First-hand Lightning Experience

Mike,

Your recent free online training video via your newsletter reminded me of several observations I acquired from my first hand lightning experience two years ago. I was at Tomahawk Scout camp near Rice Lake Wisconsin at the time. The rain had started in earnest and all of the scouts had just reported to their merit badge classes (mostly outdoors!). The camp wisely made the decision to keep the scouts together in their class locations instead of having them spread all over the camp for the next thirty minutes while they were sent back to their campsites, which also offered limited shelter. I was walking down a dirt road dressed in my usual wet weather gear; which is basically nylon shorts, a non-cotton t-shirt, and sandals.

A large lightning strike to a 75-year old oak tree occurred 100 feet away from me. The heat from the current flowing through the trunk vaporized the water in the wood and raised the internal pressure to a point where the trunk ruptured along a twenty-foot length. One fragment 4 feet long and about 4 inches in cross section made it half way to me. Small fragments of the core were strewn all over the area for 75 feet.

An arc in air from several feet up the trunk was observed going directly to the earth. Apparently the impedance change in the trunk near the ground was sufficient to allow a parallel path to ground outside the trunk.

The current flowed horizontally in the earth in most every direction through whatever parallel paths were available. Depending on the soil conditions, this might not necessarily be as much a surface current as your golf green picture and instead may have a significant depth. In any case, about seventy feet from the lightning strike, a long abandoned, buried, 16-3 extension cord was running at mostly right angles to the current radiating from the tree. This optimal conductor had such a high current flowing through it even though it was at right angles to the ground current, that it vaporized and blew out a trench of dirt twelve inches deep along it's length.

A scout leaning against a metal freezer wall in a cement floor building 500 feet away was shocked by a touch potential. I observed, but did not feel, a spark jump between my big toe and ground. I am not sure, but I expect this might have been an equalization of static charge impressed on my body from the high electric field. Lessons learned from this incident, along with your tutelage on stray and leakage current, are that you do not want to be a parallel conductor for this amazingly high current flowing in the ground. Just like freshwater drowning from electric shock, we are a pretty good conductor when compared to earth.

So don't lie on the ground in a storm. Instead support yourself as best you can on two feet placed close together. Find an insulating layer such as a lifejacket, or sleeping pad to squat on with both feet close together. Do not support yourself with your hands. I also conclude that permanent picnic shelters, typically without side walls or floor, are not adequate protection since current can pass across the ground underneath.

Cheers,
Ken Lillemo, Shoreview , MN

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