What is Fire and Gas (F&G)?

Any industrial plant must be designed to be safe. Layers of protection should be identified and implemented in order to mitigate risks on the installation and personnel. These layers of protection will make the process and its personnel safe.

A Fire and Gas (F&G) detection system is a very wide-spread and effective SIS. It detects any danger in terms of fire or combustible / toxic gas leaks and takes action to minimize the danger and prevent it turning into a fire or explosion.

A F&G detection system continuously monitors all areas and provides the operator with the information of detection/protection systems. It gives warnings to personnel of any hazardous situation and takes action depending upon the level of hazard detected (process shutdown, fire extinguish release).


In order to design a suitable fire and gas detection system, a risk analysis has to be undertaken. The resulting reports will establish the requirements for the system: which type of detectors shall be used, the speed of detection response, how many fire zones / areas shall be defined, how the warning devices will work, what information is needed for the operator, are there any redundancy or SIL requirements, and so on.


Redundancy is not a novelty anymore in the area of safety systems. Manufacturers have developed solutions for up to quad I/Os and CPUs.


F&G detection devices have improved greatly during the last years. Detection rates, response time and spurious alarms were improved by new techniques, by adding intelligence to the equipments. SIL certification according to IEC standards is also an important addition for a F&G as a SIS.

But, purchasing advanced, intelligent and certified devices does not ensure the correspondence with SIS standards. An accurate project design followed by correct installation, commissioning and maintenance is imperative for achieving and keeping a high safety level.


Traditionally, the F&G detection system is designed completely separated from the control system. Having at hand the advanced and certified field equipments as well as central units on the market, it is possible to design and implement integrated systems covering all the control and safe requirements withal taking advantage of all benefits of an integrated BPCS - SIS solution.

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If the Fire and Gas System (FGS) has to be considered as SIS then it shouldn’t give only an ALARM. It should be connected to final element to make mitigate the consequence automatically. SIS is a system that has one or more Safety Instrumented Function (SIF). SIF consists of three parts: Sensor, Logic Solver and Final element. Without final element, the FGS will reduce the overall risk and can be considered a safety layer but not SIS.


Usually F&G will not be having a final element (unlike in ESD), except for deluge systems. In O&G industry the final element would be generally a deluge valve (for open areas), where in event of confirmed fire (from a 2ooN input) will send DO to the deluge valve to open and extinguish fire.
In case of closed areas, like substations there will be an output from the fire alarm panel to the fire extinguishing system like Inergen, Co2 (which is outdated now a days) etc.

Please be noted that huge F&G systems in oil & gas industries are SIL 3 and above certified and usually single input will trigger local sounder & beacon (along with alarm on SCADA and matrix fascia) and confirmed input (2ooN) shall take tripping action, as per cause & effect.

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Actually fire and gas system don’t fulfill the SIL3 because it has low reliability and it can only satisfy higher SILs with very short proof test interval which cause headaches to maintainence team.