It would seem that a tremendous amount of energy is concentrated in the lightning bolt, capable of causing great mechanical damage to any object in its path. In fact, the real danger is not that great. Figure 1 shows a picture of a steel tip of a flagstaff from the Ostankino TV-tower with the traces of multiple lightning strikes. The size of the image is maximally close to the real one.
fig. 1. Photo of the steel tip of the flagpole from the Ostankino TV tower with traces of melting from contact with lightning
The sizes of the cavities are not that impressive. Their depth is close to 1 mm, diameter not more than 10 mm. The reason is that almost all energy of the lightning flash is dispersed along its channel several kilometers long. A very small share gets into the metal, this share is originated in the thin near-electrode layer with the voltage 10-12 V. Multiply this value to the charge of the lightning flash (maximum 300 Cl), you will get energy spent on the heating and melting of the fuselage, about ∆We = 3000 J. What is it good for? It is suitable to melt approximately 3 g of metal, if that metal is steel.
Therefore, all regulatory documents, without exception state the following rule and it is written down: if you have a surface 4 mm thick for steel, then this surface under no circumstances will melt through and overheated from the inside. Such a surface can be considered absolutely safe for lightning strikes. A lightning current will spread over this surface and nothing will happen.
fig. 2. Picture of a cap from the top of the Capitol building, Illinois state
Figure 2 shows a cap from the top of the Illinois State Capitol building (data was not verified, information is taken from an open source) with several holes resulting from lightning strikes. It can be assumed that the metal thickness of this cap is unlikely to exceed 2 mm.
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