Hydrogen Sulphide Detectors
Hydrogen sulphide is one of the most common causes of gas deaths in confined spaces. It is produced when organic matter breaks down without oxygen, and it is heavier than air, so it collects in sewers, pits and tanks.
Where H2S occurs
Sewers, manholes, pumping stations and wet wells
Water and wastewater treatment works
Tank cleaning and sludge handling
Livestock slurry and agriculture
Oil and gas, refineries and pulp and paper
UK exposure limits
EH40 sets workplace exposure limits for H2S of 5 ppm (8-hour TWA) and 10 ppm (15-minute STEL). Personal monitors are commonly set with low and high alarms at these levels, plus TWA and STEL alarms. See our EH40 reference.
Why smell is not a warning
The rotten egg smell is noticeable below 1 ppm, but at around 100 ppm H2S deadens the sense of smell within minutes. Workers have been overcome believing the gas had cleared. Only a detector gives a reliable warning.
Personal, portable and fixed detection
Personal single gas H2S monitors, including two and three-year disposables, for anyone working where H2S may be present.
4-gas and multigas monitors with H2S for confined space entry.
Fixed H2S transmitters for pump rooms, wet wells and process areas, mounted low where gas collects.
Sensor life and calibration
Electrochemical H2S sensors usually last two to three years. Bump test before each day's use and calibrate every six months; we calibrate single gas monitors of any brand for £40.
Hire an H2S monitor from £35 a week: gas detector hire
Choosing an H2S monitor
For personal protection, a single gas H2S monitor worn in the breathing zone is the minimum. Disposable two and three-year monitors need no calibration, only bump testing. Serviceable monitors cost more up front but can be calibrated and fitted with new sensors. Where H2S is one of several hazards, or for confined space entry, use a 4-gas monitor.
Typical alarm points are set at or below the UK limits of 5 ppm (8-hour TWA) and 10 ppm (15-minute STEL). Check our EH40 reference for common gases for the limits of other gases on your site.
H2S at wastewater and sewer sites
Septic sewage, sludge and wet wells release H2S, often in bursts when flows are disturbed. See our wastewater gas detection guide for detection by process stage.
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
What are the UK exposure limits for H2S?
EH40 sets 5 ppm as an 8-hour time-weighted average and 10 ppm as a 15-minute short-term exposure limit.
Can you rely on the smell of H2S?
No. H2S smells of rotten eggs at very low levels, but at around 100 ppm it paralyses the sense of smell, so a dangerous concentration can seem to disappear.
Personal or fixed H2S detection?
Personal monitors protect individuals moving around a site or entering confined spaces. Fixed detectors protect fixed areas such as pump rooms, wet wells and inlet works continuously.
How long do H2S sensors last?
Electrochemical H2S sensors typically last two to three years. Disposable H2S monitors run for two or three years and are then replaced.