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BS 6651 (Protection of structures against lightning)
clearly advises strict adherence to the provision of a conventional
Lightning Protection System (LPS) to the total exclusion of any other
device or system for which claims of enhanced protection are made.
Principle components of a conventional structural lightning protection system, in accordance with BS 6651 are:
 Air termination network
Down conductors
Earth termination network
Bonding (to prevent side flashing)
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high risk structures such as explosive factories, no part of the roof
should be more than 2.5m from an air termination conductor. This is
generally achieved by applying a 5m x 10m mesh to the roof.
However,
for most structures, a mesh of 10m x 20m is considered sufficient,
giving a maximum distance from any part of the roof to the nearest
conductor of 5m. |
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The `Zone of Protection' offered by an air termination network is
considered to be 45° for heights up to 20m. Above this height, the zone
of protection is determined by the `Rolling Sphere Method'.
This
involves rolling an imaginary sphere of 60m radius over a structure.
The areas touched by the sphere are deemed to require protection. On
tall structures, this can obviously include the sides of the building.
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