Workplace Gas & Indoor Air Quality Monitoring UK

When dust isn't the hazard, gas usually is

Plenty of UK workplace exposure risks aren't particulate. Boiler rooms and plant rooms can develop dangerous carbon monoxide leaks. Offices and classrooms with sealed-up ventilation rack up carbon dioxide levels that destroy concentration long before they become dangerous. Print shops, laboratories and spray-finishing operations generate volatile organic compounds that no IOM head will ever catch. Construction site generators, diesel plant and confined space entry all need real-time gas monitoring before anyone goes near them.

For all of these, the right tool is a calibrated, direct-reading multi-gas instrument — an electrochemical cell for the toxic gases, an NDIR sensor for CO&sub2;, a photoionisation detector for VOCs, and a catalytic bead or NDIR for the lower explosive limit. We deploy these for short-duration confined-space monitoring, full-shift personal logging, fixed-location ambient surveys over several working days, and BREEAM Hea 02 post-construction air quality testing.

Every instrument is bump-tested before deployment, calibration certificates accompany every report, and every result is compared to the relevant Workplace Exposure Limit in HSE document EH40 (and the BREEAM Hea 02 indoor air quality benchmarks where relevant). Surveys are designed and signed off by Malcolm Pounder CEnv MIAQM, a Chartered Environmentalist.

Gases & Vapours We Monitor

Common Targets & Their UK Exposure Limits

The right sensor depends on the gas. We pick and calibrate the instrument loadout to match what you actually need measured.

Carbon Monoxide (CO)

Electrochemical sensor. EH40 limits: 30 ppm (8-hr TWA), 200 ppm STEL. Critical for boiler rooms, gas-fired plant, kitchen kitchens with poorly vented appliances, underground car parks, vehicle workshops and any space where combustion takes place indoors.

Carbon Dioxide (CO&sub2;)

NDIR sensor. EH40 limits: 5,000 ppm (8-hr TWA), 15,000 ppm STEL. Values above 1,000 ppm in offices and classrooms indicate poor ventilation under HSE workplace guidance and are widely associated with reduced concentration and productivity. Essential for occupied-building IAQ surveys and post-occupancy evaluations.

Volatile Organic Compounds (VOCs)

Photoionisation detector (PID), typically 10.6 eV lamp, reported as total VOCs equivalent to isobutylene or toluene. Used for screening and hotspot location in print shops, labs, paint and adhesive applications. For BREEAM Hea 02 a parallel sorbent-tube and GC-MS sample gives the formal speciated TVOC value.

Nitrogen Dioxide (NO&sub2;)

Electrochemical sensor. EH40 limit: 0.5 ppm (8-hr TWA). Routinely needed for underground car parks, vehicle workshops, diesel plant operation and construction sites where generators or plant are running close to occupied space. NO&sub2; is also the headline pollutant for outdoor AQMA work, often combined with diffusion-tube monitoring.

Hydrogen Sulphide (H&sub2;S)

Electrochemical sensor. EH40 limits: 5 ppm (8-hr TWA), 10 ppm STEL. Essential for sewage treatment works, pumping stations, anaerobic digestion plant, wet wells, slurry pits, fish processing and tanneries. H&sub2;S is rapidly fatal at concentrations above 700 ppm and rapidly olfactory-fatigued — the nose is no defence.

Oxygen (O&sub2;)

Electrochemical sensor. Safe range 19.5% to 23.5%. Mandatory for any confined space entry — oxygen depletion below 19.5% causes rapid loss of consciousness with no warning. Enrichment above 23.5% creates a serious fire risk.

Lower Explosive Limit (LEL)

Catalytic-bead or NDIR sensor. Confined-space and intrinsically safe operations require continuous monitoring at 10% LEL alarm. Relevant wherever flammable gases or vapours can accumulate — gas plant, AD facilities, solvent stores, fuel-handling and any sewer or wet well.

Sulphur Dioxide (SO&sub2;) & other toxics

Electrochemical sensors available for SO&sub2; (0.5 ppm STEL), chlorine, ammonia, hydrogen cyanide and a range of process-specific toxics. We agree the sensor loadout up front based on the substances actually present at your site.

Where It Matters

Common Survey Scenarios

Most workplaces fall into one of these patterns. Tell us yours and we'll match the instrument and the sampling strategy.

Office & classroom indoor air quality Multi-day fixed-location logging of CO&sub2;, CO, TVOC, temperature and relative humidity. Particularly relevant where staff complain of stuffiness, headaches, dry eyes or poor concentration — usually a ventilation problem made visible by CO&sub2; in the 1,500–3,000 ppm range.

BREEAM Hea 02 post-construction IAQ Formal speciated TVOC and formaldehyde sampling to the BREEAM methodology, with sorbent tubes and UKAS-accredited GC-MS analysis. Includes the PID screening pass to locate hotspots before formal sampling.

Boiler & plant room CO surveys Direct-reading CO logging at boiler operating cycles, with screening of flue gas paths and combustion air intakes. Essential after any boiler replacement, flue re-routing or building works that affect the plant room envelope.

Underground car parks & basements Logged CO and NO&sub2; surveys against the EH40 limits, plus an assessment of ventilation rates against the BS 7346-7 and IGEM/UP/19 benchmarks for car-park ventilation design.

Confined space entry support Calibrated 4-gas or 5-gas instrument loaded for the substances present (O&sub2;, LEL, CO, H&sub2;S plus VOCs or NO&sub2; as needed). Entry-test, continuous-monitor and rescue-team coverage available.

Construction site fixed monitoring Boundary or work-area logging of NO&sub2; and CO where diesel plant operates close to occupied space, including school perimeters, hospital sites and adjacent residential property. Often paired with PM&sub10;/PM&sub25; for dust and a noise dosimeter.

Sewage, AD & water treatment H&sub2;S Personal and area H&sub2;S monitoring at sewage works, anaerobic digestion plants, wet wells and pumping stations. Logged datasets used to underpin LEV reviews and confined-space risk assessments.

Print, lab & finishing TVOC surveys PID screening of total VOCs in print rooms, finishing booths, university labs and small-batch chemistry, with sorbent-tube speciation where a substance-specific WEL is in play.

Our Method

How a typical gas survey runs

Calibration, traceability and the right sensor for the gas — nothing exotic, just done properly.

1. Scoping call 15-minute call to understand the substances, the location, whether you need continuous logging or short-duration spot checks, and any HSE or BREEAM context. Sensor loadout agreed in writing.

2. Pre-survey calibration & bump test Every sensor calibrated to certified span gas (traceable to UKAS) before the visit, with a recorded bump test on the morning of deployment. Calibration certificates accompany the final report.

3. Deployment Fixed-location logging instruments installed for the survey duration (typically 3 to 7 working days) or handheld 4/5-gas instruments deployed for personal sampling, confined-space entry support or task-specific spot checks.

4. Data download & post-calibration check Datasets downloaded on retrieval and a post-survey calibration check carried out the same day to verify sensor stability across the survey window.

5. EH40 / BREEAM comparison Every gas channel reported against the relevant EH40 WEL (8-hr TWA, STEL) and, where applicable, the BREEAM Hea 02 indoor air quality benchmarks for TVOC and formaldehyde.

6. Practical recommendations Where readings exceed a benchmark we recommend proportionate, achievable controls — ventilation upgrade, plant overhaul, source elimination, RPE programme — not boilerplate.

Common Questions

Frequently Asked Questions

What gases can you monitor in a workplace?

We use direct-reading multi-gas instruments with the appropriate calibrated sensors for each application: electrochemical cells for carbon monoxide (CO), hydrogen sulphide (H&sub2;S), nitrogen dioxide (NO&sub2;), sulphur dioxide (SO&sub2;) and oxygen (O&sub2;); photoionisation detector (PID) for total volatile organic compounds (TVOCs); non-dispersive infrared (NDIR) for carbon dioxide (CO&sub2;); and catalytic-bead or NDIR sensors for the lower explosive limit (LEL) of flammable gases. Each instrument is bump-tested before deployment and the calibration certificate is included in the report.

What are the UK Workplace Exposure Limits for these gases?

HSE document EH40 sets the relevant limits. Carbon monoxide is 30 ppm (8-hr TWA) with a 200 ppm short-term limit. Carbon dioxide is 5,000 ppm (8-hr TWA) with a 15,000 ppm short-term limit; values above 1,000 ppm in offices and classrooms also indicate poor ventilation under HSE Workplace (Health, Safety and Welfare) guidance. Nitrogen dioxide is 0.5 ppm (8-hr TWA). Hydrogen sulphide is 5 ppm (8-hr TWA) and 10 ppm short-term. Sulphur dioxide has only a 0.5 ppm short-term limit. Oxygen must remain between 19.5% and 23.5%. There is no single VOC WEL; TVOCs are reported against substance-specific EH40 limits and, for indoor air, against the BREEAM Hea 02 benchmark of 300 µg/m³.

Do you carry out BREEAM Hea 02 post-construction indoor air quality testing?

Yes. We carry out post-construction indoor air quality testing to BREEAM Hea 02 methodology, measuring total volatile organic compounds (TVOCs, benchmark 300 µg/m³) and formaldehyde (benchmark 100 µg/m³). TVOCs are typically measured by sorbent tube and thermal desorption GC-MS at a UKAS-accredited laboratory rather than by direct-reading PID, because BREEAM requires the formal speciated TVOC value. Direct-reading PID is used alongside for screening and to identify hotspots within the building before formal sampling.

When do I need gas monitoring instead of dust monitoring?

You need gas monitoring whenever the airborne hazard is in vapour or gas form rather than particulate. Common scenarios include: indoor air quality complaints in offices and schools (CO&sub2; as a ventilation indicator); plant rooms and boiler rooms (CO leak detection); underground car parks (CO and NO&sub2; from vehicle exhaust); confined space entry (LEL, O&sub2;, H&sub2;S, CO); sewage and water treatment works (H&sub2;S); print shops and laboratories (TVOCs); construction site fixed monitoring (CO, NO&sub2; from plant exhaust); and BREEAM Hea 02 indoor air quality assessment. Dust monitoring (IOM head, cyclone) and gas monitoring are separate techniques and often run together as part of a combined COSHH survey.

How much does workplace gas monitoring cost?

A typical fixed-location indoor air quality screening with a calibrated multi-gas instrument logging CO&sub2;, CO, TVOC and temperature/humidity over 5 to 7 working days, including the report, starts from around £600 to £950 plus VAT. A BREEAM Hea 02 post-construction TVOC and formaldehyde survey with sorbent-tube sampling and UKAS-accredited GC-MS analysis typically starts from around £950 to £1,400 plus VAT. Combined gas and dust surveys on the same visit attract a discount because the day-rate is shared. See our cost guide page for worked examples.

Workplace Gas & Indoor Air Quality Monitoring