Scion scientists Grant Pearce and Stuart Anderson want to get a better understanding of fire behaviour. They use the knowledge to improve the models and tools available to fire managers who use these to warn the public of possible fire risk.

The cause of fires

In New Zealand, about 99% of all fires are caused by people. Very few fires start as a result of natural causes such as lightning. A number of fires are started as a burn-off (farmers getting rid of excess vegetation), which then escapes, becoming a wildfire. Other fires are started by accidents such as sparks from trains and other machinery, power lines touching dry vegetation or coming down in strong winds, cigarettes, camp fires and fireworks. Some fires are started by arsonists (people who deliberately start fires).

The environmental component

Scientists Grant Pearce and Stuart Anderson have researched the effect of the environment on fire. This includes the influence of fuel, the weather and the terrain on fire risk.

Fuels: Dead, dry plants are potential fuel for a fire. A lot of research focuses on describing the fuels – the species of plants and how they burn, how much fuel (plant material) is present in an area and how plants respond to changes in the weather conditions. Scientists are working out how to assess an area for the amount of dead plant material it has and how to predict how dry (and easy to ignite) this fuel is.

Weather: The weather component includes temperature, humidity, rainfall and wind and how these affect the way a fire burns. Scientists have a database of daily weather and fire danger records from weather stations located across the country. They also look at historical fires and the climatic conditions at the time. They can then describe fire climate and fire risk in different parts of New Zealand.

Scientists suggest that future climate change is likely to result in increased fire danger in most areas, particularly in the eastern part of the country. Recent work with the National Institute of Water & Atmospheric Research (NIWA) has updated information on future fire weather patterns.

Terrain: Research has found that fire risk is greater when hills/slopes are involved. Fires spread faster up a slope. The scientists now want to know the particular increase in fire spread rate for different vegetation types.

The New Zealand fire danger rating system

Scientists use the knowledge of fire behaviour – how far and fast a fire will spread, how much fuel it will consume, how hot it will be, how large the flames will be, how much heat energy is produced and so on – to work out an accurate fire danger rating system. This is used to warn people about fire risk.

The most common way to warn people about fire risk is through the fire danger signs that we see on the side of the road. The signs alert people to changing weather conditions, the drying out of fuels and the likelihood of fires occurring.

Other ways to manage fire risk include:

  • limiting certain activities, like riding motorbikes through forests
  • preventing people from accessing high risk areas, like conservation areas and forests
  • reducing fuels in an area – mowing grasses along roadsides, pruning trees and burning off areas to reduce fuel in that area
  • controlling people lighting fires, by having restricted or prohibited fire seasons when fires require permits or are banned.

Firefighters managing fire risk

Firefighters in the outdoors face different hazards (like weather and terrain) to those fighting fires inside buildings. They need to know the dangers and risks they face when fighting fires out in the open.

Scion has developed a wearable system for firefighters that includes a helmet camera, a heart monitor and a global positioning system (GPS). This helps scientists to know where the firefighter is, what they are doing and how the task is affecting their heart rate. Researchers can use this information to work out what the firefighter’s workload is, how they are coping and how effectively they are putting out the fire.

    Published 17 November 2009