This Bushfire CRC and CSIRO research project examined the performance of different rainwater tanks when faced with the threat of fire through testing conducted in 2004 at the only bushfire simulator of this type in the world – at the New South Wales Rural Fire Service Eurobodalla Training Centre, on the south coast of New South Wales.
The research investigated how effective steel and plastic water tanks were in storing water during typical Australian bushfire exposures. Polyethylene (plastic) tanks were found to provide the least resistance to various bushfire simulations.
ABOUT THIS PROJECT
Project D1 Building and Occupant Protection was part of Bushfire CRC Program D: Protection of People and Property. Researchers involved in the project acknowledge the financial support of BlueScope Steel and the valuable collaboration of the NSW Rural Fire Service.
Author: Justin Leonard is a Bushfire Research Project Leader with CSIRO Sustainable Ecosystems. For more information about this research, contact Justin Leonard at firstname.lastname@example.org
Different types of rainwater tanks can play an important role in the defence of a home against a bushfire attack. Indeed, such storage tanks are critical to active and passive protection against bushfires. Anecdotal evidence already existed to suggest steel water tanks would offer greater protection to both residential and commercial properties in the event of a bushfire than alternative materials because of their non-combustibility.
However, the full result from this research has and is being used by the relevant agencies to:
Influence how building codes and planning guides are developed, particularly around bushfire-risk areas.
Help provide advice to property owners on the level of risk their homes and businesses face.
Help develop education programs for local communities.
BUSHFIRE CRC RESEARCH
Three types of rainwater storage tanks were tested in the course of this research, including:
“Conventional” steel construction BlueScope Water Waterpoints
Steel construction Pioneer Galaxy Water Tanks with Aqualiners (bladder bags)
Polyethylene constructed tanks
Each tank type was subjected to three levels of flame exposure including: Litter ignited – Leaf litter placed typically around the base of the tank and ignited to investigate and observe the influence of small amounts of leaf deposition during the fire event. Litter ignited plus radiant heat – Typical of an advancing bushfire occurring on a fire danger day of FFDI (Forest Fire Danger Index) 40, but with sufficient clearing to avoid direct flame contact with the tank. Simulation of structural fire – Full continuous flame immersion for a period of 30 minutes. Designed to simulate a worst-case structural fire exposure or influent from an adjacent combustible element. Note: Behaviour under this exposure can also help inform us as to how a tank may behave under severe bushfire conditions such as Black Saturday.
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.
While not fully explored, it was observed in site inspections and interviews undertaken by the Bushfire CRC Task Force immediately after Victoria’s Black Saturday fires of February 2009 that the test results from this research were consistent with the effects on rainwater tanks of the extreme events of that time. No further work is planned on this subject. The behaviour of these elements informs broader risk frameworks which model the interaction of all combustible and non-combustible elements in an urban environment. There is the potential now to focus on pipework and pump reliability as other essential elements in the water defence system.