The protection of a building, structure, facility or site against direct lightning strikes is the first important step in providing a comprehensive lightning protection solution (LPS). This task is achieved with lightning rods or “air terminals” appropriately positioned or placed to provide a desired “interception efficiency” or level of protection. The number of air terminals required to provide this level of protection depends on the protection area afforded by each air terminal. The correct placement and number of air terminals is determined by the “design method” that is used. These methods are typically explained in lightning protection standards around the world.
Air terminal placement methods typically fall into one of five categories, namely:
The aim of this paper is to make an objective, quantitative comparison of five different air terminal placement methods that are currently in use, under the same conditions. The five methods considered are the PAM, RSM, collection volume/field intensification method (CVM/FIM), leader inception theory (LIT) and ESE. The comparisons are made using case studies of typical structures.
The results are presented in the form of a spectrum – from most conservative to least conservative – in terms of the number of similar-height air terminals required to protect the structure. The results show that there are considerable differences between the methods. The reasons for these differences are explored in the paper. The mesh method was not included in this study as it does not provide interception of lightning strikes, rather it is a collector of lightning current once it strikes the structure