Lightning protection for thatched roofs
April 2017
Electrical Power & Protection
Thatched roofs are extremely popular in South Africa. Constructed of material such as straw, reed, grass or coconut leaves, a thatched roof is more susceptible to catching alight as a result of a lightning strike than any other roof type, according to the South African National Standard (SANS). Thatch is particularly prone to ignition because it becomes ‘fluffy’ at the surface and, if moist, methane and other flammable gases can be formed.
If recommended protective measures are not considered, the effects of lightning can cause serious damage. However, prior to providing these protective measures, it is important to analyse the risk effects described in standards guide, such as SABS 0313: 1999, SABS IEC 61662-1: 1995 and IEC 62305-2.
When a thatch roof is constructed, wire mesh is used to reinforce and secure the bundles of thatch. Should lightning strike, then current flows through the wire mesh and thermal effects (generated heat) may occur, and set the roof alight.
Dehn Africa can assist in the avoidance of lightning related disasters, and ultimately extend the lifespan of these structures, through the provision of lightning protection system components for use specifically on thatched roofs. The company has recently introduced new methods of protecting thatched roofed structures in South Africa, and it is no longer necessary to have a 30 metre long mast installed. The latest preferred external protection system for installation on thatched buildings is the high-voltage-resistant insulated lightning protection system that is compact, neat and approved by leading insurance companies and SANS.
For protection measures to be successful, air-termination conductors on thatched roofs must be installed as elevated traverses, for example: on isolating supports, with certain distances also to be kept for the eaves. Systems should be designed to provide sufficiently low impedance so that the lightning energy can follow the required route. For protection measures to be successful, air-termination conductors on thatched roofs must be installed as elevated traverses, for example: on isolating supports, with certain distances also to be kept for the eaves.
For more information contact Kirk Risch, Dehn Africa, +27 (0)11 704 1487, kirk.risch@dehn-africa.com, www.dehn-africa.com
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