Concrete Bunkers in Bushfire Prone Areas

Property design, planning and preparation are keys to saving life and property in a wildfire. However it is almost impossible to be 100% ready- there is always the chance of unexpected factors arising. These could include the fire being worst than expected, trees falling across exit routes or on top of houses, cars not starting, having a bad fall etc. In case a worst case scenario arises, having a backup plan is good insurance and provides a greater sense of security.

Our backup plan (which we fortunately didn’t need to resort to) was to shelter in our concrete bunker. It is an adapted concrete water tank with strengthened walls and roof so it can be earth covered. A metal door in the side allows access and there is provision for a vent in the roof. We installed this in 2000 and have been progressively getting it ready. Two years ago we backfilled earth around it, but have not yet covered the top with soil.
The bunker is located just metres from our back door allowing quick access in an emergency. It is next to the double brick masonry wall of the house which should shield it from fire, if the house caught alight. There is a tap located on the corner of the house to provide a water supply. The plan is to use Besser type bricks to build a retaining wall on each side of the bunker entrance and then completely cover it with soil/gravel.

There is some concern about fires consuming all available oxygen. Although we have to do further research on this aspect, we expect that the oxygen available in the structure should be adequate for the length of time we would be in there. Experts generally say that it is best to focus on fighting the fire and putting out embers until it gets too dangerous. We would only need to stay in the shelter until the worst of the front has passed, and then it would be back outside to put out what we can.


Other considerations are:-
· If it gets too hot the metal door could expand, jam or buckle. There will be no flammable material near the bunker door so this should not be an issue.
· Sprinklers could be used to continually soak the area with water.
· We will have a supply of water for drinking and fire fighting equipment inside the bunker including damp towels etc.
· Filters could be installed to prevent entry of smoke.

This view from the north shows our white 7,500 gal. water tank with the fire shelter behind. This arrangement was part of our permaculture plan. Rather than just having a water tank and a fire refuge we have achieved many extra functions from these two pieces of infrastructure.
Apart from use as a fire shelter, the bunker has an everyday use as a cellar for storage of pumpkins, spuds, fruit, wine, ginger beer etc. It has been sealed with a coating of water proof material and backfilled with gravel on all sides to ensure water drains away without causing dampness. Once it is finished it should maintain a reasonably constant temperature in winter and summer.
The backfill against the water tank helps keep the water cool and means the tank is less susceptible to damage in a fire.
The fact that this wall is largely earth sheltered sets the house down low, so embers and heat largely pass overhead.
The setup provides easy access to the roof without ladders. (Of value whenever roof access is required but particularly in emergencies.)
The earth sheltered house wall adds extra thermal mass to the house, helping to keep temperatures in the house comfortable all year.

Hopefully a concrete bunker would never be required for emergency use. However it is a good investment because, apart from providing some piece of mind, it has potential to fulfil many other functions.

Yes our Open Day was a huge wonderful success. But what did all those people come to our place to see? We’d better briefly explain our story.

We (Andrew & Heather) had an interest in gardening ever since we were children. Both of our families had small veggie patches and the concept rubbed off on both of us. As we moved from place to place we always grew a small amount of food. When we purchased our first house in 1975, one of the first things we did was establish (what was to us) a large and successful garden. Over the years though, our garden became less and less productive due to the increasing shade from large eucalypts all around.

The time came to look for a bigger block. By now we had set our sights on getting a small acreage. We scoured the papers and estate agents for 5 -20 acre blocks which incorporated our dream qualities (running stream etc.) for close to a year. We searched an area up to 100 km from Melbourne (Australia). Promising leads often turned to disappointment when we inspected properties to find they contained steep slopes (mountain goat country) or were crossed by high voltage power lines etc.

Finally just before Christmas in 1985 we answered a small ad in the newspaper which sounded ok. A visit on the following weekend clinched it. It was not 100% ideal, but it had enough positive features, for us to make a quick decision- this was the site for us. The property was a 96 acre bush block with 12 recently cleared acres. It looked like a complete disaster with row after row of windrows (trees bulldozed into long piles ready to be burned) and the dozer had turned the silty clay into fine talcum powder-like dust. Our rose coloured glasses could only see the future potential. It didn’t have a permanent stream but did have several gullies which carried water for a few hours after rainy periods. Most of the block was gently undulating with a northern slope- ideal for a passive solar house. The biggest advantage though was its proximity to Melbourne (65km from the GPO), which meant weekend visits would take less than an hour. Its biggest disadvantage was poor vehicle access and lack of services which was a contributing factor to the reasonable price being asked. We decided we could cope with the rough, one lane 4wd forestry road and as for electricity- or the more reason to go solar.

For the next ten years we got to know “the block” using it for frequent weekend trips and holidays. We gradually worked our way through many of the windrows, using them as firewood for the combustion stove and wood heater. At first we camped in a tent, then went “posh” by building a 10m by 8m tin garage which we converted to 2 bedroom accommodation and living area. It was a home away from home.

Our three children greatly enjoyed their bush holidays. The windrows became ships and jungles in their imaginations, and the hollows underneath became tunnels to be explored. To them it was like living in Healesville Sanctuary because of their frequent interactions with native wildlife, which included kangaroos, wallabies, wombats, echidnas, goannas, snakes and all sorts of birds. We decided we would not move until our children had finished secondary school, so as not to disrupt their education. In the meantime we came to understand more about the land and had time to ponder building and development.

The next critical element in our story came in 1996 when we saw an ad in the local paper advertising a permaculture course. (It seems our lives have hinged on small ads in newspapers). The course informed and inspired us and gave us the tools required to design our future house and its environs. In fact the final task in the course was to develop a permaculture design. Our property design (for our block) took weeks to develop as we tried out various possibilities and worked through issues. We were very pleased with the final outcome, which as it turned out 12 years later, has largely come to fruition.

Our First Public Open Day

On September 21, 2008 we hosted a Permaculture Open Day on behalf of Yarra Valley Permaculture Group. In the week leading up to the BIG DAY we started thinking we were mad to have taken on such a task. We were so busy getting the place ready we hardly had time to to do anything else. We squeezed a meal here and there, went to bed late and were up early the next morning. Even in our sleep we were thinking "open day thoughts". (Often waking up with the comment "I've just thought of something else that needs doing.").

Well the day came and went and what a day it was! Of all the things we imagined might have gone wrong- nothing did. We had around 600 people visit that day (including around 50 invalauble volunteer helpers), and the day's activities went smoothly and without any major hitches. Judging from the positive and enthusiastic feedback, most people found it informative and enjoyable. We certainly enjoyed ourselves.

Mind you it has taken a couple of weeks to recover. We have our energy levels back and we're starting to catch up on regular tasks that were placed on the "backburner". This week its planting spuds (something we had planned to do in August). The house is starting to get back to normal- but the garage/workshop is still tidy. That won't take long to fix.

One of the best things about the open day was the way it encouraged/motivated/forced us to get the place looking at its best and we probably finished 20 or more major jobs that otherwise would have taken months to get done.

We've told you all about the open day, but haven't introduced ourselves or told you anything about what all those people came to see. That will have to wait till the next post.