OT Lightning near miss.

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...

Glad you are okay, Simon!

Cheers, helen s

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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.)

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.

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

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.

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

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

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 <[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 mos.orgskineffect.htmlOpen ↗

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

Graeme said:

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.

All electronic equipment these days has to meet EMC
standards which means any electromagnetic signals are kept
within the box. So displays have to be able to shield
signals as well - usually the CPU clock is the main source
on a computer. Obviously you cannot simply bolt a metal
plate over the display to do it so its done with conducting
transparent films.

Quoted message said:

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

If you insist. You're wrong again. Want to borrow my hanky?

Tony