Gas detection system selection: which gas, which sensor, where to mount?
Gas detection involves three separate hazards and each requires different measurement logic: flammable gases that carry explosion risk (natural gas, LPG, hydrogen), gases that are toxic even in small quantities (carbon monoxide, hydrogen sulfide, ammonia), and oxygen level depletion. "Gas detector" should not be understood as a single device; what gas you measure, at what threshold, and where you measure it determines the entire system.
Selection guide and FAQ
Sensor technologies and areas of use
| Sensor | What it measures | Its strength | Its limitation |
|---|---|---|---|
| Catalytic (pellistor) | Flammable gas (% LEL) | Wide range of combustible gases, economical | Requires oxygen; silicon and lead vapor poisoning of sensor |
| Infrared (IR) | Combustible gas, CO₂ | Poison-resistant, operates in oxygen-free environments, long service life | Cannot detect hydrogen; high initial investment |
| Electrochemical | Toxic gas (ppm), oxygen | High sensitivity at low concentrations | Limited life that varies by manufacturer; affected by temperature and humidity |
| Semiconductor (MOS) | Combustible and some toxic gases | Inexpensive, durable | Poor selectivity — can be confused by other vapors |
| Photoionization (PID) | Volatile organic compounds (VOC) | Detects very low concentrations | Sensitive to humidity and dust, requires special application |
Where is the detector mounted? Gas density determines this
Mounting every detector at the same height is a mistake. A gas lighter than air rises and a heavier one settles to the floor; a detector at the wrong height may never see the leak.
| Gas | Relative to air | Installation height | Typical location |
|---|---|---|---|
| Natural gas (methane) | Light — rises | Close to the ceiling; per the device manual (e.g. at most 30 cm from the highest point of the ceiling) | Boiler room, kitchen, heating center |
| LPG (propane/butane) | Heavy — settles | Close to the floor; per the device manual (e.g. at most 30 cm from the floor), at LPG filling stations no more than 20 cm above ground (BYKHY 110/3) | LPG kitchen, storage, filling station |
| Carbon monoxide (CO) | Close to air (relative density 0.97) | In a room with a fuel-burning appliance, on the ceiling or 15–30 cm below it (EN 50292); in car parks per the device manual (some manufacturers recommend 1.5 m above the floor) | Boiler or water heater room, enclosed car park, generator room |
| Hydrogen (H₂) | Very light — rises rapidly | On the ceiling and in ceiling pockets | Battery charging room, UPS room |
| Ammonia (NH₃) | Light | Near ceiling | Refrigeration facility, engine room |
| Hydrogen sulfide (H₂S) | Heavy — settles | Near floor | Wastewater, treatment, well and manhole |
Design considerations
- For flammable gases the threshold is set as a percentage of the lower explosive limit (LEL) and varies by manufacturer: one manufacturer (Crowcon) typically sets the first alarm at 20% and further alarms at 40% LEL, another (Honeywell) sets two levels at 20–25% and 50–55% LEL; a domestic device may have a single threshold at 10% LEL. The regulation gives no figure; it requires the sensors of heating plants to have adjustable levels (BYKHY 112/1-ç). For toxic gases, thresholds are set in ppm according to exposure limits.
- An alarm should not only sound; it should trigger an action: shutting off the gas supply with a solenoid valve, starting the fan and, where needed, cutting the related power. The regulation also explicitly requires gas shut-off in some places (57/1, 55/11, 57/4, 112/1-ç), while in large industrial kitchens using LPG it requires an audible warning device (109/5).
- In enclosed car parks, CO detection works together with jet fan/ventilation control; running the fans according to the gas level instead of continuously reduces energy consumption noticeably. LPG and CNG vehicles may not enter enclosed car parks; in the only exception, shopping-centre car parks that admit them, ventilation runs automatically, linked to a device that detects LPG accumulating at ground level (BYKHY 60/4 and 60/4-ç).
- In areas classified as explosive atmospheres (filling stations, paint booths, battery rooms), detectors and cabling must comply with Ex-proof/ATEX requirements; standard equipment cannot be used in such areas.
- Calibration is not optional maintenance: sensors drift over time. The interval is set by the manufacturer and differs from document to document; for example, one manufacturer recommends 12–18 months for electrochemical cells and 6–8 months for semiconductor sensors in car-park CO sensors, another recommends yearly calibration. An uncalibrated detector can miss a leak while appearing to work.
- Sensors have a finite life that varies by manufacturer (e.g. one manufacturer gives a typical 1–3 years for industrial electrochemical cells, while domestic CO alarms often last 7–10 years). A sensor replacement schedule should be planned at commissioning and written into the maintenance contract.
- Central panel installation (addressable/analog) shows which specific point is alarming compared to independent devices per detector; in large facilities, this difference reduces response time.
Most plug-in gas alarms sold in shops are designed to announce a leak in a single kitchen: they are not calibrated on site, do not connect to a central panel and show a fault only on the unit itself, by light or sound. Some domestic devices can shut off a valve: EN 50194-1 classifies a device that can drive a valve or ancillary device as Type A, and one that only gives audible and visual alarms as Type B. What boiler rooms, commercial kitchens, car parks, battery rooms and industrial plants need are systems that can be calibrated, report faults and trigger an action. Comparing the two on price means comparing different jobs.
Frequently asked questions
Where should I install a natural gas detector in the kitchen?
Natural gas is lighter than air, so the detector goes close to the ceiling; the exact distances come from the device manual and vary by manufacturer: for example, one manufacturer’s datasheet places the detector at most 30 cm below the highest point of the ceiling and 0.30–4 m from the gas appliance, while the datasheet of the GST I-9602LW in our catalogue asks for 1.5–4 m from the cooker. It is not mounted directly above the cooker, next to the sink or in front of a vent or extractor hood: air movement and steam change the gas concentration locally and can cause false alarms.
Can a single detector sense both natural gas and carbon monoxide?
Some multi-sensor devices do. In a boiler or water heater room both measurements can be made in the same zone: EN 50292:2023 places the CO alarm on the ceiling or 15–30 cm below it in the room with the fuel-burning appliance, and the natural gas detector also sits close to the ceiling. Breathing height is for bedrooms and living rooms without an appliance. LPG, however, settles to the floor, so it cannot be monitored in the same device as a ceiling CO alarm; LPG needs a separate detector close to the floor.
How often should calibration be performed, and can I do it myself?
The interval is set by the manufacturer’s instructions and varies from device to device (e.g. one manufacturer recommends 12–18 months for electrochemical CO sensors and 6–8 months for semiconductor sensors); for portable monitors a function test is recommended before each day’s use. Calibration requires certified test gas of known concentration and a suitable adapter; it cannot be done by eye or with a button. Keeping calibration records for the life of the device is recommended. For Prosense detectors, we obtain the calibration certificate through the manufacturer Prosense and hand it over to you; Prosense calibrates the gas detectors it manufactures in its laboratory under TÜRKAK accreditation and issues a report.
The alarm went off but there is no gas smell present; is the system broken?
Not necessarily, but no smell does not mean no gas: carbon monoxide is odourless, and natural gas is also odourless by itself — the distribution company odorises it with THT so that leaks are noticed. So even without a smell, a gas alarm is treated as a leak: nothing that can make a spark is touched, the room is ventilated, the valve is closed and 187 (Turkey’s natural gas emergency line) is called from outside. On a CO alarm everyone leaves and 112 is called. Some sensors can be fooled by cleaning agents, paint and spray vapours; this possibility is considered only after a real leak or CO has been ruled out, and if false alarms recur the sensor type may be wrong for that environment.
Can we add a detector to my existing system?
Yes, if the panel's channel/address capacity and power supply are suitable. During the survey, the panel model, line length, and cable cross-section are verified; if capacity is exceeded, an expansion card or second panel may be required.