Direct Effects       
 
 
Electrical: As a current discharge occurs, voltage differentials raise the potential of the structure and the surrounding ground leading to dangerous ‘step and touch' potentials.

Side Flashing: The point of strike on the structure will be raised to a high potential. Side-flashing to adjacent metal in or on the structure or to service pipes and electrical services will occur.

Thermal: The instantaneous temperature of material within the discharge path will rise, leading to possible fire.

Mechanical: A peak power of about 100MW/m can be attained in a lightning discharge. The shock wave close to this strike can readily dislodge tiles from roofs of unprotected structures.

Protection Against Direct Effects

A properly designed and installed lightning protection and earthing system will overcome the effects of a direct lightning strike. The likely attachment points of lightning to a structure can be determined by a technique known as the ‘Rolling Sphere' analysis.

Air Terminals are the collectors of the lightning discharge. These may be vertical rods, known as finials, horizontal strap, or the material itself of an all metallic structure. The standards state that an all metallic structure, such as a communications tower, is self protecting and requires no additional protection. The same applies to an all metal building, tanks and pipework.

Downconductors carry the lightning discharge to ground. These may be purpose designed conductors, the frame of an all metal building, reinforcing steel, or the legs of a communications tower.

Earthing System dissipates the energy into the ground. This may consist of an array of buried horizontal strap and vertical rods, the foundation steel of a building as well as bonded connections to metallic service pipes and electrical grounds.

Despite claims to the contrary, none of the recognised world lightning standards accept the concept that any construction or device can prevent a lightning strike.