Anyone reading about good old Benjamin Franklin knows about his invention of the lightning rod, and these were pretty standard features of the older houses in the neighborhood where I grew up. But you don’t see them being added to new houses being built these days. Why is this? Are they not effective after all? Or maybe the risk of lightning strikes is so small that it’s not worth bothering with (maybe this might have changed in recent times?) Or is there something else in the construction of the newer houses that serves the same function?
Lightning Rods certainly are still being added – you can look up places on the Internet, or in the Yellow Pages. My brother-in-law has a thriving business in them.
Ah, so they’re 1920s style lightning rods.
What? Ouch! Stop that!
I believe subsequent research has not been able to show that lightning rods are effective. I’ll see what cites I can find …
Lousy archive search. Found it with Yahoo, but not with the SD’s own search engine…
I asked about lightning rods in this post (my first OP on this message board) six months before Cecil’s take on the matter.
Anyway, my OP was rather convoluted, as I presented quite a bit of contrary info purporting to explain the purpose of lightning rods. Some of the info makes for interesting reading, though.
The Valet parking annex where I work (ballys) has lightning rods on the roof.
The annex was built 5 years ago.
One possibility is that modern houses are full of grounded electrical conduit, fiberglass insulation with foil backing, etc. If lightning strikes a house, it tends to find a metal pathway, so a dedicated lightning rod doesn’t improve things that much. On the other hand, 100 years ago when the current path is all through wood and brick, you tend to get steam explosions if not fires. Maybe a few decades back the builders were still playing by the older rules.
Another possibility: today we know that, while the majority of cloud/ground lightning strikes can kill electrical devices and people, and cause wood to explode, they do not cause fires. It takes long-duration or “hot lightning” to heat up your combustible material. If a person is inside a house, chances are that they’re fairly safe from lightning… and the house is fairly safe from fires just because hot lightning is so rare.
Another: where do you live? In Tampa FL lightning is constant throughout the whole summer, but up here in Seattle we only get a couple of thunderstorms a year. If you’re in a low-lightning area, maybe lightning rods aren’t much use (and maybe the original lightning-rod fad was still tailing off when houses were built 50 years ago in your town.)
The first part makes sense to me since homes weren’t even required to be grounded back then. I kind of doubt the figerglass insulation with foil backing though.
I guess that means some guys are still adding them, but there is no doubt that it has declined markedly. The area that I live in is a hotbed of building activity, and I don’t recall ever seeing a new house with one. And to make sure, on my commute home last night I checked out the houses that I passed, and not one new house had one - the older ones frequently did (though I couldn’t see for sure in many cases).
toadspittle, thanks for the cite. It does seem to me that Cecil is citing some relatively obscure fact, that itself dates to post-1993. I’m not sure if that study could account for it, but you never know.
I’m in central Jersey these days, and I grew up in Brooklyn, which has the same climate. And even where I live now, the older houses in my immediate neighborhood all have them - none of the newer ones do.
Hey! My brother-in-law lives (and installs lightning rods) in central NJ! If you want him to put them on your house, gimme a call.
I seem to recall seeing an episode of This Old House where they had a modern company putting them on one of their projects…
Science Dopers know more than me but the lightning doesn’t strike the lightning rod. the purpose of the rod is to ionize the air to prevent the strike…Some body else can elaborate on this.
I don’t really think lightning comes in different temps, its the action of the electric on the conductor that makes heat.
Darnit! Something’s wrong with straightdope’s archives and I can’t see what Cecil wrote. The following may therefore be irrelevant.
I remember reading an essay by Issac Asimov wherein he claimed that the lightning rod was the first real invention devised according to the scientific method (as opposed to accident). One could argue that point, I guess, but in principal the lightning rod is based on solid science having to do with sharp edges bleeding off localized charges before the potential difference becomes great enough to cause a lightning stroke. I.e. the rod does not attract the lightning, it actually prevents it. You would measure a current running through the rod’s grounding cable during a thunder storm.
They make the most sense when the building is the highest point in the local area (i.e. taller than the surrounding trees) and has a flamible roof (unlike many commercial buildings). For example barns and churches, the latter of which were often built on top of hills.
In the olden days, there weren’t so many trees across the praries. Thus, it wasn’t unusual for farm buildings to be significantly the tallest things for miles around. In today’s urban/suburban environment, your house isn’t sticking out like a sore thumb - even a new subdivision with baby trees still has hundreds of houses in all directions, reducing the chances that a particular house would get struck.
Well, I’ll add to this a bit.
My parent’s house was built in 1978, it has no lightning rods. The barn build it 1920 something does have lightning rods. Since the house is out in the country, before satellite was available, people would have massive TV Atennas. We had one such atenna that was about 30 feet tall.
One time, early in the morning, lightning hit that antenna. It was mounted on concrete. Near as we can tell, lightning travelled down the antenna, then somehow through the telephone lines in the house, and also somehow made it’s way to the basement.
The result of said strike was the following:
Insulation burnt out of the wall.
Nails holding the drywall to the wall were pushed out of the wall and laying on the floor.
Everyone phone in the house was blown off the cradle.
There was a nice hole in the basement wall about 1 foot underground.
Nothing caught on fire, but it was definately smouldering.
Yikes! Lightening rods prevent some strikes, but obviously not all. The volume of air that it bleeds charge from is not that great, especially in high wind. Thus, the barn roof was protected, but not very much area around it.
Most of the electric current from the strike probably went straight into the ground. But it also created a pretty impressive EMP (Electro-Magnetic Pulse). I.e. the rapid and intense rise and fall of the electric current set up a strong magnetic field which quickly grew and then collapsed.
As this magnetic field cut through the near-by phone wires, it induced a secondary current, which happily sped into your phones. I’m speculating that the coils in the earpieces took some of the current, which created another magnetic field, which must have repelled another field created inside the phone unit, which caused the handsets to jump off their cradles.
The basement damage was probably caused directly from the lightning current flowing through the soil. Variations of soil moisture and mineral content must have routed a large percentage of the current toward the wall, causing very rapid heating. The hole in the wall was possibly caused by steam.
Not sure why the nails would have been forced out, except possibly from the steam momentarily pushing the drywall off the studs. When the drywall snapped back, it might have popped the nails out.
Naturally, all this is pure speculation on my part (I’m not an expert but I do talk like one).
The TV tower might have functioned better as an actual lightning rod (i.e. prevented the strike) if it had a sharp spike pointing upwards at the very top, and if a good-quality grounding cable had connected the spike to a copper stake driven deep into the ground.
On my drive home last night, I was wondering if the hole in the wall might have been partly caused by a hydrogen explosion. The electric current might have induced enough electrolosys to generate a small pocket of hydrogen.
The more I thought about it, the less likely it seemed to me. In normal electrolosys, you have electrodes which attract the separated hydrogen and oxygen. They provide collection points where the gasses can accumulate. In the case of lightning, you might have one “electrode” in the form of the TV tower, but the “other electrode” would basically be the ground itself. I.e. as the water separated into H2 and O2, those molocules would simply slowly migrate along the entire length of the conduction area. Also, given the short duration of a lightning stroke, there wouldn’t be enough time for a significant amount of migration of the gasses.
Any lightning experts out there have any thoughts on lightning-induced electrolosys?
Nope, this is a common misconception. It arises when lightning storms are demonstrated with a tabletop electrostatic generator. A sharp needle can spew out enough ion current to discharge a VandeGraaff machine. But if you’re using a needle, then your demonstration is not to scale. The sphere of the vandegraaff machine is supposed to be a thunderstorm, so to keep the scale correct, the “lightning rod” should be like a microscopic piece of lint on the tabletop. In other words, the lightning rod on your home cannot short out a thunderstorm.
On the other hand, lightning rods do launch a cloud of ions, and IF THERE IS NO WIND AT ALL, the ion cloud will hover above the rod. Since ionized air is a conductor, electrically the ion cloud looks like a large metal globe. The lightning rod will tend not to launch an upward leader towards any incoming lightning bolts. This MAY be a bad thing, since the incoming lightning bolt is free to strike any object not under the ion cloud (like it might strike somewhere else on your roof.) Note again, this issue only arises when the ion cloud isn’t being blown away from your house by any slight wind.
“Hot” does not refer to temperature, it refers to the duration of the lightning stroke, that’s why I put it
in quotes. “It takes long-duration or ‘hot lightning’ to heat up your combustible material.”
If you don’t believe me, search some physics and forestry websites: google: “hot lighting” +fires
How good is a tall building in protecting a home? For instance I live in Chicago. We have a lot of tall buildings. Sears Tower, Aon Building, John Hancock. If I build a house or an apt building not too high won’t lightening hit one of those buildings first. (I am presuming lightning hits them all the time and they are grounded.)