Can Fire Conduct Electricity? Why Flames Carry Current Like A Wire

Yes, but barely. A flame holds a thin population of electrically charged particles, so current can cross it, though a wood fire conducts about seven billion times worse than copper. Those particles are not made by the heat, which is far too feeble to explain how many of them there are, but by a chemical step inside the burning itself, the same effect that runs the flame ionization detector, a standard tool of analytical chemistry.

A tree comes down on a power line. It catches fire, and the flames start to pulse. Not flicker, the way flames always do. Pulse, in time with something, brightening and dimming on a beat.

This one was filmed at Apolda, in Germany, after a storm.

Videos like this turn up every storm season, and the comments always split two ways. One camp says the fire is conducting the electricity. The other says that cannot be, because fire is hot air, and air is one of the best insulators we have. Both camps have a point.

Fire does conduct electricity. It is also not the heat that lets it.

What Has To Be True For Anything To Conduct Electricity?

Start with a road.

An electric current is charge on the move. A material needs particles that carry charge. Those particles must also be free to travel. Think of them as cars on a road. No cars, no traffic, however wide the road.

Copper is a motorway at rush hour. Its atoms give up their outer electrons into a shared pool. Those loose electrons drift when you push them. There are staggering numbers of them, and they move well.

Salt water works differently. Dissolve table salt and it splits into charged sodium and chlorine particles. A charged atom is called an ion, and ions are the cars here. There are fewer of them, and they lumber rather than dart. That is why salt water conducts far worse than metal, yet well enough to ruin a phone.

Now cool air. Air is a road at 4 a.m. with nothing on it. Its molecules keep a firm grip on their electrons. Almost nothing is free to move. Conductivity measures how well a material passes current, in siemens per meter. Physicists put air below 0.000000000000001 of them. That is why power lines can hang bare in the open.

Hold on to the road. The rest of this article asks one question: how many cars does a flame have?

Is Fire A Form Of Electricity, Or Is It A Plasma?

No. Fire is not a form of electricity, and electricity is not a form of fire.

Fire is a chemical reaction. Fuel and oxygen rearrange into new molecules and release heat. The glow is the hot gas made along the way. We have a whole article on which state of matter fire belongs to. The honest answer is that it sits between the usual boxes.

The closest box is plasma. A plasma is a gas in which some particles have lost or gained electrons. It holds free ions and free electrons, mixed with ordinary neutral gas. Overall it stays neutral, because the positives and negatives balance. What sets it apart is what the road analogy cares about: a plasma has cars.

Combustion researchers are blunt about where a flame lands. A Princeton course puts it in one line: "Flame is a weakly ionised plasma." The word doing the work is weakly. A candle is not a neon tube, and it is nothing like the Sun. Only a tiny fraction of the gas carries charge.

That fraction is small. It is also not zero, and not zero turns out to be enough.

Does Fire Release Electrons? And Can Heat Alone Explain Them?

Fire does release electrons. This is where the obvious explanation collapses.

The obvious explanation is heat. Heat is motion. Heat a gas enough and its particles slam together hard enough to knock electrons loose. That process is real. It is called thermal ionization, and it is how the Sun ends up as plasma.

So does it work for a flame? Hartwell Calcote and Isadore King ran the numbers for a propane and air flame at 2,200 K (1,927 °C or 3,500 °F). That is about as hot as ordinary burning gets. Heat alone should give 17 million ions per cubic centimeter. That sounds enormous. Then you compare it with a measurement.

Experiments find between 1 billion and 10 billion ions per cubic centimeter in such a flame.

Sit with the size of that gap. The flame carries 60 to 600 times more charge than its temperature can explain. Calcote and King drew the only conclusion left. Ions, they wrote, "are produced not by thermal processes but by chemi-ionization."

Heat gets the blame for everything fire does. Here, heat is innocent.

What Is Chemi-Ionization, And How Does A Flame Make Its Own Charge?

Chemi-ionization means ionization made by a chemical reaction rather than by heat. One reaction releases enough energy to fling an electron off, right there in the flame. It takes two steps.

First, a fragment called CH meets a lone oxygen atom. CH is a single carbon still holding one hydrogen. Neither piece is a normal molecule. Both are leftovers, halfway through burning. The reaction is violent enough to eject an electron outright:

CH + O → CHO⁺ + e⁻

That is a charged particle and a free electron, manufactured on the spot. No heat required.

Second, the CHO⁺ ion meets a water molecule. Fire makes plenty of water, since hydrogen in the fuel burns to H₂O. The ion hands over a proton:

CHO⁺ + H₂O → H₃O⁺ + CO

H₃O⁺ is hydronium, a water molecule carrying one extra proton. It is the main positive carrier in an ordinary flame. It is stable enough to drift well past the part you can see.

So the cars on the road are built by the burning. Combustion is not a hot process that happens to make ions. It is an ion-making process, and always has been. Every candle you have lit, and every click of a pocket lighter, was running a chemistry experiment.

So How Well Does A Flame Conduct Electricity?

Badly. This is the part the viral videos leave out.

Researchers have measured it. One team fired microwaves through a burning pile of vegetation. They worked the conductivity out from how the beam came through. For a fire peaking at 1,240 K (967 °C or 1,773 °F), they got 0.0058 to 0.0079 siemens per meter.

Put that on the ladder. Sea water manages about 5 siemens per meter. That beats the flame by a factor of about 600. Copper reaches 58 million, which is about seven billion times better. A flame is a conductor in the way a paper straw is a crowbar.

Now look the other way down the ladder. Cool air sits below 0.000000000000001. Against air, the flame is some eight trillion times better. That is the comparison that matters. The flame is not replacing a wire. It is replacing a gap that was doing an excellent job of stopping current.

What Happens If Fire Touches Electricity?

Now back to the tree.

Saying "the flame conducted the current" is too simple. What a fire under a power line does is spoil the insulation. Vegetation fires under high voltage lines, the measurement team write, "reduce flashover voltage." They do it by raising the conductivity and temperature of the air.

A flashover is an electrical breakdown across a gap that was supposed to hold. In dry air, that gap holds off the voltage. Fill it with hot gas full of charge and the voltage it can withstand drops. Current jumps across as an arc. An arc is bright, unstable, and pulses. That is the beat in the video.

A wood fire has a second source of charge that a gas stove lacks. Plants concentrate potassium and sodium as nutrients. Burning releases them into the flame. Those metals lose an electron at the slightest push, so unlike the CH fragments, they do ionize from heat alone. The same paper calls vegetation fires "seeded with plants' omnipresent alkali nutrients." A campfire conducts better than a clean gas flame, and the reason is the plant.

So utilities treat fire under a line as an emergency. A fire near infrastructure can knock circuits out from a distance, with no branch touching anything. The hazard runs the other way too: a tree struck by lightning can carry enormous current, and the steam inside can burst the trunk apart. If you meet a downed line, stay well away and call the utility.

Can An Electric Field Push A Flame Around?

It can, and this is the cheapest way to prove a flame is full of charge.

Put a flame between two charged plates. The positive ions feel a force toward the negative plate and start to move. As they go, they collide with neutral gas molecules and shove those along too. The whole flame leans. Researchers call this ionic wind, and the Princeton notes put its speed at up to 10 meters per second.

Turn the voltage up and the flame does not just lean. The same notes show a propane flame blown clean off its burner by a couple of thousand volts. No draft, no fan, nothing touching it.

People have been poking flames with electricity for a while. The trick appears in a paper read to the Royal Society in 1814. Nobody needed to know about electrons to notice that fire answers a charged plate.

Can You Generate Electricity From Fire?

From the charge in the flame, yes. Engineers have tried.

A magnetohydrodynamic generator shoots hot ionized gas through a magnetic field. The field pushes the charges sideways onto electrodes. It makes electricity, in one paper's words, "without the need for any moving mechanical parts." Then it hits the wall this article keeps hitting. A flame conducts too badly. Real designs must seed the gas with metals that ionize at low energy and run far hotter. The idea drew serious attention in the 1960s and never displaced the turbine.

The useful application of flame ions turned out to be smaller, and far more common.

How Does A Flame Ionization Detector Work?

One standard instrument of analytical chemistry exists because flames make ions.

It runs a small hydrogen and air flame. A clean hydrogen flame makes few ions on its own. There is no carbon in it, and chemi-ionization needs those CH fragments. So the flame sits there, quiet, conducting almost nothing.

Feed any organic compound in and the picture changes. Now there is carbon, so there are CH fragments, and the flame fills with charge. A metal electrode a few millimeters above collects the ions. A meter reads the current. It runs from about 0.00000000000001 up to 0.00001 amps, so the instrument needs a careful amplifier.

The elegant part is what the current is proportional to. Organic molecules entering the flame get torn apart. The pieces react until every carbon has become the same fragment. So each carbon gives the same signal, and the response tracks the number of carbon atoms. The detector does not identify the molecule. It counts carbon.

That is not a laboratory curiosity. The US Environmental Protection Agency writes flame ionization into its air-testing rules. Method 25A reports results "as carbon equivalents", with correction factors of 2 for ethane, 3 for propane, 4 for butane. Those are the carbon counts. Somebody is measuring a smokestack right now by burning a sample and weighing the electricity.

So, Can Fire Conduct Electricity?

Yes. A flame is a weak plasma. It carries current because it holds ions and free electrons that can move.

The satisfying part is where they come from. Not the heat, which falls short by a factor of hundreds. They are built by the burning. A scrap of half-burnt fuel meets an oxygen atom, throws off an electron, and leaves a charged fragment behind. That fragment passes a proton to a water molecule, and hydronium does the carrying.

Both camps were half right, then. The fire does conduct. It is also a terrible conductor. The video does not show current running through a flame like water down a pipe. It shows a gap that used to be a good insulator and has stopped being one, arcing over and over.

Look at a candle now and the arithmetic is different. Somewhere in that quiet flame, a reaction is manufacturing charge out of the fuel. A few billion ions to the cubic centimeter. It is the same reaction that lets a machine count carbon atoms in a smokestack. It has done that in every fire that ever burned, including all the ones people sat around long before anyone knew what an electron was.