You Got <scp>LI</scp> ‐ <scp>PL</scp>

Abstract Instrumentation and controls play a significant role in preventing process safety incidents. Ensuring the reliability of instrumented systems can be challenging due to the large number of devices that need to perform when called upon. The International Society of Automation (ISA) 84 committee has issued a series of documents over the last 30 years covering how to design, operate, and maintain instrumentation and control systems in process safety applications. The requirements for safety instrumented systems (SIS) are determined by ANSI/ISA 61511. The question for many practitioners is what standard addresses requirements for designing and managing instrumented protection layers other than SIS. An emerging standard, ISA 84.91.03, pulls together several regulations and current industry practices for managing safety‐related instrumented systems. Since the term basic process control system is often confused with the plant's primary distributed control system, the new standard uses the term “low‐integrity protection layer” to cover any instrumented protection layer that is used to meet a company's risk tolerance criteria but will not be implemented as SIS. This paper provides an overview of ISA 84.91.03 to raise awareness of the requirements of the new standard and discuss the impact on typical process industry practices.