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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => AC Power and Grounding => Topic started by: David Sturzenbecher on May 27, 2016, 09:36:52 pm

Title: Lightening and cows
Post by: David Sturzenbecher on May 27, 2016, 09:36:52 pm
Not in any way audio related, but a good saftey reminder none the less.   This is from about 40 miles from me.

Title: Re: Lightening and cows
Post by: John Roberts {JR} on May 27, 2016, 10:57:18 pm
sounds like time for a barbecue..

JR
Title: Re: Lightening and cows
Post by: Jonathan Johnson on May 28, 2016, 01:39:31 am
If caught outdoors in a storm away from shelter, I'd imagine the best tactic would be to crouch in a fetal posture with your feet as close together as possible, away from trees. That would reduce voltage gradients across the body.
Title: Re: Lightning and cows
Post by: John Roberts {JR} on May 28, 2016, 10:58:08 am
If caught outdoors in a storm away from shelter, I'd imagine the best tactic would be to crouch in a fetal posture with your feet as close together as possible, away from trees. That would reduce voltage gradients across the body.
Best not to be the tallest thing around, or stand under the tallest thing around (especially if metal).

I've been caught in a couple thunderstorms while jogging and I generally play the odds that trees and power poles around me will be better targets than I am, and the sooner I get indoors the better. One time, lightning hit about a half mile away (off to my right) and it was pretty damn loud. I jogged a little faster the rest of the way in.

JR

PS: I never quite understood people playing golf in thunder storms, that seems to be asking for it. Or fishing out on a lake. I crouch in the fetal position to watch the political nonsense on TV.

[edit] I don't want to downplay the harm that lightning can cause... If you notice a buildup of static charge (like causing your hair to stand up), then maybe hit the ground, and low crawl home. [/edit]
Title: Re: Lightening and cows
Post by: Keith Broughton on May 28, 2016, 11:28:43 am
sounds like time for a barbecue..

JR
I'm in!
Gonna need a lot of charcoal ;D
Title: Re: Lightening and cows
Post by: Mac Kerr on May 28, 2016, 12:25:16 pm
I'm in!
Gonna need a lot of charcoal ;D

They may already be overdone.

Mac
Title: Re: Lightning and cows
Post by: John L Nobile on May 28, 2016, 06:54:00 pm

PS: I never quite understood people playing golf in thunder storms, that seems to be asking for it.

Seems like a nice way to go. Hit a great shot, raise the club in the air and bang!
Just don't want it to happen for quite a few more years.
Title: Re: Lightening and cows
Post by: Debbie Dunkley on May 28, 2016, 07:08:07 pm
Probably a more humane end than the alternative quite frankly......

Title: Re: Lightening and cows
Post by: Steve M Smith on May 29, 2016, 08:49:45 am
Probably a more humane end than the alternative quite frankly......

Most likely.


Steve.
Title: Re: Lightning and cows
Post by: dave briar on May 30, 2016, 08:50:46 pm

PS: I never quite understood people playing golf in thunder storms, that seems to be asking for it
That's why my Dad always carried a one iron on the course. With lightening in the area he just took it out and held it straight up over his head. Said "Not even God can hit a one iron"

   ..dave
Title: Re: Lightening and cows
Post by: Scott Helmke on May 31, 2016, 10:13:41 am
If caught outdoors in a storm away from shelter, I'd imagine the best tactic would be to crouch in a fetal posture with your feet as close together as possible, away from trees. That would reduce voltage gradients across the body.

I've been told, by serious camping people, that you should have your feet wide apart. Doesn't make any sense to me, though - I'd think you're correct about keeping feet together.
Title: Re: Lightening and cows
Post by: Nathan Riddle on May 31, 2016, 11:44:48 am
I saw this a few weeks ago, thought it was a very good guide in my humble opinion.

http://www.artofmanliness.com/2014/04/24/how-to-survive-a-lightning-strike-an-illustrated-guide/

I think the feet wide apart is pretty silly, but I haven't heard the case for/against it so I'm not really sure what to think of it beyond the surface of the statement.
Title: Re: Lightening and cows
Post by: Mike Sokol on May 31, 2016, 12:16:50 pm
I've been told, by serious camping people, that you should have your feet wide apart. Doesn't make any sense to me, though - I'd think you're correct about keeping feet together.
That's incorrect. You need to keep your feet together to minimize any gradient voltage induced shock. I have an entire forum dedicated to training camping people about electricity, and the old wives tales I hear are crazy, and sometimes very dangerous.
Title: Re: Lightening and cows
Post by: Doug Fowler on May 31, 2016, 01:09:11 pm
That's incorrect. You need to keep your feet together to minimize any gradient voltage induced shock. I have an entire forum dedicated to training camping people about electricity, and the old wives tales I hear are crazy, and sometimes very dangerous.

What about a FOH platform skinned with vinyl and aluminum?  Faraday shield or not?
Title: Re: Lightening and cows
Post by: John Roberts {JR} on May 31, 2016, 03:12:38 pm
What about a FOH platform skinned with vinyl and aluminum?  Faraday shield or not?
To mitigate lighting hazards a lightning rod mounted to a high spot can discharge the local build up of charge that can attract lightning so basically prevent lightning, and if not completely successful, steer it harmlessly away from humans, while the current from a lightning down strike will vaporize the typical lightning rod ground wire, so try to run it in a shortest straight path. The lightning rod top needs to have a sharp pointy end, or multiple points to make it easier for electrons to jump off (or on?) to discharge the local field.
=====

Lightning routinely strikes metal aircraft without harming the passengers inside so being inside a metal can might work, but general advice is to avoid strong electrical conductors.

JR
Title: Re: Lightening and cows
Post by: Dave Garoutte on May 31, 2016, 08:45:41 pm
What about a FOH platform skinned with vinyl and aluminum?  Faraday shield or not?
You need to be completely enclosed to be protected.
Electrons repel each other, so the charge is literally on the outside surface of the farraday cage (car, plane, etc).
Title: Re: Lightening and cows
Post by: Stephen Swaffer on May 31, 2016, 10:22:21 pm
What about a FOH platform skinned with vinyl and aluminum?  Faraday shield or not?

I wouldn't count on an aluminum skin-a substantial framework that you are inside of would be more effective.  As light as aluminum or steel panels are these days, I would expect them to melt or vaporize instantly.

Several years ago I was doing FOH under a tent with 20 foot tall, 5" diameter aluminum main poles.  I wondered if they would be an effective lightning rod-and whether it made under the tent safer or just a target.  Thankfully, I never learned the answer.
Title: Re: Lightening and cows
Post by: Jonathan Johnson on June 01, 2016, 12:55:24 am
I think the feet wide apart is pretty silly, but I haven't heard the case for/against it so I'm not really sure what to think of it beyond the surface of the statement.

As Mike alluded to, the concern is voltage gradients.

When lightning strikes nearby, the electricity is discharged into the ground and current radiates out from the point of strike. The further you move away from the point of strike, the greater the voltage differential between the point of strike and the measured point. Two points close together (i.e., your feet next to each other) in the vicinity of the strike will have a lower voltage differential; two points far apart (i.e., your feet in a wide stance) have a higher voltage differential.

As a general rule, your body is a better conductor of electricity than soil is. So when you have a high voltage differential -- when your stance is wide -- there is the potential for high current flowing through the body*, causing injury. By keeping your feet close to each other, you minimize the voltage differential and, therefore, the potential current through your body.

Some of the old wives' tales may be based on the idea of not being the tallest object in the area and minimizing the electric charge in your body. If this were the only concern, laying spread eagle on the ground would be best. But laying spread eagle also maximizes the voltage differential your body will experience with nearby strikes. Since a direct strike to the body is much, much less likely than a nearby strike, a crouch with closely planted feet is the safest compromise. Your height is minimized, making you a less likely target, and voltage differential between parts of your body is minimized to reduce the potential current through your body.

*It should be noted that the maxim "electricity takes the path of least resistance" is very misleading. Electricity takes ALL conductive paths, though the greatest current will be through the path of least resistance. Even if the soil has a lower resistance than your body, the voltage potential in a lighting strike is so high that the potential current through your body can still be deadly.
Title: Re: Lightening and cows
Post by: Mike Sokol on June 01, 2016, 06:47:37 am
I wouldn't count on an aluminum skin-a substantial framework that you are inside of would be more effective.  As light as aluminum or steel panels are these days, I would expect them to melt or vaporize instantly.

Several years ago I was doing FOH under a tent with 20 foot tall, 5" diameter aluminum main poles.  I wondered if they would be an effective lightning rod-and whether it made under the tent safer or just a target.  Thankfully, I never learned the answer.
During my conversations with NOAA about lighting safety, we discussed the fact that tents are perhaps the worst place to be in during a lighting storm. The metal support poles are tall enough to make them a target for a lighting strike, but don't provide real Faraday Cage protection. There's been a number of Boy Scout lighting strike incidents where exactly that happened. The Leaders took the kids into a tent during a lightning storm where they huddled on the ground. Lightning hit the ground very close to the tent, and many of the kids suffered high-voltage damage to their bodies and nervous systems.

Non-Convertable cars have been demonstrated to be safe for occupents even with a direct hit from lightning. But the cars generally don't do very well with the on-board computers fried and the tires over-pressured from the lighting that jumped the gap from the wheels to the ground INSIDE of the tires. I don't know where I saw it, but apparently that's a problem with big construction equipment that's been hit by lightning. You've seen those enormous earth movers with tires taller than you. Once they've been over-pressured by a lightning strike they can sit there like a time-bomb for days. So the next person who moves them can be in the blast zone of those tires exploding due to weakened structure. I'll see if I can find any pictures and post them later..

I think the consensus is to get the heck out of the tent and into a substantial building (or at least the truck) if lightning gets close. 
Title: Re: Lightening and cows
Post by: Scott Helmke on June 01, 2016, 08:16:23 am
What would be something that a backpacker could carry to reduce the risk of injury? For the backcountry types it's either stay in the tent, or go outside and risk hypothermia from getting soaked with cold rain.
Title: Re: Lightening and cows
Post by: Jonathan Johnson on June 01, 2016, 11:53:34 am
I don't know where I saw it, but apparently that's a problem with big construction equipment that's been hit by lightning. You've seen those enormous earth movers with tires taller than you. Once they've been over-pressured by a lightning strike they can sit there like a time-bomb for days. So the next person who moves them can be in the blast zone of those tires exploding due to weakened structure. I'll see if I can find any pictures and post them later..

I posted a link to that issue in this thread (http://forums.prosoundweb.com/index.php/topic,158574.0.html).

Here's the link again for your convenience: https://www.bkt-tires.com/around-bkt/blog/post/tire-dangers-after-equipment-lightning-strike

It would be an issue for ANY rubber-tired vehicle that is struck by lightning, not just construction equipment. The volume of air in a car tire is much lower so the potential damage is much lower, but it seems to me that given the right conditions they could still fail catastrophically.

Maybe a .22 caliber long rifle round fired at a stricken tire would be a reasonable safety release -- could be administered from a distance. I haven't tested that theory, so don't assume it's a safe way to relieve pressure.
Title: Re: Lightening and cows
Post by: Dave Garoutte on June 01, 2016, 04:02:45 pm
What would be something that a backpacker could carry to reduce the risk of injury? For the backcountry types it's either stay in the tent, or go outside and risk hypothermia from getting soaked with cold rain.
But whatever you do, take off your point hat!
Title: Re: Lightening and cows
Post by: Mike Sokol on June 01, 2016, 04:24:51 pm
What would be something that a backpacker could carry to reduce the risk of injury? For the backcountry types it's either stay in the tent, or go outside and risk hypothermia from getting soaked with cold rain.

Here's a link to the National Lightning Safety Institute's page on personal safety in lightning storms: http://lightningsafety.com/nlsi_pls.html

One thing that I know is that you don't want to be near something tall that can act as a lightning trigger. So being near the tallest trees are a bad idea. However, I'm wondering if being near a power pole with its grounding system might be an option. While you certainly don't want to be standing directly under a pole transformer (I've actually watched them blow up from lightning strikes), power poles generally have a top ground wire that's tied to all the other power pole grounds on the line. That's got to be a seriously good lightning current sink. What do you all think?  Yes, I know there's no power poles in the woods, so maybe standing under the shorter trees might be an option.
Title: Re: Lightening and cows
Post by: Stephen Swaffer on June 01, 2016, 10:44:23 pm
Yes, they would be a serious ground sink-but lightning is so much more powerful than anything we normally work with I wonder if it would be enough-or just spread the gradient over a larger area?  Around here I get nervous because fences run for miles tied to t-posts.  That should ground the fence-but that feeder the cows were around was very well grounded as well.
Title: Re: Lightening and cows
Post by: Jonathan Johnson on June 02, 2016, 01:06:17 am
Yes, they would be a serious ground sink-but lightning is so much more powerful than anything we normally work with I wonder if it would be enough-or just spread the gradient over a larger area?  Around here I get nervous because fences run for miles tied to t-posts.  That should ground the fence-but that feeder the cows were around was very well grounded as well.

The feeder may have been well-grounded, but the ground distribution was still over a concentrated area -- really, no different from a point ground such as a tree.

The common grounding through the grounded neutral conductor of the utility distribution system probably would provide some shunting of current from a direct lightning strike. However, the majority of the current likely would be to the nearest grounding electrode as that would be the path of least resistance. If the air around the conductor to that electrode becomes ionized, that also will be a current path. So you could still have a significant voltage gradient around the electrode, but it may not cover as large of an area. I wouldn't want to be standing anywhere near a power pole in a lightning storm.