A study conducted by the Building Research Establishment (BRE) in partnership with the Fire Industry Association (FIA) and other key fire detection and alarm manufacturers has concluded that multi-sensor detectors are better at rejecting false alarms.

The research was a continuation of prior research from three previous projects, which looked at the occurrence of false alarms in the UK.  Over the past 10 years, the FIA has partnered with King’s College, Buckinghamshire Milton Keynes Fire Brigade, and Scotland Fire Brigade to investigate and find solutions to the false alarm problem that perpetuates across the UK.

Those previous projects gave the general conclusion that employing multi-sensor fire detectors would help reduce the occurrence of false alarms.  Anecdotally, there were signs. However, there was a missing link: hard evidence that multi-sensors would actually reduce false alarms. 

Categories of multi-sensor detectors

12 manufacturers from the UK and Europe were involved in the research. These represented the majority of the detectors sold in the UK.  From those 12 manufacturers we put together 35 different detectors and those were tested against two standard optical smoke detectors, one commercial, and one domestic.

There are lots of different sorts of multi-sensors.  The research focused on multi-sensor detectors which comprised of a standard optical smoke chamber together with a heat sensor.  However, one of the issues with multi-sensor detectors is that they perform as they have been designed by the manufacturers, and they don’t all perform the same way. As a result, the research graded them into three categories: ‘standard performance’, ‘intermediate performance’, and ‘advanced performance’.

‘Standard’ multi-sensor detectors were those smoke/heat detectors which used the heat element to modify the sensitivity of the smoke sensor, meaning that heat was required to increase the sensitivity of the chamber. Without heat the sensor was detuned.

The ‘intermediate’ category were the detectors that used a smoke chamber design that incorporated features of the ‘standard’ detectors, but with added design benefits, for example a more specifically designed chamber to eliminate potential for false alarms, such as an insect going into the chamber, or the effect of dust which may cause a false alarm. 

The ‘advanced’ category, which the research predicted was the most likely to be the most effective at reducing false alarms, were those which had the features of the ‘standard’ and ‘intermediate’ categories, but also employed sophisticated targeted algorithms which would eliminate a false alarm.

Comparing sensitivity

Following the categorisation, the next stage of the research was to test the sensitivity of the different multisensory detectors compared to the standard optical smoke detectors.

10 different fire tests were conducted, looking specifically at the performance of the detector and their ability to detect fires. The fire tests included the standard fire tests that appear in the European standards – TF2,3,4, and 5 – which are in EN54-7, which is the European standard for smoke detectors.  TF1 and TF8 were then added, which are again standard fire tests which have been added to EN 54-29, a new standard that details specifically the requirements for smoke plus heat fire detection products.  TF1 is specifically a hot wood-burning fire that produces heat yet not much smoke, and TF8 is a fuel-burning fire that produces very little heat, but very heavy smoke. In this way, the testing represented the extreme ends of the spectrum of fires that may occur in real life.

A good fire detector needs to be used in almost every circumstance and has to be able to detect a whole range of types of fire which may be encountered depending on the fire risk.

To the 6 test fires listed above, 4 new fires were specifically designed for the research (these were not listed in EN54), to extend the range of test fire types.  These were based on fire retardant material or MDF material, creating slow burning fires, again replicating real life situations.

All of the detectors – both multi-sensors and optical smoke detectors were tested against all of the different test fires.  You might expect that in terms of sensitivity and ability to detect fires that the multi-sensor detectors would perform better. 

However, the research results were not as expected: it was difficult to differentiate very easily between the performance of the multi-sensors and the performance of the standard optical smoke detectors. Essentially, the performance of the multi-sensor detectors depended very much on the sensitivity of it – the high sensitivity detectors detecting quicker and faster than the low sensitivity detectors.  But that was the same for the standard optical smoke detectors.  That is why there was no real way of differentiating performance between the ‘old-style’ optical smoke detectors and the ‘new-type’ multi-sensor detectors.

Testing for false alarm rejection

In knowing that there was not much difference in ability to detect fires, the second test was then to test all the detectors in their ability to reject typical false alarm situations. Would the multi-sensor detectors perform better? 

The false alarm testing was developed in conjunction with the University of Duisberg in Germany; the team there had some expertise in developing false alarm testing.  In addition, bringing in a university meant that there was an element of impartiality and independence from the industry as well.

Five different false alarm tests were carried out in total: burning toast, cooking test, steam test, dust, and aerosol spray.  Other tests such as cigarette smoke and long-term dust were also considered, but these were abandoned because repeatable results were not possible due to the amounts of variability in these two tests.

What were the results?

There were two outcomes from the tests – the first being the results of the tests themselves, and the second outcome was that the initial grading of the multi-sensor detectors into ‘standard’, ‘intermediate’, and ‘advanced’ categories was correct.

During the fire false alarm tests all the multi-sensor detectors responded later than the optical smoke detectors – either the domestic or the commercial smoke alarms. For example, on the toast burning test, some of the multi-sensor detectors (those in the ‘advanced’ category) responded a good minute after the optical smoke detectors. By responding later, this demonstrates that multi-sensor detectors are not as prone as optical smoke detectors to alarm for events such as burning toast or steam, providing better overall protection against false alarms.

Additionally, the fire tests justified the way the research characterised the different types of detectors – in that they all responded in the right order, i.e. the ‘standard’ category responded first (meaning they were not as good at rejecting false alarms), then the ‘intermediate’ category alarmed afterwards, and finally the ‘advanced’ category of detectors (which had the benefit of sophisticated algorithms to filter out false alarms), responded latest.

The final conclusion? The more sophisticated the multi-sensor detector, the less likely they are to false alarm. And additionally, multi-sensor detectors are better at rejecting false alarms than optical smoke detectors of any category.

The future

With the conclusion that multi-sensor detectors are more effective at false alarm rejection, and that effectiveness increasing depending on the categorisation of the specific detector, there is scope in the future for the FIA to be involved with developing a means of grading detectors within the British and European Standards. 

The FIA, in conjunction with other industry bodies and stakeholders, are also considering the introduction of new false alarm tests that were developed for the research within the European or British Standards.  This means that detectors will come with a label identifying the level of resilience to specific types of fire.

Both of the above will help categorise detectors according to their ability to reject false alarms, ultimately meaning that users will be able to understand what they are buying, and for installation and maintenance companies to be able to recommend a category type of detector to their clients to solve a false alarm issue within a building.  This will be especially helpful where there are buildings that are particularly prone to false alarms – helping to minimise disruption to businesses and reduce strain on Fire and Rescue Service callouts.

Ultimately, this going to have an impact on manufacturers and how they are going to create their products for the future.  Designs may be re-evaluated for their level of effectiveness against false alarms – but of course further research and development of products is more expensive.  However, the benefits of developing these products may mean that we start to see even more sophisticated multi-sensor detectors on the market in the future.