Fire and gas systems and early warning at fuel terminals

A fire and gas system (F&G) is a system that detects fire and flammable or toxic gas in a facility, raises alarms and starts automatic actions, such as stopping pumps, closing valves or releasing fire protection. At a fuel terminal it watches the pump areas, loading bays, tank farm and buildings. It works alongside the emergency shutdown covered in ESD, SIS and interlock.

In short, sensors find the hazard and a logic solver decides, then the outputs act. The sections below follow that path, separate the F&G system from a building fire alarm, explain the main detector types and show how early warning and public address fit in. Newcomers can read the first paragraph of each section. Veterans will find the design and maintenance detail further down.

Four names appear in almost every terminal project, and they overlap. A building fire alarm covers offices, workshops and control rooms. An F&G system covers process areas. An early warning system (EWS) is the wider idea of catching a hazard early and showing it to operators, and an F&G system is one source of that data. PAGA, public address and general alarm, is the loudspeaker network that carries voice messages and alarm tones across the site.

The two are often mixed up because the hardware looks similar. A building system can be done well and still be the wrong tool for a pump bay, where a gas cloud can reach an ignition source before any smoke exists. Citia's fire alarm installation at RSUD Al Ihsan in Bandung is a building case. It covered the panel, the cable network, smoke and heat detectors, manual call points and horns, tested zone by zone while the hospital kept running.

A fire alarm can also be conventional or addressable. A conventional panel knows only which zone alarmed. An addressable panel gives every device its own address, so the panel names the exact detector. For anything bigger than a small room, addressable usually saves search time during a real event.

Every F&G system has the same three layers. Detectors in the field send a signal. A logic solver reads all signals and applies the cause-and-effect matrix. Output devices then act. People get alarms, the process gets trips and the fire gets extinguishing.

Gas detectors normally raise two levels. A low alarm warns operators at a small fraction of the lower explosive limit (LEL), and a high alarm at a higher fraction starts action. The exact set points and the actions come from the site's risk assessment and cause-and-effect matrix, not from a generic table.

Two design habits matter most. First, voting: asking for two detectors out of three, or two out of two, before a costly trip cuts false trips from a single faulty sensor. Second, fail-safe wiring: the logic solver monitors each loop for wire breaks and short circuits and raises a fault, so a dead detector never looks like a quiet area. For 4-20 mA loops the 4-20 mA and HART guide explains the fault ranges.

When an F&G function stops a process, its reliability target comes from the safety study. Where a safety integrity level is assigned, IEC 61511 governs how the function is specified, built and tested.

An F&G alarm that nobody understands soon gets ignored. Give each alarm a clear text, a priority and a defined response, following the alarm management practice in ISA-18.2, and keep the first-out detector on the screen so the operator sees the cause before the consequences scroll past.

Gas detector performance for flammable gas is covered by IEC 60079-29-1, which sets the construction and test requirements for fixed and portable detectors. Detectors in a classified area also need the right Ex certification, covered in hazardous areas and explosion-proof equipment.

Placement is a study, not a drawing exercise. ISA TR84.00.07 gives guidance for evaluating how well an F&G system covers its hazards, looking at where the gas or fire could start and how many detectors would see it. Practical inputs are the gas density, the wind direction, the leak points such as flanges, pump seals and loading arms, and the places where people work.

Flame detectors also need a clear line of sight, because pipe racks, scaffolding and tank walls cast shadows in their field of view. Coverage is best checked on a 3D layout of the area, then confirmed on site.

Toxic gas needs its own thinking. Hydrogen sulphide is dangerous at concentrations far below the flammable range, so a toxic gas detector alarms at much lower levels than a flammable gas detector. Its alarm usually ties into the site procedures for evacuation and breathing apparatus.

The best design fails if detectors drift out of calibration or bypasses stay open for months. Treat the F&G system like any safety function: test it on a schedule, keep the evidence and review the failures. The PLC troubleshooting guide covers safe working habits while a logic controller is being checked. Keep spares of the detector types in service, because certified Ex detectors can have long lead times.