Carbon monoxide in commercial kitchens: ventilation, flues and warning signs

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A busy commercial kitchen can burn a lot of gas in a small space. When combustion is complete and the ventilation is doing its job, the products of combustion are carried away safely. When either of those fails, carbon monoxide (CO) can build up, and you can't see, smell or taste it. This guide explains the carbon monoxide risk in a commercial kitchen, how ventilation and flues control it, the warning signs staff should report, and what duty holders need to have in place. It is written for owners, managers, head chefs and facilities teams, and it is based on HSE catering guidance, HSE and NHS carbon monoxide advice, and BESA guidance on extract cleaning.

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Commercial heating tips and advice · 6 October 2026 · Fast Commercial Boiler Help, Gas Safe 985448

Why carbon monoxide is a risk in commercial kitchens

HSE describes carbon monoxide as "a colourless, odourless, tasteless, poisonous gas produced by incomplete burning of carbon-based fuels, including gas, oil, wood and coal." It explains that carbon-based fuels are safe to use, and that "it is only when the fuel does not burn properly that excess CO is produced." Once breathed in, CO prevents the blood from carrying oxygen to the body's cells, tissues and organs.

HSE's employer guidance lists CO poisoning alongside fire, explosion and gas leaks as the dangers when gas appliances such as ovens, cookers and boilers are not properly installed and maintained. In a kitchen, HSE information sheet CAIS23 (Gas safety in catering and hospitality) explains that cooking generates products of combustion and heat, which have to be kept within safe environmental limits by the ventilation system. "If a mechanical system fails or is not working correctly, the environment may become unsafe or unfit for work."

Where carbon monoxide comes from in a kitchen

Gas cooking appliances that are not burning properly. Ranges, ovens, fryers, griddles and chargrills all burn gas close to staff. A burner that is faulty, poorly maintained or short of combustion air can produce excess CO.
Not enough make-up air. HSE information sheet CAIS10 (Ventilation in catering kitchens) says it is particularly important to ensure there is adequate make-up air for gas-fired and solid fuel appliances, "the lack of which can lead to an accumulation of combustion products, such as carbon monoxide." One of the objectives it sets for kitchen ventilation is to "provide enough air for complete combustion at fired appliances and prevent the risk of carbon monoxide accumulating."
Extraction that acts as a flue. CAIS10 notes that some gas appliances are a type (known as type B) that requires a flue. "Where extraction serves that purpose, it is considered a flue" and needs an appropriate interlocking system connecting the airflow to the gas supply. If that extract stops, the combustion products have nowhere to go.
Charcoal ovens and grills. CAIS10 warns that because charcoal ovens cannot be switched off, adequate ventilation is necessary even when the oven is covered and cooling down overnight, to prevent a build-up of carbon monoxide that could affect neighbouring properties.
Heating and hot water plant. Boilers and water heaters serving the kitchen and the rest of the building are combustion appliances too. HSE's employer guidance describes a primary school where 25 pupils and 2 staff were evacuated from a classroom after CO from an inadequately maintained boiler leaked into the room above.

Ventilation, flues and extract: the main safeguards

CAIS23 is clear that CO alarms "are only warning devices". The primary safeguards remain "providing an adequate and effective ventilation system to ensure complete combustion of gas and removal of combustion products, along with regular maintenance and servicing of all equipment by competent people." In practice that means:

A canopy and extract that suit the cooking. CAIS10 says there should be a canopy hood for every appliance and other sources generating fumes and heat, sized and with enough extraction to minimise fume spillage into the kitchen.
Clean, unblocked make-up air. Replacement air should be fresh and unadulterated from outside, and CAIS10 says make-up air "should not impair the performance of flues serving gas appliances." HSE's employer guidance says to check that all rooms with gas appliances have adequate ventilation, not to block air inlets to prevent draughts, and not to obstruct flues and chimneys.
Safe discharge. CAIS10 says never use devices that direct the discharge downward, "as they encourage down draught and re-entry of fumes into the building."
A working interlock. CAIS23 says the installer should have fitted an interlocking system so that failure of the mechanical ventilation shuts off the gas supply to the appliances, and that manual bypasses are not permitted. We explain how these work in our guide to commercial kitchen gas interlocks.
Maintained in efficient working order. CAIS10 says mechanical ventilation systems should be maintained in line with the manufacturer's or installer's instructions.

Grease, TR19 cleaning and the extract system

Grease is mainly a fire risk, but it also affects how well the extract performs. CAIS10 says a kitchen ventilation system should be easy to clean, "avoiding build-up of fat residues and blocked air inlets which lead to loss of efficiency and increased risk of fire." CAIS23 says ductwork should be cleaned regularly because the job "is often skimped", and that effective preventative maintenance and cleaning help prevent nuisance shutdowns caused by the ventilation system failing. It points to BESA's guide to good practice on the internal cleanliness of ventilation systems, TR19.

BESA's TR19 guidance sets minimum cleaning frequencies for kitchen extract systems based on daily hours of use:

Kitchen use	Minimum TR19 cleaning frequency
Heavy use, 12 to 16 hours per day	Every 3 months
Moderate use, 6 to 12 hours per day	Every 6 months
Light use, 2 to 6 hours per day	Every 12 months

BESA stresses that these are minimums, and that more frequent cleaning may be needed depending on the type of cooking, the condition of the system and the results of insurance and fire risk assessments. Extract cleaning is specialist work for a ventilation hygiene contractor, separate from gas work.

Warning signs staff should report

Because CO cannot be seen or smelled, staff need to know the indirect signs. HSE lists these signs of incomplete combustion that may result in the production of CO:

yellow or orange rather than blue flames (except on fuel effect fires or flueless appliances designed to show that colour);
soot or yellow or brown staining around or on appliances;
pilot lights that frequently blow out;
increased condensation inside windows.

In a kitchen, add anything that suggests the ventilation is not coping: fumes or steam visibly not clearing from under the canopy, a fan that is noisy, stopped or slower than usual, or extract that has been switched off while appliances are still lit. CAIS23 lists "visible escape of cooking fumes/steam" and broken fans among the signs of poor ventilation design or maintenance.

Symptoms in people matter too. HSE says early symptoms of CO poisoning "can mimic many common ailments and may easily be confused with food poisoning, viral infections, flu or simple tiredness." The NHS lists symptoms including a headache, dizziness, feeling or being sick, feeling weak, tiredness and confusion, chest and muscle pain, and shortness of breath. It notes that symptoms may come and go, may get worse in an affected room or building, and may get better after leaving or going outside. Several staff on the same shift feeling unwell in the kitchen, and better once they step outside, should always be reported.

What to do if you suspect carbon monoxide

Stop using the appliance and get people out. The NHS says to stop using appliances you think might be making CO if you can, go outside, and get medical advice as soon as possible, and not to go back into the affected building until you have got that advice. HSE also advises opening doors and windows to ventilate.
Call the gas emergency line. For a suspected CO leak or a gas smell, HSE advises calling the National Gas Emergency Service on 0800 111 999 (natural gas), or your LPG supplier for LPG, and shutting off the gas supply. If in doubt, evacuate the building.
Get medical help. The NHS says to call NHS 111 if you think you might have symptoms of CO poisoning, and to call 999 or go to A&E if someone exposed is finding it hard to breathe, has suddenly become confused, has lost consciousness, is feeling weak or has chest or muscle pain. It also says not to drive yourself to A&E.
Leave it off until it has been checked. HSE says do not use any appliance you know or suspect is unsafe, and do not turn a gas supply back on until a leak has been dealt with by a competent person. Don't reset an interlock or restart appliances to "see if it happens again".

Carbon monoxide alarms in commercial kitchens

CAIS23 says CO alarms in kitchens "should be suitable for use in the generally harsher conditions found in commercial working environments", and that domestic CO alarms "are not normally suitable and should not be used." It advises considering CO alarms or monitoring systems in the site-specific risk assessment, with an alarm maintenance regime in line with the manufacturer's instructions.

Where installed, CAIS23 says CO or CO₂ alarm systems should give an audible alarm and be interlocked to the gas pipework serving the catering appliances with an automatic gas shut-off. This "should be a fail-safe arrangement and requires manual intervention to restore the gas supply." An alarm is a back-up, not a substitute for ventilation, flues and servicing that work properly.

What staff should record and report

A short, consistent record helps the engineer find the cause. We suggest noting:

Record	What to note
Date, time and location	When it happened and which part of the kitchen or building
What was running	Which appliances were lit, and whether the extract and supply fans were on
What people saw	Flame colour, soot or staining, pilot lights going out, fumes not clearing, condensation
How people felt	Any headaches, dizziness, nausea or tiredness, and whether it eased outside
Alarms and shut-offs	Whether a CO or CO₂ alarm sounded or the gas interlock tripped
Action taken	Appliance turned off, gas isolated, emergency line called, engineer called, and by whom
Recent changes	New or moved equipment, blocked or covered air inlets, extract cleaning or repairs

CAIS10 says keeping records of design criteria, commissioning performance, maintenance requirements and of tests and inspections "will enable maintenance, modification and testing against the original specification." Keep the report with your gas safety and ventilation records.

Duty holder checklist

Maintain gas appliances, flues and pipework. Regulation 35 of the Gas Safety (Installation and Use) Regulations 1998 requires employers and the self-employed to ensure that any gas appliance, installation pipework or flue at a place of work under their control "is maintained in a safe condition so as to prevent risk of injury to any person." CAIS23 says frequency should follow the manufacturer's recommendations but "as a general rule, annual inspections are a reasonable minimum frequency."
Use a qualified engineer. In shops, restaurants, schools and hospitals, HSE says work on gas fittings must be carried out by a Gas Safe registered engineer who is qualified to do the work, and it is your responsibility to check. In premises the 1998 Regulations do not cover, such as factory canteens, CAIS23 says employers must ensure the people doing the work are competent, and Gas Safe registration is the clearest way of demonstrating that.
Provide effective ventilation. CAIS10 says the Workplace (Health, Safety and Welfare) Regulations 1992 require effective and suitable ventilation in every enclosed workplace, including kitchens.
Train staff. CAIS23 says staff who use gas equipment should be trained in how to use it and in visual checks for obvious faults, including damaged pipework and connections, inoperative flame supervision devices and smells of escaping gas, and should know what to do.
Act on concerns straight away. CAIS23 says anyone with concerns about the safety of their installation should not wait for the next routine maintenance visit or breakdown, but should seek urgent advice from a competent gas engineer and, where necessary, a ventilation expert.
Keep the extract clean. Book extract cleaning at a frequency that suits your hours of use, using BESA TR19 as the benchmark.

Where Fast Commercial Boiler Help fits

We work on heating and hot water plant in commercial premises: boilers, water heaters, calorifiers and plant rooms. We do not repair commercial kitchen cooking appliances or clean extract ductwork. For cooking appliances, use a Gas Safe registered engineer whose ID card shows the relevant catering qualifications, and for extract cleaning, a ventilation hygiene specialist working to TR19.

The boilers and water heaters that serve kitchens, hotels, pubs and restaurants carry the same CO risk if they are poorly maintained or short of air. Our commercial gas safety inspection covers heating plant, flues and plant room ventilation, and we repair commercial water heaters and calorifiers. For hospitality sites, see our hotel, pub and restaurant page, or read about our commercial gas engineers.

Safety note

Under the Gas Safety (Installation and Use) Regulations 1998, gas work must be carried out by a Gas Safe registered engineer, and we apply that rule on every site. Don't attempt DIY work on gas appliances, burners, flues or safety devices. On pressure systems, trained site staff should stick to visual and gauge checks, log the readings and report anything abnormal. Never adjust, cap, plug or test-lift a relief valve yourself.

Talk to a Gas Safe commercial engineer

Fast Commercial Boiler Help is a Gas Safe registered (985448) commercial heating business based at 4 Market Hill, Clare, Sudbury, Suffolk CO10 8NN. Our team of over 10 local engineers covers East Anglia and East London, working on commercial boilers, plant rooms, water heaters, and warm air, radiant and unit heaters. We work on commercial premises only.

Call 0800 0996 007

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Frequently asked questions

What causes carbon monoxide in a commercial kitchen?

Carbon monoxide is produced when gas or other carbon-based fuels do not burn properly (HSE). In kitchens, the usual causes are faulty or poorly maintained gas appliances, too little make-up air for combustion, extract that serves as a flue failing, and charcoal ovens left without ventilation. HSE CAIS10 says a lack of adequate make-up air can lead to an accumulation of combustion products such as carbon monoxide.

What are the warning signs of carbon monoxide in a kitchen?

HSE lists yellow or orange instead of blue flames, soot or yellow or brown staining on or around appliances, pilot lights that frequently blow out, and increased condensation inside windows. Symptoms include headaches, dizziness, nausea, tiredness and breathlessness, which the NHS says may get better after leaving the building.

Can we use a domestic carbon monoxide alarm in a commercial kitchen?

No. HSE CAIS23 says CO alarms in kitchens should be suitable for the harsher conditions of commercial working environments, and that domestic CO alarms are not normally suitable and should not be used. Where installed, CO or CO2 alarm systems should sound an alarm and be interlocked to an automatic, fail-safe gas shut-off.

What should staff do if they suspect carbon monoxide?

Stop using the appliance if you can, get everyone outside and ventilate. Call the National Gas Emergency Service on 0800 111 999 (or your LPG supplier) and get medical advice: NHS 111, or 999 for anyone struggling to breathe, confused, weak, with chest pain or unconscious. Do not use the appliance again until a Gas Safe registered engineer has checked it.

How often should a commercial kitchen extract be cleaned?

BESA TR19 sets minimum frequencies based on hours of use: every 3 months for heavy use (12 to 16 hours a day), every 6 months for moderate use (6 to 12 hours) and every 12 months for light use (2 to 6 hours). More frequent cleaning may be needed depending on the cooking, the system's condition and your insurance and fire risk assessments.

Sources and further reading

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General guidance only. This article is general information for commercial premises. It is not a substitute for advice from a competent engineer who has seen your site and equipment, or for the manufacturer's instructions. Duty holders remain responsible for their own legal compliance.