A study by Liverpool John Moores University has found that some homes in Liverpool have dangerous levels of carbon monoxide, and that residents are unaware of the problem.
As part of the research, Merseyside fire-fighters visited over 22,000 randomly selected homes and tested them for carbon monoxide. 49 of them had dangerous levels of the gas.
Data-loggers were then fitted in another 109 randomly-selected homes, and researchers found that just under half had levels of the gas that were high enough to potentially cause long-term health problems, but not always high enough to trigger a carbon monoxide alarm. Despite this, researchers say alarms are still important as they tell people if they are in immediate danger from the gas.
The most common sources of carbon monoxide are heating and cooking appliances that are not working properly. It is hard to detect as it has no colour or smell. Symptoms of carbon monoxide poisoning include confusion, headaches and vertigo.