What to Do If You Smell Gas in Your Home or Business in 2025

Smelling gas indoors is never something to ignore. It can indicate a leak or faulty appliance, and taking the right steps quickly can prevent serious harm. This article explains how to recognise the smell of gas, what to do if you detect it, and when to call for emergency support. It also covers a few common misconceptions, including whether carbon monoxide detectors can pick up a gas leak. 

What does gas smell like in the UK? 

Natural gas (primarily a mix of 85-05% methane with other gasses) itself is odourless. In the UK, an odorant is added to help detect leaks. This is usually tert-butyl mercaptan or tetrahydrothiophene, which gives off a strong, sulphur-like smell which most people describe as similar to rotten eggs. It is a deliberately unpleasant smell so that even a small leak is easy to notice.

What should you do if you smell gas inside a property? 

If you notice the smell of gas, even faintly, take the following steps immediately: 

• Open windows and doors to ventilate the space 

• Do not use electrical switches or appliances 

• Do not smoke, light matches or use any naked flames 

• Turn off the gas supply at the meter if it is safe to do so 

• Leave the building and call the National Gas Emergency Service on 0800 111 999 

Make the call from outside the building. The line is available 24 hours a day and staffed by trained professionals. 

Will a carbon monoxide detector pick up a gas leak? 

No, this is a dangerous misconception. A carbon monoxide detector will not detect natural gas. It is designed to alert you to carbon monoxide build up, which can happen as a result incomplete combustion from a faulty boiler or gas appliance.  A common cause for a carbon monoxide leak is when the flue of a boiler is obstructed, exhaust gases cannot escape properly, which can lead to incomplete combustion. This allows carbon monoxide to build up and leak back into the property. Other examples include gas fires with soot buildup or cookers used without proper ventilation. None of these things will necessarily be linked to a gas leak, or vice-versa.

Carbon monoxide (chemical symbol "CO") is not flammable like natural gas (which is mostly methane, chemical symbol "CH₄"), is extremely toxic, even in small amounts, and is otherwise entirely undetectable in that it has no smell. 

This is an important distinction, as while both can be attributed to a boiler or gas system fault (hence the confusion this causes.), they pose very different dangers and require different types of detection. A gas leak increases the risk of fire or explosion, while a carbon monoxide leak can lead to poisoning without any visible or noticeable warning signs. 

To detect a gas leak, you need a dedicated gas leak detector. Some modern alarms combine both gas and carbon monoxide detection, but always check the specification before relying on one device as these aren't hugely common.

I have no sense of smell, how can I pick up a gas leak? 

If for medical reasons you have little or no sense of smell, the safest option is to install a natural gas detector. These devices are designed to detect methane in the air and sound an alarm if a leak is present. When purchasing, make sure you are specifically buying an alarm that can detect methane (CH₄); and not just one that detects smoke, heat or carbon monoxide. 

Some detectors are plug-in, while others are battery operated, and they should be placed near gas appliances or the boiler for early warning. It is also a good idea to test them regularly, just like you would with a smoke or carbon monoxide alarm.

Special sprays also exist that can detect gas, but these are used by engineers when trying to find leaks and not to alert people to a leak.

Should you turn off your gas supply if it leaks? 

Yes but only if it is safe. The emergency control valve is usually located near the gas meter. If you know where it is and can reach it easily, turn it off and leave the property. If you are not sure where it is, or if there is a strong smell of gas nearby, evacuate immediately and wait for the emergency response team. 

If you smell gas, act fast. Switch off the supply if it it is safe, ventilate the area, and call the National Gas Emergency Service on 0800 111 999. For follow-up checks and repairs, contact Onyx Solutions. We’re Gas Safe registered and available for both domestic and commercial gas safety callouts.