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"It is ofcourse extremely toxic, but that's the least of the problem. It is hypergollic with every know fuel, and so rapidly hypergollic that no ignition delay has ever been measured. It is also hypergollic with such things as cloth, wood, and test engineers, not to mention asbestos, sand, and water, with wich it reacts explosively.
It can be kept in some of the ordinairy structural metals, Steel, copper, aluminium, etc, Because of the formation of a thin, insoluble, metal fluoride wich protects the bulk of the metal. Just as the invisible coat of oxide on aluminum keeps it from burning up in the atmosphere.
If, however, this coat is melted or scrubbed off and has no chance to reform, the operator is confronted with the problem of coping with a metal fluorine fire."
"For dealing with this situation I have always recommended a good pair of running shoes."