New Delhi Tragedy -- Is it possible to be electrocuted in a car?

Mr_Shiftright

I was just reading this terrible story about a bus travelling in India. Seems that it was filled with wedding guests and they had all their baggage tied on the roof (common practice in India).

Well, the baggage hit a power line and the news story reports that everyone in the bus was electrocuted, except for two passengers who were thrown clear.

I was always under the impression that because a car/truck/bus rode on big rubber tires, that it was not possible to be electocuted by a power line falling on your vehicle, unless of course you stepped out of it and grounded it. Seems to be a vehicle would be totally insulated from ground unless a tailpipe was dragging or some such.

How can you explain this tragedy therefore?

swschrad

weatherfolk all say stay in your car with the windows up to maximize your chances of survival if out in a wild lightning storm. lots more voltage in a bolt of lightning than in a high-tension line.

however, in india, it's a tad warm, and all the news footage I have seen over 50 years indicates that windows, if they exist, are open for the ventilation. since they are having an evil hot spell now, in spades and doubled.

this would mean that there are also likely a bunch of appendages hanging out the windows. excellent way to get roached by HV corona.

also, commercial vehicles in many parts of the world have striking chains or similar stuff dangling underneath to insure against static discharging through those nasty petrol fillers and causing fires and explosions.

seems likely enough, therefore, that the bus became a toaster oven.

mullins87

Ya' know, lots of motorcyclists are struck every year by lightning. I don't remember the number, but it really surprised me. I remember reading a story several years ago where a farmer struck a high tension line with a large piece of equipment that had ground breaking attachments. He would have been fine if he had stayed in the cab, but he thought that since the equipment was grounded all the current was going to it. Well, when he exited the cab....you can guess the rest of the story.

Back to the original story, everytime I see news or documentary video from that part of the world, if there is a bus in the footage, everyone is hanging out the window. But I had never heard of the striking chains to discharge static electricity.

swschrad

friend of mine in the TV game a few years ago did a live shot. the mast on the microwave van was sticking and wouldn't go down all the way. c'est la vie, and they pulled out. however, there happened to be a 3-phase power service to the building they were shooting at, and lordy, the mast was now a couple feet taller than when they drove in.

melted the thick, 60-mph rated aluminum mast all to hell and gone.

I understand they service the live masts more regularly now

swschrad

they have been a feature of trucks for years and years and years in this country. haven't seen the shower of sparks recently on the road, come to think of it, wonder if there is a replacement out there. static from a truck frame to a hose coupling burned out the williams pipeline filler house some 4 or so years ago here in the Twin Cities, I think they have welder-sized clip leads to ground the trucks now in the new filler house.

andre1969

that got struck by lightning about 2 years before I owned it. It was my cousin's car before I owned it, and he used to live right across the street, so that's how I knew about it. Anyway, he had the car up for sale, and for some dumb reason I bought it. It had electrical problems galore. Coincidence? ;-)

swschrad

a neighbor gave away a beautiful philco 25" (round tube, this dates me, but so what) color TV that had been whacked by lightning -- well, induced currents, not a direct strike. this was of the all-tube and proud of it generation of TV sets. not even detector diodes. looked clean enough so I took a chance. anything that takes a direct strike is probably only fit for scrap.

the entire 4th-anode section (25,000 volts) needed parts replacement, and turns out the filament worked but nothing else did on the CRT, so had to have that replaced in a shop... did the HV cage work myself. some 4 or 5 other tubes were a little weak, so I replaced them. no other parts were affected. the set worked great for over 2 years, until the flyback went out again.

amazing the tuner wasn't melted down. I have a board from a data switch that got circulating currents from cable buried among tree roots that has all sorts of parts blown off the circuit board. keep it as a reminder to keep the surge suppressors and UPS serviced around my place. so far I have "donated" two surge suppressors and a UPS to the lightning fairy in 5 years, and it was worth the price.

telitlikeitis

Some years ago, a fellow who worked for the same company as me, was driving on the beach at Daytona Beach, FL during an electrical storm. His car took a direct lighting strike, which blew out all four of his steel belted radial tires. He suffered no ill effects. The story made the local paper.

lbthedawg

Some rubber will conduct electricity, depends on the carbon content. A trick I saw done to find a misfiring coil pack involved using small jumpers made out of washer fluid hose. Since many coil packs use waste spark (one coil for two plugs) you place the small sections between the plug wire and the coil, use a test light to short the individual plug wires, obviously you don't contact the metal part of the test light.

Other small unrelated trick, watch a F1 race. When the cars come in to the pits, they have a plate that has whiskers to contact the car. Obviously a grounding plate.

Mr_Shiftright

Those bus tires must have been a great conductor, to fry 40 occupants like that. Very weird story. I guess I'll never know for sure.

alwaysfords

The grounding plate in F1 is to dissipate static electricity to prevent the ignition of the raw fuel vapors (sort of like those straps people used to use in the 70's hanging off the axles to prevent shocks when you got in and out of the car).
The recipie for getting electrocuted while in your car is based on lots of things - humidity in the air, surface below the car, size of the line on the car, etc, etc. Even though you are on rubber tires the distance between the car and the ground is pretty much nothing for big power to jump. You are only the height of the sidewall away from metal touching the ground.

andre1969

...when I was a kid. That year, 1982, we went on a long camping trip, and left the dog with my uncle, who at the time was living in the Shenandoahs in Virginia.

Well, the dog was tied to a pine tree out in the front yard, and one of my uncle's friends was on the front porch of the house, working on a chainsaw. A thunderstorm came up, but I guess everybody was in idiot-mode that day. The pine tree got struck, and as a result it got the dog, and got my uncle's friend. Both of 'em lived, but I'd imagine that guy learned a little more respect for Mother Nature that day! As for the dog, he'd hide behind the chair or jump in somebody's lap every time we had a thunderstorm after that! Oh yeah, we didn't let my uncle watch him anymore, either ;-)

alwaysfords

Sorry - in my last post I was talking about power lines when I said "size of the line", but the same is true for lightning, just replace it with "size of the charge".

Mr_Shiftright

Well that makes some sense, what you say, that the distance of the vehicle to the ground might be a determinant. A main power line can pack quite a charge that's true.

haspelbein

I don't believe that the insulating effect of the tires should be the main issue here. "Alwaysfords" pointed out correctly that the charge could jump directly from the rim to the ground.

In fact, the thing that should have saved the passengers is the "Faraday Cage" effect of the metal body of the bus, meaning that the free flow of electricity through the body would have prevented the build-up of an electric field and the associated voltage within the bus. If something lowered the conductivity of the bus' body, a local charge (lightning hit) may not have been compensated in time to avoid a discharge within the bus itself.

With an intact and conducting body/cage, grounding is not an issue. The construction of the bus' body is far more important.

Mr_Shiftright

So you mean the flow of electricity would normally flow along the outside perimeter of the bus body and then to ground, rather than "through" the interior space of the bus?

haspelbein

...just assume a cage/metal box which is a perfect conductor. Combine this with the first Maxwell equation, and you will find that the surface charges will position themselves until they cancel out the electric field inside the box. (Easier to solve for a static field, but it is essentially the same for a dynamic field also.)

Have you ever been to a science museum where they put somebody in a metal cage and have an arc of electricity hit that cage without harming the person ? A car's body performs essentially the same function.

Normally, a car is almost the safest place to be in a thunderstorm, at least from a purely electrical point of view.

Mr_Shiftright

So probably this bus had been stuffed with who knows what inside and also maybe modified in the shell, and so the "cage" lost its high rate of conductance?

Poor people. Goes to show you, if a bunch of weird coincidences and accidents and random events line up against you, you never know what will happen unpredictably.

haspelbein

Well, it also was a wire, and not a lightning strike. If the overhead rack that entangled the wire was mounted onto an internal structure, which was a better conductor than the body ... anything is possible.
Without knowing the construction of the bus, we'll probably never know.

Anyhow, it is an awful way to go. Reminds you to live every day to the fullest.

mullins87

Haspelbein is right on the money. The distance from the rim to the ground is no consideration for any sizable voltage. To further illustrate his point, take the example of an airplane being struck by lightning. From what I understand, this happens quite often. A metal skinned airplane will allow the strike to pass right on through, usually with little or no damage or injuries. However, an airplane with a carbon fiber, kevlar or fabric skin suffers a very different fate. When lightning strikes one of these, there is no metal shell to carry the voltage resulting in holes being blown in the wings or fuselage(?) along with electrical damage and sometimes injuries. Of the three mentioned above, the carbon fiber fairs the best.

alwaysfords

Carbon fiber fairs the best because it is conductive

mullins87

Aren't superconductors mainly carbon?

haspelbein

The old fashioned ones were metals. But I think we're still a nice step away from a superconducting airplane.

I once flew in a Boeing 737 after it had just been hit in-flight by lightning. They checked the plane for 2 hours, but could not find any damage. The plane was fine.

pblevine

Since there are some legit questions regarding how high voltage and/or static (Lightning) affects cars and buses, we should demand that the NTSB conduct public tests. And we should insist on the use of live test subjects - namely Taliban fighters.

swschrad

because of the oft-stated danger of more terrorist incidents. "dress-rehearsal for suicide bombings" we can call it, and get them to volunteer.

I have always held the view that those planning extreme violence should test their devices on themselves, to insure they work properly when it's time for prime-time. nothing worse than a 3-time failure in the martyr business, you just can't believe them any more.