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Lightening

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Lightening

Postby tigerlilly » Sat Aug 25, 2012 4:14 pm

This may strike some as a stupid question, but it came up as a topic of conversation on our last hike.

I thought I would throw it out to SPers, to see if you had any thoughts on this.

I was wondering if being in a tent is "safe", during a lightening storm in the mountains. If the tent/poles were "hit", would the lightening go down the poles bypassing the people safely inside?

The reason I ask is because, I once saw a display of a man in a large bird cage, and the cage was repeadedly hit by bolts. The man inside was fine, he was even able to put his hand flat against the inside of the metal cage and not be hurt.

would the same thing happen if I were in a tent?

TL
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Re: Lightening

Postby JD » Sat Aug 25, 2012 4:49 pm

Generally speaking you're safer in a lightening storm than in one that is strengthening. As for the guy in the bird cage, his safety depends on the bolts being large enough or the cage bars close enough so that the bolts can't fit through. For 3/8" bolts you'd want a pretty finely spaced set of bars.

Further reading:
1. "Faraday cage" (wikipedia): http://en.wikipedia.org/wiki/Faraday_cage
2. Recent account of lightning strike while in a tent: http://www.bbc.co.uk/news/world-us-canada-19326042
3. Backcountry lightning risk management: http://www.wec.ufl.edu/safety/BackcountryLightningSafety.pdf
4. Free English Lessons: http://www.elearnenglishlanguage.com/difficulties/lighteninglightning.html
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Re: Lightening

Postby MoapaPk » Sat Aug 25, 2012 5:31 pm

There was a very recent case of some people who survived a bad strike wile in a free-standing (full poles) tent at guitar Lake near Whitney.

http://www.bbc.co.uk/news/world-us-canada-19326042

The basis of the faraday cage is that there is no electric field inside a pure conductor that completely surrounds the reference point. Faraday cages for electronics rooms are usually made of a fine copper screen. Lightning traveling down a pole will leap to the nearest semi-conductor with a lower potential -- that might be you. In partial faraday cages (like autos), your safety depends on being away from the gaps between the pieces of metal. If your head is against a steel roof in the storm, the current may choose to go through your head.
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Re: Lightening

Postby boyblue » Sat Aug 25, 2012 6:52 pm

I wish I knew the source for this, but I read about two hikers camping in a tent near Bishop Pass in the High Sierra in the early 70's. Lightning hit the tent and, sadly, one or both were killed. I'm not an expert, but I think that even if the lightning passes safely through the poles, the ground currents could potentially cause injury or death. There were a couple of times when I would squat in my tent on my folded sleeping pad, sleeping bag and extra clothing for protection. (Did I mention quaking in terror?) In many years of backpacking and climbing I never overcame my own fear of lightning.
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Re: Lightening

Postby MoapaPk » Sat Aug 25, 2012 7:44 pm

Oops, sorry JD, in my rush to be "helpful" I repeated much of what you referenced. The potential difference is so great with lightning, that many common-day "insulators" break down and conduct; a sleeping pad makes little difference.

Often you can get weather maps that show the actual strikes. While the lightning around here tends to concentrate on the ridges, the frequency of strikes is pretty much the same on the very summits, as well as 2000' lower. However, one doesn't want to be the highest point on the ridge, and it is easier to be among (but not too close to!) trees when lower.
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Re: Lightening

Postby boyblue » Sat Aug 25, 2012 8:16 pm

MoapaPk wrote:The potential difference is so great with lightning, that many common-day "insulators" break down and conduct; a sleeping pad makes little difference.


You're right... there would have been little or no protection from a direct hit on my tent. But it's better than nothing in the much more likely event of a strike on some nearby boulders- which is what was happening at the time.
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Re: Lightening

Postby Marcsoltan » Sat Aug 25, 2012 8:23 pm

Tent poles make direct contact with the damp ground and they also have an apex, which is where all the poles come together on top. Streams of electrically charged particles would be looking for the easiest route into the ground. Tent poles make a good route. The amount of electricity, however, may be greater than what tent poles can carry. In that case, some of the electricity can go through human body/clothing/other items inside the tent on its way into the ground. That is why the three hikers on Mount Whitney were not seriously harmed.
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Re: Lightening

Postby lcarreau » Sun Aug 26, 2012 12:49 am



Hey, Tiger ..... you spelt "lightening" WRONG! It's lightning, as in L - I - G - H - T - N - I - N - G ...

Even these "ROCK GODS" know how to spell "lightning."

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Re: Lightening

Postby MoapaPk » Sun Aug 26, 2012 4:45 am

Maybe she was talking about Michael Jackson medical procedures.
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Re: Lightening

Postby lcarreau » Mon Aug 27, 2012 3:33 am

Seriously .... think the odds would be GREATER to have a tree fall down onto your tent - which has happened here in Arizona !

Of course, we don't have many trees here, but we make up for it in CACTI ..

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Re: Lightening

Postby tigerlilly » Tue Aug 28, 2012 1:55 am

:-/ spell checka - where are you when I need you?!

What if I lined the the tent with layers of aluminum foil ? would that create the same effect as a cage/booster bag?

I read the article by NOLS, it was excellent... thanks for the link. I read it years ago, but I think they added more data to it.

It says being in a tent is worse - ?! It also mentions not to go into a cave entrance....(which I have done in the past), thinking I was "safer". (good to know!)
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Re: Lightening

Postby mrchad9 » Tue Aug 28, 2012 2:40 am

Read this article tigerlilly. The 3rd one posted by JD. It is long, but very good. It discussed the science behind lightning and avoids making recommendations based on myths or anecdotal evidence.

http://www.wec.ufl.edu/safety/backcount ... safety.pdf

The way I read it, a tent is not a safe place to be in a storm (but it isn't any more unsafe than being in the same position in the same place without a tent). A tent is not a faraday cage, and most accidents occur not from direct strikes, but from ground current. There is a tremendous amount of energy trying to dissipate through high resistance ground, and laying down (as you might do in a tent) is the worst position you could be in, regardless of whether you are in a tent or not.
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Re: Lightening

Postby JD » Tue Aug 28, 2012 2:57 am

mrchad9 wrote:The way I read it, a tent is not a safe place to be in a storm (but it isn't any more unsafe than being in the same position in the same place without a tent).

It depends. From that article: "Tents may sometimes increase the likelihood of lightning hitting that spot if they are higher than nearby objects. Tent poles
conduct ground current and may generate upward leaders."

mrchad9 wrote:A tent is not a faraday cage, and most accidents occur not from direct strikes, but from ground current. There is a tremendous amount of energy trying to dissipate through high resistance ground, and laying down (as you might do in a tent) is the worst position you could be in, regardless of whether you are in a tent or not.

Apparently it's worth getting a pad or some other insulator between you and the ground. Although the potential in a lightning strike can be 10^9 volts the ground potential gradient may be on the order of 10^5 V/m. So two appendages touching the ground 30 centimeters apart could see a few tens of thousands of volts. A pad could make make a difference in this case. And getting into the "lightning postion" to minimize the current might save your life. Make sure and point towards Mecca!
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Re: Lightening

Postby lcarreau » Tue Aug 28, 2012 3:00 am

My friend wasn't found anywhere NEAR a tent when he died.

He had been eating his lunch on the tailgate of a truck parked beneath a towering pine ... the bolt hit the tree ..

http://www.summitpost.org/thunder-lightning-in-memory-of-a-friend/422948
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Re: Lightening

Postby tigerlilly » Wed Aug 29, 2012 12:54 am

Sorry to hear about your friend. :-(
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