Carbon monoxide (CO) is a colourless, odourless, tasteless, poisonous gas produced by incomplete burning of carbon-based fuels, including gas, oil, wood and coal.
Carbon-based fuels are safe to use. It is only when the fuel does not burn properly that excess CO is produced, which is poisonous.
When CO enters the body, it prevents the blood from bringing oxygen to cells, tissues, and organs.
You can't see it, taste it or smell it but CO can kill quickly without warning.
Visit the Health and Safety Executive website for more information.
More top news
McDonald's has now extended its breakfast menus to all day - but only in the US.
Theresa May and Boris Johnson gave markedly different speeches at the Conservative party conference, Chris Ship reports.
ITV News has learned that VW is testing a new system to alert drivers whether they are affected by the emissions scandal.