Prius destroyed by lightning on hwy

Actually, lightning goes in steps, look up "step leader". About 6 ft at a time for each step. Each step ionizes that path, then it creates the next one after that, all the way to the ground. When it reaches the ground the ionized path is used by the main discharge, usually more than once (yup, lightning -DOES- strike more than once in the "same place"). As I recall, the "step leader" takes a few milliseconds to reach the ground, then the main discharge takes a few nanoseconds to reach peak discharge. For those who don't understand, a millisecond is 1/1000 of a second, and a nanosecond is 1/1000th of a millionth of a second. So no, the forward motion won't break the step leader, and, you don't have time to "duck". Just be happy you can say "what was that?"

A few years ago we had a Chrysler mini-van hit on the highway beside Lake Wabamin. Blew out a tyre and destroyed the engine controls (ignition module and computer). Nobody hurt. Faraday cage protected them (everything in the car is raised to whatever potential that final step had so nothing in the car saw any significant current). But the EMP effect will destroy electronics - make things conduct that shouldn't, over-current other things. Not healthy for electronics! It's hard to predict exactly what will happen, but we do know the -minimum- current is around 2kAmp, and I've seen lots of data of strikes in the 150 kAmp range on the Forestry lightning detection network. Explosive!

The Prius is no more or less susceptible than other vehicles.

Oh, and the tyres aren't a very good insulator. Fine for 12V, not so good for millions of volts.

Hummm, auto "correction". Changed t y r e to tire, without asking or whatever. SIlly forum!

 

yep, spell check has become a disaster, along with the rest of the site.

 

Speaking strictly from electrical theory, not lightning familiarly, shouldn't I expect the main discharge to take microseconds to reach peak discharge, not nanoseconds?

This timeframe is based on the speed of light, about one foot per nanosecond. For a 10,000 foot spark, it takes at least 10,000 nanoseconds or 10 microseconds for a wave to propagate from one end to the other. The main bolt current ought not to be ramping up faster than that.

 

Thanks for all the clarifications. BTW I read that lighting actually goes upwards and not downwards. I have to read Wikipedia a bit about it.
I really didn't consider EMP. But I am still wondering why electronics within a Faraday cage like the motor area would have to blow or get induced currents. Inside the Faraday cage there are no currents and potential is zero. Isn't it?

 

There are both positive and negative lightning strikes. The negative ones usually come from the bottom of the cloud. The positive ones usually come from the top of the cloud, and are usually much more powerful (the charge builds up for a much longer period of time before discharging.

Please define "goes up" or "goes down". What goes up or down? If you're talking of negative strikes, it's electrons coming down from the cloud. But these days we also talk of "lack of an electron" as an entity, described in electronics as a "hole". They go up. It's the opposite for positive strikes. I prefer to just think of lightning as a single entity that happens instantly (because it does in my time frame).

Thank god I can say, "what was that".

 

I was going to add that the time to peak discharge is based on the risetime of the pulse we see with the lightning detectors (but the forum was busy doing other things I guess, and wouldn't let me continue). The rise time we see is usually around 2 nSec. I -assume- that indicates the time to peak discharge. But we all know what "assume" stands for, right?

Just for your info., when we watched the pulse induced either from a direct hit or EMP induction, into the power grid, we see a pulse with a peak energy frequency of about 100 kHz at our building outlets, even though the lightning pulse has a peak energy frequency in the 100 to 150 MHz region. I presume the electrical grid acts as a giant filter. This also informs us that those "filters" you can buy that have VHF filtering (small inductors and capacitors) won't be very effective for a 100 kHz pulse. The best units we found were transformer types, that "tuned" the primary or secondary to around 60 kHz, followed by an RC filter, tuned to around 10 kHz. Protected sensitive electronics from lightning pretty well, with attenuation of around 40 dBV. They also allow connecting the neutral and ground lines together at the secondary, eliminating "common mode" pulses. That means pulses between neutral and ground. The ones between line and neutral are dealt with by the filtering. Nothing to do with our cars, but interesting just the same.

 

You are not totally safe in a car. Best to hide in a closet and hug your teddy.

However, I did a grounding grid that focused electricity underground away from the house box with no return. Still got a direct hit on my underground conduit (BWO a tree) going to the shed in which the bare ground in the trench back fed through the old telephones lines by way of the grounding rod at the box connected to the old telephone box..
Jumped from the telephone line to my TV COAX and melted the wires.
After it fried a bunch of stuff I disconnected all wires associated with the old telephone coax grounded to the service panel ground. .

Remember "life will find a way"? Electricity will also.

 

The car frame only approximates a Faraday cage, it is far from ideal.

An ideal cage would have no resistance, and no holes to allow radio waves to enter. The car frame has measurable DC resistance, and higher AC resistance. If that small resistance is subjected to a 100,000 amp spark, the I*R drop from one end to the other can easily exceed the damage threshold of the attached electronics.

Cage openings such as the large windows and door holes sharply limit the shielding at higher frequencies (shorter wavelengths). As an example, compare AM to FM radio reception when passing through a metal truss bridge. The AM signal (1 MHz, very long wavelength compared to the truss openings) pretty well vanishes, while the FM signal (100 MHz, wavelength similar to truss openings) barely changes, usually having little perceptible signal/noise ratio degradation. Heldheld FM radios inside the car usually work too, as a reasonably good signal still gets through the windows. Cell signals, 800 MHz and higher, fly through these holes just fine.

David (above) indicates that much of lightning energy is in the 100-150 MHz range, which is consistent with the claimed 2 nanosecond rise time. The car frame makes a poor cage in that band.

In short, while the car frame provides considerable human protection against the lethality of lightning strikes, the electrics and electronics can still get fried.