Lightning delay
 

First game of the season last night and Mother Nature wasn't ready for it to start. A two hour lightning delay before the opening kick kept me awake much later than I wanted. In Georgia, they must wait 30 minutes after the last lightning strike before the players go out on the field, then a 30 minute warm up before the game. We thought all quieted down when 26 minutes after what we thought was the last strike, a bolt hits behind the visiting stands. Argh! The 7:00 kickoff happened at 9:00.

The refs last night did a great job keeping the kids safe and keeping the pressbox informed. But now I get to do another game tonight on five hours sleep. Where's the coffee? :eek:

Isn't the subject line a self-contradiction? ;)

But seriously, I've seen a field ringed with tall light towers and closed for lightning. Those metal towers would be such effective lightning protection, there's no way lighting could strike inside that ring, but they closed it anyway.

Robert

That's when we would have gone home.

I don't know who told you such nonsense. I just hope it doesn't get you killed.

Nonsense.

From the NOAA:

"Lightning does not always strike the tallest object."

And

"While tall pointy isolated objects are statistically more likely to be struck,
by lightning, it’s not nearly reliable enough to rely on for safety. Lightning can still strike you near the tall
object. Besides, the lightning electricity will likely spread out along the surface of the ground and can still kill
you over 100 Ft from the “protecting” object. NO PLACE OUTSIDE IS SAFE NEAR A THUNDERSTORM!"

I'm not going to be the one standing in the middle of the field to test this theory.

Oh, c'mon, waltjp... it must be fun
:D

We had delays Thursday night. What was supposed to be 2 frosh games that started at 5 ended up starting around 6:30. We cut the quarters back to 6 minutes in game one and 8 minutes in game 2. The visiting team didn't even get there until around 6:15, so we the delay itself didn't mean much. Didn't get done until right after 10:00, so late night.

One near miss in my lifetime was quite enough, thank you. :D

True.

Also true.

False!

The situation described was not one of a single tall pointy conducting object near the place to be protected, in which case the single mast could indeed draw lighting to the area and possibly conduct it thru the ground to hurt someone near it. Rather, it was one of a ring of such masts. The area in the center of such a ring would be as well protected as could be. Even if lightning were to strike one of the masts, by induction the ground current would run away from the ring rather than thru it.

While it is true that lightning could still strike in the middle of such a ring, and that current could be conducted thru that area, it would be no more likely than would be the case for someone in a bldg. To say that it would be dangerous to be within it would be the same as saying it's dangerous to be in a bldg. in the middle of lightning.

And yes, if I weren't looking to get out of the rain, I would go into the middle of such a ring of masts for lightning protection.

If you don't believe me, try experimenting with a spark coil and a ring of pins pointing in one direction from a conductor. See if you can ever get a spark to land in the middle, or for the current from a discharge to be conducted thru the middle. Of course the pins have to stick out far enough compared to the size of the ring, as was the case with this ring of metal light towers.

Robert

Let's see....NOAA or Robert...tough call here, but I gotta go with the NOAA.

Near miss? That was a near HIT!

Have to say I agree with you. I was about 6 years old and gathered in front of my house with my brother and a couple of other friends. The lightning strike hit in the road about 25 feet from us. Oddly, it missed all of the taller trees, telephone poles, houses, chimneys, tv antennas (remember them?), etc. So much for Mr. Goodman's theory about lightning hitting the tallest object.

Up in my neck of Canadian woods, if we see lightning, the game is delayed until 15 minutes of no-lightning weather is observed. What people do after we initiate this process is up to them.

If they're tall enough & good enough conductors and surround the road, it will.

Why do you think a bldg. is considered lightning protection for its occupants? Only because it contains conductive & grounded pipes & wires in the walls. The roof over it does nothing. Strip away everything but the pipes, downspouts, etc. and what would you see? A bunch of conductive masts surrounding the occupants. So what makes you think those same conductive masts would not provide the same protection outdoors?

Robert

Oh, you mean if they enclosed the road - sort of like a domed stadium? Well, unfortunately, the road wasn't enclosed and neither was your football field. I say we all take your advice and tell the players and anyone else in attendance to seek shelter inside of a safe building.

I have to agree, in principle, with Mr Goodman. However, it is a lot more complicated than that. My college degree was in electrical engineering, though I admit I don't work in a field now that applies any such knowledge to high voltage situations (I'm a digital guy working at 5V or less).

We spent plenty of time on examples of applying Gauss's law to conducting enclosures. The best example is our professor sitting in a large wire mesh cage, i.e. a Faraday cage, about 5' x 5'. A student was challeged to try and shock the professor using a Tesla coil. The Faraday cage dissipated any charge before it could reach our professor. This exhibited the fact that the electric field inside a conducting enclosure is 0. Electricity always flows along the field lines of an electric field, from high potential to low potential (i.e. voltage). No electric field, no flow of electricity, no getting shocked.

However, I will say that all the examples we worked with, the gaps in the mesh were so close that they could effectively be ignored. Thus, for all purposes of calculation, it was a solid conductor. In the lightning example above, the gaps between the conductors may be too large to ignore. In this case, there may be an electric field in and around the field that could make it dangerous. I agree with NOAA, that the probability of being struck by lightning is extremely low, but not low enough for me to be confident standing on the field in a lightning storm. And also, with the possible electric field in and around the field, the ground currents, even if lightning struck a tower, could be dangerous.

No. I'm saying that the way those tall metal masts surrounded the field and stands (Mitchel Atheletic Complex, Nassau County NY) was as good as the way the metal pipes, etc. in a bldg. surround its occupants in terms of lightning protection. The roof on a bldg. adds nothing, because it's not conductive, and has no pipes or wires running thru it -- unless there's an antenna.

If the ratio of the height of the surrounding conductive structures to the width of the road was like the field at Mitchel, the road would've been as well protected as a bldg.

Robert

But at least in the basement of a bldg., the ground currents problem would be the same as out in a field. If you can get off the ground floor, or into a vehicle with insulating tires (rubber), then you're safe from the ground currents from a nearby strike.

But with a ring of metal masts all pointing in the same direction, the potentials at the time of a strike on any of those masts will be such as to carry ground currents away from the ring, not thru the ring. The middle of that ring is the safest place to be.

Could it be better with wires overhead? Sure, then you'd really be in a cage. But most bldgs. don't really provide a Faraday cage. Fortunately for DC, it doesn't matter.

If you could see the height and spacing of those towers compared to the size of the field they surrounded, you'd agree.

Robert

I agree with this. But getting off the ground floor protects you because when you go up a level, you are now protected by a fully enclosed cage (i.e. there is wiring and plumbing below, in the ceiling of the room below). But I am suggesting that the field with a ring of high towers may not provide the same protection as a Faraday cage.

Your assumption is that all the masts are connected electrically to form this ring. And that the connections are large enough to support the current of the lightning strike. If either of these are not true, then there is potential for the currents to flow from one mast to another, possibly through the center of the ring.

But, like I said, it is _highly_ improbable. But not high enough for me.

It doesn't matter if it is AC or DC. Electricity _always_ flows from high potential to low potential along electric field lines. In a Faraday cage, there is no electric field, thus no flow of electricity.

But I would argue that a building does come close to approximating a Faraday cage. There is wiring and plumbing in the ceiling. Thus each room (except possiblethe ground floor) are close approximations of Faraday cages.

But even in the ring case I'm not sure that the current would always flow away from the ring, unless the rings were connected electrically and there were connections below the playing field.

I don't know. Like I said, I agree in principle, but the reality of the situation is different. And besides, even if it was safe on the field, would it be safe for those near the towers? Such as the stands? Or the parking lot? There would have to be a pretty wide berth around those towers' bases to ensure safety.

No, I'm just assuming they're up in the same air, and that there's nothing "funny" (insulating) about the ground between them.

That's what I noticed about that field. The stands were inside the ring of light towers. They built them really tall, too, which is good for lighting a game; less chance of looking into the lights when you look up.

Robert

That's my point. The ground is the insulation and the conductor. An insulator is nothing more than high resistance. Get the potential (i.e. voltage) high enough, and all insulators become conductors. Thus during a lightning strike, the ground becomes that conductor.

In order for it to function as a Faraday cage, i.e. to eliminate the possibility of any electrical field being present within the ring, they would have to be electrically connected with a low resistance path. The ground would be the electrical connection, thus would be the path for any discharge. Anybody between the towers would be at risk. A lower resistance path, such as heavy gauge wires between the towers, would protect against these currents.