Ember attack

An ember attack is a naturally occurring event. During a bushfire, burning parts of trees such as twigs, branches or leaves become temporarily airborne and can be carried away upwind of the bushfire. An 'ember attack' occurs when many embers are carried by winds in a cluster. The Stringybark species of Eucalypt is particularly notorious for contributing large flaming sections of bark that due to their size, weight and shape, can be carried up to several kilometres away. The movements of embers from a bushfire are the primary cause of spotfires, which contribute to the continued spread of a bushfire.

They mostly occur close to the source of the fire, usually following a heat explosion within vegetation in which material is ejected from the explosion and creates a cluster of embers, or during high winds in which burnt material is carried away from flames before it can be fully combusted. An ember attack can be an eerie sight in dark conditions as the glowing embers leave a small light trail in our vision similar to that of a camera set to a long exposure time. Images of ember attacks caught on film are often used by the mass media to aid in the depiction of a bushfire as a dramatic event.

Effect on firefighting

Ember attacks have the potential to start small fires ahead of the main fire trapping firefighters between the two fires. They can also lodge themselves within firefighting equipment, clothing and vehicles. Ember attacks are particularly dangerous to an individual's exposed skin and face.

Effect on property

If an ember lands on a particularly combustible object such as a housemat or a garden bush, or several such embers hit the house within a period of time (or even enter through a timber framed window), they may ignite parts of the house and eventually cause the entire house to burn down. Property owners often underestimate the danger of an ember attack even after the bushfire has passed.

Because embers can be carried away from a bushfire by the wind, they pose a threat to houses that one would intuitively assume are far enough away from the fire. Fire authorities advise vigilance by home owners before and after a fire front passes. Embers can ignite combustible materials outside the home. A danger also exists of embers entering the home, in particular the roof space, requiring occupants to inspect for signs of fire in the roof.

In Australia, evaporative air conditioners are known to ignite from ember attack. Ember attack causes the filter pads from evaporative AC to ignite, and the fire spreads through the roof space destroying the home. Ember Guards also known as Ash Screens are recommended to protect your aircon from Ember Attack.

References

• Fact sheet on New South Wales fire brigade's website
• Commonwealth Scientific and Industrial Research Organisation (CSIRO) experiment