Where is the safest place in a lightning storm?

“I am an avid fly fisherman and frequently find myself on the river in a raft during lightning storms. We always have a debate at these times on where we are safest . . . pulling into shore or staying on the water. . . Since I have heard one is safe in a car when lightning strikes I wonder if the raft floating on the water is insulated … and therefore the safest place to be.”

We spoke with some scientists about your question, and they all agreed that — under no circumstances — should you remain on the water during a lightning storm. If your raft is made of rubber, you might feel that you’re well insulated, but don’t kid yourself. Typical lightning flashes travel 10 to 15 kilometers and can deliver as much as 100 thousand amps of current. In comparison, a toaster uses about 10 amps of current. If lightning strikes the water near you, it will have no trouble traveling through a few extra centimeters of rubber.

So, if you’re on the water and a thunderstorm approaches, get to the shore and seek shelter on land. Try a building or car. If neither is available, look for a cave, cliff wall, or a group of trees. Never take shelter under an isolated tree –it’s also a good target for lightning.

The typical lightning flash

In a car, you might think the rubber tires protect you from lightning that strikes the ground nearby. But this isn’t so. Rubber tires provide some protection from lightning traveling through the ground — but the insulating limits of rubber only provide a little protection. A typical lightning flash can have 20,000 amp current peaks! Rubber just can’t offer that kind of protection.

Lightning that can travel such a long way through the air — several kilometers — isn’t halted by a few inches of rubber. Don’t fool yourself. You’re safer in a car or a building than you are in a raft on the river, but you’re never completely safe from lightning.

Some typical amperage (current) values:

  • 100 watt light bulb == 1 amp
  • toaster == 10 amps
  • t.v. set == 3 amps
  • car battery (while cranking) == 50 amps

Lightning occurs when opposite electrical charges build up in storm clouds and at Earth’s surface. In a thunderstorm, updrafts of warm air carry particles and raindrops up. The motion of the drops through the air causes static charge to build up — like clothes tumbling in a clothes drier. The air insulates this charge for a while, but when it becomes too great, the air is said to “break down” — letting the charges flow down toward the oppositely charged ground — just like electricity in a wire.

There has to be a channel between the cloud and ground to neutralize the charge that is built up between them. Lightning is lazy — it wants to take the path of least resistance. The original lightning pathway is initiated by the cloud itself, but you don’t see that part. Then something very interesting happens. The last 50 meters of the pathway, a segment of the pathway forms from the ground up to meet the rest of the path.

It’s as if the cloud has a long arm — it’s reaching out for a handshake — and the ground is reaching up with a short arm — and then they shake hands. Once they do, the pathway is like a wire for the electrons in the clouds.

The last bit, the handshake from the ground — is called a “dart leader” — and the “step leader” is the bit that comes down from the clouds.

After the path is established, the current then moves up the channel from the ground, as electrons move down the channel from the clouds. The current moving up is the high luminosity that you see from a lightning flash, although you perceive it as light traveling downwards. The pathway is first established downward, but the bright light then comes from Earth’s surface and travels up towards the clouds.

Most lightning flashes happen this way, although in some, the current actually does travel down towards the Earth, as electrons move up toward the clouds.

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