[ V_step = \fracI \cdot \rho2 \pi r ]
The first step is calculating the "Collection Area" ($A_d$), which represents the effective ground surface area over which a lightning strike to the structure is probable. lightning protection calculation
Where:
[ A_d = L \times W + 2 \times (L + W) \times H + \pi \times H^2 ] [ V_step = \fracI \cdot \rho2 \pi r