Lightning protection of residential and public buildings - answers to frequently asked questions in the design

Lightning protection of space engineering, aircrafts and skyscrapers - all these problems can not fail to fascinate experts on atmospheric electricity. Still, for any of them it is useful to come down from heaven to earth, to feel the daily tasks of the designer, who often has to look for reliable and cheap means of lightning protection of traditional residential and office buildings of quite moderate height. I have often met designers at the seminars and it seems I've learned to look at lightning protection with their eyes.

1. Standardization of lightning protection of residential and public buildings

Life in the Soviet Union accustomed the older generation to an excessively respectful relation towards the standards. We cannot say it is a really bad habit. A high-quality standard definitely protects against foolishness, provided that it is not contained in the regulations. The socialist system did not acknowledge private property, and this was the reason of many absurdities in relation to lightning protection requirements. Until now, the current national standard "Instructions for lightning protection of buildings and structures AD 34.21.122-87" strictly regulates protection against direct lightning strikes of industrial buildings, exterior industrial plants, public buildings, even cowhouses, but in relation of residential houses it is applied on the residual principle.

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The article includes the section Volume of lightning protection defined by the customer

2. We calculate the frequency of lightning strikes into the building

The developer, who has decided to build this or that building, is fairly concerned about potential loss of property. He has the right to know what and to what extent can be damaged by lightning, the probability of emergency situation and how much the means of lightning protection will cost for an almost 100% risk elimination. All these data will be requested from the designer, and only then, having received a comprehensive response, the developer decides whether he needs a more reliable lightning protection compared with those miserable crumbs that are prescribed by AD 34.21.122-87. The designer should be prepared for the answer. For that, he should first of all estimate the frequency of direct lightning strikes into the designed building.

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3. Remote effects of lightning

The overwhelming majority of such impacts is determined by the influence of the electromagnetic field of lightning either on power line wires of the protected building or on the electrical communications in its internal volume. From the point of estimation of hazardous electromagnetic influences, the line type is of fundamental importance. In the ​​modern urban area, energy supply of residential buildings, as a rule, is carried out through an underground shielded cable from the nearest substation. The level of active pickups is minimal here. It is often simply not taken into account due to a very low probability of hazardous exposures. Any significant pickup is excited only when the lightning current entirely gets into the shell of the underground cable.

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The article includes a section Features of remote lightning effects on large high-rise buildings

4. What should be protected from direct lightning strike?

The answer to this question is simple. In modern residential and office buildings, the first things to suffer from lightning are the roof and equipment that is installed on it. The designed lightning rods are provided to protect them. Are lightning-proof roofs possible? They certainly are. Lightning cannot do anything with the steel sheet 4 mm thick. For copper this value should be increased to 5 mm, for aluminum - 7 mm. Such ponderous roof can be imagined somewhere on the royal palace or mansion of a pop star. Typical houses get along with metal tile or metal sheets with metal thickness of less than 1 mm.

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5. What kind of lightning protection to orient to?

The standard IS-153-34.21.122-2003 gives no instructions for that. The older document AD 34.21.122-87 classifies residential and office buildings to the last III category of lightning protection and even then in exceptional cases. It will be necessary to talk to the customer again, explaining to him that the recent Russian regulations IS-153-34.21.122-2003 operates with the protection zones with reliabiliy F = 0.9 and higher. For the average unprotected cottage, with an expected 1 lightning strike in Tlightn = 50 years of operation, installation of lightning rods with reliability of 0.9 will increase the estimated time up to 500 years (on practice slightly less because installation of a lightning rod, although low, will increase the maximum height of the building, and , consequently, the frequency of lightning strikes). Even by the standards of English mansions it is quite a decent time in which lightning would be not the first on the list of other dangerous hazards.

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6. What is better - a series of lightning rods of minor elevation or one high?

It seems that the designers like single lightning rods, especially rod ones. The conical surface bounding the protection zone is easily made by elementary formulas. If the object is entirely located within the scope of this cone, protection against direct lightning strikes with the required reliability is guaranteed. There is nothing to worry about. I'll try to show on a certain example, that the situation is not so simple and obvious.

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