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March 9, 2019


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Carbon monoxide detectors

The strengths and weaknesses of combined carbon monoxide smoke detectors

The installation of a carbon monoxide alarm and a smoke alarm should be a key component of fire safety and the protection of occupants in all buildings or dwellings. Here, we run through how carbon monoxide and smoke detectors work, and the potential benefits of using combined alarms for detection of carbon monoxide gas and smoke particles in one device.

How do carbon monoxide detectors work?

Carbon monoxide (CO) is produced when carbon fuels don’t burn fully and can be fatal or cause permanent health damage. According to the NHS, there are around 60 deaths a year associated with carbon monoxide poisoning in England and Wales alone.

Incorrectly installed, poorly maintained or poorly ventilated household appliances are some of the most common causes of CO exposure. Fuel burning appliances, in particular, need to be maintained by a professional (a gas appliance, such as a gas boiler should be regularly serviced by a Gas Safe Registered engineer in the UK, for instance), to guard against the potential risks.

Because the gas has no smell or taste, it can be very difficult to detect without a functioning alarm system. It is therefore advised to have a carbon monoxide detector situated near any appliances that burn fuel which detect when carbon monoxide is in the air. In the UK, it should comply with British Standard EN 50291. Audible alarms are advised, with a high risk of carbon monoxide poisoning from CO gas when asleep, due to the lack of smell.

Types of carbon monoxide detectors

A simple definition for a carbon monoxide fire detector is: “A detector which senses ambient levels of CO to warn of the presence of fire“. At the risk of labouring the point, they are fire detectors not CO alarms, nor are they smoke detectors. They respond purely to carbon monoxide gas, and not to smoke.

Patch or ‘blob’ detectors are generally pieces of plastic placed in a room that will change colour when high levels of carbon monoxide touch the detector. This oxidises the strip, changing it to carbon dioxide, therefore notifying the user of a risk. Advantages of these types are that they are relatively cheap, costing as little as a few pounds or dollars. However, they do require users to keep a regular eye on them as they don’t sound any audible alarm, by which time it may be too late. The strips or blobs often need replacing every few months, too.

Electronic CO detectors are the most common type used. While costing a little more, they will emit an audible sound if CO is detected, therefore alerting anyone in the vicinity there is a problem immediately.

Some electronic detectors are sealed, meaning users can’t tamper with devices. Batteries can last up to 10 years, but the devices do need to be replaced eventually – an alarm will usually notify the user if the batteries have run out. Sealed detectors are often used in rented or social housing, so that tenants can’t remove them or take the batteries out, potentially contravening legislative requirements by building owners or managers.

Pros and cons of combined carbon monoxide smoke detectors

There are a variety of types of carbon monoxide detectors. These include:

  • Sealed battery carbon monoxide detectors
  • Replaceable battery carbon monoxide detectors
  • Smart carbon monoxide detectors
  • Patch carbon monoxide detectors

The advantages of a CO detector are relatively obvious. They detect when the carbon monoxide level of gas that is in the air, therefore alerting individuals there is a problem and to leave or ventilate the room to ensure they do not fall victim to CO poisoning.

Smoke detectors, on the other hand, detect levels of smoke in a particular area. They do this either via ionisation or photoelectric devices. Ionisation smoke alarms have a small amount of radioactive material between two electrically charged plates which ionises the air – smoke entering the chamber will then disrupt this current and activate the alarm. Photoelectric devices are generally considered better for smoldering fires, as they aim a light source into a sensing chamber at an angle away from the sensor – when smoke enters the chamber, the light is reflected onto the light sensor, triggering the alarm.

However, there are some devices that promise to detect both CO and smoke. These combination alarms are said to provide the protection of two separate devices in one system, with sensing technologies that work together to detect fires and the odourless, colourless gas of CO. In effect, this makes sense, as carbon monoxide will often build up as a result of a fire. When a fire burns in an enclosed room, the oxygen in the room is gradually used up and replace with carbon dioxide – once this has built up, the fuel is prevented from burning, which produces carbon monoxide as a consequence.

The advantages of such detectors are that they require less space to fit than two separate units. They may be particularly useful for those with smaller living areas, where ceiling space is at a premium, for example.

In addition, alarms are said to raise different warning messages for smoke and CO, ensuring users don’t get confused.

But why wouldn’t everyone buy these? Well, while there are a few dual units available on the market from the likes of Google and Kidde, the vast majority of products on the market are specialist CO or smoke detectors.

This ties in with best placement advice for devices. Heat alarms, for instance, should be placed in the kitchen or garage, whereas dwelling units, such as landings and bedrooms would be more appropriate for smoke and CO alarms to avoid false alarms.

It is always advised that a professional installer is used to fit and service alarms, regardless of whether it is a combined carbon monoxide smoke detector or not. If there are any concerns over leaking gas or the CO alarm is continually going off, a Gas Safe Registered (in the UK) should be consulted.

Download: Fire Strategy – A Director’s Briefing

Access new fire safety expertise by downloading the free Barbour Director's Briefing, and learn how to create a 'carefully devised plan of action' to make your fire strategy more comprehensive than ever. In this free Director’s Briefing, Barbour EHS provides key information relating to the Regulatory Reform (Fire Safety) Order 2005 in England and Wales, including what is required from the responsible person of a property.

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