Tuesday, November 23, 2010

A lot of bunk about bunkers

A lot of bunk has been talked about bunkers. One big problem with relying on any bushfire refuge or bunker is how to get to it safely in bushfire conditions. Another is that the more people are dependent on shelters, the more homes are left unattended to be destroyed. As each burning house send off embers to ignite other houses the rebuilding costs for a shelter-dependent society will escalate.
Private bunkers need to be well away from the house and trees, and connected to the house by a vegetation-free path sheltered from radiant heat. They need to be roomy enough for the number of people who use them. Crowding not only quickly uses up the oxygen in it, but will further heat people already sweltering because of the hot day. They may faint. They may suffer heat stroke. They may suffocate. They may dehydrate. In the shipping container type you could suffocate and roast. Think of the recent death of a prisoner transported in a metal-lined van on a day of high air temperature. A concrete type recently advertised locally would not allow shelterers to stretch or stand, and it entrance could be blocked by a fallen tree.
Probably the best use for private bunker is for emergency storage of precious possessions. Those with enough money to consider constructing ‘bunkers’ would do better to put the money into safety aspects for the house: roll down metal shutters to protect windows, insulating and sealing the roof/ceiling space, building-in the subfloor space, installing low-flow roof sprinklers. And their time in learning how to safely protect it.
Community shelters need to provide: access early on each day of announced bushfire danger and for its duration; to be clear of flammable vegetation for at least 40 metres and entirely clear of wood-chip mulch; sufficient parking clear of flammable trees, grass and wood-chips; space to accommodate local evacuees plus tourists. They should be solid buildings with protected windows and doors, secure roofs, sheltered exits, a roof able to withstand winds over 150 km/h and secured with cyclone clips; Metal roll-down window and door shutter -or fire-rated solid-core doors with metal-mesh screens and draught stoppers; entry/exit sheltered on 3 sides by a 2 m radiant heat shield; ventilation that does not admit smoke; a small reinforced spy- window; roof and ground sprinklers, with a large reserve water supply, independent of mains pressure; facilities for water, food and rest; amenities for babies and the frail; shade and water for pets; sufficient toilets.
Well constructed bushfire shelters (now forgotten and unused) were purpose-built for some schools in the Dandenong Ranges in 1989, following my investigations into the dangerous conditions of designated community refuges - a great many of which had been schools. My Complete Australian Bushfire Book was the major resource for architects.

Photos (c) Joan Webster

Bushfire shelter built for Sassafras Primary School, Dandenong Ranges, Victoria, 1989

You can learn more about the benefits and disadvantages of bunkers, community refuges and an in-house 'withdrawal room' in The Complete Bushfire Safety Book.