Dangers of lightning
When we think of how lightning can hurt us, we often think of a direct strike injuring or killing a person. However, a direct hit from lightning is responsible for only a small percentage of lightning-related injuries compared to other causes.
Lightning injuries are also be caused by:
- ground current
- side flash
- contact (with an object struck by lightning)
- upward leaders
- direct strike
- blunt trauma
Fig. 1 - This chart shows the six ways a lightning strike can kill or injure a person.
| Cause of lightning injury | Percentage of total lightning injuries |
|---|---|
| Ground current | 40-50% |
| Side flash | 20-30% |
| Contact | 15-25% |
| Upward leaders | 10-15% |
| Direct strike | 3-5% |
| Blunt trauma | unknown percentage |
Here’s how it works: a lightning strike heading for the ground typically hits an object, like a tree or a tall pole. Then the current disperses through the ground until it dissipates. Research shows that a lightning strike that makes contact with the ground can travel up to 10 metres. People have even been injured 15 to 30 metres away from where a lightning strike has hit the ground.
Ground current and/or side flash are responsible for 60% of lightning injuries or deaths. When adding the percentage of people hurt by contacting lightning through a fence post or tree, it increases up to 75%.
Lightning danger definitions
Ground current
Lightning enters the earth, travels through it and voltages are set up in the ground. One part of your body contacts one voltage, and another part contacts a different voltage. The difference in voltage is what drives the current through your body. In the image, when lightning hits a tree, you can see the lightning streak down the tree and into the roots. Even if you are not standing directly underneath the tree, lightning can travel through the roots and create a ground current.
Fig. 2 - An example of lightning hitting a tree and how it creates ground current injuries
Lightning hits the tree, travels down the trunk and into the roots. Lightning contacts a person standing on the roots about 10 metres away from the tree. The current from the lightning follows the roots through to the person. The image of the person becomes a skeleton.
Side flash
Lightning can travel down an object before jumping to a nearby victim. In the image, lightning hits a tree and travels half way down the trunk and exits, hitting the person standing nearby. Never seek shelter near a lone tree or other tall object, as a side flash can splash lightning from these tall objects onto a nearby object to reach the ground.
Fig. 3 - An example of lightning hitting a tree and how it creates side flash injuries
Lightning hits the tree and travels down the trunk. The lightning strike exits halfway down the trunk and onto a person standing nearby. The person is struck by lightning on the side of his body. The image of the person becomes a skeleton.
Contact
Lightning can make contact through an object a person is touching or holding onto, such as a tree, wire fencing or telephones poles. In the image, lightning hits the tree, travels down the trunk and exits onto the person leaning against the tree. When inside a house, either a corded telephone or water pipe such as a faucet can also cause this type of lightning-based injury.
Fig. 4 - An example of lightning hitting at tree and how it creates contact injuries
Lightning hits the tree and travels down the trunk. A person leaning against the tree comes into contact with lightning. The image of the person becomes a skeleton.
Upward leaders
During a lightning storm, the atmosphere around and below the storm clouds is electrified. Upward leaders happen when currents of positive charge start growing upward from the ground from elevated objects. If a downward moving charge (known as a stepped leader) and an upward leader meet, a conductive path will be formed and a lightning stroke will occur. Other upward leaders in the area of the main stroke still carry a charge. This charge is much smaller than the main stroke, but it is still large enough to cause injury or death. That’s why it is always safer to stay indoors during a storm.
Direct strike
Lightning connects directly to the victim. Only 3% to 5% of lightning fatalities result from a direct strike.
Blunt trauma
Blunt trauma occurs when a shock wave on the ground throws a person up to three metres away, causing injuries. Blunt trauma can also occur from injuries related to fire, explosions, or falling objects that are caused by the lightning strike. When a tree is hit by lightning, branches can explode off and hit a person standing underneath.
Fig. 5 - An example of lightning hitting a tree and how it causes blunt trauma injuries
Lightning hits the tree. A large tree branch breaks off from the tree and falls on a person standing underneath the tree. The person falls to the ground.
Surface arc
High current surface arcs are associated with ground currents. They appear in photographs as bright arcs of light radiating from a strike point like spokes of a wheel, in the air just above the ground’s surface.
The graphic below illustrates some of these phenomena.
Photo: © Johnny Autery, 1984; Illustration: © John Gookin, 2010
Fig. 6 – Examples of surface arc phenomena
Panel A: A typical lightning strike to a tall tree. There are two upward leaders that did not attach to the downward leader.
Panel B: Some upward leaders do not attach to the downward leader but still carry hundreds of amps and are quite dangerous.
Panel C: A surface arc is associated with ground current and can go tens of meters from the strike point.
Panel D: Side flash splashes some of the current onto a nearby object as an additional path to the ground.
Ultimately it is two types of lightning strikes (ground current and side flash) that account for 60 to 80 per cent of all the lightning strikes that see people being killed or injured.
As always with lightning it is important to remember: When thunder roars, go indoors!
To find out what else you can do to keep yourself safe from lightning, visit our section on Lightning Safety
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