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Preventing false alarms
Barry Sargent of Nittan discusses how housing associations can significantly reduce the number of false alarms in their properties
W
hile optical detectors remain dominant, true growth has come from multi-sensors as installers and specifiers realise the benefits to be had.
The typical fire alarm multi-sensor comprises optical smoke and heat
sensors, although other variations exist. They vary dramatically in design, from basic models where there is 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. Consequently, their ability to detect fires while discerning false alarm sources is a very mixed bag indeed.
THE BENEFITS That said, most multi-sensors offer a number of benefits over single sensor detectors. There’s the obvious time and cost benefits of being able to install one device in place of two and the aesthetics of only having one alarm on the ceiling. They can also make the job of alarm specification much easier. But top of the list, and the main reason for the ever-increasing popularity of the multi-sensor, is the reduction in false alarms. Last year’s Briefing Paper from the Building Research Establishment (BRE) -
‘The performance of multi-sensors in fire and false alarm tests’ – has provided concrete evidence of this. Following testing of 35 different optical heat multi- sensor detectors (representing the full range of those available in the marketplace at that time), the BRE estimates that potentially 38.1 per cent of observed false alarms could have been reduced if they had been present.
THE LIMITATIONS The BRE Briefing Paper concludes: “this research has shown that, 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.” While offering improved performance over standard optical detectors, they
do have limitations. In fact, the BRE research demonstrated that, although delayed somewhat, in all cases alarms were given from non-combustion materials such as steam, dust or aerosol. 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 detectors have been configured (or can be configured at installation) to be less sensitive which is a compromise that is not always acceptable or ideal.
SOLUTIONS WITH A DIFFERENCE So, the multi-sensor doesn’t provide the complete solution to false alarms and the quality and price vary dramatically. Still, they do perform better than single sensor alarms. But what if you could combine this principle of ‘two is better than one’ by adding another factor into the mix? Dual optical heat multi-sensors, such as Nittan’s EV-DPH Multi-Sensor, do exactly that by integrating a dual optical alarm technology with heat sensors to provide a very sensitive, but truly discriminatory device. The dual optical alarm technology is based on particle light scattering theory, but instead of just using the standard Infra Red light, found in optical alarms, it also employs blue LED to provide a more accurate measurement of particles within the chamber. Using a complex algorithm to calculate the ratio of these light sources, which operate at different wavelengths, the detector can determine the particle size and thus
www.housingmmonline.co.uk | HMM August/September 2019 | 39
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