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.

November 29, 2005

Ms. Lois M. Ferson
Manager of Standards Services
67 Alexandria Drive
P.O. Box 12277
Research Triangle Park, NC 27709

Dear Ms. Ferson:

Thank you for your October 25, 2004 letter to the Occupational Safety and Health Administration (OSHA), on behalf of the Instrumentation, Systems, and Automation Society (ISA), regarding a consensus standard jointly issued by the American National Standards Institute (ANSI) and ISA that may be applied under OSHA's Process Safety Management (PSM) standard, 29 CFR 1910.119. We apologize for the delay in our response.

Background: ISA is an ANSI accredited organization. In March 2000, OSHA issued a letter to ISA, in which OSHA responded to questions pertaining to ANSI/ISA 84.01-1996, "Application of Safety Instrumented Systems for the Process Industries." Since then, based on experience gained from its use and the availability of newer technology, ISA has updated and modified ANSI/ISA 84.01-1996. This new standard — ANSI/ISA-84.00.01-2004 Parts 1-3 (IEC 61511 Mod), "Functional Safety: Safety Instrumented Systems for the Process Industry Sector," has been approved by ISA and by ANSI. With this background, ISA is again requesting a response to the following questions:

Question 1: Does the modification of corporate standards to comply with ANSI/ISA- S84.00.01-2004 Parts 1-3 (IEC 61511 Mod) ensure compliance with related areas of 29 CFR 1910.119?

Response: As stated in our
March 23, 2000 response, the PSM standard contains a number of requirements for equipment associated with a covered process, which may include Safety Instrumented Systems (SIS). OSHA considers the revised ANSI/ISA - S84.00.01-2004 Parts 1-3 (IEC 61511 Mod) to be recognized and generally accepted good engineering practices for SIS. Therefore, if an employer chooses to use S84.00.01-2004 Parts 1-3 as a basis ("code or standard employed") for SIS, and meets all S84.00.01-2004 Parts 1-3 requirements and other OSHA PSM requirements related to SIS, the employer will then be considered in compliance with OSHA PSM requirement for SIS.

Question 2: We are interested if your agency views ANSI/ISA-S84.01 as the benchmark OSHA will use to measure compliance with 29 CFR 1910.119?

Response: As stated in our previous response, the PSM standard is a performance-oriented standard. Therefore, employers have the flexibility in complying with the requirements of PSM, including, among other aspects, the use of recognized and generally accepted good engineering practices. With respect to SIS, as stated in our previous response, OSHA does not specify or benchmark S84.00.001-2004, Parts 1-3, as the only recognized and generally accepted good engineering practice. Additionally, it is important to note that an employer not covered under the PSM standard may be in violation of the General Duty Clause, Section 5(a)(1) of the OSH Act, if the employer's use of SIS results in a serious, recognized hazard to employees. In support of a Section 5(a)(1) citation, industry consensus standards, such as ANSI/ISA - S84.00.01-2004, can be used as evidence that a hazard is recognized and can feasibly be abated.

Thank you for your interest in occupational safety and health. We hope you find this information helpful. Please be aware that OSHA's enforcement guidance is subject to periodic review and clarification, amplification, or correction. Such guidance could also be affected by subsequent rulemaking. In the future, should you wish to verify that the guidance provided herein remains current, you may consult OSHA's web-site at
www.osha.gov. If you have any further questions, please feel free to contact the Office of General Industry Compliance Assistance at (202) 693-1850.



Richard E. Fairfax, Director
Directorate of Enforcement Program