Climate & Earth M&G's Science Voices

MG’s #Science Voices: Is lightning’s ‘blast’ as bad as its strike?

cloud-ground-lightning10_20846_600x450How close does a person have to be to a lightning strike to be at risk? How far does this pressure blast wave extend? Ryan Blumenthal, a PhD candidate at the University of the Witwatersrand, has been researching lightning’s pressure blast wave effect on humans for the past 10 years.

This newly emerging field is known internationally as keraunomedicine or keraunopathology (“kerauno” is Ancient Greek for “lightning” or “thunderbolt”). This field includes aspects of electrical engineering, mechanical engineering, meteorology and climatology, as well as physiology.

During a lightning strike, the temperature of the lightning bolt channel is raised to about 24 700°C, in a few microseconds. This causes the temperature around the channel to rise suddenly, meaning that the pressure in the channel suddenly increases to several atmospheres, as does the volume of space it occupies.

This sudden rise in volume causes a sudden cylindrical pressure shock wave, which may reach pressures of more than 10 to 20 atmospheres (1013,25 kPa to 2026,5 kPa) in the vicinity of the lightning bolt channel. This is enough pressure to form a crater in a concrete pavement.

In South Africa, approximately 80 to 100 people will die because lightning strikes each year and approximately seven times as many people will be struck and survive.

These lightning-strike survivors may suffer severe disabilities, many as a result of lightning’s invisible blast wave, and therefore we need to study this phenomenon, understand it and find out how to protect ourselves from it.

South African law classifies a lightning-related death as an “unnatural death”, which means that it requires a full medico-legal examination, involving a full autopsy and inquest. Every aspect of the lightning-related death needs to be documented, so it can be included in the international guidelines and warnings to prevent more deaths. Our duties as scientists are simple: to protect ourselves, the other person and all of mankind.

* This is an revised extract from Ryan Blumenthal’s article in the Mail & Guardian’s New Voices supplement, published in 2014. The publication was the culmination of a six-month-long Mail & Guardian project to teach postgraduate science students how to turn their academic writing into something the public can read and enjoy.

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