Visual alarms on fire alarms continue

We are continuing once again from the previously blog on the visual units on fire alarm systems.

The introduction of a mandated harmonised standard sets a base level for product performance. Fire alarm system engineers can therefore be reassured that when approved fire alarm equipment such as strobes are installed in accordance with the manufacturer’s recommendations, they will provide the defined level of illumination in the protected premises. Under the specification, manufacturers have to classify their products as C, ceiling mounted; W, wall mounted; or O, open class devices. In a fire alarm system, both C and W devices will be the primary types used, with some specialised applications having type O devices as well. The C class units often taking the form of a detector base sounder-strobe, fitted between the fire detection in the form of a multi-sensor, smoke or heat detector and its base. W class devices will be either stand-alone strobes or combined sounder-strobes. The key performance indicators are that the output of the device must be greater than 2 candela (cd) and less than 500cd, and the flash rate must be between 0.5 and 2.0Hz.

Ceiling-mounted strobe coverage

The critical requirement from a fire detection manufacturer’s point of view is that each model must be tested to demonstrate compliance with the standard’s requirements. For ceiling-mounted fire alarm devices, the manufacturer must define the maximum height at which it can be installed, set at a standard 3m, 6m or 9m. A wall-mounted fire alarm system device must be installed at a minimum of 2.4m from the floor. The coverage volume, defined by the manufacturer, in which the output meets the minimum required illumination of 0.4 lumens/m² (lux) on a surface perpendicular to the direction of the light emitted from the device is the key performance measure.

Wall-mounted strobe coverage

Further relevant documents are BS 8300, which concerns the design of buildings to meet the needs of disabled people, and LPS1652, Code of Practice for Visual Alarm Devices used for Fire Warning, currently at Draft 1.0 status and published by LPCB.