The Monitor - Gas and Flame Detection News

Feature Article:.

Can a Fire and Gas System Be Considered
a Safety Instrumented System?

SIL - Safety Integrity Levels

There has been much industry debate over the categorization of Fire and Gas Systems (FGS) as Safety Instrumented Systems (SIS), especially as the concept of functional safety matures in the marketplace. Fire and gas detection field devices and technologies are fundamentally different from other forms of plant instrumentation.

Incorrect detector placement and poor environmental conditions can prevent the product from detecting a hazardous gas leak or flame, even when the unit is functioning properly. When a safety hazard is undetected, then the appropriate safety action (shut down, deluge, venting, etc.) cannot be initiated. Because of this, many end-users and system integrators are wondering if the functional safety standards are applicable to a FGS.

A legitimate argument can be made both for and against the classification of a FGS as a SIS. Those that oppose the concept typically believe that because of the operating characteristics of fire and gas detection equipment, a FGS should only augment a plant safety system and not be considered a critical safety function. If a properly functioning FGS comprises a SIL 2 logic solver, a SIL 2 sensor, and a SIL 2 final element, but fails to see the hazardous gas or flame and effectively eliminate or mitigate the hazard, then the SIL 2 risk reduction factor of 100 has not been achieved.

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