Many gas users are not fully aware of the potential dangers of the appliances around them.

In some cases they do not find out until it is too late.

• An average of about 30 people in the UK are killed each year by carbon monoxide from gas appliances.

• However, the death toll has been falling in recent years, from 44 in 1992-93 to an estimated 21 in 1996-97, according to Health and Safety Executive figures.

• The natural gas used to fuel water heaters, fires and boilers is not poisonous, but poorly installed or inadequately maintained appliances can give off potentially lethal CO.

• CO can also build up in a room if chimneys, flues and vents are blocked, or if there is not enough fresh air in the room to keep the gas burning properly.

• The gas cannot be seen, tasted or smelt, but in sufficient concentrations it can cause death within a matter of hours.

• Early symptoms of poisoning include drowsiness, sickness, headaches and chest and stomach pains. Many victims do not suspect CO is to blame and fail to get their appliances checked after minor poisonings, with sometimes fatal consequences.

• Pregnant women were this year warned of the dangers of carbon monoxide after a woman whose gas fire was wrongly fitted lost her child.

• Tell-tale signs of faulty appliances include excessive soot production, flames burning yellow or orange rather than the normal blue and pilot lights repeatedly blowing out.

• To prevent CO poisoning, the Gas Safety (Installation and Use) Regulations ban fitting of appliances by anyone not registered with the Council for Registered Gas Installers (CORGI). DIY installation is illegal.

• The regulations also require landlords to have appliances checked at least every 12 months by a CORGI-registered fitter and to provide records of checks to tenants.

• Breaches of the regulations attract substantial fines. Other negligent landlords have been charged with manslaughter.

• Anyone concerned about whether their gas fitter is registered can ring CORGI on 01256 372300.