To make sure a planned burn is successful, Forest Fire Management Victoria (FFMVic) needs to consider many factors and conditions. An important part of this is measuring the fuel moisture content of a burn site.
So, what is fuel moisture content?
Fuel is any grass, leaf litter, twigs, bark, and other live vegetation which can burn. How moist (whether it is wet, damp, or dry) it can dictate whether a planned burn goes ahead or not.
Dense, coarse forest fuels, such as stumps and logs, may burn and smoulder over several days, while grass and other fine fuels ignite easily and burn quickly. A burn may be postponed if the fuel is too wet to light, or so dry that the fire could do damage or be hard to control.
On the day of the planned burn, the burns officer checks the fuel moisture levels of the area set aside for burning.
The fuel moisture readings show the burns officer how much moisture is in the fuel, so they have an idea of the intensity of the planned burn and whether the objectives of the burn can be safely met.
To check the fuel moisture content, a sample of the litter is fed into a fuel moisture meter. The machine then sends electronic pulses through the sample, measuring its conductivity and then returns a measure of the moisture held within the sample. Repeating this at different sites around the burn unit, the burn officer uses the average as the final fuel moisture level.
The ideal fuel moisture level required for a planned burn to go ahead is between 9 and 16% depending on the objectives of the burn.
Below 9% means the intensity of the burn will be too high. Above 16% means the intensity will be too low to burn the fuel successfully.
While the fuel moisture content is a key factor for a planned burn to go ahead, the temperature, relative humidity, wind speed and even rainfall must be also considered. Other factors for consideration include topography, lighting pattern, vegetation type and the amount of time that has passed since the area last had a fire.
'FFMVic will only conduct a planned burn when the conditions are right. We weigh up all the weather, fuel, topography, and risk factors – and how they interact – to decide if the objective of the burn can be achieved safely,' Gary Turnham, Senior Fuel Management Coordination Officer said.
When conditions are right, the burn can go ahead. If not, the conditions will be assessed, and the burn will be scheduled when the conditions are right.
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