Preventing electrocution from fallen overhead line on a vehicle

[Sahib]

Just two days before, a bus carrying many passengers came in contact with a 11 kV overhead line in Rajasthan State, India. At least 16 passengers were killed and many were injured due to arcing. The news is below
http://www.naharnet.com/stories/en/181894
It is apparent that a current was established through those unfortunate passengers, while passing from the bus to the ground despite the fact that the bus was having rubber tyres.
There was at least one incident reported in the Readers Digest in which a truck also came into contact with a MV overhead line. But the people inside it were not injured, even when there was arcing from the truck to the ground.
So what is the safety lesson?

 

[ActionDave]

Stay away from public transit.

 

[iwire]

It is apparent that a current was established through those unfortunate passengers, while passing from the bus to the ground despite the fact that the bus was having rubber tyres.

Do you understand how electrcity works?

There was at least one incident reported in the Readers Digest in which a truck also came into contact with a MV overhead line. But the people inside it were not injured, even when there was arcing from the truck to the ground.

I guess not.

 

[Sahib]

It is apparent that a current was established through those unfortunate passengers, while passing from the bus to the ground despite the fact that the bus was having rubber tyres.

Do you understand how electrcity works?

Yes. But tell me what might have happened.

There was at least one incident reported in the Readers Digest in which a truck also came into contact with a MV overhead line. But the people inside it were not injured, even when there was arcing from the truck to the ground.

I guess not.

What is your guess?

So what is the safety lesson?

 

[Haji]

Sahib:
You may address such questions to him, while he is sober.

 

[Ragin Cajun]

Electricity with find any path it can, basic theory. The so called "rubber" tires are a carbon compound, and carbon is conductive, think motor brushes. Granted the tire isn't pure carbon, but enough carbon.

I really don't see any way to prevent such, even a electrostatic shield likely would be useless. Remember 11KV will have significant current involved and will start burning where it conducts through a path. It WILL seek multiple paths and burn away.

RC

 

[kwired]

Recently had a farmer towing tall machinery with a tractor contact a 69kV line in area where I live. POCO's are always running public service ads on radio stations around here and one of them tells some things to do should you be in a situation like that.

The guy stayed in the tractor, used his cell phone to call for help, did not touch anything - especially metallic objects and remained calm until it was safe to do anything - he was never harmed. Good luck getting a bus full of passengers to remain calm like this though.

 

[K8MHZ]

Were the people in the bus or on it?

 

[kwired]

Were the people in the bus or on it?

That is how you sell 75 tickets for a ride on a 50 passenger bus

 

[K8MHZ]

That is how you sell 75 tickets for a ride on a 50 passenger bus

All kidding aside, my question is legitimate. The article does not tell us where the bus passengers were riding and it is very common in India for people to ride on top of them or anywhere on the outside one can get a grip.

If people were riding on the outside of the bus, the 'safety question' will have a bit of a different answer than if they were all completely inside.

 

[kwired]

All kidding aside, my question is legitimate. The article does not tell us where the bus passengers were riding and it is very common in India for people to ride on top of them or anywhere on the outside one can get a grip.

If people were riding on the outside of the bus, the 'safety question' will have a bit of a different answer than if they were all completely inside.

Well there is still non electrical safety questions if passengers are riding on the outside of the bus, maybe not in India though.

But take a situation like pictured there and run that bus into a high voltage line - 16 killed is probably a low number of casualties, especially if more then one conductor of different potential is within reach of those on the bus.

 

[ptonsparky]

When I read about this a few days ago I was surprised there were not more killed.

A local small contractor managed to snag a primary with his truck box. He just happened to leave the truck between cycles of the primary protection. POCO could not believe he lived while exiting the vehicle. He should have been dead.

I have no idea what the protection of primary lines in India is like compared to here in the States. Doesn't look good from most of the pictures we see. Granted we most likely see only the worst.

 

[GoldDigger]

If for some reason (fire?) you cannot remain inside the vehicle, the procedure is to jump with both feet out of the vehicle, sticking your landing with both feet close together (possible step potential), and then shuffle dlowly away.

 

[don_resqcapt19]

The bus is partially isolated from the earth by the tires and the metal is energized at line voltage. Any contact between the bus and the earth will result in a shock.

The tires are somewhat conductive (the black color is mostly from carbon) and there may be a voltage gradient in the earth around the bus and that too can result in a fatal shock.

Assuming that the tires or other parts do not catch on fire, the safest is to say in the metal bus until the power is disconnected. If there is a fire, you must exit the vehicle using the procedure that GoldDigger posted.

 

[Steve Sink]

Goldigger is right. Stay in the vehicle unless it is too dangerous to stay. And then jump clear of the vehicle, making sure not to touch the vehicle and the ground at the same time. Make sure to land with your feet together and hop away, or shuffle your feet. There have been many people killed who have been near cranes that got into primary and had the boom energized. They were killed because of step-potential.

 

[Electric-Light]

How birds can stand on primary. Then, we tend to feel dispersed current less than localized current.
You feel the static if your finger tip arcs over to your car, but if you grasp your key, then touch the car, you don't feel it much.

If it hasn't arced on the rim, then it probably won't arc over a step stool.

 

[just the cowboy]

Goldigger is right. Stay in the vehicle unless it is too dangerous to stay. And then jump clear of the vehicle, making sure not to touch the vehicle and the ground at the same time. Make sure to land with your feet together and hop away, or shuffle your feet. There have been many people killed who have been near cranes that got into primary and had the boom energized. They were killed because of step-potential.

Here is a step potential shorting out between the table legs in my basement after a lightning strike, good thing the kids just left that area.

 

[Sahib]

Well, Gentlemen, thanks for your replies.

The passengers were all inside the bus (there were 50, while the bus capacity was about 54)

There would have been a potential gradient along the inside metallic surface of the bus at the instant of contact of the bus with the overhead line and this might have caused the fatalities. One clue to it may be the arc burns sustained by the injured other passengers.

I think the lower the resistance of the metallic body of the bus, lesser is the danger of electrocution in such cases. So I propose regular testing of any vehicle for minimum electrical resistance.

What do you think?

 

[ptonsparky]

Propose all you want, getting it done is another.

My thoughts would be more to making sure the Primary stays where it should, educating the drivers and hoping for the best.

How often to these types of incidences occur?

 

[don_resqcapt19]

Well, Gentlemen, thanks for your replies.

The passengers were all inside the bus (there were 50, while the bus capacity was about 54)

There would have been a potential gradient along the inside metallic surface of the bus at the instant of contact of the bus with the overhead line and this might have caused the fatalities. One clue to it may be the arc burns sustained by the injured other passengers.

I think the lower the resistance of the metallic body of the bus, lesser is the danger of electrocution in such cases. So I propose regular testing of any vehicle for minimum electrical resistance.

What do you think?

I would really doubt that the tires would let enough current flow through the metal parts of the bus as to have enough voltage drop to cause a shock hazard due to a voltage gradient within the bus.