PSI Explained: Electrical Supply and Distribution Systems

CalOSHA’s PSM regulation (Title 8 CCR §5189(d)(3)(A)(9)) uniquely requires that the “information pertaining to the equipment in the process shall include: Electrical supply and distribution systems”. None of the other California or Federal process safety regulations (FedOSHA PSM, USEPA RMP, or CalARP) contain such a requirement. As such, literature describing best practices for implementation of this requirement are lacking. For example, IIAR’s Process Safety Management & Risk Management Program Guidelines, Vol. 1 & 2 does not make mention of the requirement.

The Center for Chemical Process Safety (CCPS) has published Guidelines for Auditing Process Safety Management Systems which includes the following explanation of Electrical Supply and Distributions Systems in Table 9.2 (Page 292) “U.S. State PSM Audit Criteria and Guidance for Auditors – Process Safety Information”:

Audit Criteria: California OSHA – Process Safety Management of Acutely Hazardous Materials

9-C-25. In addition to the information required for equipment for the OSHA PSM Standard and EPA RMP Rule, the process safety information shall also include: Electrical supply and Distribution systems.

Source: California Code of Regulations, Title 8 Section 5189

Auditor Activities: Auditors should check electrical supply and distribution systems, which should be found in the engineering or project records. These are typically shown on electrical one-line diagrams.


A one-line diagram is essentially a simplified power flow diagram that graphically depicts the paths for power flow between components of an electrical system. Consistent with the recommendation of CCPS, we recommend obtaining electrical one-line diagrams from an electrical engineer/contractor who designed or installed the chemical process. For older chemicals processes where this information is no longer available, an as-built one-line diagram can be developed by a qualified electrician.

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