Property: A silent killer in our homes

CARBON MONOXIDE (CO), a colourless, odourless, tasteless and non- irritating gas, is the greatest cause of accidental poisoning in the home.

At least 60 people are known to die every year in the UK as a direct result of acute CO poisoning, but because it cannot be detected by the senses, and because the initial symptoms of carbon monoxide poisoning are quite general (headaches, tiredness, dizziness) the true figure may be much higher, perhaps thousands. Carbon monoxide has been investigated in connection with cot death syndrome, for example, and may also trigger heart attacks in people suffering from coronary heart disease.

Carbon monoxide is produced by the incomplete combustion of any fuel: natural gas, coal, oil, wood or petrol. Many fatalities result from faulty gas appliances, but solid fuel fires or stoves can be equally dangerous if chimneys are blocked or ventilation is inadequate. Charcoal barbecues used indoors can be fatal, as can car exhaust fumes in a closed garage. A leaking silencer can also allow carbon monoxide levels to build up inside a car while it is being driven.

Most poisoning, however, takes place within the home. Research has shown that more reported cases occur in houses, including owner-occupied ones, than in flats; and two-thirds of victims are women, with the most common age group being 30 to 45. So the perception of carbon monoxide poisoning as an occasional tragedy affecting students in cheap bedsits may not be quite accurate.

Certainly the CO poisoning cases that hit the headlines are usually of this sort - tenant in poorly-maintained rented accommodation killed by faulty gas heater. A recent death in Ipswich, for example, resulted from a gas fire being vented into a chimney that had previously been capped off with concrete; the landlord and his plumber were found guilty of manslaughter. But fatal poisoning cases, tragic though they are, are only part of the story. It seems that chronic poisoning, from regular exposure to low levels of carbon monoxide, may be a far more serious problem than has been realised. David Jenkins, of the Royal Society for the Prevention of Accidents (RoSPA) said: "Many thousands of people are suffering from low-level carbon monoxide poisoning without realising it - they think they just have a dose of the flu."

In fact a recent study found that family doctors are almost incapable of recognising non-fatal CO poisoning; out of 77 cases, only one was correctly diagnosed. The misdiagnoses included flu, viral infections, chronic fatigue syndrome and mental illness, including depression.

Carbon monoxide poisons humans and other mammals by combining with haemoglobin in the blood to form carboxyhaemoglobin, reducing the ability of the blood to transport oxygen around the body. There is a blood test that can detect this, but it must be carried out within a few hours of the reported poisoning, before the blood returns to normal.

Unfortunately, the same study also found that when victims were offered such a test, it was often taken too late to offer meaningful results, and in other cases test results were misinterpreted. This lack of adequate diagnosis is worrying, since some symptoms are known to persist for two to three years after carbon monoxide poisoning ceases; memory loss, neck and back pain and deep muscle pain are typical long-term effects.

So it seems that the best course of action is to take responsibility yourself for keeping your home free of carbon monoxide. This involves three things: ensuring the correct functioning of all combustion devices such as boilers, gas ovens and hobs, fires and stoves; making sure that your home has adequate ventilation at all times; and fitting carbon monoxide detectors.

All boilers should be serviced on a regular basis. The main faults to look out for are soot build-up around the flue or on the heat exchanger, which may restrict the passage of exhaust gases, and incomplete combustion of the fuel - with a gas appliance this will be indicated by a yellow or orange flame instead of a healthy blue one. Wall-mounted water heaters, such as the ubiquitous Ascot, can be a source of problems. Some models had simple convection flues to the outside; others had no flues at all, and relied on room ventilation to disperse the exhaust gasses. Water heaters of this type, and the older floor-mounted central heating boilers, take their combustion air from within the room, so sealing off draughts - for example, by fitting replacement double-glazed windows - might cut down the air intake and cause incomplete combustion.

Most modern gas boilers are fitted with either balanced flues or fan- assisted flues, both of which take combustion air from outside the building and so are not affected by draught-proofing.

Gas appliances should be checked by a plumber or heating engineer registered with the Council for Registered Gas Installers (Corgi).

Ventilation is a key factor and may account for the apparent growth in carbon monoxide poisoning as homes are now more insulated, draught-proofed and sealed. In the past, low levels of carbon monoxide may have been ventilated away by natural air leakage, but the sealed environment of many homes now means that it can build up to harmful levels. The Building Research Establishment recommends a basic ventilation rate of at least one air change per hour in all habitable rooms, either by natural convection through air vents or by extractor fans, but if a room is heated by a solid-fuel fire there needs to be a much greater amount of air coming in. If you find yourself feeling sleepy in front of the fire, it may be due to lack of oxygen, or carbon monoxide poisoning, or perhaps both.

Carbon monoxide detectors have become notably smaller and cheaper in recent years, and should now be considered an essential second line of defence.

The cheapest type of detector is a small cardboard patch (such as the SleepSafe, pounds 5.49), which changes colour if carbon monoxide is present. It will not give you an audible warning, but is cheap, available from DIY stores and may be useful as a check if you suspect you have a faulty appliance. Battery-operated carbon monoxide detectors that sound an alarm, like smoke detectors, are available for around pounds 30 from plumbers' merchants, British Gas Services and some DIY stores; they have a limited life of up to five years.

Mains-powered detectors, such as the Technotrend CO-350 and the NightHawk, cost around pounds 50. The latter has a constant digital read-out, which provides reassurance that the instrument is still working. Ideally, detectors should be fitted in all rooms where fuel is being burned. RoSPA suggests this is important in rooms with coal fires or wood-burning stoves, and if you are an amateur mechanic you should consider fitting one in the garage.

q The Technotrend CO-350 detector is available by post from Technotrend, 01252 407900. For details of the Nighthawk detector call Kidde Safety on 0161 624 9591. Advice leaflets are available from British Gas, 0800 181565, and RoSPA - send stamped addressed envelope to Safety Policy Division, RoSPA, 353 Bristol Road, Birmingham B5 7ST.

How to prevent CO poisoning

q Get heating systems and gas appliances checked annually.

q Check chimneys, flues and vents for blockages, corrosion and loose connections.

q Use bottled gas or paraffin heaters only in well-ventilated rooms. Do not use them overnight or in bedrooms.

q Do not use barbecues or charcoal grills indoors or in enclosed spaces.

q Do not run a car, motorcycle, lawnmower or other engine inside a closed garage.

q Fit carbon monoxide detectors in all rooms where appliances are used.