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Ultralight crew protect gel trial
Manager Research and Innovation David Nichols is heading a project team investigating the use of injection-sprayed polymer gel for crew protection on slip-on units and ultralight tankers.
CFA is leading the research in consultation with industry, DEPI, and AFAC agencies. As part of this experimental phase, a vehicle was recently test burnt at the New South Wales Rural Fire Service (RFS) field testing facility managed by the CSIRO at Mogo.
“Ultralights carry very little water – only about 400 to 500 litres,” says David. “Our crew protection systems on medium and heavy tankers use a lot of water so there’s no such system on the ultralights. We have about 150 ultralights and slip-on units and DEPI, the RFS and CFS [Country Fire Service in South Australia] also have a significant small tanker fleet. We’re all exposed if it comes to a bushfire burnover and need to expand the way we protect our crews.”
The Mogo burn involved an ultralight covered in polymer gel placed on top of a 10 x 10 metre propane grid punctuated by burners. The activated grid simulates the progression of a bushfire flame front with radiant heat building up and leading to a burnover of the vehicle before moving away.
“We relied on a steady prevailing wind over the bushfire flame front grid to simulate a moderate intensity fire,” explains David. “It was 5000 kilowatts per square metre which is life threatening.
“We used a gel injection system which combines the liquid gel and water at the nozzle to form a very viscous substance. It’s sprayed over the vehicle through a crew protection system and only uses about 40 litres of water.”
The polymer gel soaks up hundreds of times its weight in water, creating millions of tiny drops of water protected by a polymer shell. The water-absorbent polymers act as a thermal protective blanket.
“Radiometers helped us understand radiant heat and thermocouples monitored the temperature on the inside and the outside of the vehicle,” continues David. “The temperature recorded was between 700 and 900 degrees centigrade outside the cab during the burnover phase but 45 degrees centigrade below the window level inside behind the drop-down curtains. Higher up in the cab, though, it got to 60 degrees centigrade. It was survivable inside the ultralight cabin.”
The Mogo test certainly confirmed that the gel is a good insulator and flame retardant but it’s not without problems. David searches for every synonym for the word “slimy” to describe the gel which is very hard to remove as it rehydrates with water contact and gets inside everything it touches. The crew would survive because of the gel but the vehicle is not likely to be salvageable.
“These gels were introduced in the wildland fire business about 10 to 12 years ago to protect buildings,” says David. “The US Forest Service has used them to protect park buildings and infrastructure threatened by wildfire, but there are environmental implications when using gels.
“We used a more environmentally-friendly vegetable-oil based emulsifier for the Mogo test and, of course, the EPA would look into any gel we proposed to use operationally.
“We’re comfortable with the performance of the gel injection system so far but still at the experimental stage with this project overall.”
These systems may also have an application in field command vehicles.