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How were 300 reindeer killed by a single lightning strike?

Image of a reindeer herd in Norway
In late August, 300 reindeer were killed by a single lightning strike in Norway, an incident that showed the deadly potential of high-voltage electricity, including the dangers posed by fallen power lines.

Incident in Norway underlines the danger of high voltages on the ground

At BC Hydro, we have a great respect for the power of electricity, and we stick to specific safety guidelines to stay safe around electricity, on and off the job. But once in a while, the science of electricity becomes big news, such as with a recent report that 300 reindeer were killed by a single lightning strike in Norway.

We particularly like wired.com's version of the story because it investigates the science of how it happened, and it uses terms, such as "step potential", that you don't usually hear about outside of a utility like BC Hydro.

The article explains that when current is flowing through the ground following an accident (or lightning strike), the step potential is the difference in voltage between the points contacting the ground; in this case, the reindeer's legs.

Because the voltage at each "step" is different, it causes the current to continue flowing from one leg to the other. For these reindeer, this path caused the current to travel straight through their hearts, killing the poor creatures instantly.

Chart explaining step potential
When electrical current flows through the ground from a fallen power line or a lightning strike, the 'step potential' is the difference in voltage between the points contacting the ground. Electricity passing through a human or another animal can be fatal.

Down. Danger. Dial.

While we don't have that much in common with reindeer (aside from those of us who share a love of leafy greens), this story is a reminder of how we can all stay safe around power lines. Earlier this year, we told you about our newest public safety campaign – Down. Danger. Dial. If it's down, it's a danger, stay back 10 metres and dial 911.

"This situation is exactly why we remind people to shuffle with their feet together as they move away from the downed line – taking normal steps will cause a step potential, and result in electricity flowing through you, possibly causing harm," says Jonny Knowles, BC Hydro's public safety lead. "Also, you can't be too sure how far the current has travelled from its point of origin, so it's best to continue shuffling and move at least 10 metres away from the fallen line."

"When a voltage source, like a bolt of lightning or a fallen power line, hits the ground it creates a lot of electrical pressure at that point," says Marc Spencer, a senior safety advisor with BC Hydro. "That pressure spreads out, much as the ripples spread out when you throw a rock into a pond. The electrical pressure, or voltage, is different at each point as it dissipates over a distance."

With a fallen power line, it's important to know that even if you're standing a distance away, you could still be in danger if you're within the range of what would have been the pond "ripples". Each walking step within this distance creates a step potential and a path for the electricity to continue travelling – through you.

Just as with these unfortunate reindeer, the power could still be flowing through the ground, and walking normally could create a perfect path for the current to flow from the ground up through one of your legs and down the other, potentially causing serious injury.

Always remember to shuffle with your feet together until you're at least 10 metres, or a bus-length, away from the source of the accident. This will ensure the current keeps flowing past your body through the ground, so that you can escape, unharmed. As you do this, it might be helpful to warn anybody in the surrounding area to also stay back, especially young children.

If you need a reminder of safety around power lines, check out bchydro.com/besafe.