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.

March 10, 1994

Mr. Lynton D. Barnett
Corporate Manager Equipment & Maintenance
American Cyanamid Company
One Cyanamid Plaza
Wayne, N.J. 07470-8426

Dear Mr. Barnett:

This is in response to your July 1st, letter requesting interpretation of the Process Safety Management (PSM) of Highly Hazardous Chemicals (HHC's) standard, 29 CFR 1910.119. Specifically, you requested clarification on whether the PSM standard applies to the following scenarios.

1. A utility system (e.g. steam or cooling water) is connected to a PSM covered process and supplies the process with either heat or cooling. During the process hazard analysis, it was determined that the failure or upset of the utility system has no adverse effect on the process. Is the utility system in this case also to be considered a covered process?

2. A process vessel in a PSM covered process has a level control system as the basic process control system. In addition, there is a high level alarm and a high, high level alarm with an interlock to shut down the supply pump. Should the basic level control system be included for consideration under 1910.119(j) - Mechanical Integrity or just the alarms and interlocks?

3. On the same process vessel in (2) above there is a pH meter used solely for quality checks of the product. Does this instrument have to be considered under the 1910.119(j) - Mechanical Integrity requirements?

A utility system connected to a PSM covered process would have to be addressed in the Process Hazard Analysis. You note that the Process Hazard Analysis indicates that the utility system has no adverse effect on the process. Nonetheless, the utility system, as described above, continues to be a consideration in a covered process. For example, modifications may be made to a process that might change the impact of the utility on the process. Additionally, if you have several covered processes served by the utility system, then you would have to consider the impact of the utility system in the Process Hazard Analyses of those processes as well.

By 1910.119(j)(1)-Application, the mechanical integrity standard applies to controls (monitoring devices and sensors, alarms, and interlocks). The level controls you describe including the basic level control, the high level control, and the high, high level control are considered covered process controls to which the 1910.119(j) mechanical integrity standards apply.

Use of the pH meter solely for product quality checks, such that it has no impact on the safety of the process, would not be covered by the 1910.119(j) mechanical integrity provisions of the PSM standard.

We appreciate your interest in occupational safety and health. If we can be of further assistance, please do not hesitate to contact us.


H. Berrien Zettler, Deputy Director
Directorate Compliance Programs