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How to detect carbon monoxide – the ‘silent killer’

10 January 2018 ( 27 January 2020 )

Research reveals that 36% of British households don't have carbon monoxide detectors installed, despite these life-saving devices being simple and inexpensive to install.

Carbon monoxide alarm
Fit a carbon monoxide alarm to detect the invisible, odourless and deadly gas

36% households in the UK do not have a carbon monoxide alarm, according to a poll conducted by reichelt elektronik, an online electrical retailer, and of those 9% did not know what a carbon monoxide detector is and why they would need one, while 52% of the people without one said they know what they are but see no need for one. And yet, according to stats from the Office for National Statistics, around 50 people a year die from carbon monoxide poisoning, most of them in their own homes.

The problem is that carbon monoxide is incredibly hard to detect. It’s known as the ‘silent killer’ with good reason, but that description only covers one of its features, as it’s also odourless, colourless and tasteless. All fossil-fuel appliances emit CO, so if you have a gas boiler, an open fire, gas stove or have a petrol or diesel car, you’re potentially at risk and should have a quality CO alarm.

It’s likely that the enigmatic nature of this gas accounts for the relatively low level of public knowledge of the risk. Unlike fire, CO won’t destroy your home and your possessions - events that make a highly visual impact.

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Symptoms of carbon monoxide poisoning

Accurate diagnosis of CO is a nightmare, as the symptoms are so similar to other far more common ailments. Victims may feel shivery, have headaches, and be generally run down. Although these symptoms are similar to flu, CO poisoning will not result in a rise in body temperature.

Nausea, vomiting and dizziness are other symptoms, which can be confused with gastroenteritis or food poisoning. Most of us will feel some of these symptoms at some time or other (and probably ignore them), so it’s understandable why CO symptoms may be ignored or misdiagnosed: not least as most relatively-mild sufferers will start to feel better once they are out and about. A breath of fresh air really is the antidote in this case.

Anyone who is feeling under the weather to such an extent that they visit a doctor’s surgery could be told to go home and wrap-up warm. If you think about it, this is the worst thing to do; by shutting all the windows and pumping up the heating the affects of CO poisoning will be accelerated.

And, if the worst happens, some health professionals may reasonably conclude that death was as a result of natural causes or existing medical conditions. This is because of the way CO affects the body. It binds with haemogloblin, an element of blood that would otherwise carry oxygen around us. In short, it deprives the brain, heart and other vital organs of the life-source we need.

However, with swift treatment the effects of mild CO poisoning can be reversed. Victims are given 100% oxygen via a mask until the level of carboxyhaemoglobin in the blood falls to less than 10%. The level of CO in the body is established via a blood test.

Q I'd like to know if you have a carbon monoxide monitor in your home?

Dr Mark Porter responds

I have two. One near our boiler and one in the room where our granddaughter sleeps when she comes to stay. Accidental carbon monoxide (CO) poisoning accounts for around 250 deaths and life-threatening injuries every year in England and Wales, but these are the tip of a much larger iceberg. Lower exposure chronic CO poisoning may not be as dramatic, but it is far more common, and much easier to miss because it mimics so many other conditions – from food poisoning and flu to depression and chronic fatigue.

Nearly one in ten houses and flats surveyed by the Health and Safety Executive in 2007 had higher than acceptable levels of CO. Traditionally associated with poor-quality housing, recent changes in legislation have meant that the appliances in rented accommodation are now likely be checked more often than those in more affluent homes. 

Carbon monoxide is clear and odourless, and just because you can’t see or smell anything doesn’t mean there isn’t an issue. Unless you have your appliances regularly checked, and have a CO monitor, then you can’t be sure your boiler, log burner, fire or gas hob isn’t poisoning you. I recommend them to all my patients —along with smoke alarms. Combination monitors detect both.

Extract taken from Saga Magazine, February 2020. For more invaluable advice from Dr Mark, subscribe to the magazine today!

How to detect monoxide gas

CO is almost undetectable unless you have a decent detector in place. But it is possible to spy some tell-tale signs that dangerous levels of carbon monoxide may be in the atmosphere. Alarm bells should ring if you spy soot or yellowy-brown stains on or around fuel appliances.

Excessive condensation in rooms where appliances are installed is another indicator that all is not right. If you have a gas cooker, small yellow or orange-coloured flames instead of vibrant blue ones may also hint at a problem. A pilot light that frequently blows out is a further notice of possible dangerous levels of CO.

If you spot any of these signs, take immediate action to limit the potential risk of CO poisoning by opening windows and doors and by calling the National Gas Emergency Service (NGES) on 0800 111 999.

The NGES advises consumers to ventilate the area by opening doors and windows and call the emergency line. You should never leave cars and motorbikes running in closed environments, such as garages, as these emit large quantities of CO.

Read surveyor John Conlin on how to test a smoke alarm correctly

CO detectors

There is a vast array of carbon monoxide detectors on the market, although these can be categorised as either spot detectors or audible detectors.

Spot indicators are fixed to or near to appliances and change colour if significant levels of CO are present. They are not recommended as they do not produce an audible alarm, so unless you regularly check them (and even if you do, they won’t help when you are asleep) they are of limited value.

Audible alarms look similar to typical smoke detectors. They are battery-operated, either being fitted with a tamper-proof battery, or utilising AA batteries. These devices are available from DIY sheds, supermarkets and online. A cross section of European Standard EN 50291 audible alarms is presented in the following table. All emit an audible alarm of 75DB to 85DB.

Even with an audible alarm fitted, it’s advisable to have gas boilers and working chimneys, flues and vents serviced on a regular basis as there are believed to be around 50 deaths from carbon monoxide poisoning each year in the UK, according to data from the Office for National Statistics.

Where to position carbon monoxide alarms

CO alarms will come with guidelines from the manufacturer, but generally you are advised to position CO alarms about 1-3 meters away from the source of carbon monoxide. You should put one on every storey of your house as carbon monoxide can build up on a single level without spreading to the rest of the house.

Unlike smoke alarms, CO alarms should ideally not be positioned on the ceiling. This is because heated air rising to the top of the room can prevent carbon monoxide from rising. Instead, place your CO alarm high on the wall or on a shelf about 15cm below the ceiling.

You should avoid your alarm being too close to sources of heat or humidity such as showers, radiators and fireplaces, and away from windows where the fresh air might prevent the CO being picked up.

Landlords and their legal obligations

As of October 2015 if you rent out your property you are legally required to install carbon monoxide detectors in all rooms with a solid fuel appliances such as log burners and coal fires. Landlords are required to make sure the alarm is working on the day the tenancy begins. 

Although there are as yet no legal requirements to install a carbon monoxide alarm without a solid fuel appliance present in the property it is still a good idea to provide one in rooms with boilers and gas ovens. 

Find out more about the CO and smoke alarm requirements for landlords from the Residential Landlords Association.

Carbon monoxide alarms

The following is s a cross-section of the type of alarms available on the UK market that comply with European Standard EN 50291.

Model Battery type
Aico Ei208 Sealed tamper-proof
5 years
Read reports on your tablet or phone with the AudioLINK app.
Aico Ei261ENRC Mains 5 years Read reports on your tablet or phone with the AudioLINK app. £57.99
FireAngel CO-9B AA 7 years
FireAngel CO-9D Sealed tamper-proof
7 years Digital room thermometer
FireAngel CO-9X Sealed tamper-proof 7 years Automatic self-check facility £23.99
Honeywell H450EN Sealed tamper-proof
6 years 7 year life £20.00
Kidde 7CO AA 10 years For boats, homes and caravans £25.26
Kidde 10SCO 9V 10 years Combined smoke/CO detector. £18.98

*Prices subject to change.

Further advice

The Health and Safety Executive has advice on carbon monoxide.
The NHS has a raft of information and a video explaining the symptoms and dangers of CO.
If you believe that an appliance is leaking CO contact the National Gas Emergency Service on 0800 111 999.
Carbon Monoxide – Be Alarmed is a national campaign website focusing on all matters CO.

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The opinions expressed are those of the author and are not held by Saga unless specifically stated. The material is for general information only and does not constitute investment, tax, legal, medical or other form of advice. You should not rely on this information to make (or refrain from making) any decisions. Always obtain independent, professional advice for your own particular situation.