Fire with a battery and steel wool

Electric current heats every conductor it flows through. With thick cables you hardly notice, but a very thin wire gets hot quickly because the current has to squeeze through a tiny cross-section. Finest steel wool consists of countless such wafer-thin threads. When it touches both terminals, a short circuit forms, and the threads at the contact points glow immediately.

On top of that, iron this fine actually burns in air. A thick nail does not, because it carries heat away too quickly. The fine threads, however, have a great deal of surface for their mass. That is why the glow spreads through the pad even after the battery has been removed.

Use the finest steel wool you can get. Coarse wool of the kind used for scouring glows poorly or not at all. Pull a piece apart loosely to make an airy pad – air is important for the glow to continue.

Prepare your tinder bundle completely before you put the battery to the wool. The glow in the wool lasts only briefly. Brush both terminals across the wool, put the glowing pad straight into the nest and blow gently. In a light breeze the wool often glows especially strongly because it gets more oxygen.

The battery must be charged. Batteries lose charge over time, even sitting in a cupboard. If you keep this method in your emergency kit, check the battery regularly and replace it in good time. Steel wool rusts when damp and then works less well; packed dry and airtight, it keeps for a long time.

The biggest danger is not making the fire itself but carrying the materials. Pack steel wool and batteries separately in different closed bags. Cover the battery terminals with the protective cap or a piece of tape. That way nothing can cause an accidental short circuit.

Never use lithium-ion cells, phones or power banks. If they are short-circuited, they can overheat, swell, catch fire or even burst. That is far more dangerous than the small fire you actually wanted to make.

Burning steel wool throws sparks and drops glowing crumbs. Work on a non-flammable surface such as soil, stone or sand, and keep clothing, hair and fingers away. If you do get burned, cool the spot at once with cool, not ice-cold, running water; for large or deep burns, call the local emergency number (112 in the EU). Always check the local rules before making a fire.

The method is a good addition to an emergency kit at home or in the car because it needs almost no practice. Even people who have never made a fire can get an ember this way. It is also a vivid experiment to show children, under supervision, that electricity produces heat.

It is less suitable as a main method: the battery may be flat, the wool may rust, and you only get an ember, not a finished fire. A lighter or matches remain the first choice. The battery method is a trick for when those are missing.