T 1.3 Lightning

Lightning is the most significant threat to a building and the information technology in the building during a thunderstorm. A lightning strike can release current strengths of up to 200,000 amperes at voltages of up to several 100,000 volts. This enormous amount of electrical energy is released and dissipated within 50 to 100 microseconds. A lightning strike of this order of magnitude at a distance of approximately 2 km will still cause voltage spikes in the electrical cables in the building that could lead to the destruction of sensitive electronic devices. The closer the lightning strike is, the greater the indirect damage resulting from the strike.

If a building is hit directly by lightning, then damage will be caused by the dynamic energy released by the lightning strike. This can lead to damage to the building structure (roof and façade), damage caused by subsequent fire, or damage to electrical devices due to overvoltage.

Various commercial weather services provide information for a fee on the risk of lightning strikes for different regions. In Germany, such providers include, among others, the National Meteorological Service (Deutsche Wetterdienst at www.dwd.de) or the Lightning Information Service offered by Siemens (BLIDS, www.blids.de).

Examples:

• At a large German airport, lightning struck in close proximity to the control tower. In spite of having an external lightning protection system installed (in the form of a lightning rod), the automatic fire extinguishing system was triggered in the IT area, paralysing all airport operations for 2 hours.
• In addition to direct damage, lightning strikes also have more far-reaching consequences. One often reads reports similar to the following: In April 1999, lightning struck a high-voltage power line near Darmstadt and caused a brief power failure affecting about 80,000 people.