The Lightning Rod as a Danger (PDF)

This book investigates the physical effects of a lightning flash on a person near the down conductor of a lightning protection system. These effects are the touch voltage, the step voltage and the side flash. For this purpose, a full-scale simulation model of the human body with a resistance of 1000 ohms was first created. In the simulation model, the body can touch the down conductor or be placed close to it. Furthermore, the specific resistance of the earth is varied. Likewise, insulating layers such as asphalt can be incorporated into the simulation model. Also, special cases like water permeable layers or water layers on an asphalt layer can be calculated. In post-processing, all relevant values can be determined, such as the energy converted in the body, the charge, the current and the voltage applied to the body. A comparison with the permissible limit values then shows for the lightning protection classes whether there is danger or not and provides information on necessary measures. There is a risk for death and injury if the down conductor is touched. However, there is also a risk of a side flash if a person is standing next to a discharge. Site isolation with dry asphalt is effective, but there is a residual risk of surface discharges. In real situations with wet asphalt, water-permeable layers or asphalt with a water layer, however, there is a great risk of death or injury. Equipotential bonding with an earthing grid is a necessary but not sufficient solution with regard to the induced voltage at negative subsequent stroke. Therefore, the situation must always be examined on a case-by-case basis with regard to the safety requirements. The only effective measure to prevent injury and death due to touch voltage is an insulating down conductor in conjunction with equipotential bonding. The measures for reducing the touch voltage, such as site insulation and equipotential bonding, basically also apply to limiting the step voltage. A risk calculation according to IEC 62305-2 gives the mean time between two events of injury and death MG = 1/RA. The tolerable risk is: RA = 0,0001 or MT = 10.000 years, equivalent to one death in 10.000 years.