Explosive Extinguisher

Since Kitty Hawk, the fear of fire in a fuel tank has haunted airplane pilots and manufacturers. Armor plate and pumping systems for getting inert gas into the waste space in fuel tanks have both been tried. Neither method has ever been completely satisfactory. Last week, at Britain's Royal Aircraft Establishment at Farnborough, R.A.F. officers learned that a planned explosion, set off at just the right time, may prove to be the best way to prevent an accidental explosion from getting out of hand.

This explosion-to-prevent-an-explosion is the unexpected byproduct of research conducted by a pair of English chemists, W. G. Glendinning and A. M. MacLennan. Four years ago, the two scientists set out to compare the "explodability" of kerosene and gasoline vapors. When they first blew up test mixtures of kerosene mist, they discovered that the intricate process of combustion was much slower than they had expected. It took all of one-hundredth of a second for the expanding pressure of the explosion to rise one pound per square inch. That left "bags of time," they decided, to quench an accidental explosion before it could cause any damage.

MacLennan and Glendinning took a container about as big as a grapefruit, filled it with fire-extinguishing fluid (carbon tetrachloride) and placed a small explosive charge inside. This "bomb" and a small pressure-sensitive switch to set it off were put in a fuel tank. Then the tank's dangerous vapors were ignited by an electric spark. In the first split second, the expanding pressure wave tripped the switch. The "bomb" burst, sprayed its contents into the tank and snuffed out the newborn explosion.

Now, with a few years of testing and improvement behind them, Inventors MacLennan and Glendinning are convinced that their "bomb" can be used in any industry where explosive dust or gas is a hazard. Veteran combat pilots who saw the "bombs" demonstrated at Farnborough, and who have seen exploding fuel tanks destroy a plane in a great puff of smoke and flame, had only one question: "When do we get them?" The British Ministry of Supply hopes to install the new extinguishers on British military planes within a year.

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