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Fire detection goes to extremes

Rowland Davies, marketing services manager for Apollo Fire Detectors, explains the fire product choices for hazardous areas.

Modern fire detection equipment has been developed with two primary aims - saving lives and protecting property. However, there are some environments in which these essential electrical products could themselves become a fire risk, because they can provide a source of ignition.

In environments such as chemical processing sites, oil refineries and fireworks factories, where explosive substances may be present, any spark could be catastrophic. The risk is most commonly caused by gas or vapour which, if mixed with oxygen in the air in the right quantity, can cause an explosion. This risk may be present continuously, intermittently, or may arise as the result of an accident.

Even where the mixture of fuel and oxygen is conducive to fire, an explosion cannot occur without a source of ignition. Therefore, electrical equipment installed in potentially explosive atmospheres must be fully shielded.

Various methods have evolved to ensure that electrical equipment cannot cause an explosion in these circumstances. The two most common methods are flameproofing and intrinsic safety (IS).

IS and flameproofing

Flameproofing consists of a strong and closely fitting enclosure that protects the contents.

There are, however, some limitations. Flameproofing, for example, is not acceptable for areas where an explosive gas/air mixture may be continuously present or present for long periods. Flameproofing is not suitable for smoke detectors, because the smoke cannot penetrate the flameproof enclosure and so the sensor will not pick it up. While flameproof flame and heat detectors are available on the market, they can be cost-prohibitive. Many people therefore opt for intrinsically safe (IS) fire detectors.

Equipment installed within a hazardous area should be certified by a third party. Within the UK, the main independent approval bodies for testing to the European standards (EN54) are the Loss Prevention Certification Board (LPCB) and the British Standards Institute (BSI). Approvals bodies specialising in IS certification include Sira and Baseefa.

There is an important distinction to be made regarding certification of fire detectors for potentially explosive atmospheres. The European standard

Equally, IS certification simply indicates that the product is not a source of hazard when installed in an explosive atmosphere: it does not guarantee that the fire detector will actually work. Specifiers and users should, therefore, ensure that fire detectors for IS applications comply with both the functionality requirements of EN54 and the safety parameters for intrinsic safety.

There are two main IS certifications: IECEx is recognised worldwide, while conformance with the ATEX Directive is required within all EU member states. IS products which meet IECEx or ATEX requirements are designated by the code Ex ia, b or c by the Notified Body. Electrical products conforming to the ATEX Directive also carry the CE Mark.

Product choice

The need for IS fire detection can arise in a variety of circumstances, some of which may not be immediately obvious. Paint stores, where there is a high likelihood that vapours could accumulate, are one such example.

Apollo makes IS products that are fully compatible with standard fire detectors, so that any areas like paint stores can be covered by adding an IS fire detector or two into an otherwise standard fire detection system. This is achieved by adding a spur, equipped with an isolator, to the main fire system to accommodate the IS detectors.

Both conventional and analogue addressable IS fire detectors are available. Like their standard counterparts, conventional IS fire detectors are more suited to situations where there is a simple need for alarm and uncomplicated evacuation. Analogue addressable IS devices are more suited to larger, more complex built environments where more sophisticated levels of monitoring and reporting of environmental fluctuations are required, or where large numbers of people or complex building layouts may make phased evacuation a desirable option.

EN54, parts 5 and 7, sets out criteria for heat and smoke performance respectively. Compliance with EN54 will therefore give assurance that the device in question is fit for purpose – i.e. it will reliably detect the products of combustion – but does not ensure it will operate within the safety parameters required for explosive atmospheres.

Intrinsically safe equipment is specially developed for use in potentially explosive atmospheres. Essentially, IS equipment operates at such low power and with such small amounts of stored energy that it is incapable of causing ignition. This must be true whether the device is operating under normal conditions or if a fault, or combination of faults, occurs.


This method is most valuable when high power levels are unavoidable. Where flameproof equipment is interconnected, flameproof wiring must also be used.

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