Is It Safe to Start a Fire with a Car Battery?

car battery jumper cables fire
Shorting out jumper cables is a great way to generate sparks to get a fire going, but that doesn't mean it's safe. J. Ronald Lee / Moment / Getty

Question: Is it safe to start a fire with a car battery?

I was watching a show the other day, and they used a car battery to start a fire. It seemed like a good way to get a fire started in an emergency if there was something else wrong with your car, but I was wondering if it’s actually safe. Is shorting out a car battery to create sparks and start a fire actually safe, or would it be better to use a different method, even in an emergency situation?

Answer:

Starting a fire by shorting out a car battery has been done on a number of reality shows, and while it does work if you have appropriate tinder available, there are a number of safety concerns that you need to be aware of. Since car batteries can explode under the right circumstances, it’s absolutely imperative to take the necessary measures to avoid creating those circumstances. There are also a handful of ways to start a fire using your car battery that doesn't involve a direct short and a lot of other ways to start a fire in a survival situation that doesn't involve your battery at all.

Car Batteries, Hydrogen Gas, Sparks, and Grievous Bodily Harm

For those who aren’t already aware, the reason that car batteries can—and do—explode is that they release hydrogen gas during electrolysis. That means any battery that has recently been charged, especially one that went dead first, may have hydrogen gas lurking inside its cells.

It also means that hydrogen gas may be present near the battery or leaking out of the cells.

Since hydrogen gas is highly flammable, all it takes to blow up an otherwise benign car battery is to introduce a spark to exactly this sort of explosive situation. This is why the safest way to hook up jumper cables is to connect the negative cable to a good, solid ground that isn’t anywhere near the battery itself.

If any sparks are generated when hooking up jumper cables, you want them to be as far away from the battery as possible.

Starting a Fire With Sparks From a Car Battery

The basic idea of keeping sparks as far away from your car battery as possible holds true if you absolutely have to start a fire via this method. The safest way to do this would be to hook your cables up to the battery first and take care not to create any sparks with the other ends until and unless they are as far away from the car as possible.

In theory, briefly touching or brushing jumper cables together to generate sparks, which are then capable of igniting appropriate tinder material, should be safe if you keep the whole thing away from the battery. However, shorting out a battery does carry the additional risk of exposing an internal fault and causing an explosion anyway.

Car Batteries and Internal Sparks

When a car battery is well-maintained and in a state of good repair, the internal lead plates will be covered in an electrolyte and there will be little or no hydrogen gas present. If your battery fits that description, then there is very little chance of it blowing up. However, most batteries fall short of that idea, which is why shorting out a car battery to start a fire may cause an explosion even if you keep the sparks far away from your vehicle.

The issue is that if one or more of the vents in a car battery fail, you can end up with a buildup of hydrogen gas even if the battery hasn’t been charged recently. And you can also end up with an internal short or fault via a phenomenon called “treeing.” When you short out the battery to create sparks for a fire, and the battery is suffering from these or similar problems, it can explode.

If you’re far away from the battery when it explodes, you are unlikely to be injured. However, the explosion is still likely to spray acid all over your engine compartment, and there is always the possibility of a larger electrical fire starting in the process.

Other Ways to Start a Fire With a Car Battery

The easiest and safest way to start a fire with a car battery is to use the cigarette lighter. In fact, if you think about it, that’s exactly what car cigarette lighters are designed to do, albeit on a somewhat different scale. So if your car has a cigarette lighter, using the red-hot coil to light your tinder will be both easier and safer than using sparks from jumper cables.

The problem with using a cigarette lighter to start a fire is that some cars ship without the lighter portion and non-smokers often remove them anyway since they only use their cigarette lighters as 12v accessory sockets anyway.

If your car doesn’t have a cigarette lighter, there are still some other options you can try.

Starting a Fire With a Car Battery and a Pencil

Rather than creating sparks and a direct short by touching jumper cables together, it’s also possible to start a fire by connecting jumper cables to a pencil. This is done by exposing the lead on both ends of the pencil and connecting the jumper cables to opposite ends. The lead heats up and eventually ignites the wood, effectively starting a fire.

While this may or may not be safer than simply starting a fire with sparks, it’s important to note that it’s still potentially hazardous. The fire will typically start quite suddenly, so you have to be ready to disconnect your jumper cables to avoid burning yourself. It’s also quite possible that the jumper cables could be damaged or even ruined.

Starting a Fire With Steel Wool and a Car Battery

Another way to start a fire with a car battery is to connect jumper cables to the battery and then connect them to the edges of a clump of steel wool. The safest way to do this is to clamp one cable to the steel wool and then touch the other clamp to the other side. The steel wool will typically ignite very quickly, after which you can disconnect the cables and use the burning steel wool to ignite some other type of tinder that you have ready to go.

It’s important to note that while this does work, it’s also possible to set steel wool on fire without your car battery. In fact, if you have a 9-volt battery in your car, that’s a much safer, and just as easy, way to set steel wool on fire.

Staying Safe Starting Car Battery Fires in Emergency Situations

While starting a fire with sparks from jumper cables connected to your car battery may be dangerous, there are definitely survival situations where the dangers would outweigh the risks. If you’re stuck in a snowstorm, and you need to start a fire to stay warm, then that’s a risk assessment you will have to make. Running your car heater will only last until you run out of gas, while starting a fire will last as long as you can keep the fire going with whatever wood or other burnable you can safely scavenge in the area.

The better option is to plan ahead and have a cigarette lighter plug in the glove compartment if you don’t smoke, or even leave an everyday carry or emergency survival bag in your car that contains items like tinder and a firestarter or even some steel wool. If you find yourself in an emergency situation without any of that, then by all means, sparking jumper cables is an option, just make sure you take the necessary precautions to avoid severely injuring yourself in the process.