Why being in a car during a lightning storm is the safest place to be
As watcher of weather, both as as a one-time storm chaser as well as a person who gets sent email about weather of all kinds, I’ll have to say I’ve never seen anything like this video. The National Weather Service lighting safety page reports that a person’s odds of being struck by lightning are around 1 in 775,000 at any given time with 1/10,000 in an 80 year lifetime. Capturing the event live on video has to be even higher odds.
A police car dashcam captured footage of a direct lightning strike the roof of a Toyota Landcruiser carrying a senior Russian official on a rainy Russian day – while driving down the freeway.
I was even more struck by the odds of the lightning hitting the SUV while there are taller light poles along the freeway and taller buildings in the vicinity. It was just a case of being in the wrong place and the wrong time.
While the internal electronics for the SUV are possibly fried, the occupant wouldn’t be.
So why is being in a car during a lightning storm is the safest place to be? Two words – Faraday Cage. From Wikipedia:
A Faraday cage or Faraday shield is an enclosure formed by conducting material or by a mesh of such material. Such an enclosure blocks external static and non-static electric fields. Faraday cages are named after the English scientist Michael Faraday, who invented them in 1836.
A Faraday cage’s operation depends on the fact that an external static electrical field will cause the electric charges within the cage’s conducting material to redistribute themselves so as to cancel the field’s effects in the cage’s interior. This phenomenon is used, for example, to protect electronic equipment from lightning strikes and electrostatic discharges.
A Faraday cage is best understood as an approximation to an ideal hollow conductor. Externally or internally applied electromagnetic fields produce forces on the charge carriers (usually electrons) within the conductor, generating electric currents that rearranges the charges. Once the charges have rearranged so as to cancel the applied field inside, the currents stop.
If the cage is grounded, the excess charges will go to the ground instead of the outer face, so the inner face and the inner charge will cancel each other out and the rest of the cage will retain a neutral charge.
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Note: The SUV has steel belted radial tires, and thus is essentially grounded as lightning easily jumps that dielectric gap.
h/t to WUWT reader Newton Love
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and, of course, I communicated that incorrectly…
that would be 1/775,000 in a year, with about 400 strikes per year
Reblogged this on WrAnTz and commented:
Have always known about the Faraday effect for cars but have never heard of a one being struck while being driven. Amazing.
“””””….._Jim says:
September 27, 2012 at 11:37 am
wayne says September 27, 2012 at 10:37 am
Doesn’t lightning always just follow the path of least resistance?
…
Ummm … no. It begins as a chaotic process involving gas molecules in a strong static electric field, with free electrons stripped from some gas molecules which begin to impinge on other gas molecules and at some point an ‘avalanche’ effect takes over eventually resulting in a ‘plasma path’ through which the bulk of the electron ‘charge’ is transferred……””””
The hell you say _Jim; you certainly did !! Dunno how I skipped over that. And what’s more, you covered all the bases in a more concise and cogent statement than I did.. Sorry Mate, I’ll pay more attention.
And further on the static electric field business, some commenters have implied that it is some sort of high frequency RF effect.
Not so; but once the discharge gets going, you do get a gigantic high field EM pulse effect (Transient) and simple signal theory explains that that will generate a broad spectrum of EM waves depending on the length of the pulse, and things like the rise and fall times of the pulse; and of course in the wild random streamer structure, it will be a complex pulse.. It will take something in the 5-20 microseconds range to reach earth, and last somewhat longer than that. In practice, it turns out that the RF spectrum is actually concentrated in the audio range from a few Hertz to a few KHz. A lightning strike at one point on earth will launch an EM wave train that propagates through the ionosphere, guided also by the earth magnetic field, so some time later, and echo will be received on the other side of the earth. This arriving signal, will partially reflect from the partially conducting ground plane, and return via the filed guiding to the original or nearby location. This bouncing back and forth can occur several times.
There are listening stations at strategically located places, that co-operatively record these signals , to generate interleaving signals of the very same lightning strike. As it turns out, the ionospheric transmission path is dispersive, so the different audio frequency waves travel at different speeds and the higher frequencies get there first (usually), which is the same as waves on water. So the signal received at each station is a whistle that starts out high frequency and sweeps to a lower frequency as the slow pokes arrive. So each subsequent transit, is further stretched out so the two listening stations can match their records, and see the beautiful interleaving of chirped signals.
They are actually called “Whistlers ” by those who study these atmospheric EM phenomena. Well there are also Howlers which as I recall chirp up in frequency rather than down, and then there is “dawn chorus” and some other named types.
The DSIR in Wellington NZ used to be one such recording station hooked to another station in Scandinavia somewhere. I spent a summer there in the early 1950s when they were doing that stuff. Well I was doing my Radio-Physics courses at the time.
I was mowing the 10th fairway on a Toro 5100D when lightning struck the roof. For a few seconds prior to the strike I could feel my hair standing on end and the air smelled different. Then a huge flash followed by the biggest bang I ever heard. I could see the flash moving down the window posts and the arms of the mower. My vision afterwards had streaks like when you look at an arc flame or at the sun. The mowing electronics were fried but the diesel engine started right up again and the hydraulics were fine. There were 5 rectangular burnt patches on the turf where the cutting units completed the circuit. No-one believed me until they saw those patches and the couple of scortched and blackened spots on the roof.
I would be remiss if I didn’t include these two references on the subject of ESE Devices (which roughly includes “Franklin Rods’ as well as other devices) regarding the shape and propensity to ‘attract’ or ‘get hit’ more or less often per my address to/discussion above with wayne:
From: http://www.lightningsafety.com/nlsi_lhm/early-streamer-emission.pdf
Titled: “A review of studies on Early Streamer Emission and Charge Transfer System conducted in Malaysia”
I extract this part re: sharp tips vs blunt tips (where they observe that blunt tips get ‘hit’ *more* often than sharp tips – which at first pass sounds counter-intuitive, but that has been the reported observation by researchers):
A similar observation is made in this document on Pg 15, 2nd paragraph, 9th line down:
http://www.nfpa.org/assets/files/PDF/Research/ESE_Air_Terminals_segment_1.pdf
Titled: Early Streamer Emission AIr Terminals Lightning Protection Systems,
Literature Review and techniacl Analysis,
by NFPA
By these observations, then, allowing or enhancing corona discharge, allowing a ‘bleeding off’ of charge locally into the local air parcel at/near ground level, it appears that the voltage difference seen by a descending stepped leader could be reduced such that the strike does _not_ occur to the sharp-tipped Franklin Rod or ESE device, but rather some other unlucky ‘target’ in the vicinity will get zapped as the stepped leader approaches and causes the ‘avalanche’ breakdown toward that target instead … using this technique there would appear to be some degree of ‘protection’ that could be obtained … and therein also lies the claim by ESE Device manufacturers.
Given the nature of lightning though, the ESE devices deployed in real-world situations have not always ‘warded off’ lightning strikes as intended, but it appears to me that in these situations nobody provided any ‘targets’ for the impending lightning bolt to strike either … the simple deployment of an ESE Device will not ward off an on coming bolt, rather, it looks to me like the deployment of blunted Franklin Rods are what are called for; perhaps manufacturers have found it unwise to advertise (or recommend for installation!!) a device that is warranted to attract lightning?
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My wife and I “read” a verbal biography of Ben Franklin while driving up to the Shenandoah Valley for vacation (All touring and historical, new museums and new monuments every day!). Yeah – We’re nerds. Both engineers. Even have our private research librarian MS/programmer MS/math BS/physics BS as a daughter.
The “sharp point” vs “blunt point” arguments – for and against!! – his lightening rods were vehemently discussed, printed, written, and argued in his day across every continent and in every scientific society of the day.
Best summary:
Yes, lightening rods only protect a limited area – You NEED an well-grounded lightening rod on YOUR house to prevent a lightening bolt from burning YOUR house when lightening strikes YOUR house.
However, your lightening rod will not protect your neighbor’s house, nor the far end of your (big) house nor your nearby barn unless it is very far up above the rest of the area. In that case, your big tall lightening rod WILL attract more lightening than a short unprotected house or unprotected barn without any lightening rod at all.
An ungrounded or poorly grounded lightening rod, or a too-short lightening rod will NOT protect your house as well as it should do if it were properly grounded and attached, and MAY attract stray lightening bolts that would have otherwise gone done someplace else.
Up close – where all easy-to-do demonstrations and laboratory tests and simple experiments tend to be run – a sharp-pointed lightening rod is much, much more effective than Franklin’s opponents in the French legislature and scientific societies’ “rounded end” lightening rods.
However, in the real world where a building is several thousand feet below the clouds and their various static electric charges, the actual little bitty point on a little bitty lightening rod is meaningless. Round or sharp, the thousands of feet of travel for the initial charge can’t “find” the few feet of improved attraction distance that a sharp point rod provides.
Thus, either lightening rod “point” is equally good.
Ummm … are there any cites or references you can provide (like I provided)? Conjecture has its place, but I always like something I can ‘lay’ my eyeballs on …
Note also: I am not about to provide advice, counsel, hints or recommendations on what type, make or model of air terminal, ESE Device or FR (Franklin Rod) for protection of any structure, building, dwelling, barn or abode … the above postings by me, at least, are for DISCUSSION purposes ONLY. My best advice is to consult a PE in your area whose practice is lightning protection, or become informed, learned and practiced and perhaps credentialed (and aware of NEC requirements) yourselves in order to adequately address any and all safety concerns (no one needs to try and ‘engineer’ a lightning rod system ONLY to endanger themselves and family owing to erroneous materials selection or incomplete or unsafe construction of same.)
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This just in (had it parked in a tab in Chrome) – for those who might want to roll their own or read the recommendations of the National Fire Protection Association:
NFPA standard #780, “Standard for the Installation of Lightning Protection Systems”, 2004 Edition
A brief excerpt of the ‘scope’ and ‘purpose’ sections:
1.1 Scope.
1.1.1 This document shall cover traditional lightning protection system installation requirements for
the following:
(1) Ordinary structures
(2) Miscellaneous structures and special occupancies
(3) Heavy-duty stacks
(4) Watercraft
(5) Structures containing flammable vapors, flammable gases, or liquids that give off flammable
vapors
1.2 Purpose.
The purpose of this standard shall be to provide for the safeguarding of persons and property from hazards arising from exposure to lightning.
– – – – – – – – – – – – – – – – – –
This document spells out the size of ‘air terminals’, size of conductors, recommendations where to mount the air terminals on various roof topologies, ‘Zone of Protection’ calculations, etc.
For the entire thing see:
http://uqu.edu.sa/files2/tiny_mce/plugins/filemanager/files/4310333/Appendix_-_NFPA_Standard_780_2004.pdf
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_Jim, now that aspect of actually bleeding off charges by very sharp points does make some real sense but I was speaking of all of these effects included. You can see that effect from various geometries about a Van der Graaf generator or Tesla coil and I’ll stand corrected on a couple of my statements not being so clear. But also keep in mind that if sharp points are in fact locally bleeding the charge differential that does also make that path more resistant so another metallic object at same distance not bleeding charges will then become the path of least resistance. Will you agree to that?
@ur momisugly Anyone:
Here’s a neat lecture on Faraday cages:
(see the demo near the end of this video)
http://ocw.mit.edu/courses/physics/8-02-electricity-and-magnetism-spring-2002/video-lectures/lecture-5-electrostatic-shielding-faraday-cage/
Here’s another lecture on static charges and electric fields on a non-smooth surface (ie. sharp points):
http://ocw.mit.edu/courses/physics/8-02-electricity-and-magnetism-spring-2002/video-lectures/lecture-6-high-voltage-breakdown-and-lightning/
When I was in Florida as a kid, I remember mom driving in the rain. The other side of the road was dry as could be, while we were getting pounded. At a stop light the car in front of us got hit by lightning. It was the car closest to the light poles. Totally hit the lower lying car and skipped the pole.
Luckily, not hit personally or in a car.
However, our last house was hit and it killed our (vinyl, LP) turntable: the copper on the PSU pcb was evaporated and nicely painted the interior of the plinth. That’s as close as I ever want to be!