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Safety & Lifesaving
Portable Gas Detectors
Portable Gas Detectors covers the personal and transportable monitors that warn the wearer of flammable gas, hydrogen sulphide, carbon monoxide and oxygen deficiency, plus their docking stations and sampling pumps.
Each monitor is an intrinsically safe instrument with consumable sensors and a rechargeable battery. Its remaining sensor life, battery health and calibration history matter more than its age.
What a personal monitor does
A personal monitor samples the air at the wearer's breathing zone and alarms by sound, light and vibration when a reading passes a set point. The common four-gas monitor reads flammable gas in %LEL, oxygen in % volume, and H2S and carbon monoxide in ppm. Single-gas H2S monitors are worn by everyone near the well on sour wells. Five and six-gas models add sensors such as a photoionisation detector (PID) for volatile organic compounds or a second toxic sensor.
Configurations
| Type | Use | Note |
|---|---|---|
| Single-gas, disposable | H2S or CO worn all shift | Fixed life counted from activation; no recalibration or new sensor |
| Single-gas, serviceable | H2S, CO or O2 | Sensor and battery replaceable |
| Multi-gas, diffusion | Clip-on monitor for general work | Reads only where it is worn |
| Multi-gas, pumped | Pre-entry testing of tanks and pits | Draws a sample through a tube |
| Transportable area monitor | Temporary perimeter during hot work or well testing | Some link wirelessly to a controller |
Key specifications
| Parameter | Why it matters | Typical classes or units |
|---|---|---|
| Sensor set | Must match the gases on your risk assessment | %LEL, % vol O2, ppm H2S and CO |
| LEL sensor type | Catalytic needs oxygen; IR cannot see hydrogen | Catalytic bead or infrared |
| Ex marking | Decides which zones it may enter | Ex ia IIC T4, EPL Ga for Zone 0 |
| Alarm set points | TWA and STEL alarms for toxic gases | ppm, set to your exposure limits |
| Data logging | Proves exposure and bump test history | Event and datalog memory |
Standards and certification
- IEC 60079-29-1 covers the performance of flammable gas detection in portable units.
- EN 45544 covers toxic gas measurement and EN 50104 covers oxygen deficiency and enrichment detectors.
- The Ex certificate, usually Ex ia, applies only with the battery pack and sensors it lists. A third-party battery voids it.
- In the US, intrinsically safe portable units carry a listing for Class I, Division 1, Groups A to D.
The ISEA statement on validating portable gas monitors recommends a bump test or calibration check before each day's use, and a full calibration if it fails. Most makers follow that rule in their manuals.
Failure modes and inspection
- Electrochemical sensors run down from manufacture. Read each sensor's date code.
- Catalytic LEL sensors read low after silicone or H2S exposure, and read wrong in oxygen-deficient air.
- Lithium-ion packs lose capacity and may not last a 12-hour shift.
- Pump diaphragms and inlet filters block, and the low-flow alarm must work.
- Cracked housings, missing gaskets or a damaged sensor grille compromise the IP rating and intrinsic safety.
On a used monitor, check the sensor dates and the event log first, then run a full calibration with certified gas and a bump test of every alarm.
Documentation
- Serial number, model and Ex certificate.
- Date of manufacture of each sensor and of the battery pack.
- Calibration and bump test records, ideally exported from the docking station.
- Firmware version, which decides compatibility with your docking stations and software.
Integration with your fleet
Monitors from the same maker as your fleet share docking stations, calibration gas mixtures, chargers and spare sensors. A docking station automates bump tests and calibration and stores the records an auditor asks for. Check that the gas mixture the station needs matches the cylinders you already stock.
Refurbishment and what never to buy used
A serviceable monitor can be refurbished with new sensors, a new battery pack from the maker, new filters and a full calibration. Never buy a used disposable single-gas monitor, because its remaining life cannot be extended or verified. Avoid any unit with a missing date code or a battery of unknown origin, and expired calibration gas.
For fixed detection in the same areas, see gas and H2S detection. For respiratory protection during entry, see breathing air systems.
FAQ
Frequently asked questions
How often should a portable gas detector be bump tested?
Bump test it before each day's use, as the ISEA statement on portable gas monitors recommends and most makers require. If it fails, run a full calibration before use. A docking station can do both and keep the records.
Can a used disposable H2S monitor be reused?
No, a disposable single-gas monitor has a fixed life counted from activation and cannot be recalibrated or re-sensored. Buy these only new and sealed, with the activation deadline printed on the pack in date.
Can I fit a cheaper battery to a portable gas monitor?
No, fit only the battery pack the Ex certificate lists. A different pack voids the intrinsic safety certification and may overheat in a hazardous area. Check the pack's date code on a used monitor as well.
Why does my LEL reading drop in a confined space?
A catalytic bead LEL sensor needs oxygen to burn the gas, so it reads low when oxygen is deficient. Always read the oxygen value first. An infrared LEL sensor avoids this but cannot detect hydrogen.
What should I check on a used multi-gas monitor?
Check the date code of every sensor and the battery pack first. Then download the event log, inspect the housing and gaskets, and run a full calibration and bump test. Confirm the firmware works with your docking stations.
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