Short answer: choose a gas or environmental meter by the hazard you need to measure — specific gases, oxygen level, particulates, noise, electromagnetic fields or airflow — then by sensor technology, alarm thresholds, response time and how you will verify it with bump tests and calibration.
How do gas and environmental sensors work?
Electrochemical sensors produce a small current proportional to the concentration of a target gas such as carbon monoxide, hydrogen sulphide or oxygen. They are selective but have a limited life.
Catalytic bead (pellistor) sensors detect flammable gases by measuring heat released when gas burns on a heated element, reporting results as a percentage of the lower explosive limit (LEL).
Non-dispersive infrared (NDIR) sensors measure how much infrared light a gas absorbs at a characteristic wavelength. They are common for carbon dioxide.
Optical particle counters estimate PM2.5 and PM10 by detecting light scattered from particles drawn through a chamber.
Sound level meters use a microphone with frequency weightings such as A-weighting, which approximates human hearing, and C-weighting for peak sound pressure.
EMF meters measure electric and magnetic fields, and some also detect radio-frequency energy.
Anemometers measure air speed using a vane, hot wire or cup rotor; many calculate airflow when you enter the duct area.
Which instrument do I need?
| Instrument | Measures | Typical use | Limitation |
|---|---|---|---|
| Single-gas detector | One gas, e.g. CO or H₂S | Personal monitoring | Only detects its target gas |
| Multi-gas detector | O₂, LEL, CO, H₂S (common set) | Confined spaces, utilities | Sensors need bump tests and replacement |
| CO₂ monitor (NDIR) | Carbon dioxide | Ventilation checks, greenhouses | Not a safety alarm for CO |
| Air quality monitor | PM2.5, PM10, VOC, temperature, RH | Workshops, offices, homes | Low-cost VOC sensors are indicative |
| Sound level meter | dB(A), dB(C) peak | Noise assessments, events | Meter class affects accuracy |
| EMF meter | Electric, magnetic, RF fields | Surveys, troubleshooting | Readings depend on distance and orientation |
| Anemometer | Air velocity, flow, temperature | HVAC balancing, extraction checks | Probe placement matters |
What specifications should I compare?
Target gases and ranges. Confirm each sensor's gas and measuring range matches your hazards.
Alarm settings. Look for adjustable instantaneous and time-weighted alarms. HSE publishes workplace exposure limits in EH40, which employers use as a reference when assessing exposure under COSHH.
Response time. Quoted as T90, the time to reach 90% of the final reading.
Bump test and calibration. Gas detectors should be checked with test gas to confirm they alarm, and calibrated as the manufacturer specifies.
Sound meter class. Class 1 and Class 2 instruments are defined by IEC 61672-1; Class 1 has tighter tolerances.
Data logging. Useful for noise surveys, air quality trends and exposure records.
How are they used in the UK?
Employers must control exposure to hazardous substances under the COSHH Regulations 2002, with EH40 setting workplace exposure limits. Gas detection is part of safe working in confined spaces, sewers, farms with slurry pits, and workshops using solvents.
The Control of Noise at Work Regulations 2005 set lower and upper exposure action values and limit values; HSE's noise pages explain how employers assess and reduce noise. A sound level meter supports those assessments.
At home, carbon monoxide is a serious hazard from faulty fuel-burning appliances, and HSE explains the warning signs. Landlords in England have duties regarding smoke and carbon monoxide alarms, explained in the government's booklet. A handheld meter is not a substitute for a fixed CO alarm.
What mistakes should I avoid?
- Assuming a CO₂ meter detects carbon monoxide. They are different gases and different sensors.
- Skipping bump tests before use in hazardous areas.
- Using an expired sensor. Electrochemical sensors have a finite life.
- Measuring noise at the wrong position. Measure near the worker's ear position, as assessment guidance describes.
- Reading EMF at random distances. Fields fall off sharply with distance; record the distance.
- Placing a particle monitor next to a heat source or in direct airflow.
How should I look after a gas detector?
Keep a simple log for each detector showing bump test dates, calibration dates and any alarms in use. Store detectors in clean air, because leaving them in a contaminated van or plant room can shorten sensor life. Check filters and inlets for dust or water, which slow the response, and keep the battery charged so the detector is never switched on half-ready. When a sensor fails a bump test, remove the instrument from use until it has been calibrated or repaired.
Frequently asked questions
What is a four-gas detector?
A portable detector that commonly monitors oxygen, flammable gas (as % LEL), carbon monoxide and hydrogen sulphide — the typical hazards of confined spaces.
How often should I bump test a gas detector?
Follow the manufacturer's instructions and your risk assessment; many workplaces bump test before each day's use.
Is a CO₂ monitor useful for ventilation?
Yes. Rising CO₂ indoors indicates poor ventilation relative to occupancy, which is why such monitors are used in offices and classrooms.
What noise levels require action at work?
The Control of Noise at Work Regulations 2005 set action values and limits based on daily exposure and peak sound pressure. HSE's noise guidance explains the levels and duties.
Can an EMF meter tell me if a level is safe?
It measures field strength. Interpreting results requires comparing against the relevant guidelines for the frequency and situation.
What should I check before ordering?
Before you order any detector or meter, write down the measurements or tasks it must handle, the range and accuracy you need, where it will be used and who will use it. Compare those notes with each product's specification sheet rather than its headline features, and keep the manual and any certificates with the instrument once it arrives.
Shop gas and environmental detectors
Browse gas detectors, air quality monitors, sound level meters, EMF meters and anemometers in our Gas & Environment Detectors collection.
Sources
- HSE – EH40/2005 Workplace exposure limits
- HSE – Noise at work
- legislation.gov.uk – The Control of Noise at Work Regulations 2005
- HSE – Carbon monoxide (gas safety)
- GOV.UK – Smoke and carbon monoxide alarms: explanatory booklet for landlords
- legislation.gov.uk – The Control of Substances Hazardous to Health Regulations 2002
