Hazardous Substances in Hospitality

Cellar Gas and CO2: A Life-Threatening COSHH Hazard

Why Carbon Dioxide in Cellars Can Kill and How to Control It

Quick answer

Carbon dioxide in a pub or bar cellar is the most serious COSHH hazard most hospitality businesses will ever handle, because it can kill quickly and without warning. Cellars use carbon dioxide and mixed carbon dioxide and nitrogen gas to dispense beer and to add fizz, supplied in pressurised cylinders or bulk tanks. Carbon dioxide is heavier than air, colourless, and odourless, so a leak in a cellar, which is often a confined, poorly ventilated basement, can build up to dangerous levels at floor level where someone is working without any sign that anything is wrong. There have been fatalities in licensed premises from exactly this. This article covers the hazards of cellar gas, how it is used, and the controls, monitoring, and procedures that keep cellar staff safe.

Carbon dioxide in a cellar can kill quickly: it is heavier than air, colourless, and odourless, so leaks accumulate at floor level unseen.
Cellars are often confined, poorly ventilated basements where escaped gas does not disperse.
A fixed carbon dioxide detection and alarm system is the key control wherever cylinders or tanks are kept.

Assess cellar gas as part of your COSHH records Read a gas safety data sheet

Key takeaways

Carbon dioxide in a cellar can kill quickly: it is heavier than air, colourless, and odourless, so leaks accumulate at floor level unseen.

Cellars are often confined, poorly ventilated basements where escaped gas does not disperse.

A fixed carbon dioxide detection and alarm system is the key control wherever cylinders or tanks are kept.

The HSE workplace exposure limits for carbon dioxide in EH40 are the benchmark a cellar should stay well below.

Never enter a cellar to rescue someone without knowing the atmosphere is safe, because the air itself is the hazard.

Why CO2 in a Cellar Is So Dangerous

Carbon dioxide is used to push beer from keg to tap and to carbonate drinks, stored in pressurised cylinders or a bulk tank, sometimes as a mixed gas with nitrogen. The danger comes from three properties combined. It is heavier than air, so a leak sinks and accumulates at the lowest point, which is the cellar floor where people stand and work. It is colourless and odourless, so there is no smell or visible cloud to warn anyone. And a cellar is frequently a confined basement with limited ventilation, so escaped gas does not disperse. As the carbon dioxide concentration rises it displaces oxygen and acts directly on the body: raised levels cause headaches, dizziness, and rapid breathing, and higher levels cause unconsciousness and death within minutes. The HSE has workplace exposure limits for carbon dioxide in EH40, and the EH40 long-term and short-term limits are the benchmark a cellar should stay well below. Crucially, someone overcome by carbon dioxide often cannot save themselves, and a colleague who rushes in to help can become a second casualty.

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How Leaks and Build-Up Happen

Gas escapes in ordinary ways. A cylinder valve or regulator leaks, a connection is not tight, a line fails, or a cylinder is changed badly. Bulk carbon dioxide tanks can vent. Because the gas is silent and invisible, a slow leak overnight can fill a closed cellar so that the first person down in the morning walks into a dangerous atmosphere. Confined, badly ventilated cellars make this far worse, and many cellars in older pubs were never designed with gas safety in mind. Routine tasks raise the risk: changing kegs and gas cylinders, cleaning beer lines, and working alone in the cellar mean staff spend time at floor level where carbon dioxide collects. The classic fatal sequence is one person overcome in the cellar and a second going down to help without realising the air itself is the hazard. This is why cellar gas needs engineered controls and clear procedures rather than relying on people noticing a problem.

Controls, Monitoring, and Emergency Procedures

Cellar gas should have its own COSHH assessment and strong, mostly engineered controls. The most important is a fixed carbon dioxide gas detection and alarm system in any cellar where carbon dioxide cylinders or tanks are kept, set to warn before levels become dangerous, with an alarm that sounds in the cellar and ideally at the bar. Good ventilation, natural or mechanical, helps prevent build-up. Secure cylinders upright so they cannot fall and damage a valve, check connections and regulators regularly, and maintain the gas system. Set procedures for the high-risk tasks: train staff to change cylinders and clean lines safely, and put rules around lone working so nobody is in the cellar alone with gas without a way to raise the alarm. The single most important emergency rule is that if the alarm sounds or someone is found collapsed in the cellar, nobody enters without knowing the atmosphere is safe, because the air is the killer and a rescuer can become the next victim. Call the emergency services and ventilate from outside.

What to do next

Fit a fixed CO2 alarm in the cellar

Install a carbon dioxide detection and alarm system in any cellar holding cylinders or a bulk tank, set to warn before levels become dangerous and audible at the bar.

Secure cylinders and maintain the gas system

Keep cylinders upright and restrained so valves cannot be damaged, and check connections, regulators, and lines regularly for leaks.

Set rules for lone working and emergencies

Limit working alone in the cellar with gas, train staff on safe cylinder changes, and make the no-entry rescue rule clear: never enter until the air is confirmed safe.

Common mistakes to avoid

Mistake

Relying on smell or sight to detect a CO2 leak

Instead

Carbon dioxide is colourless and odourless, so a leak gives no warning. A fixed gas alarm is the only reliable way to know the cellar atmosphere is safe.

Mistake

Rushing into the cellar to rescue a collapsed colleague

Instead

The air is the hazard, so a rescuer can be overcome too. Do not enter until the atmosphere is confirmed safe; raise the alarm, call emergency services, and ventilate from outside.

Frequently asked questions

Why is carbon dioxide in a cellar so dangerous?

It is heavier than air, colourless, and odourless, so a leak sinks and builds up at floor level with no warning. In a confined cellar it displaces oxygen and can cause unconsciousness and death within minutes.

Do I need a CO2 alarm in my pub cellar?

A fixed carbon dioxide detection and alarm system is strongly recommended, and effectively expected, wherever carbon dioxide cylinders or a bulk tank are kept in a cellar. It is the key control because the gas gives no sensory warning.

What are the exposure limits for carbon dioxide?

The HSE publishes workplace exposure limits for carbon dioxide in EH40, with long-term and short-term limits. A cellar should be kept well below these, which is why ventilation and a gas alarm matter.

What should staff do if the cellar gas alarm sounds?

Do not enter the cellar. Keep everyone out, ventilate from outside if it is safe, and if someone is collapsed inside, call the emergency services and do not go in to rescue them until the atmosphere is confirmed safe.

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