Severe Fire Behaviour
Relative Humidity (RH) – Temperature Crossover
When RH falls below temperature there is high potential for severe fire behaviour.
When cross-over is predicted by forecasters a warning or advisory will be issued to firefighters.
Cross-over can occur on a localized level.
SEVERE FIRE BEHAVIOUR CAN OCCUR WITHOUT A CROSS-OVER!
Sudden Change in Wind Speed and/ or Direction.
Sudden change in wind speed can elevate fire behaviour and increase rate of spread.
A surface fire can change to a crown fire.
Sudden change in wind direction changes which portion of the fire is most active, (the head), and the direction of spread. Both can adversely affect firefighter safety.