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With increasing pressure from fire and rescue services to reduce false alarms, manufacturers have come up with a range of multi-sensor detectors to help confirm real fires. But in being so focussed on stamping out false alarms, are we in danger of throwing out the baby with the bathwater? asks Rowland Davies.
Eliminating false alarms is an important consideration when designing and specifying a fire detection system, but sometimes it seems that this one aspect of fire detection is beginning to obscure other priorities – like actually detecting fires!
Starting from first principles, what is a false alarm? It is an alarm raised by the fire detection system that turns out not to have been triggered by a genuine fire. False alarms can be caused by poor system design, poor or non-existent maintenance, a change of use of rooms or buildings without a review of the detection system, poor staff discipline and by the fire detection system itself.
Possibly the most difficult cause of false alarm to eradicate is that of equipment reacting exactly as it is designed to, but where the triggering phenomenon is not smoke from a genuine fire. In the majority of cases, the false alarm occurs because the system has sensed something that looks like smoke particles, but is later discovered to come from another source. Dust, particles from burnt toast and steam are among the major culprits.
Manufacturers have invested considerable resources in developing technology to combat this type of false alarm. Solutions include proven multisensor detectors, which combine smoke and heat detection elements, and dual sensor optical detectors working on the principle of particle size detection.
Multisensor detectors – which commonly combine a heat sensor and an optical smoke sensor – have been readily adopted for use in general purpose applications, particularly since the restrictions on ionisation technology came into force. These devices are now proven in the field to reduce the incidence of false alarms in circumstances where high levels of steam or cooking activities are deemed to be a risk factor.
Analysis
The dual optical detector is a more recent introduction. This type of device uses two internal LEDs which, it is claimed, enable evaluation of the phenomenon to which the detector is reacting. For instance, particle size can be determined, which should enable the device to identify any steam entering the chamber – because water vapour has larger particles than smoke from a fire.
While laboratory tests can be used to demonstrate this proposition, care must be taken to ensure that an event which causes both smoke and steam to be present should not give an unwanted result. This type of device must not reject the smoke as well as the steam, or a genuine alarm will be suppressed with potentially serious consequences.
Of course, the fire industry has a series of robust standards – such as EN54 – that can give reassurance about the appropriate performance of fire detection products, whether established or newly introduced. However, with devices like multisensors and dual optical detectors this is not as simple as it may seem.
Both types of device are capable of operating in a number of different modes, sometimes referred to as sensitivity settings. These different settings are provided to enable users to select the most appropriate operating mode for the local environment in which that device is sited – in itself a mechanism for false alarm reduction. In other words, you can select just how sensitive you want the device to be to a particular phenomenon (e.g. heat or smoke) depending on whether it is, say, in a hotel bedroom with an en suite shower or in a communal corridor in a house of multiple occupation.
If the detector has passed the approvals test in every operating mode – which may include time delays before giving an alarm – then the installer or commissioning engineer has the freedom to chose the most appropriate setting and be certain that the device is approved. If the test house approval does not apply for some of the operating modes, it limits the choice of setting available.
Liability?
This could lead to the device being less effective than it could be if all the modes were approved. It could even lead to the device invalidating insurance cover if it is found to be programmed for a non-compliant setting in the event of a fire. Where a product is found to be non-compliant, there are also serious implications for the ‘responsible person’ under the Regulatory Reform (Fire Safety) Order and for the installer.
As an industry, we are going to have to start asking ourselves some serious questions. We need to decide whether the possibility of legal action and financial penalties is a risk we are prepared to run, in order to reduce false alarms. This conflict of aims – however theoretical it may appear at present – is likely to arise more often as technology continues to evolve and programming becomes increasingly sophisticated.
In order to continue making the right choices in life-critical situations, we must not be seduced into believing that being able to identify non-fire products, such as steam, is somehow an end in itself. The first principle of fire detection must always be to detect the products of combustion – smoke, heat and flame – as quickly and as accurately as possible.
Rowland Davies is marketing services manager of Apollo Fire Detectors.