You cannot smell it, taste it or see it, but carbon monoxide (CO) can kill in an instant, or more slowly.
Symptoms are often like a flu or cold, which makes it difficult to diagnose.
It is produced by faulty or badly ventilated boilers, cookers, or open fires. It can build up when flues, chimneys or vents are blocked. Lit barbecues can emit carbon monoxide, as can apparently extinguished embers.
Millions are at risk from this silent killer and nearly one person a week dies, with about 4,000 people having to be hospitalised with non-fatal health problems, ranging from headaches and drowsiness to lasting brain and nervous system damage.
Young children and elderly people are particularly at risk because their bodies are less able to withstand the effects. Pregnant women are putting their unborn child at risk.
The only way for people to protect themselves is by installing an audible alarm. And it is wise to have your boiler regularly serviced by a registered and qualified engineer. But nearly half of us do not have an audible alarm and have not had our boiler serviced in the last year.
Carbon monoxide alarms are available at supermarkets, DIY stores high street shops, or from energy suppliers.
The CO Be Alarmed campaign has provided me with a few free alarms, which are available while stocks last. Phone my office on 0191 234 2493 to check if any are left.