Lightning protection at a construction site

An old Russian proverb says, that one should bring his child up when he/she is lying across the bench, not along. The situation with lightning protection is similar on the whole. The regulaton of the Instruction on lightning protection AD 34.21.122-87 start to worry when the walls of the building under construction will raise to 20 m. It is quite a careless regulation. You need to begin at once, as soon as the place for the foundation is defined. The first but crucial question - what soil is there at the construction site?

E. M. Bazelyan, D. Eng. S, Professor;
G. M. Krzyzanowski Power Engineering Institute, Moscow;
acknowledged Russian expert in grounding and lightning protection

1. Soil condition analysis

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2. Measuring grounding resistance of the foundaton

Do not rush with the measuring of ground resistance of the foundation made. All recommendations about its use as a grounding device are bacsed on the fact, that the water-repellent concrete drains the moisture from the ground together with the salts that have been dissolved in it. In the result, the reinforcement bars of the foundation occur in the same environment, as those placed directly in the ground. Moisture diffusion from the ground to the concrete takes a lot of time. It is better to wait 1-2 months for control measurements.

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3. What lightning rods are required at the construction site?

Instruction on lightning protection AD 34.21.122-87 gives an unambigous answer to this question (p.1.11). Starting from the height 20 m, all construction sites with the working personnel should be protected from direct lightning strikes by lightning rods, providing zone B. This prescription reveals a certain contradiction. Because in the same regulation, the buildings already built should be provided with lightning protection only at the height more than 30 m, and only in case of their removal from other buildings to the distance more than 400 m. There is nobody to explain this variant reading.

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4. Lightning rods in high-rise construction

Any construction starts from the zero circle, but the height of the walls grows, and together with it, the requiremenrs to lightning protection grow. As it has just been mentioned, the frequency of lightning strikes increases with the height of the construction (at the extreme - proportionally to the square of height), and the reliability of lightning rods operation reduces. The problem is most accurate in high-rise construction, where the height is the maximal outline dimension.

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5. On what lightning rods to orientate?

Before to start talking about height and number of lightning rods, we should stop on their conception. A construction site raises and that is why a constant re-installation of lightning rods is inevitable. Stationary devices on welding are little applicable here. The already mentioned paragraph 1.1. of the instruction AD 34.21.122-87 indicates the possibility of using bolt connections for the installation of temporary lightning protection. This should be the primary orientation, simplifying the frequent replacement of lightning rods to a higher level.

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6. Thunderstorm danger at the project site

Any high-rise building attracts lightning strikes and transports their current to the ground. From these positions, the type of lightning has no significant meaning, because the current of dozens of kiloamper can be produced by the upstream lightning. The level of construction completeness is also irrelevant. It is important, that the object walls would rise above the ground to hundreds of meters and that is why the number of lightning strikes into it is measured by the dozens per year.

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