Firefighters were battling massive wildfires Monday that have ravaged Los Angeles and killed at least 24 people, with officials warning of incoming dangerous winds that could whip up the blazes further. Forest fires spread due to a combination of wind, vegetation and hilly terrain. VIDEOGRAPHIC
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00:00Forest fires spread due to a combination of wind, vegetation and hilly terrain. Wind fans
00:15the flames, affects the direction of the fire and transports embers and burning particles
00:21which allow the flames to jump over roads or fire breaks. Vegetation fuels fire. The
00:27drier the forest, the faster the fire spreads, travelling at up to 5km an hour. The more
00:33bushy the forest, the faster the fire spreads, particularly if the undergrowth isn't regularly
00:38cleared. A carpet of dry leaves is perfect fuel. In hilly areas, upward slopes tend to
00:45accelerate the fire, while it decelerates downhill. In high risk areas, aerial spotters
00:51carry out surveillance all day long. As soon as a fire is detected, trackers discharge
00:58water mixed with a flame retardant, a fireproof salt which helps prevent vegetation from burning.
01:05If the fire develops, Canadair planes carrying greater volumes of water go back and forth
01:10over the zone, dousing the flames with their 6,000 litre cargo. On the ground, firefighters
01:17are dispatched, coordinated by a command post to ensure they're not injured by the
01:21tonnes of water being dropped from the air. Two strategies are possible. Offensive, whereby
01:26firefighters get as close as possible to the blaze surrounding it from all sides. Or there
01:32is the defensive strategy, fire crews wait for the fire to reach them, while protecting
01:37vulnerable areas by establishing a line of vehicles to intervene by dousing the flames.
01:43In certain cases in uninhabited areas of forest, forest rangers can light tactical
01:49fires under the supervision of the fire brigade, creating scrubbery zones which act as fire
01:53breaks and can stop the fire in its tracks. This technique tends to be used in Canada
01:58and the United States.