Carbon Monoxide Monitoring
Gas Hazards · Gas Hazards overview
Carbon monoxide (CO) is a colourless, odourless and tasteless toxic gas produced by every form of incomplete combustion. Carbon monoxide monitoring and carbon monoxide testing protect workers in any UK environment where engines, boilers, ovens or other combustion sources operate in shared airspace.
Why carbon monoxide exposure is a workplace problem
Carbon monoxide binds to haemoglobin with around 240 times the affinity of oxygen, displacing oxygen transport in the blood. The early symptoms of workplace CO exposure — headache, dizziness, nausea, slowed reaction times — are easy to misattribute to fatigue, dehydration or a long shift, which is why carbon monoxide exposure incidents in industry are often identified only when several workers report the same symptoms.
CO is also the most common cause of fatal occupational gas poisoning in indoor work environments. Because it cannot be detected by smell or sight, the only practical defence is calibrated CO monitoring — fixed where combustion plant runs continuously, portable for surveys, and personal for workers who move between zones.
Common workplace sources of carbon monoxide
Carbon monoxide is generated anywhere fuel burns incompletely. The sources that produce most UK workplace CO exposure are predictable and well understood.
- LPG and diesel forklifts operating indoors — particularly in warehouses, cold stores and goods inwards
- Diesel and petrol engines in workshops, MOT bays, vehicle test stations and emergency generators
- Gas-fired ovens, dryers, kilns, furnaces and direct-fired space heaters
- Boiler plant with faulty combustion, blocked flues or compromised flue integrity
- Hot-work and cutting operations in poorly ventilated bays — secondary CO from process heat
- Combustion gases drifting indoors from adjacent loading bays, plant rooms or external operations
Atmospheric risk from carbon monoxide
CO is close to the density of air and disperses through a workspace rapidly. In practical terms this means that a single faulty source — a misadjusted burner, a forklift with a failing catalyst, a blocked flue — can raise the carbon monoxide concentration across an entire warehouse, workshop or kitchen within minutes. Concentrations are usually not uniform: zones close to combustion sources, low-ceiling areas and corners with poor air movement tend to be worst.
Carbon monoxide also accumulates over a shift. Workers exposed to moderate CO concentrations for several hours can develop significant carboxyhaemoglobin levels even where the peak reading at any moment is unremarkable. A defensible CO monitoring programme has to capture both peaks and time-weighted exposure.
Carbon monoxide monitoring and testing approach
Modern electrochemical CO sensors are accurate, stable and well-suited to fixed, portable and personal monitoring. The combination of these three monitoring modes is what gives an employer a defensible picture of workplace CO exposure.
- Fixed CO detection mounted at breathing-zone height in indoor combustion environments — warehouses, workshops, plant rooms
- Portable multi-gas instruments with CO and O₂ channels for surveys, leak hunting and pre-task checks
- Personal CO monitors clipped to the worker's lapel for full-shift carbon monoxide testing
- Datalogging across a shift to capture peak excursions and time-weighted average exposure
- Combustion analysis of suspect appliances to confirm or eliminate them as sources
When to commission carbon monoxide testing
Workplace gas testing for CO is normally triggered by symptom reports, new combustion equipment, or audit findings. It is also good practice to test seasonally — colder months bring closed doors, reduced natural ventilation and higher heating use, which together increase indoor CO build-up risk.
- Worker reports of headaches, dizziness or unexplained tiredness in combustion environments
- Introduction or modification of LPG, diesel or petrol equipment used indoors
- Changes to building ventilation, doors, partitions or extract systems
- Audit findings or insurer requirements for evidence of CO monitoring
- Investigation of CO alarm activations or near-miss events
- Seasonal review for indoor combustion environments at the start of winter
Carbon monoxide in the wider workplace gas picture
CO almost never travels alone. Combustion gases produce CO, CO₂, NOₓ and a variety of particulates simultaneously, and combustion plant rarely sits in isolation from other gas hazards. A credible carbon monoxide monitoring programme should be scoped alongside CO₂ monitoring, NOₓ assessment for diesel-rich environments and a review of any forklift emissions or other combustion sources in the same airspace.
Frequently asked questions
What carbon monoxide alarm levels are normally used in UK industry?
Two-stage alarms are the norm — a low alarm at a level that prompts investigation and ventilation, and a high alarm at a level that prompts evacuation. The specific set points should reflect the workplace atmospheric standards used for full-shift and short-term occupational CO exposure in the UK, and should be agreed in writing as part of the site's CO monitoring procedure.
Is a domestic CO alarm enough for a workshop or warehouse?
No. Domestic CO alarms are designed for residential exposure scenarios and typically have higher trigger thresholds, slower response times and no logging or maintenance regime suitable for workplace use. Industrial CO monitoring uses calibrated, bump-tested instruments with appropriate alarm levels and documented inspection records.
How often should portable CO instruments be calibrated and bump-tested?
Bump-testing before each shift of use is the recommended practice for portable CO instruments used in workplace gas testing. Full calibration is normally carried out at the manufacturer's recommended interval, often every six to twelve months, against a traceable test gas. Records of both should be retained.
Can carbon monoxide testing identify the source of a CO problem?
Yes, by combining datalogging with a structured survey. Time-stamped CO profiles correlated with operational events — engine starts, oven cycles, forklift movements, door openings — usually localise the dominant source within one or two visits. Combustion analysis of suspect appliances then confirms or eliminates them.
Who should specify CO monitoring for a site?
Fixed and portable CO monitoring is normally specified by a competent safety engineer or occupational hygienist working from the site's combustion sources, layout and ventilation. Personal carbon monoxide exposure assessment should be carried out as part of a wider workplace gas exposure assessment by a competent practitioner.
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