A fire and gas system, usually written F&G, is the safety system that continuously watches a facility for the early signs of a fire or a gas release and then acts - warning people, triggering mitigation, and often initiating a shutdown. It is the sense-of-smell of an oil and gas installation, detecting hazards before they become incidents. This guide explains what an F&G system detects, how it decides to act, and where it fits.
Fire and Gas System (F&G) in one line: A fire and gas (F&G) system is a safety system of detectors, a logic solver, and mitigation outputs that senses fires and hazardous gas releases and responds automatically. Detectors include combustible gas, toxic gas (such as H2S), flame, smoke, and heat sensors; on confirmed detection the system alarms personnel, activates mitigation like deluge or ventilation, and can initiate an emergency shutdown. It is a key detection layer feeding the wider safety instrumented system.
An F&G system combines several detection technologies because no single sensor catches every hazard. Combustible gas detectors (catalytic bead or infrared) find flammable clouds before they reach an ignition source, usually alarming at a fraction of the lower explosive limit. Toxic gas detectors (electrochemical) watch for H2S and other poisons at parts-per-million levels. Flame detectors (ultraviolet, infrared, or UV/IR) see an actual fire, and smoke and heat detectors cover enclosed spaces. Open-path gas detectors span a whole area with a beam.
Detection alone does not act; a safety-rated logic solver evaluates the signals against configured thresholds and voting logic. Voting - such as requiring two detectors to confirm before executing a high-consequence action - guards against a single faulty sensor spuriously triggering a deluge or shutdown. Many F&G systems use tiered logic: a single detector at low alarm warns operators, while confirmed detection by multiple sensors escalates to automatic mitigation and ESD.
On confirmed detection the F&G system drives its outputs: audible and visual alarms and public-address messages to alert and evacuate, mitigation such as firewater deluge, foam, ventilation, or HVAC damper closure, and initiation signals to the emergency shutdown system to isolate and de-energize the affected area. Like other safety functions, critical F&G actions carry SIL requirements and are designed to a defined reliability.
F&G coverage is designed around where releases and fires are credible: wellheads, separators, compressor and pump buildings, gas processing units, loading areas, and enclosed spaces such as analyzer shelters and turbine enclosures. Detector placement follows the physics - gas heavier than air is watched low, lighter gas high, and detectors are mapped so a release of a given size cannot go unseen. This detector-mapping study is a formal part of F&G design.
H2S detection deserves special mention in sour service. Hydrogen sulfide is lethal at low concentrations and dulls the sense of smell, so fixed toxic gas detection with clear alarms and escape guidance is a life-safety essential around sour wells and gas plants. F&G ties directly to emergency shutdown here: a confirmed toxic or combustible release can trigger isolation and evacuation before the cloud finds an ignition source or a person.
The F&G system operates on its own and does not wait for a remote system to act. Monitoring adds oversight and evidence: which detector alarmed, at what concentration, and what mitigation fired. A cloud SCADA such as Merobix can read F&G alarm and detector-health status over Modbus, DNP3, or OPC UA so a control room or on-call engineer sees a release the moment it is detected and so detector faults and bypasses are trended - while the detection, voting, and mitigation logic stays fully independent inside the safety system.
A household smoke alarm detects one hazard in one room and sounds a local horn. A fire and gas system is an engineered safety system that fuses multiple detection technologies - combustible gas, toxic gas, flame, smoke, and heat - across an entire facility, applies voting logic to confirm real events, and drives coordinated outputs: alarms, firewater deluge, ventilation, and emergency shutdown. Its critical functions carry SIL requirements.
Because the outputs are high-consequence - a firewater deluge or a facility shutdown is disruptive and expensive - the system often requires two or more detectors to confirm before it executes automatic mitigation. This voting prevents a single faulty or contaminated sensor from spuriously triggering a shutdown, while still alarming operators on the first detection so nothing is ignored.
F&G is a primary detection layer that feeds the emergency shutdown (ESD) system. When detectors confirm a fire or a hazardous release, the F&G logic can initiate an ESD to isolate and de-energize the affected area and, at higher levels, shut down and blow down the facility. F&G detects and mitigates; ESD removes the energy and inventory that would feed the incident.
This page references the standards, specifications, and official documentation published by the organizations below. Editions, product capabilities, and documentation change over time - confirm current requirements and specifications directly with the source.
Last reviewed: July 27, 2026. Merobix is not affiliated with, endorsed by, or sponsored by these organizations; their names are used only to identify the standards and products discussed.
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