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The majority of standards around the world utilize the Rolling Sphere Method (RSM) or derivatives of this, which is based on the simple Electrogeometric Model (EGM) for striking distance. The RSM uses a fixed striking distance (length of lightning upward leader), typically 45 m, for all strike points, irrespective of the structure height or width. This means that a point on a building of height 5 m is assigned the same capture area and strike probability as a point on a 100 m building. This fundamental limitation results in a practical under-design of low structures, and practical over-design on taller structures, resulting in unnecessarily high costs for the end user. | The simple Rolling Sphere Method does not account for the physical basis of the upward leader inception process and the importance of the structure height or the geometry and height of the air terminal. There are other design methods available (such as the Collection Volume Method) which take these important factors into account. |