Multi Gas Detectors
Multigas detectors carry five or six sensors in one portable instrument. They cover the standard confined space gases and add the extra hazards your risk assessment identifies, so one monitor protects the user instead of two or three.
Typical sensor combinations
Utilities and sewers: LEL, O2, H2S, CO plus CO2 or a second H2S range
Combustion and tunnelling: LEL, O2, CO plus NO2 and SO2
Water treatment: LEL, O2, H2S, CO plus Cl2 or ClO2
Refrigeration and agriculture: O2 plus NH3 and CO2
Petrochemical and tank cleaning: LEL, O2, H2S, CO plus a PID for VOCs or benzene
When 4-gas is not enough
A 4-gas monitor covers LEL, O2, H2S and CO. If your COSHH assessment identifies another toxic gas, or if you need VOC readings, move to a multigas instrument rather than adding a second detector that may not be worn or checked.
PID-equipped multigas monitors
A photoionisation sensor measures volatile organic compounds in ppm and is calibrated with isobutylene. Correction factors convert readings for specific compounds. For benzene specifically, a benzene-selective PID is more reliable; see PID and VOC monitors.
Pumps and sampling lines
Some gases are reactive and stick to tubing, so readings through long sample lines can be low and slow. Chlorine, chlorine dioxide, ammonia and many VOCs are affected; use the shortest practical line, the correct tubing material and allow extra time.
Cross-sensitivity
Electrochemical sensors are selective but not perfect. Hydrogen can push up CO readings; SO2 and NO2 can affect other toxic sensors. Where interfering gases are present, ask us to specify filtered or compensated sensors.
Buy, hire or calibrate
Hire a multigas monitor from £85 a week: gas detector hire
Calibration for any brand: £90 per instrument: calibration and service
Compare with 4-gas monitors
Choosing sensors for your site
Start from your COSHH and DSEAR assessments: list every gas that could be present, where, and at what concentration. Then check each gas against its UK exposure limit in our EH40 reference for common gases. A sensor must be able to measure reliably at and below the limit, which rules out some sensors for gases with very low limits such as phosphine or chlorine dioxide.
Think about what else is in the air. Many electrochemical sensors react to other gases, so a reading on one channel may be caused by a different gas. We can advise on sensor combinations that avoid this, or on filters for specific interferences.
Hire for occasional or changing hazards
Where hazards change from job to job, such as shutdowns, decommissioning or contaminated land, hire lets you match the sensors to the task. Multigas monitors are available from £85 a week and PIDs from £135 a week, calibrated and certificated before dispatch.
Bump testing and calibration
A bump test exposes the detector briefly to a known gas to prove that the sensors respond and the alarms sound. It takes about a minute and should be done before each day's use. A full calibration adjusts each sensor against certified gas and is normally needed at least every six months, or sooner if a bump test fails, the monitor has been dropped or it has seen a high exposure.
Our calibration service covers any brand of portable or fixed detector at standard rates by instrument type: from £40 for a single gas monitor, £50 for a 4-gas monitor, £90 for a multigas monitor and £140 for a PID. Each instrument comes back with a traceable calibration certificate.
Training your team
A detector only protects people who know how to use it. Our gas detection training covers start-up checks, bump testing, reading alarms and what to do when one sounds. We run on-site courses anywhere in the UK from £750 a day, or a three-hour online session from £350.
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
When is a 4-gas monitor not enough?
When the risk assessment identifies a gas outside LEL, O2, H2S and CO, such as SO2, NO2, NH3, Cl2, HCN, PH3 or VOCs. A multigas monitor adds one or two extra sensors so a single instrument covers every hazard.
Can a multigas monitor include a PID?
Yes. Many 5 and 6-gas monitors accept a photoionisation sensor for VOCs alongside the standard four, useful for tank cleaning, refineries and contaminated land.
What is cross-sensitivity?
Electrochemical sensors can respond to gases other than their target. For example, some CO sensors respond to hydrogen and some H2S sensors to SO2. Choose sensors with filters or compensation where interfering gases are present, and ask us if you are unsure.
How much does multigas calibration cost?
We calibrate any brand of multigas monitor for £90, excluding VAT and parts.