Changes were made in the British Standard in 2017 regarding positioning of fire beam detectors. These changes have been generally accepted in South Africa and are listed in the updated SANS 10139 shortly to be released by SABS.

Here we attempt to provide clarity on the positioning of fire beam detectors.


This has not changed beams can be mounted a maximum of 15 m apart and no more than 7.5 m from the side wall.

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These distances must be measured horizontally.

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There are three steps to consider when mounting beam detectors.

Step 1. – First choice

For apex ceilings detectors must be installed in the apex of the roof within 600 mm from the top of the roof. The next detector can be installed up to 15 m away.

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Step 2. - Obstructions

If it is not possible to achieve line of sight to the receiver / reflector the beam detector can be mounted at a lower distance up to a maximum of 10% of the height of the apex from the floor. Example: If the roof is 15 m high, the beam can be mounted anywhere down to 1.5 m from the apex.

This applies to a maximum of 2.5 m from the apex and this must be recorded as a variation in ALL the relevant system documentation (including certification).

Should this option be selected, the spacing of the beams must be reduced from the maximum of 15 m to 10 m apart.

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Step 3 – Lower installation positions

Should Steps 1 and 2 not give a clear line of sight for the beams, the requirement used for stratification needs to be implemented.

The height selected where the beams can be mounted determines the coverage of the beam by calculating 12.5% of the height of the beam from the floor. i.e. if the beams are mounted 10 m from the floor the spacing of the beams is reduced to 2.5 m apart (10 x 12.5% = 1.25 m).

If there is no likelihood of a fire starting above the beams the apex beam may be excluded. This must be recorded as a variation in ALL the relevant system documentation (including certification).

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By Keith Norgate – FSIB Fire Systems

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