The Great Bridge

by David McCullough

  This same reporter singled out William Kingsley standing “conspicuously above all the others” and wrote, “He appeared calm and collected and preserved well his equanimity, but a few words of conversation with him showed him to be anxious for the work.” Collingwood, who had not been in the caisson since the day before, was also interviewed and talked of the grave dangers involved with flooding it. Roebling, who remained on hand through the whole morning, would say only that he thought everything would turn out satisfactorily, but that naturally the work would now be delayed some.

  By half past three the caisson was entirely filled with water. The compressed air had been replaced without any sudden loss of support. The total quantity of water required was 1,350,000 gallons, which if not quite enough to float a battleship of the day was fairly close to it.

  A careful watch had been kept on the pressure gauges during the whole operation; when it appeared that the air was escaping too rapidly, the compressors were started up again. When the water got to within two feet of the roof, the valves used for releasing air were closed off and the balance of the air escaped slowly through leaks and two small pipes. At one point during this stage, pressure dropped suddenly and inexplicably from nineteen to ten pounds.

  After the caisson was flooded, the water in the shafts was kept ten feet above tide level, where it stayed with only a little feeding, indicating how very watertight the caisson had become at forty-odd feet below the river.

  Still, the prospects looked dim. That night George Templeton Strong, the noted diarist of the time, wrote, “Caisson of the East River bridge was severely damaged by fire yesterday. I don’t believe any man now living will cross that bridge.”

  The caisson remained flooded for the next two days, during which time there was an inquiry conducted by the Brooklyn fire marshal. Some of the New York papers, on their editorial pages, questioned what sort of management had allowed such an accident to occur. The Herald said the damage done would cost $250,000. Incredibly, the World implied the fire had been an act of sabotage, that directly or indirectly, it had been the doing of someone connected with the ferry company. The Eagle ridiculed such speculation and worried about what effect the whole incident might have on the morale of the men who had to carry on with the work. But after the fire marshal’s hearing on Saturday, everyone calmed down considerably and it was pretty well concluded that much too much had been made of very little. Collingwood and Farrington both said they did not think the damage would run to more than five hundred dollars. Collingwood thought they had been set back two days at most. C. C. Martin said, “All that the fire has done is to burn little spaces between the beams, very probably very small ones which will not in that mass of timber affect the stability of the structure in the slightest.”

  It was also reported by one of the assistant foremen that the man named McDonald, who supposedly started the whole thing, had not been seen or heard from since.

  Roebling had testified separately earlier in the day. He was still feeling some paralysis, he said. He too thought the damage had been minor and reported that the caisson had settled only two inches during the flooding, which he said was less than the average daily rate of descent. He left no doubt at all that this highly precarious operation had been very successfully executed and would perhaps prove even beneficial to the caisson in the long run, since the timbers had been getting too dry.

  Monday morning the air pressure was restored, the water pushed out in about six hours. It all ran out over the tops of the water shafts. When Roebling and the others went down inside, everything seemed to be in good order, beyond a few blocks crushed and some posts thrown over. The structure itself appeared tighter than before due to the swelling of the timbers.

  The fire marshal went into the caisson a little later with C. C. Martin and reported that he watched Roebling and the others at work, checked things over, and said that if he had not been told differently, he would never have known there was any fire at all. There was not the least sign of fire below, he said, except through one small opening and he concurred that the damage had been very slight.

  Work was resumed immediately. The brick piers, about a third of the way built by then, were finished in another two weeks and the caisson was lowered the final two feet to rest upon them.

  The day before Christmas the men began filling the work chambers with concrete. To save time and cut the quantity of concrete needed by a third, the shoe of the caisson was allowed to sink into the ground three feet deeper than the average level of the caisson floor, which meant that headroom inside was reduced from nine and a half feet to six and a half feet.

  The concrete consisted of one part Rosendale cement, two of sand, and four of a fine gravel from the Long Island beaches, where it had been washed perfectly clean by the surf. Outside the caisson the weather by now had turned so cold that the concrete had to be mixed below. So like the bricks for the piers, cement, sand, and gravel were all brought down through the supply shafts, which for some several weeks had been functioning quite flawlessly.

  The shafts were iron tubes forty-five feet long and twenty-one inches in diameter, with doors at top and bottom. When the upper door was open, the lower door would be held shut by the pressure in the caisson and locked by two iron clamps worked by levers. Any material needed below would simply be dumped down the shaft and the upper door, which closed up, not down, would be pulled shut. Then compressed air would be allowed to enter the shaft from below, closing the upper door tighter still. As soon as the shaft was filled with compressed air, the lugs on the lower door would be removed, the door would fall open, the contents in the shaft would drop into the chamber. The system was fast, uncomplicated, and quite safe so long as the attendants responsible for it used their heads.

  But it was only two weeks after the fire that again something went wrong. Every so often a load of bricks would get jammed in a supply shaft and the usual method of breaking the jam was to drop a weight down on a rope. But this time the men above decided instead to dump in a second load, then signaled for the men below to open the lower door while they neglected to close the upper door. The second load loosened the first, the two together landed on the lower door with a force greater than the air pressure against it from inside, and since the lugs on the door had been opened as directed from above, the door fell open.

  Instantly there was an enormous, earsplitting rush of air out of the caisson. Stone and gravel shot from the shaft as if from a cannon. The men on the top dove for cover or fled as fast as their legs would carry them. Had any one of them had the least presence of mind, he could have closed the shaft instantly and had everything locked up tight quite simply by just reaching over and pulling at the rope connected to the upper door. It would have taken no effort whatever. The explosion of air from below would have slammed the door shut. But nobody did that.

  Roebling was one of those trapped inside the caisson at the time. The noise, he said, was so deafening that no voice could be heard. Water was pouring in from the water shafts. The lights went out. The air, he said, was full of a dense, impenetrable mist. Men were stumbling all over one another, running in terror, smashing into pillars, tripping and falling in the pitch-darkness, nobody sure where he was going.

  In an instant the water was up to their knees. The river had broken in, they all thought.

  “I was in a remote part of the caisson at the time,” Roebling wrote, “half a minute elapsed before I realized what was occurring and had groped my way to the supply shaft, where the air was blowing out. Here I joined several firemen in scraping away the heaps of gravel and large stones lying under the shaft, which prevented the lower door from being closed.” It took from two to three minutes for them to clear the door. Then they had it shut and everything was all over. Fifteen minutes later the pressure was restored.

  Roebling had kept his head under the most nightmarish conditions, and when nobody else had. He had analyzed the situation in an instant and moved swiftly to put a stop to it. In the eyes
of many, it was as commendable a demonstration of cool command as anything he had done on a Civil War battlefield.

  Later, in his formal report to the directors, he wrote:

  The question naturally arises, what would have been the result if water had entered the caisson as rapidly as the air escaped? The experience here showed that the confusion, the darkness and other obstacles were sufficient to prevent the majority of the men from making their escape by the air-locks…Now it so happens that the supply shafts project two feet below the roof into the air chamber; as soon, therefore, as the water reaches the bottom of the shaft it will instantly rise in it, forming a column of balance and checking the further escape of air. The remaining two feet would form a breathing space sufficient for the men to live, and even if the rush of water were to reduce this space to one foot, there would be enough left to save all hands who retained sufficient presence of mind.

  It is not known whether he had realized this before the supply shaft blew out.

  Again, as after the “Great Blowout,” an examination was made to determine what effect the impact of sudden weight had had upon various internal supports and particularly on the new brick pillars. By the time Roebling and the others got the supply shaft door closed, pressure in the chamber had dropped from seventeen to four pounds. He reckoned, therefore, that for several minutes the weight on the pillars was twelve tons to the square foot. Still, they showed no signs of strain, which was the clearest demonstration possible of their capacity to bear up under the load they were designed for and proof certainly that Roebling had been right to put them in. More important, the subsoil beneath the pillars, on which the bridge was to bear, had also withstood this same tremendous pressure.

  But Roebling would be granted precious little time to take pride in the way things were being handled. Work on the masonry above had stopped because of the weather. Eleven courses of stone had been laid up within a wooden cofferdam, the top of the stonework being about even with the river at high tide. But the people manning the dump carts were still about, along with a number of others who looked after this or that piece of equipment, and they had begun noticing a strong smell of turpentine that seemed to be coming from air bubbles being forced up through the caisson. Large deposits of frothy reddish-brown pyrolignic acid, or “wood vinegar,” as the men called it, had also been found, indicating, as Roebling said, “that a destructive distillation of wood had been going on.”

  Acting on what he called very unpleasant suspicions, Roebling quietly ordered Farrington to start drilling into the roof again. About two hundred borings were made to determine for everyone’s satisfaction just how extensive was the internal damage from the fire.

  Most of it seemed to be confined to the third and fourth courses of timber, as had been expected, but as nobody had imagined, it also extended out laterally in every direction, in some places as much as fifty feet, or about five times farther than anyone had judged earlier. Equally disturbing was the discovery that the compressed air was rushing out of every bore hole, which meant that any attempt to cut into the roof to make repairs would result in an enormous drain on pressure.

  Roebling decided, however, that if the air chamber were filled in with concrete around the edges, the pressure might now be released entirely with no harm. He had decided, in other words, that he could trust the brick pillars to support everything. So if maintaining pressure was no longer the vital concern, then holes as large as need be could be cut overhead and the damaged areas seen to properly.

  Still, as he wrote, “It was very desirable…to gain time and do as much as possible at once, while air pressure was yet on.” It would be necessary therefore to plug the boreholes and at the same time compensate somehow for the honeycomb of charred pine they all pictured overhead.

  Accordingly cement grout was injected into all two hundred boreholes. It was no easy task and it took quite some time. Roebling had a cylinder and piston fixed to a quarter-inch pipe. The cylinder was filled with liquid cement, placed under a borehole, the pipe inserted, then the cement forced up the hole by a screw jack. The technique worked well for the most part. The cement could be forced a good ten feet into the timber and appeared to spread out laterally to some distance. But the moment it met any resistance, all the water would be squeezed out, and to budge the charge another inch became impossible. So a thinner mixture was tried and it was found that the suction of compressed air alone, through the holes, was enough to draw this up the pipe and into the timberwork.

  By the time they were finished, six hundred cubic feet of cement had been pumped into the caisson roof. The leaks had been stopped and a number of new boreholes in the area of the trouble failed to reveal a single place without its own vein of hardened cement. “We already flattered ourselves that this filling might answer every purpose…” Roebling wrote.

  But just to be sure, he had a great hole, six feet across, cut into the roof through five layers of timber, directly over the spot where the fire had originated. And by opening up the roof this way they discovered that they had been exceedingly proficient in their work and that it had been a great mistake. The cement had indeed filled every crack and crevice, but most of the timber beneath the cement was covered with a layer of soft, brittle charcoal, anywhere from one to three inches thick.

  It was a crushing revelation. It meant that every last bit of the cement put in so laboriously would have to come out, and any charcoal there was would have to be found and scraped away. There was no other alternative Roebling said. The caisson roof, the timber platform upon which the bridge tower would stand, had to be absolutely, permanently solid. He could take no chances on that. He could no more let it go this way then he could launch a ship with rotten timbers.

  The immense, painstaking job of restoration that followed took a force of eighteen carpenters three full months to complete, working night and day. It was like gigantic dentistry, as someone said. To say that the work was extremely disagreeable, as Roebling did in his report to the Board of Directors, was to greatly understate the situation.

  Not until the cement was all chopped out did anyone realize the full extent of the fire. Instead of one opening into the roof, five had to be cut, slowly, laboriously, each one three to four feet square and five feet deep or more. Above the original opening it was found that the fire had not only turned the third and fourth courses of timber to charcoal, but it had burned right through the sheet tin between courses four and five, destroyed the fifth course and made a start on the sixth. To judge by the traces it left, the fire had advanced mainly as a slow, intense charring that expanded equally in all directions. But in numerous places it had been strangely erratic, due no doubt to the multitude of leaks that fanned it. Roebling noted, for example, that a single 12-by-12 timber would be burned away for thirty feet, while one just like it directly alongside would be untouched. And since the courses had been laid up at right angles to one another, the fire had had opportunity to branch off in a zigzag pattern, jumping from one timber to another, heading off left or right, up or down.

  Damaged timbers were carefully scraped clean and all jagged edges were squared off with chisels. Every foot of burned wood was cut out. New cement was rammed into the smaller places, while new timber was cut to size (in lengths of eight to ten feet usually), rammed into all the larger openings with a screw jack, and securely bolted.

  The burned channels that wandered laterally between the big vertical openings were generally about two by three feet in dimension. All such channels had to be gouged out by hand, then filled in in the same manner. The men worked like coal miners along such veins, inching forward on their backs or sides, with barely enough room to move, digging out charcoal instead of coal, imprisoned in a mountain of wood instead of earth. For hours at a time a man would be confined to a single spot, unable to turn around, his only light a little bull’s-eye lantern, and breathing candle smoke, cement dust, and powdered charcoal. Because the air pressure had been greatly reduced by the openings that had been cu
t, the ventilation was dreadful and the heat remained near 90 degrees.

  “After everything was filled up solid,” Roebling wrote, “a number of five-foot bolts were driven up from below so as to unite both the old and new timber into a compact body.” He also had forty iron straps bolted against the roof from below, and inside the air chamber, directly under the line of the fire, he had great square blocks of traprock set in the concrete that was being put down over the rest of the chamber floor.

  When the repairs were at last completed Roebling reminded everyone that there were still eleven perfectly sound layers of timber above the first four. And in his final report he stated, “From the faithful manner in which the work was done it is certain that the burnt district is fully as strong, if not stronger than the rest of the caisson.” Most people believed him.

  The fire and its aftermath had been a sobering experience. It had delayed the work two, possibly three months. With the payroll running about eleven thousand dollars every two weeks, this meant a loss of some fifty thousand dollars at least, on that score alone. The fire had done much to reinforce the arguments of the skeptics, of whom there were still plenty on both sides of the river. This said one New York paper was the “main mischief” of the whole unhappy affair. But it had also been a brutal physical and mental ordeal for many of the men, and for Roebling in particular, whose strength had never quite returned since the night he collapsed in the caisson. He was a changed man after that, his assistants would say later.

  Had he decided early that night to flood the caisson, in spite of the boulders beneath the water shaft, then things might have gone differently. But if he ever speculated about that, it was only in private.