“The least dangerous place to be during a bushfire is below ground in an open area,” writes CLIVE WILLIAMS, who is reprising  some practical advice about surviving a bushfire. 

Every year Australians are surprised by the ferocity of bushfires and shattered when their properties are destroyed. 

We need to plan appropriately for living in bushfire-prone areas because, as the current crisis demonstrates, they are only becoming more devastating.

Property protection measures should include mandatory installation of rooftop sprinkler systems, use of fire-resistant housing materials, appropriate housing design and more rigorous management of the local combustible environment.

But as I have long advocated, it should also include a properly prepared, sensible refuge of last resort. 

The NSW Rural Fire Service’s bushfire advice is “leave early, your safest choice” or “decide to stay, only if you’re well prepared”.

However, RFS data shows most houses destroyed by bushfires could have been saved if someone had stayed behind to extinguish burning embers and spot fires. 

The main dangers in a bushfire are radiant heat and convective heat. Radiant heat travels in a straight line without heating the space itself. It turns into heat when it contacts a cooler surface. This is what you experience when you stand around a campfire.

Convective heat requires air movement, such as you experience with a blast of hot air. When flames or hot gases move past a surface, the hot molecules transfer their heat to available surfaces. Both types can kill quickly during a bushfire.

Other dangers for humans and animals are burning embers, falling debris, superheated air and smoke inhalation.

Bushfire smoke contains invisible small particles, gases (carbon monoxide, nitrogen oxides and volatile organic compounds) and water vapour. (A P2 rated mask will protect from smoke particles; breathing through a dry cloth is a fallback option.)

What are the stay-and-survive options? Constructing a safe area within a house is not a sensible choice. 

During World War II, the inadequacies of cellars and basements for fire protection became apparent during the allied incendiary attacks on Hamburg and Dresden.

Cyclonic firestorm winds – that could reach well over 800 degrees Centigrade – caused buildings to explode and collapse, trapping occupants under the rubble. (Up to 25,000 died in Dresden alone.)

Other bad survival choices for unprepared rural residents are taking refuge in above-ground water tanks (due to water-boiling and asphyxiation risks), baths covered by blankets inside houses (due to the risk of the house burning), and any location where part of the body may be exposed to radiant heat.

The least dangerous place to be during a bushfire is below ground in an open area.

During Australia’s early colonial history, crude “bushfire bunkers” were used in clearings around remote towns and logging operations. They typically comprised a zigzag ditch dug a couple of metres into the ground, covered with logs with a metre of earth spread on top of them, leaving a small below-ground entrance and exit.

The bunker protected the occupants from radiant and convective heat, and still gave them access to the thin layer of breathable air that runs along the ground below the smoke.

In the UK, from early 1939, home defence authorities supplied materials to households so that residents could construct Anderson shelters to be dug into the back garden to provide protection against incendiary bombs and firestorm effects.

Anderson shelters were intended to accommodate up to six people. They consisted of galvanised iron panels bolted together, with one containing a door.

Internally, the shelters were 1.8 metres high, 1.4 metres wide and two metres long. They were sunk into the back garden and covered with a minimum half metre of soil.

Because they were also designed to withstand nearby bomb explosions, Anderson shelters were structurally stronger than would be required for bushfire protection.

It should therefore be possible to design and install a mass-produced Anderson-like structure to withstand bushfires for well under $1000.

A bushfire bunker would require a prefabricated nonflammable framework, a hole in the ground to put it in, a fireproof access point, and to be low maintenance.

Such a framework should be built to a government-approved standard and the cost to consumers subsidised by government to encourage its adoption.

For those who are determined to stay to protect their property, or leave it too late to flee, such a well-prepared bushfire bunker would provide their best chance of survival.

I should add that this article was first written and published in January 2020. It seems that state governments are slow learners.

Professor Clive Williams MG is director of the Terrorism Research Centre in Canberra (clive.williams@terrint.org)