Safety instrumented system

A Safety Instrumented System (SIS) consists of an engineered set of hardware and software controls which are especially used on critical process systems. A critical process system can be identified as one which, once running and an operational problem occurs, may need to be put into a "Safe State" to avoid adverse Safety, Health and Environmental(SH&E) consequences. Examples of critical processes have been common since the beginning of the Industrial Age. One of the more well known critical processes is the operation of a steam boiler. Critical parts of the process would include the lighting of the burners, controlling the level of water in the drum, and controlling the steam pressure.