Lightning is a common occurrence in the summer months and the spectacular shows can draw viewers out of their homes.

Although lightning can be exciting and beautiful to watch, it is dangerous and must be viewed safely.

Every year, lightning is responsible for about 10 deaths and causes 100-150 injuries in Canada.

Direct strikes from lightning only represent about 10 per cent of those lightning deaths and injuries. Most are cause by either ground currents (when lightning strikes the ground, sending a current through the victim) or by what are known as 'side flashes.' Those happen when lightning strikes a tall object (like a tree), travels part of the way down that object and then jumps to the victim nearby. 

Lightning safety tips

  • According to Environment Canada, a good rule of thumb is "when thunder roars, go indoors."
  • If you are in a vehicle, roll up the windows and avoid touching the radio or ignition.
  • Avoid touching household items that are plugged into electrical outlets, plumbing and corded phones.
  • Avoid taking showers or baths during a thunderstorm.
  • Do not stand under a tree or in a gazebo during a thunderstorm. (Only fully enclosed structures with wiring and plumbing will provide protection.)
  • Rubber boots will not protect you from lightning strikes.
  • If you are stuck outside, stay away from tall structures. Stay in low-lying areas and be on the alert for local flooding caused by heavy downpours.
  • Stay tuned to the forecast and the Canadian Lightning Danger Map, which predicts the areas at greatest risk of being struck by lightning in the next 10 minutes.

Why cars provide protection

A common myth is that the rubber tires on a vehicle insulate and provide safety from lightning strikes. While cars are a relatively safe place to be, it's the vehicle's metal shell — not the tires — that are actually protecting you. 

The metal shell of the car sets up what is known as a Faraday cage, which blocks electromagnetic fields from travelling inside the vehicle. When a bolt hits a vehicle, the charge travels through the conducting metal of the car around the occupants to the ground. 

That means that vehicles without that "Faraday cage," such as convertibles with canvas tops, will not offer the same protection during a storm. 

What causes lightning?

Lightning not only strikes while a storm is overhead, but can hit well ahead of an approaching storm, or in the thunderstorm's wake.

It is a sudden electric discharge that occurs within a cloud or between a cloud and the ground. 

si-lightning-strike

This dramatic image was posted by Tourisme Péninsule Acadienne. (Tourisme Péninsule Acadienne)

For lightning to occur, there must be a separation of charges within a storm cloud. The turbulent winds in the cloud help to separate those charges. The high concentration of negative charges at a cloud's base will cause a build up of positive charges on the ground and on tall objects. 

When the difference in charge between the ground and the cloud base becomes great, you get lightning.

The negative charge in the cloud moves downwards in a jagged path. As that happens, the air above tall objects on the ground continues to build a positive charge. When these negative and positive charges make a connection, the negative charges from the cloud flow rapidly to the ground. This movement begins where the positive and negative charges connect near the ground, and work their way upwards toward the cloud base, which causes the flash that we see. This entire process happens within seconds. 

Around the lightning stream, the air gets incredibly hot very quickly. A bolt of lightning is roughly 27,700 C, or about five times hotter than the surface of the sun. 

As the air is heated, it releases a shock wave, which we hear as thunder. Because light travels faster than sound, we see the flash before we hear the thunder.