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How to Deal With CO Detectors and False Alarms

Everyone hates it when a smoke alarm goes off for the wrong reason. We know this as a false alarm. False alarms are a real headache for the resident, but they are even worse for a landlord as they are costly, involving a visit to the property more often or not by an electrician in the case of smoke alarms and a plumber in the case of CO alarms.

With the increasing use of Carbon Monoxide (CO) alarms in rented property as a further life saving device, does the false alarm problem double? And what do you do when a CO alarm goes into what you think is another false alarm?

Well, CO alarms are very different from smoke alarms and false alarms are very unlikely. They do not alarm when the toast is burnt or when you've had an extra hot steamy shower. When a CO alarm indicates the presence of CO it must not be ignored.

Ei Electronics – Europe's largest manufacturer of smoke and CO alarms – has seen a few worrying incidents where complaints were made about CO alarm false alarms, when the alarms where actually working very well indeed. The outcomes could have been very different.

In the first instance, a woman who had purchased and fitted another manufacturer's CO alarm was rightly concerned when it went into alarm. She called out her gas supplier who checked the boiler, found nothing wrong and said the CO alarm must be faulty. The woman rang the manufacturer who said that it may have come from a faulty batch and sent her a replacement alarm. The alarm went off again, she repeated the process with the same result. This, in fact, happened four times. Whilst waiting for another replacement alarm to arrive, the woman decided it was best to be on the safe side and purchased another manufacturer's CO alarm – Ei. The Ei CO alarm also went into alarm at which point she rang Ei who sent her an Ei206DEN CO alarm which has a built in digital read out feature. The alarm showed 80ppm of CO in her kitchen, however, she measured 165ppm in the corridor outside her flat. It transpired that the Carbon Monoxide was coming from the flat below her – and no less deadly for it.

The other incident is actually from a housing association. Ei received two Ei261ENRCs CO alarms which were reported as false alarming. Ei has vigorous testing facilities and put the returned alarms through their paces to find they were performing accurately. Ei immediately advised the housing association that the alarms are working and that therefore CO must be present in the properties from which they were taken. The housing association was taken aback and started an immediate investigation into the source of the leak.

The moral of these two stories – or should we call it a warning – is to approach claims of "false" alarms from CO alarms carefully. Unlike smoke alarms where dust, cooking fumes etc. can cause false alarms the same problem does not exist with CO alarms.

That is because CO alarms work very differently from smoke alarms. When CO is present, it enters the sensor through a gas diffusion hole. A graphite filter prevents any external contaminants from entering. A Platinum sensing electrode then catalyses the oxidation of the CO. Combined with the water present in the electrolyte, this reaction causes the voltage to rise and consequently, a small current flows between the two electrodes. This output is directly proportionate to the amount of CO gas present. The microchip in the unit then activates the LED/horn/display to give a warning applicable to the CO level sensed.

As you can see, it's a complicated process, which is why CO alarms are considerably more expensive than smoke alarms and also why they very rarely go into false alarm. In fact, the main reason for them to false alarm is not from external contamination, but if there is something wrong with the alarm itself. If you get a good quality CO alarm from a reputable manufacturer – avoiding the cheap influx from the Far East which have been blighted with problems and product recalls – then this should never be a problem.

For added reassurance, install a CO alarm that provides you with more information than simply an alarm warning. Some alarms feature high- and low- level LED indicators with a special pre alarm LED indication for detection of CO at 50ppm, while others have a digital displays which show the current level of CO present. When the levels detected reach dangerous levels, a red warning LED combines with an integral built in sounder outputting 85Db(A) at 3 metres to provide a full audio-visual warning. Other indicators confirm mains power supply and fault indication. Some alarms also come with a manual Test/Hush button, gas test facility and a memory feature which enables the user to tell if CO has been detected during a period of absence.

A landlord is, of course, required by law to check all gas appliances by an approved engineer every 12 months. But this is not nearly adequate protection as things can and do go wrong between inspections and, what's more, CO is given off as a by-product of virtually any combustion process; any household appliance that burns coal, oil, bottled gas, paraffin, wood, petrol, diesel or charcoal can be a potential source of CO. Let's not forget, CO is an extremely dangerous – lethal – gas. You can't smell it, see it and you certainly can't hear it. The only way to detect it is by fitting a good quality CO alarm. Because of this it is now a legal requirement for landlords to ensure a CO alarm is fitted and working at the beginning of every tenancy in dwellings that have a fuel-burning appliance.

For landlords, if you have taken the sensible precaution to fit a CO alarm, it is essential that you take note of your tenants when then they tell you the CO alarm has gone into alarm. Never make the presumption that it is a false alarm – always assume the alarm is caused by CO being present and take action. Tell your tenants to open all the windows and get out of the property and then call the gas company. And don't forget, as we have seen from our first incident, if CO can't be detected in that specific property, investigate the possibility of it coming from outside the dwelling.

CO poisoning is extremely dangerous. The first symptoms are often a slight headache, at concentrations around 15% COHb. As poisoning progresses, your headache gets worse and you begin to feel sick, dizzy and drowsy – a bit like flu, which makes it difficult to diagnose. If poisoning continues undetected, the results of even relatively low exposures over time can be permanent lung damage, heart damage, brain damage or death. Most victims die in their sleep from a strong leak – some in just minutes. The family pets tend to die first, then babies, small children or the elderly. Healthy adults tend to take longer to die, but they will be killed just the same.

Fitting a quality CO alarm is the only way to detect CO. Reacting to it when alarming is the only way to protect the residents.


Reviewed: 30/12/2019 (doc:126 V1.1). Our articles are reviewed regularly. However, any changes made to standards or legislation following the review date will not have been considered. Please note that we provide abridged, easy-to-understand guidance. To make detailed decisions about your fire safety provisions, you might require further advice or need to consult the full standards and legislation.


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