No smoke without fire?

Notifier by Honeywell, fire detection, fire alarm
250 000 nuisance fire alarms across the UK last year — Derek Portsmouth.

There are nearly 700 nuisance fire alarms every day in the UK, causing much inconvenience and breeding complacency — but they can be avoided, as Derek Portsmouth of Notifier by Honeywell explains.

One of the most common problems faced by those responsible for safeguarding public buildings is the challenge of designing and implementing an efficient fire safety solution.

Anyone staying at a 5-star hotel, going to their local leisure centre or visiting a museum will automatically expect that the owner or operator of the site will sound an alert promptly in the event of a fire. Yet providing the level of protection we expect can be a complex process for the fire-system manufacturer, specifier, installer and maintenance contractor.

The diverse nature of public buildings means that each fire-safety solution must be designed to meet the unique requirements of the site.

Older public buildings, for example, can be inherently complex in nature and, if listed, will present difficulties in both system design and installation. In refurbishing Kentish Town’s century-old public baths, for example, Camden Town Council had to respond to visitors’ desire to enjoy the splendour of the building’s late-Victorian architecture while benefitting from the very best in modern fire-safety design.

Similarly, protecting a museum holding priceless artefacts presents a very different challenge from, say, a university campus or shopping centre where the primary driver is to ensure large numbers of residents or visitors can be evacuated quickly and safely from a multi-building site.

Yet there are some common denominators. In every case, a balance must be struck between ensuring the earliest possible warning of a fire-related incident and avoiding false or nuisance alarms — and within the most cost-effective solution.

In one sense, the latest Government statistics are encouraging. In the year 2011/12, the number of false alarms nationally fell by 9% over the previous year and by nearly 40% over the past decade.

The less-good news is that there were still almost 250 000 nuisance alarms across the UK last year, creating an unsustainable cost of £1 billion to the public purse, as well as the constant risk of diverting vital fire and rescue services in the event of a real fire. Research also shows that recurring false alarms also breeds complacency among building users, making them less reactive to a real fire signal.

Only a small minority of nuisance alarms are the result of deliberate or malicious intent, with most due to poor system design or maintenance. Equally, although part of what is a welcome decline in the incidence of false alarms is down to greater awareness and better fire-safety management, again, most of this is due to the availability of better fire-detection technologies.

The right equipment can make a huge difference here. For example, Isle of Anglesey County Council previously suffered countless unnecessary call outs at its high-rise residential blocks, yet since upgrading its fire safety equipment there have been no false activations.

When combined with the correct installation, service and maintenance practices, intelligent system design and the latest fire detection technology can offer the flexibility to ‘engineer out’ false alarms — even in difficult-to-protect environments such as heritage buildings or sites attracting high volumes of occasional visitors.

The continued development of multi-criteria sensors offers early warning of a real fire by detecting different fire types more quickly, while at the same time providing a high level of resilience against false alarms. Such sensors are defined as ‘intelligent’ in that, just like a human being, they ‘look, smell and feel’ the environment and ‘think’ before acting.

So how does this work? Fires occur when there is an ignition source, fuel and oxygen. Common to all fires is the fact that they produce particulates, heat and carbon monoxide and, when a flame is produced, a light signature.

However, fires take many different forms, and a simple optical detector will not always provide the sensitivity or intelligence to identify a real fire. A slow, smouldering fire that produces large amounts of smoke and carbon monoxide but little heat will provide a very different signature from, for example, an alcohol fire producing high temperatures very quickly without any evidence of smoke.

A multi-criteria detector can have up to four sensing technologies, depending on the environment to be protected. In addition to standard optical smoke protection, other technologies that can be incorporated within a single device can include a heat sensor, infra-red sensor and a carbon monoxide sensor.

Optical sensors operate on a principle of how much airborne particulate is present. Particulates are present in small amounts at all times in the form of dust and are also produced as steam from a shower or aerosol use. However, none of these activities produce heat, carbon monoxide or flame. The sophisticated ‘brain’ of a multi-criteria sensor understands this, combining and analysing the data from each sensing element to provide a rapid response to a real fire yet remain highly resistant against false-alarm incidents.

Other features include self-optimising sensitivity adjustments and a drift-compensation facility. As the detectors accumulate contamination between cleaning intervals, the sensitivity is not increased by this contamination. However, when the level of contamination decreases, the detectors automatically become more sensitive again, ensuring coverage is not compromised.

Modern fire-alarm solutions also include advanced systems programming. For example, these may incorporate multiple device dependency, in which the first alarm provides a warning, with full response only if a second alarm is signalled. Similarly, a time-delay system will give an initial signal to on-site staff, who have a pre-determined period in which to investigate and confirm the alarm.

Day/night programming is also suitable for environments where the risks vary significantly according to the time of day. In each case, to be properly effective it is essential that such systems are commissioned by a qualified and experienced fire-system designer.

A comparatively small investment in the latest intelligent technologies typified by multi-criteria devices together with system design and effective maintenance, can in many cases stop, or at least delay, the false activation of an alarm. The fire service will save money and be less frustrated by unwanted call outs. For the public-building operator, its occupants and visitors, it will minimise potentially costly disruption and, potentially, save lives.

Derek Portsmouth is national sales leader UK & Ireland, Notifier by Honeywell.

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