Science: Gas Storage Tanks

Illuminating gas engineers were amazed last week. They could not account for the explosion in Pittsburgh of a gas storage tank said to be the largest in the world. Supposedly, it was empty; workmen were repairing its top. Suddenly, unaccountably, the tank, capable of holding 5,000,000 cu. ft. of gas, blew up. It caused two lesser (and full) gas tanks to explode; it blew buildings apart; it killed some two dozen people, injured several hundred.

Many large U. S. cities have similar tanks within the corporate limits. New York tanks contain enough gas for 15 hours service, Chicago’s for 16 hours, New Orleans’ for 9½ hours, San Francisco’s for 11 hours.† They cannot explode under any circumstance which gas engineers can imagine.

Gas cannot explode unless it is mixed with air. The tanks are constructed to keep air out, and in any case, since the stored gas is under pressure, gas would escape through any leaks; air could not enter.

When a tank must be repaired, these standard precautions are regularly followed: The top part of the tank, which slides like a cuff or sleeve over the base, is lowered and the gas squeezed out until only 2% or 3% of gas is left in the tank. Then the top is raised and air sucked in. This procedure is repeated until the percentage of gas to air is only .004. Then the valves are shut off and the gas main is disconnected. There are, of course, lightning arresters and guards against smokers.

So efficacious have been these methods of preventing gas tank explosions that, until the Pittsburgh instance there were only two such explosions in this country. One was at Houston, in 1910, the other at Columbus in 1919. At neither was anyone hurt.

† They contain artificial gas. Artifical gas is made by heating coal in ovens. What remains of the coal is coke. Natural gas occurs under the earth and is pumped from wells through the mains, to customers. The longest gas main in the world connects the Texas natural gas field with Denver—400 mi.