How do firefighters fight bushfires?

Three things every fire needs

Every fire needs three ingredients: heat, fuel and oxygen. Scientists call this the fire triangle. Take away any one side of the triangle, and the fire goes out.

Almost everything firefighters do is a way of breaking the triangle. Spraying water cools burning material, taking away heat. Clearing away leaves, grass and branches takes away fuel. Smothering flames, for example with soil, cuts off their oxygen.

In the bush, the fuel is mostly the fine stuff: dry leaves, twigs, bark and grass less than about 6 millimetres thick. Bigger logs and branches do burn, but they usually burn well behind the front of a fire.

Why bushfires spread

CSIRO scientists describe a second triangle, the fire behaviour triangle: weather, fuel and the shape of the land. These three things decide how fast and how fiercely a bushfire moves.

Weather matters a lot. Hot, dry days dry out the fuel, and the stronger the wind blows, the faster a fire spreads. Wind can also carry burning bits of bark and leaves, called embers, well ahead of the fire, where they can start new spot fires.

The shape of the land matters too. Fires race uphill, because the flames lean towards the plants in front of them and heat and dry them out first. As a rule of thumb, a fire's speed doubles for every 10 degrees of uphill slope. Going downhill, fires usually slow down. Fires in grassland also spread faster than fires in forest, because grass is finer fuel.

Crews on the ground

Most of the hard work happens on the ground. Firefighters use fire trucks carrying water and hoses, and many firefighters are volunteers. The NSW Rural Fire Service calls itself the world's largest volunteer fire service, with nearly 70,000 volunteers in about 2,000 brigades.

Crews also build control lines, strips where fuel has been cleared away with hand tools and machines, so the fire has nothing to burn when it arrives. Sometimes they carefully light a backburn along the inside edge of a control line. It burns up the fuel in the path of the bushfire, so the main fire runs out of things to burn.

After the flames have passed, the job is not over. Crews do blacking out, also called mopping up: putting out or removing burning material near the control line so the fire cannot flare up again.

Help from the sky

Aircraft are a powerful part of the team. According to the National Aerial Firefighting Centre, their jobs include firebombing, which means dropping water, foam or fire retardant on or in front of a fire to slow or stop it spreading. Aircraft also map fires with infra-red sensors, carry firefighters to remote places and move equipment.

Larger helicopters are most often used for firebombing. Australia has also relied on some very large firefighting aircraft from overseas, such as Air-Crane helicopters like the one in the photo at the top of this page.

Aircraft work together with the crews below them. Pilots can reach steep or remote country quickly, while ground crews make sure the fire is really out.

Getting ready before summer

The best time to fight a bushfire is before it starts. Hazard reduction means lowering the amount of fuel before the hot months, by carefully planned burns, slashing undergrowth or clearing fuel by hand.

For thousands of generations, Aboriginal people have used cultural burning to care for Country. These are cool, slow, low burns, led by Aboriginal fire practitioners and Elders, that leave a patchwork of burnt and unburnt land. Animals have time to move away, and the patches help plants and animals thrive. Around 75 per cent of Australia's native plants respond well to fire, and many need it to regrow.

Families can get ready too. The NSW Rural Fire Service suggests four simple steps: discuss what you will do if a fire threatens, prepare your home, know the alert levels, and keep up to date with fire information. Clearing leaves from gutters, keeping grass short and checking the daily Fire Danger Rating all help. On the most dangerous fire days, fire services advise people in bush fire risk areas to go somewhere safer early, well before any fire arrives.

📚 Words to know

Fuel

Anything that can burn. In the bush, it is mostly dry leaves, twigs, bark and grass.

Ember

A small burning piece of bark, leaf or twig that can be carried by the wind.

Control line

A strip cleared of fuel so that a fire stops when it reaches it.

Backburn

A fire lit on purpose by firefighters to burn up fuel in the path of a bushfire.

Hazard reduction

Lowering the amount of fuel in an area before fire season, for example with a planned burn or by clearing undergrowth.

🧪 Try this: be an ember scientist (no fire needed)

1. Tear a sheet of paper into small scraps about the size of a fingernail. These are your pretend embers. Also collect a few heavier things, such as small leaves, bottle caps and coins.
2. Put a desk fan or hair dryer (on the cool setting) at one end of a hallway or table. Ask an adult to help set it up safely.
3. Drop one item at a time in front of the fan on its lowest setting. Measure how far each one travels with a tape measure, and write it down.
4. Now try the highest setting. How much further do the light scraps go? This is why strong winds can carry embers far ahead of a bushfire.
5. Finish by talking with your family about your household's bush fire plan. The NSW Rural Fire Service suggests having that chat over dinner, when everyone is together.