Carbon monoxide (CO) is one of the most persistent hazards in industrial settings, yet its risks are frequently underestimated. It has no colour, no smell and no taste. Workers can be exposed to dangerous concentrations without any immediate awareness, and the effects of prolonged, low-level exposure can build slowly over months before they become apparent.
Understanding how to monitor and manage CO is becoming a pressing concern for health and safety professionals.
This article examines the chronic health risks associated with low-level CO exposure, why it deserves closer attention, and what effective monitoring looks like in practice.
The risk of low-level CO exposure
The immediate dangers of high-concentration CO poisoning are well documented; it is a gas that can kill. What is less frequently discussed are the effects of repeated exposure to CO levels that fall below the threshold for acute symptoms.
In the UK, the workplace exposure limit (WEL) for carbon monoxide is 20 ppm as an eight-hour time-weighted average, with a short-term limit of 100 ppm over 15 minutes. Exposures that hover near or just below these limits, day after day, carry their own serious consequences.
The HSE’s carbon monoxide awareness guidance makes clear that early symptoms of CO poisoning can mimic (and be easily mistaken for) many common illnesses or ailments such as food poisoning, viral infections, flu, or excessive fatigue. Even if workers are not exposed to fatal levels of CO, they can still suffer serious harm if they breathe in the gas over a prolonged period. Chronic, low-level exposure can produce persistent headaches, dizziness, nausea, loss of consciousness, and stomach or chest pains. As these symptoms are easily attributed to other causes, occupational CO exposure often goes unrecognised for some time.
What makes CO poisonous?
CO binds to haemoglobin in the blood with an affinity far greater than oxygen, forming carboxyhaemoglobin and restricting the blood’s ability to deliver oxygen to cells and organs. Even modest, sustained elevations in carboxyhaemoglobin place ongoing stress on the cardiovascular and central nervous systems. Common appliances that can produce CO and cause poisoning include gas boilers and cookers, paraffin heaters, wood, gas and coal fires, and portable generators. As carbon monoxide sensor manufacturers DD Scientific note, the potential hazards of carbon monoxide are amplified in poorly ventilated and enclosed spaces, where the gas can accumulate over time without any sensory warning to those present.
The HSE’s guidance on CO in construction and industrial environments reinforces the need for health and safety managers to adopt the Assess, Control, and Review model as far as CO detection and prevention are concerned. This emphasises the need to identify the tasks and situations where CO may be emitted, eliminate or reduce carbon monoxide risks as much as possible, and ensure that controls are effective and used appropriately by the wider workforce.
On a broader level, the risks of CO exposure illustrate precisely why continuous, automated monitoring is so important in any space where combustion equipment, generators, LPG appliances or confined working conditions are present.
Detection standards and best practice
Electrochemical sensors remain the gold standard for industrial CO monitoring. They offer reliable sensitivity at the low ppm ranges relevant to occupational exposure limits and can be configured as fixed or portable units. Fixed detectors suit enclosed or semi-enclosed spaces with consistent conditions, while portable units allow workers to carry monitoring into areas where CO levels may fluctuate, such as confined spaces, loading bays, or plant rooms.
For those looking to build a broader understanding of how CO sits within the wider framework of hazardous substance control, our guide to COSHH symbols and hazard classification provides a helpful reference point for how toxic gases are categorised and managed under UK regulations.
Sensor calibration and maintenance are equally important. Sensors drift over time, and a detector that was accurate at installation may give unreliable readings years later if it has not been regularly checked against certified calibration gas. Alarm setpoints should also be reviewed whenever there are changes to process equipment, fuel sources, or building layout.
As industrial sites introduce alternative energy sources alongside existing combustion infrastructure, reviewing the full gas monitoring setup becomes worthwhile, since CO risks from existing equipment do not diminish simply because additional hazards have been added.
Compliance as a starting point
Meeting the WEL for carbon monoxide is a legal baseline, but it is certainly not a safety guarantee. Chronic exposure below those limits can still cause lasting harm to workers in environments where combustion sources are poorly managed or ventilation is inadequate.
Investing in the right sensors, positioning them correctly, maintaining them rigorously, and setting alarm levels that reflect current WELs are all practical steps for preserving worker health and safety.
The challenge is ensuring that the insidious, gradual nature of low-level CO exposure is taken as seriously as the more visible hazards that tend to dominate industrial safety planning.
