Fixed Gas Detection Systems
Fixed gas detection monitors a permanent gas risk around the clock. It protects plant rooms, boiler houses, battery rooms, cold stores, laboratories, car parks and process areas where a portable detector alone is not enough.
How a fixed system fits together
Sensor and transmitter: detects the gas and sends a 4-20 mA, digital or wireless signal.
Control panel: shows readings and alarm states, and logs events.
Outputs: sounders and beacons, ventilation, gas solenoid shut-off, and signals to a BMS or fire panel.
Detection technology by gas
Flammable gases: catalytic (pellistor) or infrared sensors; IR cannot detect hydrogen.
Toxic gases such as CO, H2S, NH3 and Cl2: electrochemical sensors.
CO2 and many hydrocarbons: non-dispersive infrared.
Oxygen depletion in inert gas stores and labs: electrochemical or long-life O2 sensors.
VOCs: PID transmitters.
Coverage and placement
Place sensors close to likely leak points and where the gas will accumulate. Heavier-than-air gases such as CO2, LPG and H2S collect low; lighter gases such as methane, hydrogen and ammonia rise. Toxic gas sensors protecting people should be in the breathing zone. Ventilation airflow, obstructions and access for calibration all affect positions.
Alarm philosophy
Most systems use two or three alarm levels: an early warning that starts ventilation, a higher level that evacuates and isolates gas supplies, and a fault alarm if a sensor fails. Toxic levels are set with the EH40 exposure limits in mind; flammable alarms are usually at 10% and 20% LEL.
Supply, installation and commissioning
We supply transmitters, panels and accessories to your specification or your consultant's design. Use our fixed gas detection quote builder to list what you need, or call us to discuss a site survey.
Service contracts
Fixed systems need regular calibration and functional testing, typically every six or twelve months. Our engineers calibrate each sensor, test alarms and outputs, and issue service records. Ask us about a six-monthly or annual contract.
What we need from you
We supply fixed detection equipment to a specification. To quote, we need the gases to be detected, the area classification where flammable gases are present, the number and location of detection points, and how alarms should be signalled. If you do not yet have a specification, your system designer or insurer can help define one.
Keeping a fixed system working
Fixed sensors drift and age in the same way as portable ones. Each detector should be gas tested and recalibrated at least every six months, or at the interval the manufacturer and your risk assessment specify. Alarm outputs, relays and any shutdown or ventilation actions should be tested at the same visit, and the results recorded.
Keep sensors clear of paint, dust and wash-down water, and check sinter heads and weather protection for blockage. Replace electrochemical sensors at the end of their rated life rather than waiting for them to fail.
Portable detection alongside fixed
Fixed detection protects an area; it does not protect someone working away from a sensor. Staff entering plant rooms, pits or tanks should still carry a personal monitor. See our 4-gas monitor guide.
Talk to our engineers on 01489 326031 or email sales@7solutions.co.uk. We supply, hire, calibrate and train across the UK.
Frequently asked questions
What does a fixed gas detection system include?
Sensors in transmitters at the risk points, a control panel that displays readings and raises alarms, and outputs such as sounders, beacons, ventilation fans or gas shut-off valves.
Where should gas sensors be placed?
Near likely leak sources and where gas will collect: low for gases heavier than air such as CO2, LPG and H2S, high for lighter gases such as methane, hydrogen and ammonia, and in the breathing zone for toxic gases where people work.
Do you design fixed gas systems?
We supply equipment to your specification or your consultant's design, using our quote builder or a site survey to confirm what is needed, and we service and calibrate installed systems.
How often should a fixed system be serviced?
Typically every six or twelve months, depending on the manufacturer, the gas and the risk assessment. A service includes calibration of each sensor and a functional test of alarms and outputs.