Lightning begins high up in the clouds
A. Lightning begins high up in the clouds, sometimes as high as 25,000 feet (7,600 metres) above the earth’s surface. As it descends toward the ground, the electricity is searching, searching, searching for something to connect with. It steps, almost stair-like, in a rapid-fire series of roughly 50-metre increments. Once lightning is 50 metres or so from the ground, it searches again, like a pendulum, in a nearby radius for “the most convenient thing to hit the fastest,” says Ron Holle, a US meteorologist and long-time lightning researcher.
Prime candidates include isolated and pointed objects: trees, utility poles, buildings and occasionally people. The entire cloud-to-ground sequence happens blindingly fast.
B. The popular perception is that the chance of being struck by lightning is one in a million. There’s some truth here, based on US data, if one only looks at deaths and injuries in a single year. But Holle believes that statistic is misleading. If someone lives until 80, their lifetime vulnerability increases to 1 in 13,000. Then consider that every victim knows at least 10 people well, such as friends and family. Thus any individual’s lifetime probability of being personally affected by a lightning strike is even higher: a 1 in 1,300 chance.
C. Holle doesn’t even like the word “struck”, saying it implies that lightning strikes hit the body directly. In fact, direct strikes are surprisingly rare. Holle, Cooper and several other prominent lightning researchers recently pooled their expertise and calculated that direct strikes are responsible for no more than 3-5% of injuries. Justin believes that he experienced what is called a side flash or side splash, in which the lightning jumps from something that has been struck – such as a tree or telephone pole – hopscotching to a nearby object or person. Considered the second most common lightning hazard, side splashes inflict 20-30% of injuries and fatalities. By far the most common cause of injury is ground current, in which the electricity courses along the earth’s surface, ensnaring a herd of cows or a group of people sleeping in a tent or a grass-thatched hut.
D. What should you do if you find yourself stranded a long way from a building or car when a storm kicks up? Some guidance is available: avoid mountain peaks, tall trees or any body of water. Look for a ravine or a depression. Spread out your group, with at least 6 metres (20 feet) between each person, to reduce the risk of multiple injuries. Don’t lie down, which boosts your exposure to ground current. There’s even a recommended lightning position: crouched down, keeping the feet close together.
In his cubicle at the control centre of the US National Lightning Detection Network (NLDN) in Tucson – operated by Vaisala, a Finnish environmental observation company – Holle has accumulated stacks and stacks of folders filled with articles and other write-ups detailing a seemingly endless litany of lightning-related scenarios involving people or animals: deaths and injuries that have occurred in tents, or during sports competitions, or to individuals huddled beneath a golf shelter or a picnic shelter or some other type of shelter.
That word whitewashes the reality, as so-called “shelters” can become “death traps” during a lightning storm. They provide protection from getting wet – that’s it.
E. On a series of large screens lining two walls of a room at NLDN’s offices, one can see where cloud-to-ground lightning is flashing in real time, picked up by strategically positioned sensors in the US and elsewhere. Satellite data has shown that certain regions of the world, generally those near the equator, are lightning dense. Venezuela, Colombia, the Democratic Republic of the Congo and Pakistan all rank among the top 10 lightning hotspots.
Initially, lightning safety campaigns promoted the 30/30 rule, which relied upon individuals counting off the seconds after lightning flashed. If thunder rumbled before they reached 30, lightning was close enough to pose a threat. But there’s been a move away from that advice, for various reasons. One is practical: it’s not always easy to figure out which rumble of thunder corresponds to which lightning flash. For simplicity’s sake, everyone from schoolchildren to their grandparents these days is advised: “When thunder roars, go indoors.”
Education isn’t the only reason lightning deaths have steadily declined in the US, Australia and other high-income regions. Housing construction has improved. Jobs have moved indoors. In the US alone, annual fatalities have fallen from more than 450 in the early 1990s to fewer than 50 in recent years.
F. There’s always room for improvement, though. Arizona, for example, ranks high in the US when looking at lightning deaths per state population. Holle’s theory is that people stay outside longer in the desert as the rain isn’t necessarily heavy during storms. That’s why casualties can occur, even before the storm arrives, with people dallying on their way to shelter while lightning stretches out in front of the dark clouds.
G. Still, people in high-income countries have it easy compared with those in regions where people have no choice but to work outside in all conditions, and lightning-safe buildings are scarce. One analysis of agricultural-related lightning deaths outside the US revealed that more than half of them occurred in India, followed by Bangladesh and the Philippines. The victims were young (in their early 20's for the men, early 30's for the women) and were often working in farms and paddy fields.
Some lightning deaths go unreported or are missed entirely. It might appear, for instance, that a fire killed an entire family. But that assumption misses a key piece of the tragedy. Sometimes it is lightning that sets the grass roof ablaze, temporarily paralysing the family members within, so they are unable to escape the flames.