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Lightning Explained, Part 2
The scientific views expressed in this article are those of Dr. Farouk A.M. Rizk as explained by Amir Rizk. Dr. Farouk Rizk is the former VP (Research Laboratories), Hydro Quebec, and former Scientific Director at IREQ. Amir Rizk (B.Sc., phys, MBA) is VP of Lightning Electrotechnologies Inc and a student of Dr. Rizk. Any technical matters dealing with lightning protection adhered to previously published, peer reviewed material.
When it comes to issues like the minimum conductor thickness for lightning currents, grounding and bonding, the information contained in standards such as IEC 62305 and NFPA 780 are well founded in science and unlikely to change in the foreseeable future.
However when it comes to something as fundamental as the shape of a lightning rod (air terminal) and where it should be placed, there is controversy.
The not so good
During the process that rejected a proposal to issue an NFPA Standard for Early Streamer Emission (ESE) lightning protection technology, some interesting issues were raised. (More on ESEs below). The Bryan Panel, deemed independent, reliable and respected by the NFPA Standards Council, produced a report that concluded there was no technical validation for ESE technology and in addition, it also raised questions as to whether or not technical validation existed for conventional lightning protection systems.
In response to this, among others, a report in support of conventional lightning protection was produced entitled, "The Basis of Conventional Lightning Protection Technology: A Review of the Scientific Development of Conventional Lightning Protection Technologies and Standards". This report was prepared by the Federal Interagency Lightning Protection users Group 2001, which to the objection of some, included members of the NFPA 780 Technical Committee. This document produced no new research but drew a different conclusion from the Bryan Panel Report.
The document was deemed sufficient by the NFPA Standards Council to maintain the status of NFPA 780, although its decision stated: "The Council has not attempted to independently review each piece of literature cited in the report nor has the council attempted to independently answer the question of technical validity of NFPA 780."
A real problem with the prescriptions in NFPA 780 is that they ignore the role played by the grounded structure to be hit. They assume a constant striking distance or an equal probability of a direct hit to the ground, to the corner of a tall building, the edge of a building, etc. This defies observation and theory. The result is a practice of blindly placing a rod every 20' without consideration for building height or topology. This can be wasteful and excessive in terms of the use of materials while still not offering adequate protection.
-- continued on page 2
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