Fire & CO Alarms
New alarm typesand what you need to know
Martyn Walley, National Technical Manager, Aico Ltd, looks at what is changing in the fire alarms market and how this will affect the advice that you give to customers.
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n the domestic Smoke Alarm sector there have traditionally been three alarm types: Optical, Heat and Ionisation. These different sensor types react best to certain fire types. As a
result, specification and installation requires a good knowledge of BS5839 Part 6 (the British Standard for domestic smoke alarm installation) and Building Regulations, to ensure the best levels of detection for a property. But changes are afoot! The new breed of Multi-Sensors, which combine two traditional sensing elements in one alarm, are rising in popularity. What’s more, there’s a further alarm type to hit the market, which combines fire detection with another life safety device – Carbon Monoxide (CO) detection.
So what alarm type should be used and where? Let’s start with the best known alarm types. As the name might suggest, Optical Alarms essentially ‘look’ for smoke using a pulsed light beam in the sensing chamber. They are most effective at detecting smouldering fires with large particles, such as produced by burning furniture, and are less likely to react to the type of invisible smoke produced by cooking fumes; so are ideal for circulation spaces such as hallways close to kitchens and landings as per BS 5839-6. Ionisation Alarms use a small radioactive source to detect the invisible
smoke particles given off by fast-flaming, clean burning fires such as bedding and clothing. Ionisation Alarms have mostly proven so popular because they have been around the longest (they were the first commercially available Smoke Alarms) so are the most familiar and generally are priced lower than other alarm types, making them the default alarm choice. However, with greater understanding of fire alarm types and a wider choice of alarms now available, Ionisation Alarms are slowly falling out of favour because they can be over sensitive to cooking fumes and are deemed old technology now. Generally, we’d recommend restricting their use to bedrooms. A Heat Alarm doesn’t detect smoke at all, but instead reacts to
temperatures of 58ºC, as per BS 5446, or over. A Heat Alarm should only be used in a kitchen or garage and only as part of a Fire Alarm system that also includes Smoke Alarms. Furthermore, all of the alarms within that system must be interconnected to meet British Standards (a solo Heat Alarm in a property is not an option). The most common alarm system to be fitted in domestic properties is
Heat Alarms go in the kitchen; Optical Alarms are for circulation spaces, including hallways and landings; and Ionisation Alarms should be avoided as there are more suitable options, advises Aico.
a Grade D one, which requires one or more interlinked mains powered Smoke and Heat Alarms each with an integral stand-by supply. Interlinking is essential as it provides an earlier warning for residents and the best chance of escape. When one alarm goes off, all the other alarms on the system activate – and there’s little chance of the occupant sleeping through that noise!
A Multi-Sensor Fire Alarm uses both Optical and Heat sensors within the same alarm unit and interprets the signals to get a better understanding of what’s really happening in the immediate environment. Due to this,
it benefits from a quick response to both slow smouldering and fast flaming fires yet is more tolerant to kitchen fumes and contamination.
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