Phoenix Journal · Extraction
Carbon monoxide is colourless, odourless and produced every time a gas or solid fuel appliance burns fuel poorly. In a busy kitchen the warning signs are easy to mistake for a long shift - which is exactly what makes it dangerous.
Case postmortem
The headaches started mid-service, and by the end of the week two chefs had gone home nauseous and light-headed - and nobody had thought to blame the chargrill roaring away in the corner.
It was a mid-sized restaurant kitchen running a gas six-burner range, a salamander and a solid fuel chargrill under a single extraction canopy. On paper it was well equipped. In practice, the extraction fan had been quietly losing performance for months as grease built up inside the canopy and ductwork, and a fault on the gas interlock had been "temporarily" bridged out by a well-meaning engineer so the burners would keep lighting during a busy weekend. The temporary fix was never undone.
By the time the kitchen porter felt too dizzy to climb the cellar stairs, carbon monoxide had been accumulating during every service for weeks. What follows is a plain account of how that happens, what the rules actually require of you, and the practical steps that would have stopped it long before anyone got hurt.
Carbon monoxide (CO) forms whenever a fuel - natural gas, LPG, charcoal, wood - burns without enough oxygen to complete the reaction. Burn cleanly and you mostly get carbon dioxide and water vapour. Starve the flame of air, or let the products of combustion linger instead of being drawn away, and you get carbon monoxide instead. It is colourless, it is odourless, and at the concentrations that matter it gives you almost nothing to react to until people are already unwell.
Three things failed together in this kitchen, and it usually takes more than one.
First, the combustion air and the extraction had degraded. A greasy canopy and a partly blocked duct do not just slow the removal of smoke and steam - they starve the space of the airflow the appliances need to burn cleanly and to carry combustion products outside. As airflow drops, incomplete combustion rises, and the very system meant to clear the fumes is the thing quietly failing.
Second, the gas interlock had been defeated. Under BS 6173:2020, gas catering appliances should not be able to run unless the mechanical ventilation is proven to be moving enough air. The interlock exists precisely so that a failing or switched-off fan cuts the gas rather than letting appliances keep burning into a stagnant room. Bridge it out and you remove the one automatic safeguard designed for this exact scenario.
Third, there was no working commercial-grade CO alarm. A domestic detector had been stuck to the wall years earlier, well past its stated life and never designed for the heat, grease and humidity of a commercial kitchen. It never sounded.
The legal backdrop is not vague. The Control of Substances Hazardous to Health Regulations 2002 (COSHH) treat carbon monoxide as a hazardous substance you must assess and control. HSE’s workplace exposure limit for CO is 20 ppm as an 8-hour time-weighted average, with a short-term limit of 100 ppm over any 15-minute period (EH40). The Workplace (Health, Safety and Welfare) Regulations 1992 require effective and suitable ventilation in every enclosed workplace, and the Gas Safety (Installation and Use) Regulations 1998 sit over all of it. None of these were being met.
The numbers that matter
Those limits are lower than many operators assume, and they are easy to breach quietly. Early carbon monoxide exposure looks exactly like a hard shift - headache, tiredness, nausea, poor concentration, dizziness. Staff put it down to heat and long hours, symptoms ease on days off, and the pattern repeats. That ambiguity is the real hazard: the gas does not announce itself, and the people most exposed are often the least likely to link how they feel to the appliance beside them.
Solid fuel appliances deserve particular attention. Tandoori ovens, charcoal grills and wood-fired ovens are a well-known CO source, and HSE publishes specific guidance for them (information sheet CAIS26) because they can produce dangerous concentrations even where gas appliances are well managed. If you run solid fuel, the risk assessment and detection need to account for it directly rather than assuming a gas-focused setup covers you.
None of the failures above needed new technology to prevent - they needed the existing safeguards kept in working order and a competent eye on the parts you cannot see. If you want a kitchen where carbon monoxide simply cannot build up unnoticed, work through the following:
It is tempting to file grease cleaning under fire safety and detection under gas safety, as if they were separate worlds. They are not. The same restricted airflow that lets a grease fire spread is the airflow your appliances rely on to burn cleanly and to vent combustion products away from your staff. When a duct clogs, both problems grow at once. Treating extraction cleaning as part of your carbon monoxide controls - not just your fire controls - closes a gap that catches out a lot of otherwise careful operators.
Much of this documentation converges when someone independent looks at your kitchen. Interlock records, gas certificates, CO alarm servicing and duct-cleaning reports are the sort of evidence a competent assessor expects to see laid out, and it is worth knowing what a fire risk assessor wants to see on arrival so the same paperwork does double duty. A kitchen that can produce clean, current records for all of the above is almost always a kitchen where the physical safeguards are genuinely working.
Questions
There is no single line in law that says "fit a CO alarm", but COSHH 2002 requires you to assess and control the carbon monoxide risk, and in most gas or solid fuel kitchens a working commercial-grade CO alarm is the practical way to meet that duty. It should be a detector designed for the catering environment, not a domestic model, sited to the manufacturer’s instructions and audible over a busy kitchen. For solid fuel appliances such as tandoors and charcoal grills, HSE guidance treats an audible CO alarm as an expected control measure.
HSE sets a workplace exposure limit for carbon monoxide of 20 ppm as an 8-hour time-weighted average, with a short-term limit of 100 ppm over any 15-minute period (published in EH40). These are lower than many operators expect and can be breached without anyone noticing, because early symptoms - headaches, tiredness, nausea - look like the effects of a long, hot shift. If exposure regularly approaches these figures, your ventilation and appliances need attention rather than tolerance.
Grease-laden ductwork restricts airflow, and that airflow does two jobs at once: it carries combustion products such as carbon monoxide out of the building, and it helps feed the clean burning that stops CO forming in the first place. As a duct clogs, extraction weakens and incomplete combustion rises together. Regular deep cleaning to a measured standard keeps the system moving the volume of air your appliances and gas interlock were designed around, which is why extraction cleaning belongs in your CO controls as well as your fire controls.
Phoenix Duct Clean · by the numbers
The right kit only helps if the system stays clean. Phoenix degreases canopies, filters and ductwork to TR19 Grease - UK-wide, overnight.