Multi-Criteria Fire Protection – the Way Forward?

20th November 2011

Electrical Times publishes article by John Simpson, Notifier by Honeywell sales leader

The past century has seen dramatic changes in the way in which people, property and the environment have been protected from fire, driven in major part by broader technological advances such as the introduction of microprocessors.

From the earliest ionisation smoke detectors to the very latest multi-criteria fire protection devices, the ultimate goal has been to reflect the human being’s ability to use different senses to make a rapid and accurate judgement on the presence or otherwise of a fire and react accordingly.

For many years, ionisation-based detection was seen to provide the best form of fire protection – and was certainly the cheapest to produce. Yet in addition to environmental concerns, it was prone to false alarms in high air velocity and humidity environments and manufacturers have worked to find suitable ways to replace ion detectors.

As a result, different types and levels of multi-criteria device have emerged. Most typically offer a combination of optical and thermal elements, capable of picking up fast-flaming fires which generate little smoke but a great deal of heat, for example. The disadvantage is that the reaction to an increase in temperature is slower than that to smoke.

In addition, infrared (IR) detection is better suited to picking up invisible particles produced by fire and is also able to provide a rapid response, but on its own is restricted by dependence on line-of-sight. Airborne particulates are a common source of false alarms for optical devices and here, carbon monoxide (CO) detectors not only provide additional fire detection capability but also minimise false alarms by differentiating between dust or steam and smoke.

From a technology stand point, much of this development has been essentially evolutionary. However, the ability in particular to incorporate IR within a point detector in this way marks a major advance in recent fire safety technology.

Intelligent response

All fires have three elements in common, in that they produce CO, heat and smoke. The proportions however will be different in each case, as will the time when each element is released. Similarly, a fire will almost certainly produce a changing light signature, primarily as a result of flame development.

Just as a human being picks up on these changes through the use of different senses, the latest sophisticated multi-criteria devices combine the four sensing elements of CO, IR, smoke and heat detection within a single unit, in order to detect different kinds of fire faster.

Further, with sensors managed by advanced algorithms these can be configured to operate normally at a high immunity level, instantly changing to become very sensitive to fires as soon as fire characteristics are sensed. Critically therefore, transient nuisances are ignored, so minimising the false alarm rate.

Future developments

So, is multi-criteria detection the way ahead for fire protection? This would certainly appear to be the case, as CO devices, for example, are becoming more commonplace and combined optical/thermal devices move from their earlier niche positioning to more mainstream application.

More broadly, the fire industry generally across Europe is moving – slowly yet demonstrably - from a stance of ‘let’s detect fire better’ to one which might be characterised as ‘let’s prevent false alarms’.

Not surprisingly, the reason for this is primarily economic, as the cost of downtime or lost business increases together with a loss of confidence in the system itself. As a result, the reduction in false alarms is now a principal focus for product development within major fire safety equipment manufacturers.

And here, critically, multi-criteria sensors are inherently less prone to false alarms than their single sensor counterparts, as it is more difficult to falsify two criteria than one, three more than two, and so on.

At the same time, as development concentrates on providing increasing resilience against false alarms, so infrared technologies are also proving significantly more capable than optical detectors in picking up fast flaming fires in delivering equivalent performance to earlier ion detectors. So, in the case of those manufacturers developing dual frequency or dual angle optical detectors, for example, though a step forward these do not provide the true replacement provided by an infrared solution.

Thus, from the perspective of both earlier fire detection and minimising false alarms, the concept of multi-criteria detection has established itself as a mainstream technology response.

Key applications

Having said that multi-criteria detectors are moving centre-stage, two caveats should be introduced at this point. First, as a relatively expensive solution, full multi-criteria protection is ideally suited to those applications where the cost of downtime to the business is especially significant.

In such situations, though the early detection capability of a multi-criteria solution is valuable, resilience against false alarms is likely to be the determining factor from a commercial perspective.

Thus, multi-criteria protection is ideally geared for use in such environments as hotels who offer refunds in the case of evacuations for false alarms, financial institutions undertaking large volumes of high value transactions or mission-critical areas within airports, for example. At the same time, it is well-suited to sports and leisure industry applications, where there are often large numbers of people in a single location.

Similarly, multi-criteria protection is an example of general application, so will not be suited to other areas where the cost of downtime is significant. As a result, industrial processes which use chemicals that become airborne and can be aggressive to plastics, or environments where major temperature variation is commonplace, will continue to require specialist detectors.

Yet as in any newly-emerging technology, as the cost of multi-criteria devices comes down and the differential with traditional fire detection solutions narrows, so their application will inevitability become broader.