> Effects of lightning strikes > Direct effects


Thermal effects: These effects are linked to the amount of charge associated with lightning strikes. They result in fusion points melting holes of varying sizes at the point of impact of materials with high resistivity. For material which is a poor conductor, a large amount of energy is released in the form of heat. The heating of water vapour contained in the material results in very high abrupt localized pressure which may cause it to explode.

Effects due to the initiation : In the event of a lightning strike a large increase in the ground potential of the installation will occur depending upon the grounding network and soil resistivity. Potential differences will also be created between various metal elements. Hence the need to pay particular attention when installing earth rods and inter-connection of metal structures adjoining the conductors.

Acoustic effects - thunder: Thunder is due to the sudden increase in pressure (2 to 3 atmospheres) of the discharge channel developed by the electrodynamic forces during the lightning flash. The duration of a thunder clap depends on the length of the ionized channel. For high frequencies, propagation of the spectral components released by the shock wave is perpendicular to the channel. For low frequencies, propagation is omnidirectional; hence the different forms of rumbling or claps heard by an observer depending on the distance and orientation of the successive channels used by the lightning flash.

Luminous effects : A lightning strike nearby violently sensitizes the retina of an observer. The eye is dazzled and vision is lost for several long seconds.

Electrodynamic effects : Electrodynamic effects between conductors and other parts occur due to large magnetic field of the lightning current.. This results in substantial mechanical forces, both attractive and repulsive, that are all the stronger when the conductors are close together or the current is high.

Electrochemical effects : The fleeting nature of lightning impacts (compared to stray ground currents) mean that these effects are highly negligible and without influence on earth rods.

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