Forensics

Lightning Claims

Forensic Services Newsletter

The advent of mass television documentaries has provided everyone with a good appreciation of the reasons for the origin of lightning events. We are also aware of the massive energy contained in strikes and the potential for damage.

Distribution of one million lightning flashes throughout the world.

Less well known are the ways by which lighting causes damage. Ignorance in these areas has given rise to lightning myths. Another problem is the enormous variation in lightning frequency around the world. People from one country can be unduly skeptical about the number of claims arising from another country or even part of a country.

On the claims that we are consulted on, we find that about 50% are not in fact caused by lightning. Many claims of lightning damage have their origin in voltage surges from the transmission line, and routine electrical breakdown. Poor maintenance is the cause of many of the latter, with accumulated dirt, moisture and corrosion allowing alternative paths for current tracking, with subsequent electrical damage.

There are three ways by which lightning causes damage.

Lightning flashes, both vertical and horizontal, over Sydney Harbour.
  1. Direct strikes : These can be spectacular and their appearance is usually so convincing that consultants are rarely asked to provide an opinion on the direct damage. The strikes can melt metals, fracture stone and masonry and ignite combustible materials.

  2. Current tracking : Any conductor or semiconductor is capable of carrying a current into a building. A conductor does not have to part of an electrical circuit. It might be a steel water pipe or even a damp wall. Even thought the conductivity might be low, the voltage and current that accompanies a lightning strike can be so high, that even a diversion of less than 0.01% can amount to voltage and currents capable of damaging both electrical and more especially electronic circuits.

  3. Induction : The electronic fields generated by lightning can induce currents in circuits that have no direct or indirect link to the strike itself. This is the mechanism of damage that gives rise to most difficulties in insurance claims.
A smorgasbord of flashes.

You have all heard the expression, lightning doesn't strike in the same place twice. When current tracking and induction are taken into account, it becomes apparent that lighting does not have to 'hit' the exact same place for certain items of equipment to suffer repeated damage over the years. When this is combined with the fact that in some parts of S E Asia, there are tens of strikes per square kilometer each year, it is apparent that for all practical purposes, lightning can strike in the same place twice.

Regards,





Barry Dillon