On 4/8/2005, Peter Macinnis wrote:

On another list, I mentioned an occasion on Sydney's North Head, where a lightning strike nearby caused our hair to move enough so we could feel it. When we saw our hair rise again, we headed off fast for the cover of a car.

Another list member said that what we should have done was to discard metal objects, as these "attract lightning". My gut reaction is that it would be foolish to hold a metal rod up high, but that change in the pockets, for example, would have no effect.

The comment came from an American, and I think they are all taught about Ben Franklin sending up a kite with a key on the string.  What ARE the scientific principles that spell out the best defences against lightning?


Merrill Pye responded:

I catch that show sometimes on SBS when I'm home early but too depressed to watch 7:30 Report on ABC. It's a great blend of science, technology and 'boy-style'* fun. A good alternative to the Jackass type show.

Bolt thru head, lightning - I am irresistably reminded of the movie versions of Frankenstein's monster; Is there an Igor in the house?



*Explosions, embarrassing bodily functions, bad smells, quite a bit of cars and machinery involved in crashes & smashes.



Hilly van Zuylekom wrote:

>  What ARE the scientific principles that spell out the best defences
> against lightning?

I don't know all the scientific principles, I only remember a few from my high school years:

Lightning is attracted by metal, water, high objects: A person (ca 65% water), standing under a tree (ca 30% water): not a good idea.

I was always intrigued by the Cage of Faraday where the electric charge stays on the outside of the cage (car) so that there is no electrostaticity within the cage (don't touch the metal after the car is hit).

My old science teacher would be impressed that I remembered, he always thought that science and girls didn't go together...ah well, that was a long time ago!

I saved the tips underneath from the Internet some time ago and most of it confirms what I was taught as a child. My grandfather owned a peatfarm and spend most of his working life in the fields so I guess that his experiences with thunder and lightning were not based on
science but on experience and knowledge. Among other things I was told that if I was ever caught in a thunderstorm, outside on my pushbike, with no houses or barns in sight, I had to get off my bike, put it down, move away and lie down in a ditch until the storm passed!
Funny the things one remembers!

                     -------
Personal Lightning Safety Tips

1. PLAN in advance your evacuation and safety measures. When you first see lightning or hear thunder, activate your emergency plan. Now is the time to go to a building or a vehicle. Lightning often precedes rain, so don't wait for the rain to begin before suspending activities.

2. IF OUTDOORS...Avoid water. Avoid the high ground. Avoid open spaces. Avoid all metal objects including electric wires, fences, machinery, motors, power tools, etc. Unsafe places include underneath canopies, small picnic or rain shelters, or near trees. Where possible, find shelter in a substantial building or in a fully enclosed metal vehicle such as a car, truck or a van with the windows completely shut. If lightning is striking nearby when you are outside, you should:

    A. Crouch down. Put feet together. Place hands over ears to minimize hearing damage from thunder.

    B. Avoid proximity (minimum of 15 ft.) to other people.

3. IF INDOORS... Avoid water. Stay away from doors and windows. Do not use the telephone. Take off head sets. Turn off, unplug, and stay away from appliances, computers, power tools, & TV sets. Lightning may strike exterior electric and phone lines, inducing shocks to inside
equipment.

4. SUSPEND ACTIVITIES for 30 minutes after the last observed lightning or thunder.

5. INJURED PERSONS do not carry an electrical charge and can be handled safely. Apply First Aid procedures to a lightning victim if you are qualified to do so. Call 911 or send for help immediately.

6. KNOW YOUR EMERGENCY TELEPHONE NUMBERS.

Teach this safety slogan:
"If you can see it, flee it; if you can hear it, clear it."


Gerald Cairns replied:

I am not so sure about the reliability of your last principle. When our kids were young we took them camping and fossiking near Scone NSW and camped on the banks of a creek near some pine trees. The weather looked fine but a storm built up at dusk just as I was sitting on the floor of the tent with the gas bottle and lamp between my knees lighting it. Our son was looking out of the window at the storm when there was an almighty deafening crash. Son fell back screaming with pain in his ears and I looked at the crown jewels to see if they were still there. Then we smelt burning and I grabbed the fire extinguisher and ran outside to find the grass on fire at the base of a pine tree maybe 30 cm from the trunk and about a couple of metres from the tent. Fire was put out and on investigation the strike point was identified as a small very blackened hole in the ground about the size of a 20 cent piece in the centre of the fire. The tree was not touched yet the bolt must have passed down through numerous branches to reach the spot where it stuck.

I reckoned we had learned enough of lightning that night so we quickly vacated the tent and placed all spare fuel etc. a safe distance away and spent a wild and uncomfortable night in the car. Fortunately no more near misses occurred but all I can say from this limited experience and one other is that the process appears to be highly unpredictable except for certain well known dangerous activities like balloons on wires etc.

The other "near miss" was quite recently when I opened the back door to go upstairs having shut down all electronics until the storm had passed as is our routine and I was blasted backwards under the house by a bolt that struck without warning very very close but on later investigation when the rain had stopped the strike point was not found. I suspect Peter took the safest option. There is an emeritus professor of electrical engineering at UQ, Prof. Matt Darveniza Lightning & Transient Protection Pty Ltd, who has developed a folding aluminium tripod under which you can crouch and according to him be relatively safe. He has demonstrated himself using discharges up to hundreds of thousands of volts but I am not volunteering.

His hypothesis seems sound and to work but his safety device has been ignored commercially. His advice is to crouch down with feet as close to gether as possible. I am not sure if he is still active but I do have a phone number if anyone wants it.


Gary Dalrymple responded:

In a slightly different context, beyond the 'cone of silence' effect of mobilephone repeaters/towers and the six watts at 1 cm Vs howmany watts at hownany metres: as people complain about them being 'too close' to schools and playing fields, surely it must occur to some protesters that these structures make excellent supplimentry lightning rods to keep the kiddies safer?

Currently bathing in the refracted glory of 1,000 watts per square of Nuclear Fusion powered EMF

David Martin related:

An interesting (and scary) anecdote.

I had a similar experience in the UK many years ago. Whilst picking strawberries in an open field on a thundery day, my hair stood on end quite spectacularly. There was no lightning though, despite the immense amount of charge passing over the ground - a worry at the time nevertheless!

Some physics now.

There is no theoretical reason why metal would "attract" lightning. So far as I'm aware, there is no experimental evidence either: this is just another "old wives' tale".

The physics of lightning is not completely understood, however. The main reason is that the electric fields, generated by electric charge in thunderclouds, are generally too small (by a factor of about ten) to initiate lightning strikes.

Some recent work supports the idea that the trigger for a strike is a charged particle cascade initiated by a cosmic ray. There was an article in Scientific American recently (as I recall), but see, e.g.

http://en.wikipedia.org/wiki/Lightning#Runaway_breakdown_theory

This would mean that lightning strikes, although broadly confined to the region of high electric field under a thundercloud, would be otherwise
essentially random.

As regards protection, it follows directly from Coulomb's law that the *static* charge on a conducting object sits on the outside; hence the idea of a Faraday cage, inside which there is no charge and no electric field. A lightning strike is far from a static event, however. Nevertheless, if the material is highly conducting, charge flows to the surface in a much shorter time (picoseconds) than the duration of the strike (microseconds) so the strike is relatively static. You're probably safest inside a car - the metal chassis would be a reasonably effective Faraday cage. The relative safety of a car, of course, has nothing whatever to do with the "insulating" rubber tyres: a few centimetres of rubber is no insulation at all at a billion volts.