How dangerous is it, really, to be in a pool during a thunderstorm?
—Jay Gengelbach
What would happen if you were taking a shower when you were struck by lightning? Or standing under a waterfall?
—same3chords
What would happen if you were in a boat or a plane that got hit by lightning? Or a submarine?
—SoobNauce
What if you were changing the light at the top of a radio tower and lightning struck? Or what if you were doing a backflip? Or standing in a graphite field? Or looking straight up at the bolt?
—Danny Wedul
What would happen if lightning struck a bullet in midair?
—Timothy Campbell
What if you were flashing your BIOS during a thunderstorm and you got hit by lightning?
—njsg
Before we go any further, I want to emphasize something:
I am not an authority on lightning safety.I am a guy who drawspictures on the internet. I like when things catch fire and explode,which means I do not have your best interests in mind. The authoritieson lightning safety are the folks at the US National Weather Service:
http://www.lightningsafety.noaa.gov/
Ok. With that out of the way ...
To answer these questions, we need to get an idea of where lightning islikely to go. There’s a cool trick for this, and I’ll give it away righthere at the start: Roll an imaginary 60-meter sphere across thelandscape and look at where it touches.
They say lightning strikes the tallest thing around. That’s the kind ofmaddeningly inexact statement that immediately sparks all kinds ofquestions. How far is “around”? I mean, not all lightning hits Mt.Everest. But does it find the tallest person in a crowd? The tallestperson I know is probably Ryan North (paleontologists estimate he stoodnearly five meters tall at the shoulder). Should I try to hang aroundhim for lightning safety reasons? What about other reasons? (This isprobably why you people ask the questions on this blog, not me.)
But how doeslightning pick its targets?
This video, captured byTom A. Warner, might be the single coolest piece of footage I’ve everseen. It shows a bolt of lightning recorded at 7,207 frames per second.The 33-second video represents barely a tenth of a second of real time.There are lots of slow-motion videos of lightning, but this is by farthe best I’ve found.
Tom’s video gives an idea of how lightning moves. It starts with abranching bundle of charge—the “leader”—descending from the cloud. Thisis what you see in the first part of the video. It spreads downward atspeeds of tens to hundreds of kilometers per second, covering the fewkilometers to the ground in a few dozen milliseconds.
The leader carries comparatively little current—on the order of 200amps. That’s still enough to kill you, but it’s nothing compared to whathappens next. Once the leader makes contact with the ground, the cloudand the ground equalize with a massive discharge of more like 20,000amps. This is the blinding flash you see. It races back up the channelat a significant fraction of the speed of light, covering the distancein under a millisecond—all within a single frame of that video.
(Technical detail: while it’s called a “return stroke”, charge is stillflowing downward. However, the discharge appears to propagate upward.This effect similar to how when a traffic light turns green, orwhatevercolor, the cars in front start moving,then the cars in back, so the movement appears to spread backward.)
So the place on the ground where we see a bolt “strike” is the spotwhere the leader first makes contact with the surface. The leader movesdown through the air in little jumps. It’s ultimately feeling its waytoward the (usually) positive charge in the ground. However, it only“feels” charges within a few tens of meters of the tip. If there’ssomething connected to the ground within that distance, the bolt willjump to it. Otherwise, it jumps out in a semi-random direction andrepeats the process.
This is where the 60-meter sphere comes in. It’s a way to imagine whatspots might be the first thing the leader senses—the places it mightjump to in its next (final) step.
To figure out where lightning is likely to hit, you roll the imaginary60-meter sphere across the landscape (for safety reasons, do not use areal sphere). This sphere climbs up over trees and buildings withoutpassing through anything (or rolling it up). Places the surface makescontact—treetops, fenceposts, and golfers in fields—are potentiallightning targets.
This means you can calculate a lightning “shadow” around an object ofheight h on a flat surface.
The shadow is the area where the leader is likely to hit the tall objectinstead of the ground around it:
\[\text{Shadow Radius}=\sqrt{-h(h-2r)}\]
Now, that doesn’t mean you’re safeon the ground around it—often, itmeans the opposite. After the current hits the tall object, it flows outinto the ground. If you’re touching the ground nearby, it can travelthrough your body. Of the 28 people killed by lightning so far thisyear, 13 were standing under or neartrees.
With all this in mind, let’s look at possible lightning paths for thescenarios in the questions.
How dangerous is it, really, to be in a pool during a thunderstorm?
Pretty dangerous. Water is conductive, but that’s not the biggestproblem—the biggest problem is that if you’re swimming, your head ispoking up from a large flat surface. But lightning striking the waternear you would still be bad. The 20,000 amps spread outward—mostly overthesurface—buthow much of a jolt it will give you at what distance is hard tocalculate
My guess is that you’d be in significant danger anywhere within aminimum of a dozen meters—and further in fresh water, because thecurrent will be happier to take a shortcut through you.
What would happen if you were taking a shower when you were struck bylightning? Or standing under a waterfall?
You’re not in danger from the spray—it’s just a bunch of droplets ofwater in the air. It’s the tub under your feet, and the puddle of waterin contact with the plumbing, that’s the real threat.
What would happen if you were in a boat or a plane that got hit bylightning? Or a submarine?
A boat without a cabin is about as safe as a golf course. A boat with aclosed cabin and a lightning protection system is about as safe as acar. A submarine is about as safe as a submarine safe (a submarine safeis not to be confused with a safe in a submarine—a safe in a submarineis substantially safer than a submarine safe).
What if you were changing the light at the top of a radio tower andlightning struck? Or what if you were doing a backflip? Or standing in agraphite field? Or looking straight up at the bolt?
What would happen if lightning struck a bullet in midair?
The bullet won't affect the path the lightning takes. You'd have somehowto time the shot so the bullet was in the middle of the bolt when thereturn stroke happened.
The core of a lightning bolt is a few centimeters indiameter.A bullet fired from an AK-47 is about 26 mm long and moves at about 700millimeters every millisecond.
The bullet has a copper coating over a lead core. Copper is afantastically good conductor of electricity, and much of the 20,000 ampscould easily take a shortcut through the bullet.
Surprisingly, the bullet handles it pretty well. If it were sittingstill, the current would quickly heat and melt the metal. But it’smoving along so quickly that it exits the channel before it can bewarmed by more than a few degrees. It continues on to its targetrelatively unaffected. There are some curious electromagnetic forcescreated by the magnetic field around the bolt and the current flowthrough the bullet, but none of the ones I examined changed the overallpicture very much.
What if you were flashing your BIOS during a thunderstorm and you gothit by lightning?
