ISA-84.1, Application of Safety Instrumented Systems for the Process Industries

Published in 1996. As told by Angela Summers and Paul Gruhn.

Dr. Summers says ISA-84 has not simply rocked the world of instrumentation and controls; it has affected process safety strategies across most of the process industry. It spawned an entire industry of specialized professionals and credentialing programs centered around ISA-84 compliance. It also initiated the widespread use of SIL-certified programmable controllers across multiple industry sectors. ISA-84 has become foundational to our current approaches to designing and managing instrumented safeguards.


What is really amazing, says Summers, is how impactful ISA-84 has been to other organizations that write standards and practices. “I have worked with various API, ASME, and CCPS committees on how to address their scope and stay in conformance with ISA-84. I have also worked with government agencies on incorporating ISA-84 into regulatory audits, regulations, and guidance documents.”

Summers says that when she joined the ISA84 committee in the 1990s, she was fortunate enough to meet and be mentored by the thought leaders she met there: Ken Bond (Shell), Vic Maggioli (DuPont), Charlie Hardin (Celanese), and Robert Adamski (ExxonMobil). Very quickly, Maggioli, who was the ISA84 committee chair for many years, gave her opportunities to contribute. She joined the IEC 61511 committee in the late 1990s at the request of Sam Mannan, director of the Mary Kay O’Connor Process Safety Center at Texas A&M University until his death in September 2018.

Gruhn says ISA-84.1 (also known as the emergency shutdown systems standard) led to the development of International Electrotechnical Commission (IEC) standards on functional safety, product and personnel qualification programs, new books, new products, new software, and recognition by regulators around the world: “In short, it changed the industry.”

Relays have been used in safety applications for almost 100 years, says Gruhn. Solid state systems (that did not use software) were developed by several vendors in the 1970s. General-purpose programmable logic controllers (PLCs) have been used in some safety applications since the 1970s. Safety PLCs have been available since the early 1980s. Yet at that time there was no industry agreement on what steps to include in a project life cycle, how to determine the performance required of a system, how to model the performance of hardware and software, and much more.

The development of a standard was proposed to ISA in the early 1980s. The original charter of the standard was to cover software-based logic solvers only, and field devices were not included in the original scope. The scope was expanded in the early 1990s.

Ten years of deliberation brought consensus on the system life cycle, methods to determine the required system performance (safety integrity level [SIL]), methods to analyze the performance of hardware and what to include in the calculations, factors to include in the design of a system, and factors to consider in the operation, maintenance, and changes of a system. The first edition of the standard, released in February of 1996, was approximately 40 pages long, and had five informative annexes totaling almost 60 pages.

Gruhn says the IEC started developing functional safety standards in the mid-1990s. The ISA84 committee actively participated in the development of the IEC 61511 standard for the process industry. That standard was first released in 2003 and was adopted as ANSI/ISA 84.00.01-2004 one year later with the addition of one sentence. That is a three-part standard; part 1 (the normative portion) was over 90 pages. Part 2 (an informative document) was also over 90 pages. Part 3 (another informative document summarizing various SIL selection methodologies) was over 60 pages.

The Occupational Safety and Health Administration published interpretation letters stating that it considered the first and second editions of the ISA-84 standard as “recognized and generally accepted good engineering practice” (RAGAGEP). The IEC released a second edition of 61511 in 2016. After a one-year period of editorial changes, the ISA84 committee accepted the new standard verbatim (although it added a new U.S. forward in Part 2). It is now ANSI/ISA 61511-2018. The ISA84 committee has also written eight technical reports totaling more than 1,000 pages over the past 15 years. They further explain the standard and ways of implementing its requirements, says Gruhn.


This article is part of September/October 2020 InTech—the ISA 75th Anniversary Special Edition