by John Robertson
There is a very good report of the recent big fire on our website. This is about a few specific things evident on the ground. These were well-known to firies of old but they seem to get forgotten and have to be re-learned by each generation.
Fire creates its own climate. Late on Saturday afternoon on the Tamborine-Oxenford Road below Eagle Heights Hotel the temperature was 37 degrees and the humidity 21%. At the same time on the Mountain the temperature was 21 degrees and the humidity 58%. Needless to say it was the fire that made the difference. And the very different climate made a very big difference to the intensity of the fire. (Very intense firestorms such as those round Canberra in 2003 can create their own cyclonic winds with speeds up to 250 kph. These can do as much damage as the fire itself.)
The danger of a superficial backburn. The intense fire on Saturday was in an area which had, ostensibly, been backburned four days earlier. That there was a mass of highly-combustible, light fuel remaining was all too obvious. Flying sparks and embers threatened, and in a few cases succeeded, in starting fires on the opposite side of the road. All were extinguished. The area is in the Gold Coast and we did not have first hand experience of the initial burn but, acting in support of the Gold Coast Brigades, we had plenty of the return match on Saturday. Such a superficial backburn can happen when fuel is drying out after a wet spell and the top layer is dry but those underneath are still damp. Unless the firefighters doing the backburn take especial care to get all the fuel alight to its full depth the fire may consume only 20% or so of the fuel leaving the remaining 80% to burn fiercely following a wind change.
The effectiveness of a beater in early attack on spot fires. When spot fires start, time is of the essence in stopping their spread. Hoses take time to deploy. A firefighter with a beater can get to the spot(s) very quickly and knock down the flames before they have a chance to spread. It is good to have hoses follow up but their job is so much easier if a beater has gone in front. For this the ‘Western’ type beater with its large, one-piece flap is much better than a straggly-hose beater.
Correct hose use to moderate a required burn. This is similar to the hose use needed to correctly control the burn of a timber stack in a vulnerable zone. On Saturday there were instances where fairly large heaps of fuel (bypassed in the original backburn) were next the road. For safety they needed to burn out completely but they burned with such intensity that the sparks and embers threatened to cross the road. In this situation it seems intuitively right to direct the hose(s) at the flames and sparks and onto the surrounding vegetation. Not so. Old firies know that water should always go to the seat of the fire and never on the flames. The correct technique is to use a water jet for just a few seconds to put a litre or two of water into the heart of the fire. That quells the fire momentarily by cooling but the main effect is that the water immediately flashes to steam. That steam reduces the oxygen content above the fire enough to suppress the flames and sparks. The fire recovers quickly and repeat performances are needed every few minutes. The result is a burn that reduces all the fuel to ash, good control of flames and sparks and a tiny water consumption compared to the alternative. It worked a treat on Saturday.