ABSTRACT
When an item is considered safety critical, it is a particular piece of equipment, a control system, or a protective device that, upon failure, could lead to a hazardous situation that could result in an accident or directly cause an accident that could cause harm to people and the environment. The term Safety Critical Element (SCE) refers to any component of an installation whose failure has the potential to cause or contribute substantially to the release of a hazard. The safety critical elements are those items that are intended to serve as last lines of defense in the event of a major incident at a major hazard facility. Safety critical elements and equipment that are often confused should be differentiated, as explained in this chapter. It is the intent of this chapter to provide some detailed information about the essential SCEs and the associated equipment and facilities, such as Emergency Shutdown Systems (ESD), Fire and Gas Detection Systems (FGDS), safety relief and blowdown systems, flare monitoring, and passive firefighting systems.
