OT Lightning near miss.

Quoted message said:

I remember when I was rung up whilst out on a the bike, and told that
lightning was on the way, and got a lift home. My sister proclaimed
"You've got rubber tyres on, you'd have been fine". The fact that if
there's enough PD to arc through god knows how many thousand feet of
air to get to me on my conspicuous bit of metal in the middle of
nowhere, it's going to have no trouble arcing the few inches or so
from my BB / rim / pedals to the ground seemed to go straight over her
head...

Might the rubber help to limit the existence/size of the little 'feelers'
or whatever the little ground to air thingies are?

(apologies for the highly technical jargon used.)

Simon Mason said:

Regarding the cyclist who was killed by lightning at an airfield
recently, I had my own near miss on Sunday evening. Saw a storm
brewing out west around 1900 so did not venture out. While pottering
about in the garage the whole of the outside world suddenly became a
brilliant blue-white colour accompanied instantly by a *very* loud
bang.

I expected the house to have been hit and damaged but all seemed OK,
I'm just glad I wasn't out in the garden at the time!

I remember when I was rung up whilst out on a the bike, and told that
lightning was on the way, and got a lift home. My sister proclaimed "You've
got rubber tyres on, you'd have been fine". The fact that if there's enough
PD to arc through god knows how many thousand feet of air to get to me on my
conspicuous bit of metal in the middle of nowhere, it's going to have no
trouble arcing the few inches or so from my BB / rim / pedals to the ground
seemed to go straight over her head...

In news:[email hidden],
Doki <[email hidden]> typed:

Quoted message said:

Mark Thompson said:

Quoted message said:

I remember when I was rung up whilst out on a the bike, and told
that lightning was on the way, and got a lift home. My sister
proclaimed "You've got rubber tyres on, you'd have been fine". The
fact that if there's enough PD to arc through god knows how many
thousand feet of air to get to me on my conspicuous bit of metal in
the middle of nowhere, it's going to have no trouble arcing the few
inches or so from my BB / rim / pedals to the ground seemed to go
straight over her head...

Might the rubber help to limit the existence/size of the little
'feelers' or whatever the little ground to air thingies are?

(apologies for the highly technical jargon used.)

God knows. I've no real understanding of how arcing / plasma works,
but I wouldn't trust a bike tyre to keep me safe. You're alright in a
car because it works as a Faraday cage - you could have conductive
tyres and it wouldn't matter.

This one actually comes up pretty frequently. Maybe it should be in the FAQ.
IIRC you're correct, but I think there are quibbles with that description.

A

Mark Thompson said:

Quoted message said:

I remember when I was rung up whilst out on a the bike, and told that
lightning was on the way, and got a lift home. My sister proclaimed
"You've got rubber tyres on, you'd have been fine". The fact that if
there's enough PD to arc through god knows how many thousand feet of
air to get to me on my conspicuous bit of metal in the middle of
nowhere, it's going to have no trouble arcing the few inches or so
from my BB / rim / pedals to the ground seemed to go straight over
her head...

Might the rubber help to limit the existence/size of the little
'feelers' or whatever the little ground to air thingies are?

(apologies for the highly technical jargon used.)

God knows. I've no real understanding of how arcing / plasma works, but I
wouldn't trust a bike tyre to keep me safe. You're alright in a car because
it works as a Faraday cage - you could have conductive tyres and it wouldn't
matter.

Glad you are okay, Simon!

Cheers, helen s

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On Tue, 29 Jun 2004 18:22:20 +0100 someone who may be "Doki"
<[email hidden]> wrote this:-

Quoted message said:

You're alright in a car because it works as a Faraday cage

In theory and usually in practice. However, this does depend on the
nature of the windows, which may be such as to "let in" the
lightning. I would not stake my life on it.

The suits that staff wear to work on/inspect live 400kV overhead
lines have a plastic visor that covers the face. This has built-in
thin metal strips which are connected to the rest of the suit (which
also has thin metal strips woven into it. This maintains the
integrity of the Faraday cage.

--
David Hansen, Edinburgh | PGP email preferred-key number F566DA0E
I will always explain revoked keys, unless the UK government
prevents me using the RIP Act 2000.

David Hansen said:

On Tue, 29 Jun 2004 18:22:20 +0100 someone who may be "Doki"
<[email hidden]> wrote this:-

Quoted message said:

You're alright in a car because it works as a Faraday cage

In theory and usually in practice. However, this does depend on the
nature of the windows, which may be such as to "let in" the
lightning. I would not stake my life on it.

The suits that staff wear to work on/inspect live 400kV overhead
lines have a plastic visor that covers the face. This has built-in
thin metal strips which are connected to the rest of the suit (which
also has thin metal strips woven into it. This maintains the
integrity of the Faraday cage.

Whilst lightning most likely could get through the windows, wouldn't it
normally go for the highest point on the car (ie, roof or radio aerial?).

On Tue, 29 Jun 2004 18:12:05 +0100, "Doki" <[email hidden]>

Quoted message said:

I remember when I was rung up whilst out on a the bike, and told that
lightning was on the way, and got a lift home. My sister proclaimed "You've
got rubber tyres on, you'd have been fine". The fact that if there's enough
PD to arc through god knows how many thousand feet of air to get to me on my
conspicuous bit of metal in the middle of nowhere, it's going to have no
trouble arcing the few inches or so from my BB / rim / pedals to the ground
seemed to go straight over her head...

Wet tyres make a reasonable conductor of electricity.

In article <[email hidden]>,

Simon Mason said:

Regarding the cyclist who was killed by lightning at an airfield recently, I
had my own near miss on Sunday evening.

January 1st 1997, my shiny nearly-new desktop computer got struck
by lightning and went out. Since everywhere was closed, I had a very
anxious couple of days before verifying that the power supply had
protected the rest of it, so replacing that (and accepting a charred,
blackened corner of the motherboard) was sufficient to have it working.
That machine is still my desktop box today.

--
Nick Kew

David Hansen said:

On Tue, 29 Jun 2004 18:22:20 +0100 someone who may be "Doki"
<[email hidden]> wrote this:-

Quoted message said:

You're alright in a car because it works as a Faraday cage

In theory and usually in practice. However, this does depend on the
nature of the windows, which may be such as to "let in" the
lightning. I would not stake my life on it.

The suits that staff wear to work on/inspect live 400kV overhead
lines have a plastic visor that covers the face. This has built-in
thin metal strips which are connected to the rest of the suit (which
also has thin metal strips woven into it. This maintains the
integrity of the Faraday cage.

In neither actually. Faraday cages are all about static electricity.
Lightning strikes are anything but static as currents are flowing (and
big ones at that). What protection you have if any is provided by the
an effect known as skin depth which constrains the current to run in the
outer layers of the car body, assuming it is metal and not plastic.
You can get a shock inside a car, especially if you touch the
metalwork in two places.

Tony

I don't think it matters whether it's static or not. Some years ago, on a
QED programme I think, they drove a car around under a high voltage
electicity grid (thousands of amps there)! with 2 people in the car. They
didn't feel a thing. You could clearly see the arcing above and below the
car to ground.
The original post reminds me of when I was in Italy about 4 years ago and
staying around lake Iseo. I went out on what ended up to be a 55 mile ride
one afternoon. When I was about half way, on the other side of a mountain
with no short route back there were some bad storms brewing up with alot of
lightening in the distance. It was getting really dark and at the time I had
no idea where I was. I went round this roundabout, under a bridge and
suddenly there was a huge flash and a loud bang at the same time right
behind me!
Well, I don't think I've averaged a speed like that since!
Thankfully though it was only just spitting with rain.
"Tony Raven" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

David Hansen said:

On Tue, 29 Jun 2004 18:22:20 +0100 someone who may be "Doki"
<[email hidden]> wrote this:-

Quoted message said:

You're alright in a car because it works as a Faraday cage

In theory and usually in practice. However, this does depend on the
nature of the windows, which may be such as to "let in" the
lightning. I would not stake my life on it.

The suits that staff wear to work on/inspect live 400kV overhead
lines have a plastic visor that covers the face. This has built-in
thin metal strips which are connected to the rest of the suit (which
also has thin metal strips woven into it. This maintains the
integrity of the Faraday cage.

In neither actually. Faraday cages are all about static electricity.
Lightning strikes are anything but static as currents are flowing (and
big ones at that). What protection you have if any is provided by the
an effect known as skin depth which constrains the current to run in the
outer layers of the car body, assuming it is metal and not plastic.
You can get a shock inside a car, especially if you touch the
metalwork in two places.

Tony

Tony Raven <[email hidden]> wrote in
news:[email hidden]:

Quoted message said:

What protection you have if any is provided by the
an effect known as skin depth which constrains the current to run in
the outer layers of the car body, assuming it is metal and not
plastic.

And this effect is largely determined by the frequency of the electrical
discharge. Put simply, the higher the frequency, the closer to the
surface of the conductor the current flows. In high frequency
electronics they often use conductors which are plated with gold. This
is also one of the myths used to rip off audio geeks, "It's gold plated,
it gives a much clearer high end." This is of course "Total Bollocks
(TM)" as skin effect only really comes into play at much greater than
audio frequencies. It starts getting interesting when you're playing
with microwave frequencies, so if you're trying to improve the sound of
Celine Dion then gold ain't going to help (using wet spaghetti as a
conductor would certainly help her sound more bearable though).

If lightning was of much lower frequency then a car would give little
protection. Also, a car is not a particularly good Faraday cage. If it
were it would certainly solve the problem of people using their mobile
phones whilst driving!

Graeme

Graeme said:

If lightning was of much lower frequency then a car would give little
protection. Also, a car is not a particularly good Faraday cage. If it
were it would certainly solve the problem of people using their mobile
phones whilst driving!

A Faraday cage wouldn't help at all with mobile phones. Whether mobile
phone signals get out depends again on skin depth. You could readily
build a perfect Faraday cage and make mobile phone calls from inside.

Tony

Paul Saunders said:

I don't think it matters whether it's static or not. Some years ago, on a
QED programme I think, they drove a car around under a high voltage
electicity grid (thousands of amps there)! with 2 people in the car. They
didn't feel a thing. You could clearly see the arcing above and below the
car to ground.

It matters a great deal to understanding the safety of cars in a
thunderstorm. It is commonly assumed you are "inside a Faraday cage"
and therefore safe. You are only safe if you take appropriate
precautions, which I am sure QED will have been forced to do by the test
site they visited, but people have been killed inside cars in lightning
strikes.

Tony

Tony Raven said:

David Hansen said:

On Tue, 29 Jun 2004 18:22:20 +0100 someone who may be "Doki"
<[email hidden]> wrote this:-

Quoted message said:

You're alright in a car because it works as a Faraday cage

In theory and usually in practice. However, this does depend on the
nature of the windows, which may be such as to "let in" the
lightning. I would not stake my life on it.

The suits that staff wear to work on/inspect live 400kV overhead
lines have a plastic visor that covers the face. This has built-in
thin metal strips which are connected to the rest of the suit (which
also has thin metal strips woven into it. This maintains the
integrity of the Faraday cage.

In neither actually. Faraday cages are all about static electricity.
Lightning strikes are anything but static as currents are flowing (and
big ones at that). What protection you have if any is provided by the
an effect known as skin depth which constrains the current to run in the
outer layers of the car body, assuming it is metal and not plastic.
You can get a shock inside a car, especially if you touch the
metalwork in two places.

Faraday cages have nothing to do directly with static electricity. A
Faraday cage is just a conductive shell which completely surrounds
a space. If the shell is perfectly conductive, in a DC field the
voltage at each point on the outer (and inner) surfaces of the shell
must be the same (because any voltage differences that might build up
are conducted away). This means that the voltage at all points inside
the shell is the same, and if there is no voltage differences then there
is nothing to electrocute you.

Faraday cages don't work perfectly in the real world. Firstly, if there
is a large enough current flow (as in a lightning strike on the top of
a car), there might be a significant voltage difference between the roof
and the floor, simply because of the current flow and the resistance of
the metalwork. The current might be 30,000A at its peak, and the
resistance of the metalwork will be at least a few tens of milliohms
even if it's a fully welded construction from top to bottom, so V=IR
drops mean that you can have some hundreds of volts difference between
the roof and the floor pan. That's enough to electrolux you.

Secondly, as the frequency increases such that the wavelength is of
the order of the size of the cage, or smaller, you will get voltage
differences between parts of the cage. That's because (very simply put)
the charges don't have time to equalise in the high-frequency field
no matter how good a conductor, because the fields that move them can
only travel at the speed of light (whatever that is in the conductor)
and the speed of light is the reason you have a wavelength in the first
place. Most prequency components in lightning are below anything that
would cause concern in a car, though.

A car's protection has nothing to do with a skin effect. After all,
the "outer layer" of the door pillars, for example, is partly inside
the car, and there is no continuous outer layer on a car body. While
it may be true that most of the current flow is very close to the metal
surface, this just exacerbates the IR voltage drops in the car body
(because you have the same current flowing in a thinner and therefore
higher resistance section of metal) and will make the problem worse,
not better.

The advice if you're in a car is to stay in it, and don't touch anything
metal. Stay in it, because the car's better equipped to handle 30,000
amps flowing through it without dying, and don't touch anything metal
because even a small gap is enough to insulate you from the several
hundred volts that could be developed between the top and bottom of
the car. Keeping as far as possible from the windows is probably also
a good idea to offer some protection from secondary field sffects.

--
Trevor Barton
Isotek Electronics Ltd, 9 Clayton Wood Bank, Leeds, LS16 6QZ, UK.
Tel: +44 (113) 275 1339, Fax +44 (113) 224 9827
Remove X from [email hidden] before replying.
Views expressed are my own and not necessarily those of Isotek Electronics Ltd.

Tony Raven <[email hidden]> wrote in news:2kf8hkF1ilboU1@uni-
berlin.de:

Quoted message said:

A Faraday cage wouldn't help at all with mobile phones. Whether mobile
phone signals get out depends again on skin depth. You could readily
build a perfect Faraday cage and make mobile phone calls from inside.

You're right, sorry, I was getting some of the nonsense we were taught in O
grade physics mixed up with the slightly more accurate stuff I learnt at
university. However, a perfect Faraday cage would definitely address the
problem of drivers using mobile phones as they would not be able to see out
:-)

Graeme

Trevor Barton said:

Faraday cages have nothing to do directly with static electricity. A
Faraday cage is just a conductive shell which completely surrounds
a space. If the shell is perfectly conductive, in a DC field the
voltage at each point on the outer (and inner) surfaces of the shell
must be the same (because any voltage differences that might build up
are conducted away). This means that the voltage at all points inside
the shell is the same, and if there is no voltage differences then there
is nothing to electrocute you.

Is the wrong answer. There is no field inside the cage _if_ the
electricity is static in which case the charge is uniformly distributed
over the outside and there is equipotential inside. The conductivitity
of the cage is not a significant factor providing it conducts. If
currents are flowing then as you note there are potential differences
between different parts of the cage depending on the current and
resistivity of the cage. There is therefore no longer an equipotential
inside and fields can exist inside even a perfect "Faraday cage".

See http://www.mos.org/sln/toe/skineffect.html

Tony

Graeme said:

You're right, sorry, I was getting some of the nonsense we were

taught in O

Quoted message said:

grade physics mixed up with the slightly more accurate stuff I learnt at
university. However, a perfect Faraday cage would definitely address the
problem of drivers using mobile phones as they would not be able to see out
:-)

Wrong again ;-) Are you using an LCD display on your computer? It has
transparent conductors coated on the glass to apply the electrical
signals to the pixels. You could construct a Faraday cage out of such
conducting material that you could not only phone out of but also see out of

Tony

Tony Raven <[email hidden]> wrote in
news:[email hidden]:

Quoted message said:

Wrong again ;-)

Hey, I'm on a roll here :-)

Quoted message said:

Are you using an LCD display on your computer?

Yes, thanks to the generosity of an ex-employer who gave me an ex-demo
one.

Quoted message said:

It
has transparent conductors coated on the glass to apply the electrical
signals to the pixels. You could construct a Faraday cage out of such
conducting material that you could not only phone out of but also see
out of

I've been kind of mixing the ideas of skin effect and Faraday cages and
my lack of doing anything electrical for years is *really* showing. If
you start playing about with RF would the shielding effect of such a thin
conductor not fail? I know a very thin sheet of gold should do the trick
at GSM frequencies, but I don't know how transparent that would be.

Go on, tell me I'm wrong again, I can take it (sniff).

;-)

Graeme