What is happening in this video of a tree being electrocuted?
July 10, 2021 1:38 PM Subscribe
I just saw this TikTok of a tree on fire because it’s touching a power line and I want to know more.
How did this happen?
Why doesn’t it happen more often?
How do I ensure it never happens anywhere near me?
If you saw this happening near you, how would you safely get away?
How far away would be a safe distance from which to watch this?
How do they stop it?
Any other relevant tips or facts?
How did this happen?
Why doesn’t it happen more often?
How do I ensure it never happens anywhere near me?
If you saw this happening near you, how would you safely get away?
How far away would be a safe distance from which to watch this?
How do they stop it?
Any other relevant tips or facts?
How: wood/bark, while not a very good conductor is conductive. Especially if it is wet. The wire it is touching is bare (ie doesn't have any insulative material over the metal). When the tree touches the wire it "grounds" the wire directing some of the available power into the ground and the resistance to the current flow turns the tree into a heater. If it is conductive enough then enough current will flow to heat the wood/leaves/bark until they catch fire. And because the burning doesn't much reduce the current flowing the electricity flow continues to heat the wood ensuring it will continue to burn until the fire is self sustaining.
It pretty much happens all the time in locals with overhead lines and trees. I once worked at the end of 80 forested kilometers of overhead powerline and our power went out 30-40 times a year on average. And that was only trees large enough to trip the substation breaker.
Prevention is by trimming trees such that they can't contact the wires.
If you were standing right next to the tree you would shuffle away keeping both feet on the ground and never separating them (ie heal and toe without raising your feet off the ground) until you were at least twice as far away as height of the power line.
Safe observation limits are farther than that because the tree can sometimes explode from internal heating. I'd want to be at least 50 meters away.
The utility will cut the power and then fire fighters can extinguish as normal. Some times the tree burns it self out
posted by Mitheral at 2:31 PM on July 10, 2021 [2 favorites]
It pretty much happens all the time in locals with overhead lines and trees. I once worked at the end of 80 forested kilometers of overhead powerline and our power went out 30-40 times a year on average. And that was only trees large enough to trip the substation breaker.
Prevention is by trimming trees such that they can't contact the wires.
If you were standing right next to the tree you would shuffle away keeping both feet on the ground and never separating them (ie heal and toe without raising your feet off the ground) until you were at least twice as far away as height of the power line.
Safe observation limits are farther than that because the tree can sometimes explode from internal heating. I'd want to be at least 50 meters away.
The utility will cut the power and then fire fighters can extinguish as normal. Some times the tree burns it self out
posted by Mitheral at 2:31 PM on July 10, 2021 [2 favorites]
The answers for 1 and 2 are that most power lines in residential neighborhoods are insulated, which prevents foliage growth on trees from being as much of a problem most of the time. In this case, either the insulation failed somehow, or the line wasn't insulated at all; as it looks like it might've been a high-voltage line, I'd suspect the latter. That said, power companies and property owners should be regularly inspecting and trimming back trees growing near power lines to avoid having to rely on intact insulation.
posted by Aleyn at 2:36 PM on July 10, 2021 [3 favorites]
posted by Aleyn at 2:36 PM on July 10, 2021 [3 favorites]
That’s a high voltage line, but less-violent tree/power line fires are super common, especially after a storm pushes trees over. (My local FD district gets 1 “tree branch smoking on a power line” or “pole on fire” call after every big storm, on average. There have been 2 in the past 4 days, and our district is less than a mile in diameter.)
I suppose if you live in a place without trees or above-ground power lines you could avoid it. Power companies trim trees back but they can’t control how they come down in a storm. Just call 911 if you see it happening. They’ll call the FD and the power company, who will clear the area to a safe distance, turn off the power, put out and/or cut down the tree/pole, and do any repairs to the wire. It’s pretty routine.
posted by tchemgrrl at 4:16 PM on July 10, 2021 [1 favorite]
I suppose if you live in a place without trees or above-ground power lines you could avoid it. Power companies trim trees back but they can’t control how they come down in a storm. Just call 911 if you see it happening. They’ll call the FD and the power company, who will clear the area to a safe distance, turn off the power, put out and/or cut down the tree/pole, and do any repairs to the wire. It’s pretty routine.
posted by tchemgrrl at 4:16 PM on July 10, 2021 [1 favorite]
How do they stop it?
The utility will flip a switch somewhere, or there might be a fuse or breaker that would trip along the line. Once they have confirmed power is off, the firefighters will put out the fire.
If you saw this happening near you, how would you safely get away?
From a video on what to do if a crane hits a power line "...If you are in immediate danger. And have to move, keep your feet together and slowly shuffle at least ten meters away your feet should move no farther than toe to heel never leaving the ground..."
posted by drezdn at 5:41 PM on July 10, 2021 [1 favorite]
The utility will flip a switch somewhere, or there might be a fuse or breaker that would trip along the line. Once they have confirmed power is off, the firefighters will put out the fire.
If you saw this happening near you, how would you safely get away?
From a video on what to do if a crane hits a power line "...If you are in immediate danger. And have to move, keep your feet together and slowly shuffle at least ten meters away your feet should move no farther than toe to heel never leaving the ground..."
posted by drezdn at 5:41 PM on July 10, 2021 [1 favorite]
because the burning doesn't much reduce the current flowing the electricity flow continues to heat the wood ensuring it will continue to burn until the fire is self sustaining.
There's something else going on in that TikTok as well: the tree is hot enough to emit smoke. Smoke is a combination of water vapour, water fog, volatile organic substances and organic particulates and if it's hot enough it will burn; a normal wood flame is essentially made of burning smoke.
What's happening to the tree in the video is that the tip of a branch is brushing against the wire and striking an arc, which heats the smoke it's arcing through enough to light it on fire. Flames and electrical arcs both generate plasma (conductive, ionized gas), so the arc grows into and moves through the flame, following the path of least resistance; you can see the wire end of the arc moving along the wire to the right, while the tree end moves right down inside the tree.
The heat from the electrical discharge and the flame from burning smoke makes the plasma channel that's sustaining the arc much less dense than the surrounding air, so it rises. You can see the arc arching upward off the wire as it moves to the right. Eventually, the rising stretches the arc out long enough that it's can't sustain, and it extinguishes until the tree brushes against the wire again and starts another one.
What we're seeing here is pretty much a large scale, uncontrolled version of a Jacob's Ladder, with added wood gas to make the arc burn orange as well as blue. The way to avoid this kind of thing is to keep trees trimmed so that their branches don't get close to power lines, especially the high-voltage distribution kind.
It doesn't look like the tree was hot enough to sustain combustion after the arc snuffs out, so getting this under control should have been pretty straightforward after the power got cut.
posted by flabdablet at 5:03 AM on July 11, 2021 [1 favorite]
There's something else going on in that TikTok as well: the tree is hot enough to emit smoke. Smoke is a combination of water vapour, water fog, volatile organic substances and organic particulates and if it's hot enough it will burn; a normal wood flame is essentially made of burning smoke.
What's happening to the tree in the video is that the tip of a branch is brushing against the wire and striking an arc, which heats the smoke it's arcing through enough to light it on fire. Flames and electrical arcs both generate plasma (conductive, ionized gas), so the arc grows into and moves through the flame, following the path of least resistance; you can see the wire end of the arc moving along the wire to the right, while the tree end moves right down inside the tree.
The heat from the electrical discharge and the flame from burning smoke makes the plasma channel that's sustaining the arc much less dense than the surrounding air, so it rises. You can see the arc arching upward off the wire as it moves to the right. Eventually, the rising stretches the arc out long enough that it's can't sustain, and it extinguishes until the tree brushes against the wire again and starts another one.
What we're seeing here is pretty much a large scale, uncontrolled version of a Jacob's Ladder, with added wood gas to make the arc burn orange as well as blue. The way to avoid this kind of thing is to keep trees trimmed so that their branches don't get close to power lines, especially the high-voltage distribution kind.
It doesn't look like the tree was hot enough to sustain combustion after the arc snuffs out, so getting this under control should have been pretty straightforward after the power got cut.
posted by flabdablet at 5:03 AM on July 11, 2021 [1 favorite]
Spectacular video.
I once watched from an office building as a falling branch brought a wire down on the roof of a car. Not as picturesque, but the steps in what happened were as described: everyone, including firemen, stood around and watched until the power company turned off the electricity, then the firemen put out the fire
posted by SemiSalt at 12:44 PM on July 11, 2021
I once watched from an office building as a falling branch brought a wire down on the roof of a car. Not as picturesque, but the steps in what happened were as described: everyone, including firemen, stood around and watched until the power company turned off the electricity, then the firemen put out the fire
posted by SemiSalt at 12:44 PM on July 11, 2021
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If a tree's leaf is what touched the power line, it would probably burn up the leaf and that's about it. This line is touching a branch which is wet enough (on the inside, like most living trees) not to burn up too quickly. The fact that the branch is damp and kept hitting the power line allowed the arc to heat up the trunk of the tree to the point of ignition.
Ensure it doesn't happen: trim, remove, or relocate the tree, or move the power line. Trimming is the cheap solution.
Get away: I dunno, walk away from the tree. It's a tree in flames (though not on fire as such), so it could spread the flames; do what you'd do if a house was burning-- get away from the house.
How far away is safe: I'd say twice the height of the tree. There's some danger from exploding sap pockets, which would blast bluntish wooden shrapnel into the air, and the tree could fall over or drop burning limbs. If it's tight with other trees, they are a danger as well. The house could also catch fire.
How do they stop it: they'd kill the power line power temporarily, do a radical tree trimming (this tree is probably FUBAR-- basically it got hit by lightning over and over for minutes), and then leave it to the owner to take down the tree.
It probably happens all the time, anywhere you have high voltage. I would guess that cities have some regulations about what you can build or grow near the lines, and tall trees should get caught during visual inspections, by the utility, of the line. Even if this wasn't a high-voltage line, but was, for example, a communications line, trees remain a threat if they tangle up and start putting pressure on the lines, so this is a constant concern which is usually policed by the utility. This event was probably a foul-up by the utility company in that area, failing to inspect, or someone falsified the inspection report and hit a Burger King instead.
If the Bothell in question is Bothell, WA (25 minutes from Seattle), then the City's FAQ says:
> What do I do about fallen, leaning, or overgrown trees?
Overgrown trees and green belts: If on public property, they will be inspected and trimmed if deemed necessary. If the overgrown tree is on private property and determined to be a hazard, the City will notify the property owner.
Fallen or leaning trees: If a fallen tree is a danger to citizens, vehicles, or in the power lines, call 911. Otherwise, report fallen or leaning trees to [City Public Works dept.] or submit a Citizen Action Request.
posted by Sunburnt at 2:29 PM on July 10, 2021 [6 favorites]