Electricity Explosion

[westie101]

If you've ever wondered on the sort of explosion you can get from the DNO system

http://www.bbc.co.uk/news/uk-england-northamptonshire-33006500


That is an LV underground connecting box failing!

And on the overhead system this still happens

http://www.bbc.co.uk/news/uk-scotland-edinburgh-east-fife-33007610

Reading the story it was quite survivable had the driver been aware of what to do (and also not been allowed/told to tip there!)

 

[boringoldcodger]

I'm pretty certain that I won't drive into an overhead power cable (only drive a car) but, just in case, I'd like to know what I should do (not touch any metal and ring 999 on the mobile ?).

Cheers, Graham

 

[westie101]

From the HSE document GS5
"Avoiding Danger from Overhead Power Lines"

http://www.hse.gov.uk/pubns/gs6.pdf

Emergency procedures
31
If someone or something comes into contact with an overhead line, it is
important that everyone involved knows what action to take to reduce the risk of anyone sustaining an electric shock or burn injuries. Key points are:
■ never touch the overhead line’s wires;
■ assume that the wires are live, even if they are not arcing or sparking, or if they otherwise appear to be dead;
■ remember that, even if lines are dead, they may be switched back on either automatically after a few seconds or remotely after a few minutes or even hours if the line’s owner is not aware that their line has been damaged:
■if you can, call the emergency services. Give them your location, tell them what has happened and that electricity wires are involved, and ask them to contact the line’s owner:
■if you are in contact with, or close to, a damaged wire, move away as quickly as possible and stay away until the line’s owner advises that the situation has been made safe:
■if you are in a vehicle that has touched a wire, either stay in the vehicle or, if you need to get out, jump out of it as far as you can. Do not touch the vehicle while standing on the ground. Do not return to the vehicle until it has been confirmed that it is safe to do so

The last point here covers being in a vehicle

 

[bernardgreen]

Yes stay in the vehicle until the local electricity network declare tbe lines to be dead and they have attached grounding conductors to the lines. If anyone approaches you tell them to stop and to keep at least 10 metres away from your vehicle. In wet conditions make it 20 metres.

 

[conny]

As the vehicle would, hopefully, be insulated from the ground by the tyres is it permissible to touch something metallic such as a window winder to warn people to stay clear?

Do you jump clear simply to avoid having one foot on the car and the other on the ground? In other words, can you safely stand on the door edge, grip the door sides and hurl yourself forward or should you not touch any metal under any circumstances?

 

[westie101]

One we had locally (the driver jumped)

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which was possibly a good job as the tyres were about to give loose

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[AdrianUK]

You need to jump clear without touching any part of the vehicle & the ground simultaneously.

While you are inside the cab, you are in a faraday cage. Yes, the vehicle may be sitting at 11,000V above earth (well actually 6358V.. but we'll leave that for another time) but EVERYTHING inside the cab is at this potential above earth, including the driver, so if you touch another part of the vehicle structure nothing will happen. (Birds don't get electrocuted when they sit on an 11,000V line!)

The problem comes when something that is at ground potential is introduced eg. the 'helping hand' of a rescuer. This creates a path to earth & the current follows. Good night Vienna.

I guess the risk in staying in the vehicle is that the tyres start to get hot (there will be some current flow to ground through the tyres) and start to burn. Then you have a choice..... jump CLEAR or burn.

 

[333rocky333]

But if you was still in it and the tyres burst what would happen to a person inside as hes still not the main route to earth, like the vehicle would be, id imagine a few sparks maybe a fireball and some heat, causing more injury than the actual electricity

 

[JohnW2]

The problem comes when something that is at ground potential is introduced eg. the 'helping hand' of a rescuer. This creates a path to earth & the current follows. Good night Vienna. ... I guess the risk in staying in the vehicle is that the tyres start to get hot (there will be some current flow to ground through the tyres) and start to burn. Then you have a choice..... jump CLEAR or burn.

IF one is in a position to jump. The one and only scenario of this nature I have witnessed (many many moons ago) resulted in a serious dilemma. A vehicle had crashed into a pole, and broken HV cables were draped over the vehicle. No-one knew whether the cables were still live or not. The driver was trapped in the vehicle and clearly needed urgent medical attention. Answers on a postcard!

Kind Regards, John

 

[bernardgreen]

It might be possible to use another vehicle to push the stricken vehicle clear of the fallen lines. The risks would be extremely high and the decision would require a lot of very careful thought,

 

[conny]

Or possibly instinct kicks in and you try to ram it very hard at an angle to dislodge the trapped vehicle but allow you to veer off if unsuccessful.

 

[JohnW2]

Or possibly instinct kicks in and you try to ram it very hard at an angle to dislodge the trapped vehicle but allow you to veer off if unsuccessful.

In the incident I was talking about, the vehicle was not trapped - it was the occupant inside it who was.

Kind Regards, John

 

[skotl]

Tragically, this very event happened just outside Edinburgh, on Wednesday.

http://www.bbc.co.uk/news/uk-scotland-edinburgh-east-fife-33007610

A tipper truck drove into a 11KV line. As the news report (which may not be accurate) states;

The driver is believed to have been initially unhurt but was killed when trying to leave the vehicle's cab while the tipper was still in contact with the cable.

I sincerely hope that businesses learn from this and train their employees on how to handle these situations in future.

 

[ban-all-sheds]

That is an LV underground connecting box failing!

Well, think about the energy (in kWh) dissipated in such a fault, divide by 0.64, and that's roughly how many sticks of dynamite it's equivalent to.

 

[JohnW2]

That is an LV underground connecting box failing!

Well, think about the energy (in kWh) dissipated in such a fault, divide by 0.64, and that's roughly how many sticks of dynamite it's equivalent to.

Do you (or maybe westie or whoever) have any idea what sort of currents and times we're likely to be talking about?

We often hear about 630A DNO fuses on LV systems. If that's what we're talking about, and if one guesses that the fuse would operate in ~1 second at a current of ~7000A, using your 'conversion factor', if I've done my sums right, I reckon that would equate to about 0.7 of a stick of dynamite.

Kind Regards, John