Determine the number of zones required
Based on the recommendations provided in BS 5839, determine the number of zones required to comply with the standard and adequately protect the premises. Generally, at least one zone per floor will be necessary, but other factors such as the floor area and the number of devices that can be connected to a zone should be considered. Select a control panel that provides the number of zones required, bearing in mind possible future expansion. It is better to have too many zones available than too few.
Determine the number of detectors required
Detector density is governed by the system classification and recommendations in BS 5839. Where full protection is required at least one detector should be sited in each room, and evenly spaced within circulation areas and escape
routes. Each detector within a room should include an integral sounder. Where there is more than one detector in an area it may not be necessary for all detectors to include a sounder, or the use of stand-alone sounders can be considered.
Determine the number of manual call points required
As a general rule a manual call point should be located adjacent to every exit from the premises, and at the exit from an upper floor to below. In larger premises it may be necessary to locate call points at intermediate positions to minimise the travel distance – refer to BS 5839.
Consider alarm audibility
BS 5839 recommends a general alarm sound level of 65 dB(A) throughout the building, and 75 dB(A) at the bedhead where people are sleeping. The detector integral sounder provides a ‘normal’ level of 90 dB(A) at one metre which easily satisfies this requirement within individual rooms. In circulation or open areas it may not be necessary to provide a sounder in each detector, or conversely it may be necessary to provide stand-alone sounders where there is
little or no detector coverage.
Remember, integral sounders can be simply disabled or set to low volume via the detector DIL switch if the level is too loud, but to increase the sound it is necessary to add stand-alone sounders if there are insufficient integral sounders.
Ancillary services
- Is it necessary to repeat the fire alarm indications elsewhere in the building,e.g. is there an alternative entrance that may be used by the fire brigade? Ifso a repeater panel will be required.
- Is remote silence and reset necessary, e.g. is the control panel inaccessibleat certain periods? If so select a repeater panel with remote control facilities.
- Are auxiliary outputs required to shutdown plant, close doors, etc? If so include an output unit for each signal required. Remember, the output unitrequires a separate 24 vdc supply; however, it may not be necessary to provide a separate PSU for each unit – consider the circuit loading and physical location of devices.
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This information has been referenced from an official Rafiki publication.
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