Researchers observed and recorded details of structural damage and water loss during and after exposure.
Of the different materials tested, spiral-wound steel tanks performed best under all exposure conditions. Under the first two levels of exposure, no structural damage or water loss was recorded. When faced with the adjacent structural fire simulation, steel manufactured tanks were scorched but maintained structural integrity. Small leaks at a rate of less than 2 litres per minute were recorded after a 30-minute flame immersion.
Steel Construction With Bladder Bag Style Liner
Steel construction tanks with bladder bag style liners performed next best with tanks maintaining structural integrity during all tests. A small loss of water was recorded over the top of the liner following the 30-minute flame immersion, but the bladder construction proved able to retain water during and after the fire-front, which is critical for the protection of property and assets in the event of a bushfire.
Polyethylene (Plastic) Construction
Polyethylene (plastic) constructed tanks fared worst under all levels of exposure. The first condition created a small ignition of the tank around the base and combustion of the polyethylene to a depth of 20mm in one localised area, but no water loss. Under threat from ignited litter and pre-radiation, the polyethylene tank melted and deformed to the level of the water, and while some leaks were detected and the front surface was involved in flaming combustion for some time, the tank still held water. Under simulation of structural fire the tank quickly split and collapsed, emptying itself and melting down in complete failure. This research indicates that steel construction tanks have the greatest chance of retaining their structural integrity and preventing water loss under bushfire conditions, while polyethylene tanks are at risk of total failure when adjacent combustible items are present, such as heavy forest fuels, fences, structures or even other polyethylene tanks.
It is important to state that the bladders in steel tanks so fitted survived long enough to help with defence, but the bladder would need replacement. The findings suggest that plastic rainwater storage tanks require a clearance zone of around 30 metres, free of excess leaf build up, combustible material or other plastic tanks.
This work is now informing policy and regulation where a fixed water supply is recommended or is a mandatory requirement for bushfire defence. Understanding the reliability of the stored water source and the way in which advice or regulation can give confidence to the adequacy of this supply is a significant step forward.