Is a CO2 Alarm a Legal Requirement in a Pub Cellar?

Nobody has written a Cellar Gas Safety Act, and nobody is going to. The dispense gas under a pub doesn't get its own regulation; instead it's covered by a stack of general duties, none of which were drafted with a beer cellar in mind. Operators often take that lack of a named law as a green light, treating the absence as "nothing required." That's not how the duties work: they still apply, just scattered across other rules.

The gas in a pub, bar or club cellar is carbon dioxide, or the CO2-and-nitrogen blend the trade calls mixed gas. It runs the beer and soft-drink lines, and it has nothing to do with the mains gas a Gas Safe engineer services or the carbon monoxide that comes off a charcoal grill. CO2 is about half as heavy again as air, so a leak sinks instead of clearing. It pools on the cellar floor and pushes out the oxygen, and a person working down there can suffocate.

The duties that land on a below-ground cellar

The hard core is the Control of Substances Hazardous to Health Regulations 2002. COSHH treats CO2 as a substance hazardous to health and makes the EH40 workplace exposure limits legally binding: 0.5% (5,000 ppm) averaged over eight hours, and 1.5% (15,000 ppm) over any fifteen minutes. Exceeding either is a breach of the law, and because CO2 has no smell and gives no warning, the duty is to assess the risk and monitor the air.

A poorly ventilated below-ground cellar usually meets the test in the Confined Spaces Regulations 1997 too, an enclosed space where oxygen could be displaced. Those regulations require a safe system of work and a worked-out rescue plan, not a reliance on calling 999 after someone has collapsed. They also mean nobody goes down to investigate a sounding alarm, the mistake that turns one casualty into two.

Two more rules sit at the edges. DSEAR 2002 covers the cylinder as a pressurised dangerous substance, for the risk that it fails violently rather than the suffocation risk, while a bulk tank and its pipework fall under the Pressure Systems Safety Regulations 2000. The Fire Safety Order's dangerous-substances duty, article 12, is about fire and explosion, so a non-flammable gas like CO2 sits outside it and stays a DSEAR matter.

So is a CO2 alarm a legal requirement?

No law names a CO2 alarm as a requirement. In practice, though, a typical enclosed cellar usually needs one anyway. A COSHH assessment and a confined-space assessment will normally conclude that fixed monitoring is needed, because the exposure limits can be crossed with no warning. Making sure those assessments happen is the operator's job. A competent person carries them out and decides what monitoring is needed.

BCGA Guidance Note 30, the beverage dispense code, reaches the same conclusion. Where a gas store is enclosed, such as a cellar, it states that "atmospheric monitoring with an alarm system shall be provided", and prefers fixed monitoring over a handheld meter. If the dispense gas is a nitrogen blend, one detector won't do. You need a CO2 detector and a separate oxygen-depletion monitor, because a nitrogen leak can pull the oxygen down without moving the CO2 reading.

LPG in the cellar: a flat prohibition

LPG is the exception. Regulation 6(8) of the Gas Safety (Installation and Use) Regulations 1998 prohibits installing a gas storage vessel, or an LPG appliance with automatic ignition or a pilot light, in a cellar or basement, whatever a risk assessment says. A connected cylinder counts as a gas storage vessel, so piping one to a cooking range or heater in the cellar is the offence by itself, whether or not the gas ever leaks. Like CO2, LPG is heavier than air and settles at the lowest point, which is why holiday parks keep their cylinder stores outdoors. Because it is flammable, its presence can also bring DSEAR hazardous-area zoning into play.

In Maidstone, the restaurant Mix Grill 91 ran LPG cylinders in its cellar to feed the cooking range. Maidstone Borough Council served a prohibition notice, the restaurant traded in breach of it, and on 4 March 2020 the owner received a 120-day suspended sentence and £3,694 in costs.

The records that prove it

Because the requirement comes out of risk assessments rather than a single rule, no one certificate proves it. An Environmental Health officer or an insurer will want the whole file: the COSHH assessment, the confined-space assessment and its safe system of work, the DSEAR record, the monitor's calibration and test logs, the staff training, and a Pressure Systems Safety examination scheme where there is a bulk tank. A loss adjuster will want the same after a claim.

No one has died from a dispense-CO2 leak in a hospitality cellar on the UK public record between 2005 and 2026, and no coroner has written a Prevention of Future Deaths report about one. People do still end up in hospital: in November 2015 a CO2 alarm went off in the cellar of the Banco Lounge bar in Bristol, the fire service confirmed carbon dioxide, and three people were taken to hospital. Part of the reason the record looks empty is that these cases sit with councils rather than the HSE, and council prosecutions show up in no national index. Day to day, the likelier cost is a council officer or an insurer asking for records the operator doesn't have.

The assessment and the monitoring are a competent person's work; no record-keeping tool changes that. Duty Room's part is the file itself, kept in one place per site under gas safety, ready on the day someone asks.