Lightning, which kills 2,000 people a year, can strike buildings with devastating force, as two families in the west have discovered, writes CLAIRE O'CONNELL
WITHIN THE PAST year, two houses in the west of Ireland have been struck by lightning, and their occupants have been lucky to emerge alive and without serious injury.
Last Monday a lightning bolt hit a house in Athenry, Co Galway, damaging the roof and ceilings and blowing out the electrical sockets. Ann Connell and her son James were in the house at the time, but they escaped physically uninjured – although rattled by the experience.
And last July lightning hit Sabina Berry’s house in Connemara, causing extensive structural and fire damage. Her daughter’s room appears to have borne the brunt of the strike, and she expressed relief that nobody was there at the time. “It would have been a totally different story if my daughter had been in her room. If she was in her room she would have been killed,” she said.
Lightning kills about 2,000 people around the world each year, according to the Irish Meteorological Society. So what is a bolt of lightning, and why does it come to earth?
“A lightning strike is basically a big spark, an electrical discharge or movement of electrical charge from one part of the atmosphere to the other,” says Gerald Fleming, head of forecasting at Met Éireann.
“It happens when the atmosphere builds up either a positive charge or a negative charge in one area as opposed to another.” How that “charge separation” builds up is not fully understood, but appears to happen in tall cumulonimbus clouds where particles travel up and down and bump against each other.
“These clouds have updrafts and downdrafts, and the moisture gets carried up and down in a vertical circle. Hail forms and there’s friction, and we feel that’s one of the mechanisms for this charge separation. So the top of the cloud gets negatively charged and the bottom of the cloud gets positively charged, or vice versa,” says Fleming.
That build-up of charge can be enough to overcome the air’s normal reluctance to conduct electricity, and electrons move rapidly along a channel or bolt.
In volcanoes, too, dust being pushed up in an ash cloud can also foster charge separation, resulting in lightning.
In practice many of these charged grumblings and flare-ups happen way above our heads, and we witness it as sheet lightning that passes between clouds in a storm. But the more spectacular forked version is associated with strikes from cloud to ground, explains Fleming.
“The bottom of the cloud might be very heavily charged, and it induces an opposite charge in the ground. Then you get a discharge of electricity from the cloud to the ground which we know as a lightning bolt or strike,” he says.
“It will take the shortest and easiest route between the bottom of the cloud and whatever part of the surface of the earth is closest to it. That’s often something high like a steeple or a spire, a house on a hill or a tree on a flat plain.” If lightning hits a building directly, it can damage brickwork and the electrical system, and vulnerable structures often have rods or conductors to guide the electricity safely to earth.
But when lightning hits the earth it can cause a short but powerful charge in the ground nearby, too, and this is a good reason not to lie down if you are caught outside in a flat environment in a thunderstorm, explains Fleming.
The key is to hunker down and keep low but stay on the balls of your feet to minimise contact with the ground, which could carry a charge if lightning hits nearby, he says.
Another good bet is to stay in the car, if you can. “A car is reasonably safe. The metal frame of a car forms a Faraday cage, which means effectively the charge is kept outside it. And the rubber of the tyres is a good insulator, so the car won’t pick up a lot of the electrical field from the ground if lightning strikes nearby.”
