Do commercial kitchens need a gas interlock?

What a gas interlock does

A gas interlock links the kitchen's gas supply to its mechanical ventilation. Sensors prove that the extraction (and, where fitted, the make-up air) system is running. If the fans stop or airflow drops, the interlock closes an automatic gas valve or cuts power to fully automatic appliances, so cooking cannot continue without adequate ventilation.

The aim is to protect staff from a build-up of carbon monoxide, carbon dioxide and other combustion products, particularly from flueless (Type A) cooking appliances such as ranges, griddles and fryers, which release combustion products into the kitchen.

The rules and standards

• Gas Safety (Installation and Use) Regulations 1998, regulation 27(4): where an appliance relies on a powered draught, it must not operate if the draught fails. In a mechanically ventilated kitchen that is met with an interlock.
• BS 6173 (installation and maintenance of gas-fired catering appliances for non-domestic use) requires gas appliances in mechanically ventilated kitchens to be interlocked with the ventilation, and states that overrides to interlocks are not permitted.
• IGEM/UP/19 (Edition 2, 2022) sets out the design and application of interlock devices and air quality testing in commercial catering establishments. It is not retrospective, but it recommends bringing existing installations up to standard when appropriate, and treats major refurbishment as new work.

These standards apply to commercial catering establishments, which prepare food for the public outside domestic premises: restaurants, takeaways, pubs, hotels, cafés and staff canteens. They are not intended for dwellings or primarily domestic premises such as B&B kitchens, and mobile or temporary event catering is covered by separate guidance.

How interlocks prove the ventilation is working

IGEM/UP/19 describes interlocks that monitor at least one of:

• Air flow, using an air flow or pressure switch in the duct.
• Air pressure, using a differential pressure switch across the fan.
• Fan current or power, which confirms the fan motor is drawing power under load.

Where only flueless appliances are installed, air quality (CO2) monitoring may be an option in some situations, giving a warning and then shutting off gas if CO2 levels rise too high.

The interlock can operate a single automatic valve on the kitchen supply, individual valves on each appliance, or power isolation to all fully automatic appliances. Systems commonly include a proving sequence so gas cannot be restored until each appliance's own flame protection is confirmed closed.

Existing kitchens without an interlock

A Gas Safe engineer who finds a mechanically ventilated kitchen without a working interlock will assess the risk. Depending on the appliances and ventilation, they may carry out air quality testing, advise that an interlock is fitted, or treat the situation as unsafe under the gas industry's unsafe situations procedure. Refurbishments, new appliances or a change of canopy are good times to bring the system up to standard.

Keeping it compliant

• Have the interlock tested as part of regular gas safety inspections.
• Never bridge, bypass or wedge an interlock; overrides are not permitted.
• Review ventilation and interlocks when cooking equipment or the kitchen layout changes.
• Keep the canopy, filters and ductwork clean and maintained so airflow stays within design.

Interlock work often goes alongside gas tightness testing, because adding solenoid valves breaks into the gas supply.

This guide is general information, not a substitute for an on-site assessment by a Gas Safe registered engineer. If you smell gas, call 0800 111 999.