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 https://www.osha.gov.

February 15, 1994

Mr. John Anicello
Technical Manager, Regulatory Affairs
Airco Gases
1588 Doolittle Drive
P.O. Box 2033
San Leandra, California 94577

Dear Mr. Anicello:

This is in response to your December 11, 1992 letter requesting interpretation of the Process Safety Management (PSM) of Highly Hazardous Chemicals standard, 29 CFR 1910.119. Please accept our apology for the delay in responding. Your questions and our responses follow.

Question 1: What criteria are used to establish a "remote distance" between processes which potentially may be covered by the PSM Standard?

Reply: When processes are in close proximity to each other such that an incident in one process could involve the potential release of a highly hazardous chemical (HHC) in another process, these processes are considered to be a single process (See the definition of process at 1910.119(d)). Processes which are not in close proximity are considered to be at a remote distance. Federal regulations, or national consensus standards and other criteria acceptable to OSHA, that provide at least equal safety and health to employees in the workplace, may be used to determine whether one process is at a remote distance from another process. For example, with respect to liquid HHC's, where a dike built around a liquid storage vessel to fully contain released materials, is used to prevent interaction with another vessel outside the dike and neither vessel by itself contains a threshold quantity, then this physical barrier would be considered acceptable in making the two vessels remote from each other. This is set forth in the preamble to the PSM standard, at the bottom half of column two on page 6372 of the Federal Register, a copy of which is enclosed for your use.

Question 2: Are the quantities of different Appendix A listed HHC's when stored in close proximity considered aggregate for the purpose of determining threshold quantity?

Reply: No, threshold quantity is determined by the amount of an individual, listed toxic or reactive HHC in a process, or in more than one process if they are in close proximity.

Question 3: Are the quantities of flammable liquids and flammable gases stored in close proximity considered aggregate for the purpose of determining threshold quantities?

Reply: Flammable liquids are treated separately from flammable gases for aggregation purposes. Threshold quantity is determined by the aggregate amount of flammable liquids or flammable gases in a process or in more than one process in close proximity.

Question 4: Would commercial delivery to a worksite of a HHC in small containers such that the aggregate is a threshold quantity or greater amount be covered by the PSM standard?

Reply: Both OSHA's PSM Standard and Department of Transportation (DOT) regulations apply to carriage of a covered HHC onto a worksite. Please refer to the following interpretation to determine when the PSM standard would cover the worksite process and when DOT regulation would be paramount.

Carriage of a covered HHC onto a worksite at which there is a covered process may be covered by the PSM standard depending on the circumstances in each case. The employer is responsible for providing safe workplace access for the commercial carrier to and from, and at the loading and unloading site(s). This carriage would be covered by OSHA standards to the extent that it is not covered otherwise by the Hazardous Material Regulations of the Department of Transportation (DOT) (See 49 CFR Subchapter C and particularly Part 177 - Carriage by Public Highway). These DOT regulations cover containment design, construction, maintenance (including repairs) and associated carriage operations. Operations regulated by DOT include carrier loading and unloading, cargo transfer hose connection and disconnection, attendance by a qualified person during loading and unloading and associated training.

When a threshold or greater amount of an HHC covered by the PSM standard is delivered to a worksite process which has the capacity to contain a threshold or greater amount, the process may be subject to the PSM standards. The worksite employer will be held responsible by OSHA for this determination. If the worksite employer intends that the aforementioned process not be covered by the PSM standard, he or she must have an effective program and be prepared to demonstrate to OSHA that such a program precludes an otherwise covered amount of a HHC from being in the process at any particular time. For example, the employer may be able to disperse the storage of small containers of HHC around the worksite so that there is less than a threshold quantity at any one location and so that the release of a highly hazardous chemical from one storage area would not cause the release of the other inventory stored on site. Please note that the amount of HHC carried onto the worksite in a DOT regulated vehicle is not included for the purpose of determining whether there is a threshold quantity or greater amount in a worksite process. As such, DOT regulated delivery of a HHC to a process which has a capacity less than the threshold amount would not be covered by the PSM standard.

Question 5: Would the PSM standard apply to the following scenario? A storage area involves a flammable gas located a remote distance from another storage area involving a flammable gas and each area contains less than the threshold quantity. Each storage area is a storage bank which has independent plumbing and which is used for repackaging into containers in other areas. In one location the plumbing (1/2" diameter) of each of the two totally independent systems comes into close proximity to each other.

Reply: The two processes described may be considered a single process (See the reply to question 1). When these two processes are considered a single process and collectively contain 10,000 pounds (4535.9 kgs) or greater amounts of flammable gases, the PSM standard applies. If one of the storage areas including the contents of equipment connected to it contains 10,000 pounds (4535.9 kgs) of flammable gas, then the PSM standard applies.

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


H. Berrien Zettler, Deputy Director
Directorate of Compliance Programs