Lightning on a Bike

Had to bike home from work the other day and it was threatening to rain. One of my coworkers was concerned about me getting hit by lightning on my bike. I noted that I was going through residential areas surrounded by trees and 2 story houses. If there was a strike, it would hit those. Not the guy on the bike.
How correct am I to think that?

Lightning is unpredictable. Although it usually strikes the tallest nearby object, there is no guarantee.
Also, even if it does, you can still be injured by potential differences as the bolt is grounded.

Quick Google brings upthis.

One of the worst places to be during a thunderstorm is anywhere near a tree.

Air is a pretty good electrical insulator. However, lightning is so crazy high in voltage that it will jump through quite a large distance of air. Lightning already jumped through a few miles of air just to get to the ground. Going a dozen or so yards from the tree to you is practically nothing for the lightning bolt.

Also, you only need a tiny fraction of the lightning bolt to have enough energy to kill you. To put it in perspective, the electric chair (a device specifically designed to kill people) operates at typically somewhere around 2,000 to 4,000 volts or so (different chairs over the years have used different voltages but they are all somewhere around that range). A lightning bolt is a few MILLION volts. Even if most of the energy goes down the tree trunk, if only a fraction of it splits off and goes through you, it still has more than enough energy in it to kill you.

Third, lightning going through a tree tends to make the sap instantly flash into steam and explode. Trees can split and fall over. Huge limbs can be blown off. Having a large tree limb come crashing down on top of you doesn’t tend to be very healthy for you.

Some people think that rubber tires insulate you and keep you safe from lightning. Again, lightning already jumped through a few miles of open air. It can jump a few extra inches through air to get around the rubber. That’s nothing for lightning. What makes a car safe is that it is pretty much an enclosed metal box. The lightning bolt tends to go around the outside of the box and leaves everything inside alone. Cars do have holes in their metal boxes (aka windows) and lightning does sometimes come in through a car window. I’ve seen pictures of a parked van that had lightning go in through the front window, down through the steering column, and along the way caught the interior of the van on fire.

On a bike, you don’t have the metal box around you, so those rubber tires don’t do diddley to protect you from lightning.

While it is somewhat true that lightning is more likely to strike the taller nearby houses, keep in mind that in the little area of road or sidewalk where the biker is, the person on the bike is the tallest object, much taller than the sidewalk or road curbs. And again, lightning can jump incredible distances. What’s a few hundred feet from a house to you when lightning has already gone through several miles of open air?

And one last thing. When lightning hits the ground, the voltage spreads out. So at the center of the strike you’ve got a few million volts, which decreases in voltage the further away you get. Depending on the orientation of your bike, the front wheel could end up at a potential of a few hundred thousand volts higher or lower than the rear wheel. That’s going to make current arc over to the bike frame and travel through the bike, and through you.

If you are anywhere near lightning, the best thing to do is crouch down and keep your feet together (helps reduce those voltage gradients for a nearby strike). Standing close to or under trees is about the worst thing you can do. Standing on a porch or under an overhang or in an open doorway is NOT safe. People have been killed doing that. Same for pavilions. Not safe. Inside a car is pretty safe as long as the car has a metal roof. T-tops provide less protection and soft-cover convertibles even less than that.


I just looked up the lightning statistics for this year.

30 people have been killed by lightning so far this year. 8 of those were under or near a tree.

One was on a motorcycle, putting on rain gear.

Four were on the beach. Three were in their yard or in a field. Two were in a cemetery.

Going back a few years in the statistics, trees are always the most numerous on the list, with beaches and fishing always rating pretty highly in the death statistics. There’s one or two motorcycle deaths every year, but I had to go back to 2010 to find a bicycle death. There was another bicycle death in 2008, and another in 2007. The last statistics listed were for 2006 so no info before that. So 3 bicycle deaths from lightning in the last 10 years.

When I was a kid, an older kid in my neighborhood was struck and killed by lightning riding his bike up his driveway. This was a well-wooded neighbor with plenty of large oak trees surrounding the house.

Be careful drawing conclusions from the low number struck while biking. When it’s raining out, you’re not going to have many bikers out on the road in the first place.

You mean like this? :eek:

Lightning protection professionals use the “rolling sphere” method for determining whether a particular object is likely/unlikely to be struck. In this method, imagine a sphere 300 feet in diameter, rolling across the landscape. Anything it can touch is at risk for a direct lightning strike. When it bumps into a prominent object - house, tree, antenna tower, etc. - it can roll over the object or around it, but it can’t reach things that are low and close to the prominent object. Here’s a representative sketch; much more is available with a google search on lightning and “rolling sphere.”

So the next time you’re cruising through a moderately open area, think about that model and how it applies to you and your surroundings.

Note also that even if you are shielded from a direct strike, as engineer_comp_geek points out, you are still vulnerable to the (potentially fatal) effects of an indirect strike.

Your coworker was right to be concerned.

So now we’re playing electrical Katamari.

Was the concerned coworker offering you a ride? 'Cause that would have been the nicest way to show concern.

Yikes! :eek:

Or a convenient pretext.

Glad I don’t live in Chicago.

To put some flesh on what engineer_comp_geek said above, this is a good article summarizing data and evidence-based safety strategies (weighted by strength of evidence) in the backcountry. Note that the “safety position” with feet together is in the lowest category of evidentiary support. If caught in a storm, it’s far more important to understand how to position yourself safely in the local terrain.

Only 5% of lightning injuries are caused by direct strikes. The vast majority are caused by lightning striking something else nearby (a tree or high ground) followed by “side splash” or ground current.

Crudely speaking, the most likely strike points are the local high points/objects in the vicinity of the storm; and you’re at risk of serious injury from side splash or ground current when you’re within maybe 100 feet (or a little more) of those points/objects.

Just to add: I believe the big exception to the “direct strikes are not the main risk” is on water. Humans aren’t too big, and land is rarely completely flat or featureless, so it’s unlikely that your profile when standing or sitting on a bike will make you into a local high point. But if a storm is over a lake, with water being completely flat, even the few feet that you’re raised sitting on a small boat can make you attract a direct strike.

I’ve been told that there’s a cave somewhere on Half Dome in Yosemite National Park. One day some climbers were going up when a storm came along (which they can do quickly in the Sierra Nevada Mountains). So they thought they’d seek shelter in the cave. Climbers carry a fair amount of metal on them (pitons, carabiners, hammers). Sure enough, a bolt of lightening came down & found them in the cave & killed them.

So don’t assume simply being under a bridge will necessarily protect you if you’re near metal.

I would like to add that statistics of lightning strikes are somewhat misleading. There is no way to calculate your risk from them because there are no accompagning statistics of how many people are still out vs. how many seek shelter.

For example: there was 1 fatality from a lightning strike during swimming this year. Considering that most people don’t go swimming during a thunder storm, this may well mean that EVERYONE (or 1 in 10 or some other very high %) that goes swimming gets it. Making “swimming during a thunderstorm” one of the most dangerous passtimes imaginable

Depending on the climate and latitude / longitude, the idea that lightning is only striking in a torrential downpour is not accurate based on my personal experience. Working in remote inland semi-arid type areas at relative latitudes close to the equator, there was a huge incidence of lightning strikes both pre and post heavy rain events. In these sort of areas, the rain and lightning come literally in a flash and often catch you out and about, living or working.

Check out the lightning frequency distribution map, for example link. So its not always like people biking or swimming or whatever went out there with the intent to do that activity in a storm. So the statistical bias may be less than some others propose earlier.

I’ve been about ~50-60m from a strike. I was in a vehicle at the time, and the the strike directly hit a tree off to the side of the road. I was up on a large bermed road, significantly higher than the tree, and the terrain was relatively flat - guess i was lucky the tree copped it and not my car. I will always remember the size of the strike - the tree was vaporised, and it was shrouded in a solid plasma ‘cylinder’ that to my eyes looked to be about 6m wide and 10m tall. Not a short sharp strike like often photographed. The noise was hugely loud, high pitched and shrill, like a vixen screeching directly in my ear (look up the sound a vixen makes, bloody horrible). Anyway I am not sure if the sound was the tree sap/moisture vaporising or if it was the effect of the voltage on the air locally or something else. But it scared the absolute hell out of me and I thought I was going to die if another strike came down and hit me.

cool story.

However my point stands:

  • Most people seek shelter during thunderstorms.

  • People die from lightning regularly.

  • So the chance of getting hit/hurt by lightning while you’re out during a thunderstorm must be quite high. Much higher than is suggested by the incidence of fatalities alone.