SAFETY & SECURITY Multiple benefits
With different fires presenting different challenges for buildings and occupants, Barry Sargent of Nittan looks at the factors that make multi-sensor alarms a safe choice
ires come in different forms, and different alarm sensors perform different functions; in addition, false alarms need to be minimised in order to reduce disruption for facilities. To answer these needs, multi-sensor alarms’ popularity has increased dramatically over recent years, having an attractive range of benefits. They combine two sensor types within one alarm, most frequently optical smoke and heat sensors. As different sensors detect different types of smoke and heat, and therefore different types of fire, combining more than one sensor in a single unit potentially makes for an improved response to real fires (as opposed to false alarms). It also reduces unit and installation costs, makes alarm specification far easier and, let’s face it, looks a whole lot better than having two alarms on the ceiling.
F That much you may well already be aware
of, but below are four aspects that you may not have considered before.
1. Design – and capability varies Not all multi-sensor alarms are ‘born’ equal! Just because you have specified one, don’t assume it will perform better than all single- sensor detectors. A good quality optical alarm that has been correctly specified and installed will more than likely outperform a low cost, basic multi-sensor; and by outperform I refer to their ability to detect fires whilst discerning false alarm sources. That’s because, like most things in life, you get what you pay for. The sensors vary dramatically in design, from basic models where the system provides only limited cross evaluation of the sensor values, through to highly sophisticated devices featuring advanced algorithms to assess the variation in values from each sensor in order to determine the nature of the potential fire. The Building Research Establishment’s Briefing Paper ‘The performance of multi- sensors in fire and false alarm tests’ is quite clear about this, stating: “the use of multi- sensor technology has the potential to reduce certain types of commonly encountered false alarms. However, the extent to which this
can be realised depends on the particular implementation of features designed to improve false alarm immunity. It cannot be assumed that use of simply any multi-sensor detector will impact significantly on the occurrence of false alarms from every form of fire-like phenomena.”
If you want to reap the benefits a multi- sensor can bring, it’s imperative you invest your budget wisely and don’t automatically go for the lowest cost option.
2. Potential to reduce false alarms According to official fire and rescue incident statistics in England from the year ending March 2020, of all incidents attended by fire and rescue services, false alarms made up 42 per cent compared to actual fires at 28 per cent. That’s 231,431 wasted visits; a waste of precious resources. And if that doesn’t bother you, then consider the cost implications for end users: problems that stem from false alarms are estimated to cost UK businesses around a billion pounds a year!
Reducing false alarms is therefore a major task the fire industry has been attempting to address over the years and one of the reasons for the development of the multi- sensor approach.
The BRE Briefing Paper, reporting on a test of 35 different optical heat multi-sensor detectors, estimates that 38.1 per cent of observed false alarms could have been reduced if multi-sensors had been present. That means a potential reduction in UK business losses of £381m per year.
3. Multi-sensors’ limitations While offering improved performance over standard optical detectors, multi-sensors have limitations. In fact, the BRE research demonstrated that, although delayed somewhat, in all cases alarms were given in the presence of ‘non-combustion materials’ such as steam, dust or aerosols. The delay might allow for any transient false alarm sources to disappear before the fire threshold is reached, but it does not entirely stop a false alarm in these instances. Furthermore, to ensure this delay, some multi-sensor
Problems that stem from false alarms are estimated to cost UK businesses around £1bn per year
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ADF FEBRUARY 2021
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