I recall this being mentioned in Ignition!: An Informal History of Liquid Rocket Propellants [0] : Boranes are unpleasant beasts. Diborane and pentaborane igni

I recall this being mentioned in Ignition!: An Informal History of Liquid Rocket Propellants [0] : Boranes are unpleasant beasts. Diborane and pentaborane ignite spontaneously in the atmosphere, and the fires are remarkably difficult to extinguish. They react with water to form, eventually, hydrogen and boric acid, and the reaction is sometimes violent. Also, they not only are possessed of a peculiarly repulsive odor; they are extremely poisonous by just about any route. This collection of properties does not simplify the problem of handling them. They are also very expensive since their synthesis is neither easy nor simple. But they possess one property which attracted rocket people to them as hippies to a happening. They have an extremely high heat of combustion — gram for gram about 50 percent more than jet fuel. [0] https://www.amazon.ca/Ignition-Informal-History-Liquid-Propellants/dp/0813595835 https://www.amazon.ca/Ignition-Informal-History-Liquid-Prope...