How wildfires start - and stopping them

Firefighters often refer to the fire triangle - fuel, oxygen and heat - when confronting a wildfire. Take away one of those and, they say, they can control and ultimately extinguish it.

Sometimes, it is simply heat from the sun or lightning, but even a spark from a train wheel can start a wildfire, especially in the dry conditions of summer.

It is not yet known how the fires in the Canadian province of Alberta started but most wildfires stem from human carelessness - discarded cigarettes, campfires, fireworks.

A wildfire, once it is started, can be wind-driven, slope-driven or fuel-driven, Mr Rob Gazzard, technical adviser to the Forestry Commission England, told the BBC.

If these three combine, an extremely dangerous blaze can take off, destroying thousands of hectares.

"Where a slope is going upwards at a 10 per cent gradient that would double the speed of the fire, if it's 20 per cent it would quadruple the speed of the fire," Mr Gazzard said. "That's because it's pre-heating the fuel above it. So if a fire is going up a mountain, it will go very fast."

To control and ultimately stop the fire, the fuel has to be removed "because you can't affect the weather or topology", he said.

"Using wildfire prediction tools, which look at the aspect of the slope, wind speed and direction and the topology - so the uphill, downhill - and the fuel, we work out where we can win the fire.

"So that would be downhill, out of the sun, where fuel is low and where wind plays less of a role.

"You go hours or days ahead of the fire and remove anything that can fuel it using bulldozers, tree harvesters, hand tools." Then, creating a fuel break, which is basically a big trench, around the fire can suppress it very effectively, Mr Gazzard said.

A version of this article appeared in the print edition of The Straits Times on May 10, 2016, with the headline 'How wildfires start - and stopping them'. Print Edition | Subscribe