Fire & Water

Under the coarse glacial bed of Manhattan's murky East River, sand hogs for the last year have been boring the two tubes of a midtown vehicular tunnel intended by 1940 to connect Manhattan Island with Long Island. Each 31 feet in diameter, the tubes are bored by great circular "shields." Like the mouth of a great pipe, the shield is forced ahead by hydraulic pressure, cutting two feet eight inches at each thrust into sub-bottom deposit. Between forward thrusts, workmen remove the muck within the shield, line each new section with cylindrical cast-iron casing. Keeping the river and its oozy bottom from rushing into the uncompleted tube is an air pressure of 28 pounds per square inch.* Air locks (pressure chambers) in concrete bulkheads permit workmen to enter and leave this high-pressure bubble by easy stages.

One night last week, after work had been suspended for the day, watchmen passed through the air lock of the north tube, opened the door leading to the boring shield, were met by a blast of smoke. Inside a great, licking blaze, whetted by the high oxygen content of the compressed air, was feeding on timbers, sawdust and salt hay in the unfinished bore. Backing out through the lock, they found the telephone short-circuited, the elevator not running, had to climb ten flights of stairs up the ventilating shaft to sound an alarm.

For twelve hours the fire raged, go feet below the river surface, 70 feet from shore, fought hopelessly by sand hogs with hand extinguishers, firemen who braved the terrific pressure to attack it with hoses. After a grim night of defeat, tunnel engineers resorted to extraordinary tactics. Slowly, pound by pound, they began reducing the air pressure in the fire-swept section. Just as slowly, the air wall gave way and the river it had been holding out began to muck in. In half an hour, it half-filled the section, doused the fire.

*That is, 28 lb. above the normal atmospheric pressure of 14.7 lb. per square inch.

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