When They Built The Big Bridge

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To the people of 1870 a caisson was a new and mystifying device. When six tugboats pooled their efforts to tow a 3,000-ton inverted wooden crate five miles downstream to Brooklyn from the Greenpoint shipyard where it had been built, the strange sight was a nine-day wonder. While the caisson was sunk into place on the river’s bottom and emptied by forced air compression, the newspapers printed full accounts of the principles that made it possible and comparatively safe for men to work under water in this upside-down box which covered nearly half an acre. The men were to work in special chambers of controlled air pressure, digging the stone and sand of the river bed out from beneath the four cutting edges of the great boxes until these boxes sank, at a rate of about three inches a day, to positions considered solid by the engineers. Then they were to be filled with concrete and the towers erected on top of them.

It was not easy to persuade laborers to take jobs as sand hogs, even at the alluring wages of $2 a day. After only a brief spell of wielding picks and shovels on the river bottom by the dim light of sputtering gas jets, the sand hogs went out on strike, demanding a raise to $2.25.

This was an unheard-of amount for ordinary laborers, but the work had to go on, so they got it. Oddly enough they never struck again, despite the triple hazards which soon made themselves apparent. Perhaps this docility was partly due to the fact that in the great business depression which extended roughly from 1869 to 1878, jobs were hard to find, particularly in a region where immigrant labor was abundant. But there was another factor too which must have borne weight, and that was that Colonel Roebling himself was spending more time down in the caisson than anyone else; and if the big boss could endure conditions there, why should the sand hogs revolt?

The triple hazards were blowouts, fire, and bends. Blowouts were caused primarily by the unevenness of the river bottom. It often happened that two sides of the caisson’s cutting edge would be resting on solid rock while the other two sides were in mud. In such a situation, despite all the engineers’ efforts to keep the caisson on an even keel, slight openings occasionally developed at the base. Usually the workmen’s first inkling that such an opening existed came when, with a thunderous roar, the submerged chamber’s air supply escaped through the hole and shot geyser-like to the surface.

Startling as these submarine volcanoes were to the sand hogs, they were even more startling to the masons who were working on top of the caisson to build the great stone tower which it supported. The dodging of waterspouts replete with mud, stones, and fish provided an unscheduled and sometimes terrifying break in the monotony of their labors.

The surprising thing is that these blowouts caused no more damage than they did. The worst one fortunately happened on a Sunday morning, when no one was at work. It erupted with a deafening roar, causing a stampede for blocks around and showering Brooklyn’s entire Fulton Ferry neighborhood with water and debris. If there had been workmen in the caisson they almost inevitably would have been sucked out and hurled up with the waterspout, which rose to 500 feet.

No sooner had people’s nerves calmed down alter this demonstration of subaqueous forces than there entered the second menace—fire. Here too the amazing thing is not that it happened, but that it did not happen oftener. The caisson’s principal illumination came from calcium lights and gas burners, but for close work candles often had to be used, too. In the potent compressed air all of these flames were even more dangerous than they would have been under normal conditions. Many a time a candle’s blaze returned alter it had been blown out, and the gas lights flared crazily high at the slightest shock.

 

In December of 1870, an unguarded candle’s flame ignited the roof timbers of the caisson and, driven by the potent compressed air, worked its way far into their hidden recesses. The fire resisted all efforts to stop its progress until, through the combined efforts of three fireboats and the Brooklyn Fire Department, the entire caisson was pumped full of water and left flooded for several days.

During this stubborn blaze, which carried a grave threat of destroying all the work which had been done on the Brooklyn tower, Colonel Roebling stayed down in the caisson for so many hours at a stretch that eventually he had to be carried out in a state of collapse. This disregard of personal danger was doubtless invaluable in saving the submarine work chamber, but in the long run it was a costly display of zeal for it undermined his health and increased his susceptibility to the third of the caisson’s triple hazards—the bends.