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
Despite the use of combustible cladding in tower blocks, ministers were advised that regulations were tough enough, ITV News has learnt.
A milder night across the north than last night, with rain sneaking into southern Scotland from Northern Ireland.
The singer, 31, said on Twitter that she and her partner Jonathan Powell were grieving their loss.