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КАТЕГОРИИ:






Methodological guidelines for estimation of lightning effects on human activity




The natural phenomenon of the emergence and formation of atmospheric electricity discharges - lightning is a danger to the biosphere and technosphere. Lightning can lead to buildings destruction, cause explosions and fires and as well as life loss cases. For example, in 1997 in Ukraine there were around 1400 fires (3.3% totally) caused by lightning.

Lightning is an electrical discharge in the atmospheric air over several kilometers, which occurs between clouds, within clouds and between a cloud and the ground or ground facilities. In general, the effects of lightning on the biosphere and technosphere are subdivided into two main groups: primary, caused by a direct lightning influence (direct thunderbolt), and secondary, induced by lighting discharge or skidding of high potentials to communications systems of the object.

Direct lightning influence (direct thunderbolt) causes instantaneous heating of current-conducting constructions up to melting temperature, explosion of non-conducting constructions and even building destruction.

Secondary lightning influences arise as outcome of the potentials difference appearance between metallic parts of the equipment, conduits and current-conducting wires as a result of electromagnetic and electrostatic induction from direct thunderbolt.

Electromagnetic induction. During lightning discharge in space a magnetic field appears and changes in time. This field induces an electro-moving force in metallic constructions, conduits, electric wirings. In contours with closed configuration electric current causes the heating of construction. In opened contours, for example, in conduits communications, laid on the territory of storage of fuel and lubricating liquids, electro-moving force of electromagnetic induction is able to cause sparkling or heating in places of conduits rapprochement of diverse contours, where electro-moving force is induced.

Electrostatic induction. In ground objects under thunderclouds electrical charges are induced by the value equal and contrary on sign to cloud charges. Electrostatic charges are induced on metal roofs, the water pipes and sanitary sewers, electrical wiring inside buildings and other structures. The potential between the object and the ground is higher, the higher the object. To control the appearance on and inside the buildings the potential difference between the equipment due to electrostatic induction on all metallic conducting elements of the buildings must be grounded. Skidding of high potentials in buildings takes place air, overground and underground communications (pipes, electric power line and communication line).

The most dangerous of all lightning effects in terms of buildings and structures destruction is a direct thunderbolt. Long-term observations and data suggest that the majority of fires and damage at lightning discharges is caused by direct impact of lightning strikes (direct thunderbolt).

Consequently, the lightning protection of any category must include protection against direct thunderbolt. Lightning protection system is a complex of measures designed to prevent the object from lightning discharge or to eliminate dangerous consequences of a direct thunderbolt; this complex also includes means to protect the object from the secondary effects of direct lightning influence and skidding of high potentials. The basic tasks of lighting protection are in detail considered in manual РД 34.21.122-87 «Инструкции по устройству молниезащиты зданий и сооружений».

Lightning protection system includes three categories – І, ІІ and ІІІ.

Objects of I, II categories are protected against direct thunderbolt, secondary lightning influences and skidding of high potentials to surface and underground communications.

Measures of lightning protection system of III category is focused on reducing direct thunderbolt and skidding of high potentials to ground communication.






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