top of page

Carbon monoxide poisoning

What is carbon monoxide (CO)?

Carbon monoxide (CO) is a highly poisonous gas produced by the incomplete burning of any carbon fuel such as natural gas or liquefied petroleum gas (LPG). This can happen when a gas appliance has been incorrectly fitted, badly repaired or poorly maintained.

CO can also build up if flues, chimneys or vents are blocked. Solid fuels, such as coal, wood, petrol, as well as oil, can also produce carbon monoxide when they burn.

CO can be deadly and is especially dangerous because you can’t see, taste or smell it, and some symptoms mimic the effects of viruses and even a bad hangover. It’s important to know the physical symptoms of CO poisoning to ensure you seek help quickly.

Symptoms of carbon monoxide poisoning

CO poisoning symptoms are similar to those of flu, food poisoning, viral infections, fatigue, or a hangover which makes it easy to mistake this very dangerous poisoning for something else.

The six main symptoms of CO poisoning are:

  1. Headaches

  2. Dizziness

  3. Nausea

  4. Breathlessness

  5. Collapse

  6. Loss of consciousness


Being aware of these symptoms could save your life.

There are also other signs that could indicate CO poisoning, such as:

  • Symptoms occur when you are at home but seem to disappear when you leave.

  • Others in your household (including pets) are experiencing similar symptoms at a similar time.

It’s important to know the signs of a carbon monoxide leak in your home, because knowing the signs can ensure you aren’t exposed to dangerous levels of CO for an extended period of time.

What to do if you suspect CO poisoning?

  • Don’t delay - get fresh air immediately.

  • Open doors and windows, turn off gas appliances and leave the house.

  • See your doctor immediately or go to hospital. They can do a blood or breath test to check and can advise if you need treatment for CO poisoning.

  • If you think there is an immediate danger, call the Gas Emergency Helpline on 0800 111 999 


You can also visit the NHS website for detailed information on the symptoms of CO poisoning, what action to take and the treatment that’s usually provided.

How does carbon monoxide poisoning occur?

Carbon monoxide poisoning can occur when it builds up in your bloodstream replacing oxygen. When this happens, the blood cannot carry oxygen around the body. This lack of oxygen can result in the body’s cells failing and dying.

Even small amounts of the gas can cause poisoning, and long-term exposure can result in paralysis, brain damage or even death.

What are the signs of a carbon monoxide leak?

Any of the following could be a sign of CO in your home:

  • Floppy yellow or orange flame on your gas hob or oven, rather than a crisp blue flame

  • Dark, sooty staining on or around gas appliances

  • Pilot lights that frequently blow out

  • Increased condensation inside windows


If you believe you have any of these signs, get into fresh air and contact your emergency services provider. If carbon monoxide is not found in the blood stream a competent Gas Safe registered engineer can visit the site to complete a safety check. If carbon monoxide is confirmed in the blood stream, no-one should be allowed on site until the HSE allow it.

To find engineers who are qualified to investigate the presence of CO, go to the Check The Register page on this site, and follow these steps:

  • Enter your postcode

  • Under the ‘Select appliance type’ tab choose ‘Fumes Investigation’

  • Click ‘Find’ to see the updated results.


Remember that not getting your gas appliances regularly checked, or using an engineer that isn’t Gas Safe registered, can put you and your family at risk.

How can I prevent CO poisoning in my home?

The most important thing you can do to minimise the risk of CO poisoning is to ensure that your gas appliances are safety checked annually by a Gas Safe registered engineer.

Installing an accredited carbon monoxide detector, or audible CO alarm, in your home (or business) is a good second line of defence, as they emit a sound when CO is detected. However, because a CO detector’s alarm only activates once there is CO present, you should never rely on them as your sole form of prevention.

What are carbon monoxide detectors?

Carbon monoxide detectors are an early alert for possible carbon monoxide poisoning. They can be installed in and around your home, as described in the manufacturer guidelines, and work much like your fire or smoke alarm by sounding an alarm when they detect carbon monoxide. There are a variety of models available on the market so be sure to find one that will be suitable.

Modern CO detectors look like smoke alarms (standard smoke alarms do not detect CO) and you can purchase one at most major retail outlets, including DIY stores and supermarkets. It’s advisable to fit a CO detector in every room with a gas appliance, following the manufacturer’s fitting instructions carefully. Typically, CO detectors have a lifetime of between 5-10 years. Just like your smoke alarm, remember to test your CO detector regularly.

To ensure their effectiveness, make sure any CO detector you buy is kitemarked to standards BS EN 50291-1:2010 (for domestic premises) and/or BS EN 50291-2:2010 (for caravans and boats). We don’t recommend the use of ‘black spot detector’ warning strips because their warning is too easily missed and they don’t emit a sound, so they won’t alert you if you have a CO leak whilst you’re asleep. If you’re unsure which carbon monoxide detector to get, you can ask a Gas Safe registered engineer for advice.

Been affected?

If you have been affected by CO and would like to share your story, please get in touch with us by email.

The Gas Safe Charity have created a short film explaining the sources, signs and symptoms of carbon monoxide poisoning using British Sign Language. You can view the short film at the YouTube URL below:

Carbon monoxide and gas boilers

To find out more information about CO poisoning and the risk an unsafe gas boiler may pose visit our Boiler Guide.

bottom of page