3, 1992 letter, which posed questions and projected answers with respect to the Process Safety Management standard, 29 CFR 1910.119, as it applies to workplace processes involving flammable liquids and gases. Please accept our apology for the delay in responding.

In order to simplify our responses to your questions, your proposed answers are not repeated here, nor have we attempted to re-write them. Also, you were contacted by telephone by Mr. Ronald Davies of my staff to clarify how "line" and "condensate line" related to the process described in questions 6 and 8 respectively. Subsequently, at your direction, a technical representative, who maintained the anonymity of your client communicated these clarifications to Mr. Davies by telephone as noted in the replies to these questions which follow.

Question 1: Liquefied petroleum gas is stored in an outside tank within a tank farm in a quantity of greater than 10,000 pounds. It is transferred approximately 75 feet to a separate gassing building where it is used to fill pressurized containers with small amounts of propellant gas (5 grams). The other parts of the operation are all located inside an adjacent facility. The operation is designed and operated in accordance with the Chemical Specialty Manufacturers Association guidance document for the handling of aerosol propellants and 29 CFR 1910.106. Would the tank and aerosol filling building be covered under the requirements of 29 CFR 1910.119?

Reply: Yes, flammable gases used on-site in quantities of 10,000 pounds or more as described in your question are covered under the requirements of 29 CFR 1910.119.

Question 2: Located approximately 25 feet away from the LPG tank described above in question 1 are atmospheric storage tanks of flammable liquids. None of the tanks are interconnected. The tanks contain more than 10,000 pounds of flammable liquids. Would the flammable liquid storage tanks be considered to be part of the covered LPG operations?

Reply: If an incident in the covered LPG process could involve nearby atmospheric tanks in which threshold amounts (10,000 pounds (4535.9 kgs) or greater) of flammable liquid are stored, this flammable liquid storage would be considered part of the covered LPG process. See the definition of process at 1910.119(b).

Question 3: In the example in Question 2 above, if engineering and administrative controls were in place to the extent that a process hazard analysis determined that there was no reasonable potential that a release from the covered LPG tank would involve the adjacent atmospheric storage tanks, would the adjacent tanks still be covered?

Reply: For the purposes of the "process" definition in 1910.119(b), "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 shall be considered a single process". The boundaries of the covered process which includes the LPG storage tank would extend to quantities of flammable liquids stored in separate atmospheric tanks located such that there is a reasonable probability that an event such as an explosion in the LPG process would affect the nearby atmospheric tanks and provide a potential for catastrophic release of the flammable liquids stored inside. (See the preamble discussion in the middle column of page 6372 of the PSM Final Rule published in Federal Register Volume 57, Number 36 on Monday, February 24, 1992, a copy of which is enclosed.) This interpretation is predicated on the assumption that an event such as an explosion will take place in the covered LPG process notwithstanding engineering and administrative controls required by the PSM standard to prevent catastrophic releases of highly hazardous chemicals.

Question 4: In Question 3 above, the same atmospheric storage tanks are connected to adjacent, indoor operations conducted at both ambient temperature and pressure that mix, blend and transfer greater than 10,000 pounds of the flammable materials. The transfer piping from the outside to the inside is equipped with a series of fusible link fire valves. Would the entire indoor operation which involves the handling of the flammable materials also be covered under the requirements of the standard dueto the proximity of the atmospheric storage tanks to the LPG tank?

Reply: Notwithstanding question 3, question 4 would be a covered process, independent of any other process. Atmospheric tanks containing flammable liquids that have feeder connections to processes are covered by the standard. Atmospheric tanks containing flammable liquids not having such feeder connections, such as bulk transfer terminals, are not covered. Your described process is an atmospheric tank with a feeder connection to a process and it is covered. Also, fusible link fire valves may function in a fire to prevent a catastrophic release of flammable liquid from a storage tank. However, these fusible link fire valves would not prevent a catastrophic release from a process due to containment failures including those caused by explosions.

Question 5: Quantities of flammable liquids greater than 10,000 pounds, that are not listed in Appendix A, are mixed, blended, transferred and stored as part of an operation that is done entirely under atmospheric conditions. The materials are not heated or part of an exothermic reaction. All of these operations are conducted in accordance with the requirements of 29 CFR 1910.106. Would this operation be covered under the Standard?

Reply: The flammable liquid process you described in this question is covered by the PSM standard. Since this process involves activities, that is, on-site movement and handling in addition to storage and associated transfer, the atmospheric storage and transfer of flammable liquid exemption at 1910.119(a)(1)(ii)(B) would not apply.

Question 6:

A line fills and packages small containers (one gallon or less) of flammable liquid products that are supplied from a stationary tank that contains more than 10,000 pounds (4535.9 kg) and is located approximately twenty-five feet away. The operation is conducted at both ambient temperature and pressure and in accordance with the requirements of 29 CFR 1910.106. Would the tank be covered under the requirements of the PSM standard?


The described process (storage tanks are considered a part of the process) would be a covered process unless the flammable liquid is stored in an atmospheric tank or transferred and is kept below its normal boiling point without benefit of chilling or refrigeration (See 1910.119(a)(ii)(B)). Please note that in 1910.119(b) the definition of an atmospheric tank means a storage tank which has been designed (emphasis added) to operate at pressures from atmospheric through 0.5 psig (pounds per square inch gauge, 3.45 kpa.) An atmospheric tank containing a flammable liquid that has a feeder connection to the fill process you described would not be covered by the PSM standard. The rationale for this interpretation is that the process described above only included the activities of storage and associate transfer to storage in containers which for the purpose of the PSM standard are considered equivalent to atmospheric tanks which are excepted from PSM coverage as noted previously.

Question 7: In the situation above in Question 6, if the tank is covered by 29 CFR 1910.119, would the line be covered if there were no reasonable potential that a problem at the line would involve the tank or that a problem at the tank would involve the line?

Reply: As indicated in Reply 6, the described process is covered.

Question 8: An operation involves the steam stripping of less than 10,000 pounds of flammable solvent from a carbon absorber. Is this operation covered by the Standard? If the condensate line from this operation were connected to a storage tank which held greater than 10,000 pounds of a flammable liquid, would the operation be covered? A process hazard analyses has determined that there is no reasonable potential that a catastrophic event from the stripping operation would involve the storage tank. Would the operation be covered?

Reply: The answer to your first question is "no". The answer to your second question is "yes."

Question 9: What is the difference between Hydrochloric Acid, Anhydrous and Hydrogen Chloride listed in Appendix A? Are dilute acid solutions (i.e. 30% Hydrochloric Acid) intended to be covered?

Reply: Hydrochloric acid, anhydrous and hydrogen chloride, listed in Appendix A of the PSM standard are the same highly hazardous chemical. Hydrogen chloride solutions, for example, 30 percent hydrochloric acid, would not be covered by the PSM standard.

Thank you for your interest in occupational safety and health. If we can be of further assistance, please contact us.


Roger A. Clark, Director
Directorate of Compliance Programs