A bolt from the blue

The ins and outs of the rare positive lightning strike
Lightning strikes Toronto's CN Tower. ((Jim Bradford/Canadian Press))

A pleasant afternoon on a soccer field in Brampton, Ont., went terribly wrong for two young boys and a woman who were hit without warning by a bolt of lightning on Wednesday, Aug. 12, 2009.

Kyus Caines, 5, his mother, Dulce Caines, and a three-year-old boy, whose name has not been released, were on the field when the lightning struck.

Dulce Caines and the younger boy were injured, but were released from hospital a few days later. Kyus, who bore the brunt of the strike, died in hospital on Aug. 22.

Witnesses expressed surprise and bafflement at the timing of the strike and its strength. Many described the weather at the time as being partly cloudy, with no thunder or rain.

Environment Canada meteorologist Geoff Coulson said there was a storm in the area, but it was considered "weak and a very localized event" that only produced 15 to 20 flashes of lightning.

It appears the three may have been hit by a rare type of lightning strike colloquially known as a "bolt from the blue." These strikes usually hit in what appear to be relatively calm skies, and with great force.

Thunderstorm safety tips:

  • Try to get indoors or in a car.
  • Find an area with a lower elevation, such as a ditch or culvert.
  • Never stand under trees, which are a magnet for lightning strikes.
  • If you are out in the open, don't lie flat. Instead, crouch down with your feet close together and your head down.

CBC Weather Centre

Strikes from afar

"This episode, where it came out of nowhere – they call it 'the bolt from the blue' – [occurs in] only about five per cent of lighting strikes," said Dr. Ernest Chiodo, an expert on lightning injuries.

"It is called positive lightning. It tends to be the more dangerous form of lightning."

Lightning is formed when ice crystals in clouds rub up against each other to cause positive and negative electric charges.

The positive charge migrates to the top of the cloud, while the bottom of the cloud is negatively charged, according to Environment Canada.

People injured in positive lightning strikes run the risk of suffering greater damage to their organs than those hit by negative lighting, says Dr. Ernest Chiodo. ((Sean Magennis/Canadian Press) )

Negative lightning, which occurs in 95 per cent of strikes, originates in the negatively charged bottom portion of the cloud and hits the ground directly, Chiodo said.

But positive lightning originates at the top of the cloud. It can travel as far as 50 kilometres horizontally away from the cloud before suddenly striking downward, said Chiodo.

Positive lightning also tends to be a lot more powerful than negative lightning. Positive lightning strikes can carry up to one billion volts of electricity, compared to a maximum of about 100 million volts in negative lightning, according the U.S. National Weather Service.

Because the bolt from the top of the cloud has to travel a long way to reach the ground, it must carry "an extremely large current" to complete the electric circuit between the cloud and the ground, says the U.S Weather Service.

To wit, an average flash of negative lightning could power a 100-watt light bulb for two to three months, whereas a bolt of positive lightning could power that same bulb for up to 100 years.

Disproportionate human harm

Negative lightning also typically has a very short pulse – just a few millionths of a second, Chiodo said. "However, positive lightning has a longer duration and a greater capacity to cause harm to human organs," he said.

Lightning occurs when ice crystals in a cloud rub against each other, producing an electric charge. ((Dave Chidley/Canadian Press))

The vast majority of the electricity in a lightning strike is carried around the human body, not through it. But those who have been hit can suffer severe injuries.

The chances of surviving a lightning strike are good – the U.S. National Lightning Safety Institute says nine out of 10 people hit by lightning survive. But most people hit by lightning suffer long-lasting health effects like memory loss, says Environment Canada.

Lightning strikes can also affect a person's nervous system, which can impact multi-tasking and thought-processing abilities, says Dr. Mary Ann Cooper, one of the world's leading authorities on lightning injuries. Besides injuries to the nervous system, people struck by lightning could also suffer eye damage, deafness or ringing in the ears, or amnesia.

There are around two million lightning flashes in Canada every year, according to Environment Canada. Between six and 10 people die annually, while around 70 are injured after being hit by lightning.

With files from CBC Radio's Metro Morning