Here James Hall, Technical Director for FireAngel, explores the potential issues associated with ionisation smoke alarms and why professionals should choose optical or multi-sensing alarms to provide the greatest levels of protection.

For many years ionisation sensing technology was a popular choice for specifiers and installers. Its low price point, combined with its outstanding ability to detect fast-flaming fires, saw its installation in all types of properties across the country.

However, its favourability has begun to wane over the last few years, primarily due to two reasons.

Ionisation sensing technology contains a small amount of radioactive material (Americium 241) within the alarm, FireAngelwhich gives off low levels of radiation in the form of alpha particles. This presents environmental issues regarding how they can be safely disposed of due to the radioactive materials present.

The emitted radiation ionises air in the detecting chamber. When smoke enters the detecting chamber, some of these ionised air molecules react with the smoke. This causes a change in electrical behaviour, which the alarm electronics can detect and trigger the alarm to sound.

This makes the alarm sensitive to small particles of smoke produced by fast-flaming fires, such as those produced by paper or wood, successfully providing early detection of fire.  The problem is that this also causes the alarm to be very sensitive to some spurious sources, such as cooking fumes and dust, which can lead to the creation of false alarms. The technology is therefore unsuitable for installation in circulation areas, such as hallways or close to kitchens, where cooking fumes are frequently present.  

FireAngelThese nuisance alarms can often result in residents removing or damaging alarms, meaning they are no longer protected. Specifiers and installers should therefore consider alternative technologies that will not provoke the tenant or homeowner to remove alarms, which presents potential risks to their safety.   

So what technologies should professionals be installing? The British Standard 5839-6 and UK Fire and Rescue Services recommend installing optical or multi-sensor alarms instead of ionisation smoke alarms in circulation areas such as hallways and landings as a minimum level of protection.

Optical alarms work on a completely different principle to ionisation alarms. They use infrared emitters and receivers inside a completely dark smoke chamber. When smoke enters the chamber, some of the infrared light is scattered by the smoke particles, and reaches the receiver. The greater the level of smoke in the chamber, the more light is scattered and detected by the receiver. By measuring the amount of light scatter, the level of smoke present in the room can be accurately measured. When the level exceeds the alarm threshold, the alarm sounds.

As optical detectors are marginally less sensitive to fast flaming fires, they are therefore less likely to sound in response to cooking fumes than ionisation alarms, making them more suitable for installation in circulation areas such as hallways and landings. Multi-sensor technology adds another layer of safety to the inherent reliability of an optical alarm.

FireAngel’s Thermoptek Multi-Sensor alarms monitor the temperature in the immediate environment as well as smoke. If a sudden rise in temperature is found, the smoke sensitivity of the alarm is automatically increased. This allows the alarm to provide a faster response time to all types of fires in comparison to a conventional optical-only alarm, providing individuals with the greatest amount of time to evacuate the property while providing a better level of resistance to false alarms.

With many safety product manufacturers now eliminating ionisation sensing technology from their ranges in favour of multi-sensing or optical technologies, professionals should also begin considering new and more advanced technologies in order to provide tenants with the highest level of fire protection possible.

For more information on FireAngel please call 0800 171 2009 or click here.

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