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Ground crew hoses corrosive flame retardant off a planeThe University of California at Davis' McClellan Nuclear Radiation Center has been using neutron radiography to help make certain the tanks that hold the retardant and water are in good shape--no cracks, holes or weak spots that could end up distributing the mix of retardant and water everywhere but where it's needed.
Here, a member of the ground crew at the Channel Islands Air National Guard Station in California hoses spent retardant off the tail of a specially equipped C-130 aircraft, as the plane awaits more retardant and another trip to the blaze. (Look closely and you'll see the pipes that release the retardant-water mixture, as well as streaks of orange on the tail's underside.)
The retardant is corrosive, hence the need to hose off the plane--and test the tanks.