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.

December 7, 1995

Mr. J.B. Evans
Associate Director
Operational Safety and Risk Management
Union Carbide Corporation
39 Old Ridgebury Road, Section K3
Danbury, CT 06817-0001

Dear Mr. Evans:

This is in response to your letter of August 2, addressed to Mr. Ronald Davies, regarding the Occupational Safety and Health Administration's (OSHA's) Standard, 1910.119, Process Safety Management (PSM) of Highly Hazardous Chemicals. Your concern was related to the use of a recognized third party's standard for guidance with the determination of the controls covered by the Mechanical Integrity paragraph, 1910.119(j). We apologize for the delay in responding to you.

Specifically, your letter inquired whether the use of an Instrument Society of America (ISA) Standard S91.01 would be appropriate for determining which controls are covered by the Mechanical Integrity paragraph. You attached to your letter a copy of a draft of the ISA standard, along with some correspondence between ISA and OSHA. This correspondence included a response from Mr. Shepich (Former Director of Safety Standards) to Mr. Robinson (Manager, ISA Technical Services) which stated that Safety Standards has reviewed the ISA proposed standard, and did not have any comments, except that the proposal was consistent with the OSHA PSM standard. Further, you indicated that from your conversation with Mr. Davies, "it is OK to use guidance such as this, from a recognized third party, . . ." You also stated, "such guidance could be used for the application of other paragraphs, such as Process Safety Information."

Paragraph (j)(1) of 1910.119 is intended to cover only that equipment associated with a process covered under the PSM standard. Equipment covered in this list is considered critical to process safety because of its potential for significant impact on the safety of a process involving highly hazardous chemicals if it did not maintain its mechanical integrity. If an employer deems additional equipment to be critical, it too should be considered to be covered by 1910.119(j) and should be treated accordingly.

Therefore, your records should assure a written Mechanical Integrity Program for all named equipment. The ISA Standard that you have referenced only addresses two categories of process safety equipment of those which are listed in 1910(j)(1). The categories addressed are listed in 1910.119(j)(1)(iv) and (j)(1)(v) (emergency shutdown systems and safety critical controls, respectively.)

Please note that OSHA provides for significant flexibility in program development, therefore the employer has more than one option for implementing mechanical integrity. In this regard, it is the employer's responsibility to assess and evaluate the facility's mechanical integrity program. So long as the chosen option permits and achieves compliance with paragraph (j) of 1910.119 and the remaining provisions of the standard, and accomplishes the objective and the intended goal of the standard, the employer would be regarded as being in compliance.

If you find that the ISA standard defines emergency shutdown systems and safety critical controls in a way that helps you better understand where to apply the Mechanical Integrity requirements for these types of process equipment, so long as the PSM requirements are satisfied, such guidance would be appropriate. Please note that there are additional sources of mechanical integrity guidance that may be of help to you. For example, The Chemical Manufacturer's Association offers a document, Mechanical Integrity Supplement to the Maintenance Excellence Guide, that identifies background and general program considerations for addressing mechanical integrity per OSHA 1910.119(j), contains some current mechanical integrity practices and techniques that may assist in development of procedures and implementation as well as identifies reference material, and contains some currently used samples from various CMA member companies for illustrative purposes.

Thank you for your inquiry. If you need further assistance, please contact Alcmene Haloftis of my staff at 202-219-8031.


John B. Miles, Jr., Director
Directorates of Compliance Programs