Two fifths of British people do not have an alarm to detect odourless but deadly carbon monoxide gas, a survey has revealed.
Some 40% of British adults said they had not installed an audible alarm meaning more than 20 million people could be at risk from the silent killer, according to the Katie Haines Memorial Trust, which commissioned the YouGov poll.
The trust was set up to raise awareness of the dangers of the gas following the death of Katie Haines, 31, who died from carbon monoxide poisoning in February 2010 just two months after marrying husband Richard Haines.
The survey also found that two fifths of British people (40%) did not know the only safe colour for a gas appliance flame is blue.
Of the 2133 adults questioned, 11% thought the pilot light could be yellow and still be safe, 14% thought it could orange and 4% thought it could be green, while 15% said they did not know what colour it should be.
But if flames are yellow or have a slight yellow or orange tint they could be emitting carbon monoxide, the Katie Haines Memorial Trust warned.
More than 200 people are taken to hospital every year with suspected carbon monoxide poisoning, and around 50 people are killed after being exposed to the gas, according to NHS figures.
Accidental exposure is most commonly caused by incorrectly installed, poorly maintained or poorly ventilated household appliances such as cookers, heaters and central heating boilers.
Gordon Samuel, Mrs Haines's father, will launch the sixth annual gas safety week, which takes place from September 19 to September 25, in the House of Commons on Tuesday.
He said: "My wife Avril and I lost our precious daughter Katie to carbon monoxide. Weeks after her wedding, she was poisoned by carbon monoxide leaking from a defective boiler in her home.
"We formed the Katie Haines Memorial Trust to try and raise awareness of this terrible 'silent killer' and make sure that nobody else loses loved ones in such a senseless, avoidable way."
The trust has released a video - #causeforalarm - to urge people to get appliances checked and install an audible alarm to detect carbon monoxide and prevent further tragedies.