Dave Arden, Technical Services Manager for Envelope Products at Tata Steel, give a brief overview of Lightening Protection for buildings…
BS EN 62305 :20011 is the current standard covering lightning protection to buildings and gives information on general principles, risk management, damage to structures and electronic systems within the buildings.
Part 3 “Physical damage to structures and life hazard” answers questions concerning the use of metal cladding systems on buildings.
The document confirms that metal cladding can be used as part of the air termination system of a lightning protection system providing certain conditions are met. Firstly the electrical continuity between various components is made durable and in the case it would be by side lap stitching sheets to each other and by fixing the sheets with self drilling screws to the steel purlins. The purlins are then generally bolted via cleats to the main steel frame, which in turn is connected to the earth termination system.
The roof sheets if made of steel should have a minimum thickness of 0.5 mm. It should be noted that at this thickness puncture by lightning flash can occur leading to damage of the external sheet and the insulating foam being exposed. Hot metal may cause some burning of the foam but extensive testing to various standards e.g. LPS1181, BS476 and FM show that the surface of the foam will char and prevent further combustion.
Damaged sheets can readily be replaced or in the short term covered over to prevent any possible water ingress.
It should be noted that we have been supplying panels into the market for many years and have no experience of even minor damage occurring due to lightning strike.
Finally protective paint layers applied to the steel are not regarded as insulators provided they are not more than 0.5 mm in thickness. The thickest coating we use is Colorcoat HPS200 Ultra® which is only 0.2 mm thick, well within the limit set.