Raymond A. Freeman

Using layer of protection analysis to define safety integrity level requirements

The recent publication of ANSI/ISA standard S84.01 – 2004 defines the life safety cycle for the design and installation of safety instrumented functions (SIFs) using safety instrumented systems (SISs). However, the determination of the required safety integrity level (SIL) is an activity that the process designers need to complete prior to detailed design. This article outlines an approach for the determination of the required SIL using the layer of protection analysis (LOPA) method. An example is presented along with a suggested format for documenting the LOPA, SIL, and SIF requirements in a manner that can be transferred to the detailed design team for implementation.

Assessment of Risks from Acute Hazards at Monsanto

Handling acutely hazardous materials safely is a skill that the modern chemical industry developed as it grew. The low rate of injury from exposure to reactive and dangerous substances such as chlorine, phosphorus, sulfuric acid, hydrogen cyanide, and ammonia testifies to that skill. Recently the changing structure of the industry, and especially the Bhopal disaster, have caused us to focus anew on risks from such materials. This paper describes Monsanto’s approach.