Historical information

Bushfire behaviour is influenced by many factors including temperature, relative humidity (RH), forest type, fuel quantity and fuel dryness, topography and even slope. Wind has a dominant effect on the Rate of Spread (ROS), as well as fire size, shape and direction.

Temperature and relative humidity have major impacts on fuel dryness and therefore upon the availability of fuel for combustion.

The amount of fine fuel available can increase rapidly from nearly zero when fuel moisture content is more than 16% after rain or a heavy morning dew, to many tonnes per hectare as fuel dries out later in the day and the moisture content drops below 9%. This explosive escalation in the amount of available fuel can happen over a few hours on hot and windy days.

This device is used for determining air temperature and relative humidity. It contains two thermometers, one of which is covered with a wick saturated with ambient temperature liquid water. These two thermometers are called dry bulb and wet bulb.

Once the thermometers to reach equilibrium temperatures the two thermometers are quickly read.

The figures are then used to convert the dry bulb temperature TDB and the wet bulb temperature TWB into humidity information. The wet bulb temperature is approximately equal to the adiabatic saturation temperature.

Physical description

Relative humidity meter in wooden box
two stainless steel tubes contain wet and dry thermometers
A small clock drives a fan motor in the base to circulate air