Lightning risk ′much higher for animals′ | Science| In-depth reporting on science and technology | DW | 29.08.2016
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Science

Lightning risk 'much higher for animals'

How could hundreds of animals have died in a single lightning storm in Norway? DW speaks to the head of a high-voltage lab to find out.

Norwegian authorities said Monday that hundreds of reindeer had been discovered dead on Norway's Hardangervidda plateau after local thunderstorms. The leading theory at the time of publication remains that the animals were struck and killed by lightning. Alternative theories suggest death could have come from a previous disease or due to shock resulting from a nearby lightning strike.

DW: How could so many animals die from a lightning strike?

Professor Volker Hinrichsen: Lightning usually has several points of contact. You may have different strike points in a radius of, say, one kilometer (0.6 miles). That may explain why a group of animals can be hit.

Also, when lightning terminates on the ground, very high currents have to flow - 200,000 amps, for example. And if the electrical conductivity of the ground isn't good, the current will flow very tightly to the surface. That means we'll have so-called "step voltage" along the surface of the ground - you can measure voltage differences between different points on the ground [wherever you step]. So if you take a big step, you have a voltage difference between two points that are, say, 80 centimeters apart. The current will then mainly flow through two parts of our bodies [our two legs and abdomen] but it doesn't flow through our heart. That is totally different with animals. Animals have wider steps, maybe 1.5 or two meters wide, so the step voltage is much higher. The current, if it flows through the front and back legs, will always flow through the animal's heart. So the risk of death is much higher for animals during such an event.

Norwegen 300 tote Renntiere

The scene in southern Norway

So giraffes are at a higher risk during an electric strike than, say, a mouse, because giraffes take longer steps?

That's true. Cattle, for example, are also very sensitive to lightning strikes. A little mouse has a very low risk of being hit or being hurt by a lightning strike.

And a bear walking on all fours is at high risk… but if it stands up on two legs, it's at a lower risk?

There are two different kinds of risk. If a bear is walking on all four legs, it'll take higher step voltages - but the risk of being hit is lower. If he's standing upright, the risk of step voltage is lower - but the risk of being directly hit is higher. Because he's two, 2.5 meters tall.

So bears are just out of luck?

Yes.

How can people protect themselves?

Keep both feet close together. That means you won't take high voltage between your two feet, since they're very close. And squat down into a ball.

What's the best kind of ground to stand on?

Humid soil. If you have soil where plants are growing, and that has had some rain, for example, then the soil's very humid and the electrical conductivity is very high. On the other hand, the worst case is rocky ground. In [Norway's Hardangervidda plateau], which is filled with rocks and hills, then I assume there's really rocky ground with very, very low conductivity. So that explains why step voltage is very high.

Professor Volker Hinrichsen heads the high-voltage laboratories at the Technische Universität Darmstadt

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