9
We have no precedent just like this bridge.
—WASHINGTON ROEBLING
IN ALL the thousands of years men had been building things, no one had ever attempted to sink into the earth so large a structure as the Brooklyn caisson and there were not very many places where the job would have been more difficult than the Brooklyn side of the East River.
Roebling and his assistants thought they had learned quite a lot about the ground they had to penetrate while dredging the site, but as he commented with his usual dispassion, “The material now became sufficiently exposed to enable us to arrive at the conclusion that it was of a very formidable nature, and could only be removed by slow, tedious, and persistent efforts.” Compared to this everything before had been child’s play. Now that which had looked so reasonable on paper was turning out to be quite a different matter in practice. Indeed, so bad was the first month of excavation inside the caisson, so painfully slow and discouraging, that it began to look as though the whole idea for the foundations had been a terrible mistake, that they would have to give up and try again some other way or some other place.
There was never any public awareness of such feelings, which was just as well. There was, for that matter, very little real awareness on the part of the public of what actually went on inside the caisson, the work being entirely concealed.
The best over-all view of the site was still from the deck of the ferry. So every day thousands of people on their way to and from New York got a splendid, close-up look at the three towering boom derricks swinging blocks of limestone into place and at the squads of men swarming about the masonry work or through the adjacent yards, every last man appearing to know just what was expected of him. There were half a dozen different steam engines sending up columns of black smoke and everywhere a bewildering clutter of tackle, hand tools, nail kegs, and tar barrels, stacks of lumber and great heaps of coal, sand, and stone. How anything orderly or rational might emerge from such seeming chaos was something for ordinary men to ponder in dismay.
Still, seen from above, the work did not appear all that different from other big construction projects. The activity around the gigantic new Post Office being built in New York, for example, was every bit as confusing and impressive to watch. All this was lit by the same light of day and the men appeared no different from other mortals, breathing the same good air. But down in the caisson, everyone had heard, things were different. That was the part of the work that had the most fascination and of course the fact that it was hidden away where no one could see it, except for a relative few, made the fascination that much greater.
The newspapers sent reporters down soon enough. By July better than two hundred workers were going down every day and naturally they had their own stories to tell. So as a result a picture began to emerge, of a strange and terrifying nether world at Brooklyn’s doorstep, entered only by men of superhuman courage, or by fools, and as sometimes happens with ideas that grow in the imagination, it was not so very far from the truth.
Probably the most vivid description was one given by E. F. Farrington, Roebling’s master mechanic, a plain, blunt, practical man ordinarily. There would be rumors later about who actually was doing Farrington’s writing for him, or at least dressing up his literary style, but there is no doubting the authenticity of the image.
Inside the caisson everything wore an unreal, weird appearance. There was a confused sensation in the head, like “the rush of many waters.” The pulse was at first accelerated, then sometimes fell below the normal rate. The voice sounded faint unnatural, and it became a great effort to speak. What with the flaming lights, the deep shadows, the confusing noise of hammers, drills, and chains, the half-naked forms flitting about, with here and there a Sisyphus rolling his stone, one might, if of a poetic temperament, get a realizing sense of Dante’s inferno. One thing to me was noticeable—time passed quickly in the caisson.
Even the air lock was an unnerving experience for most men the first time they went down. For some it was also an extremely painful experience. The little iron room was abundantly lighted by daylight through glass set in the ironwork overhead. But once the attendant had secured the hatch with a few turns of a windlass, the common sensation was that of being enclosed in an iron coffin. Then a brass valve was opened. “An unearthly and deafening screech, as from a steam whistle, is the immediate result,” wrote one man, “and we instinctively stop our ears with our fingers to defend them from the terrible sound. As the sound diminished we are sensible of an oppressive fullness about the head, not unaccompanied with pain, somewhat such as might be expected were our heads about to explode.” (For many the sensation did not pass and they were said to be “caught in the lock.”) Then the sound stopped altogether, the floor hatch fell open by itself, and the attendant pointed to an iron ladder leading into the caisson. The immediate wish of most men at this point, whether they showed it or not, was to get back out into the open air just as fast as humanly possible. But once the ladder had been negotiated and three or four minutes had passed, most men also found they felt reasonably steady.
The initial view of the caisson interior was generally something of a shock, once the eyes had adjusted to the light. The six big chambers looked something like vast cellars from which a flood had only recently receded. Every post and partition, every outside wall, and the entire ceiling were covered with a slimy skim of mud. Every man in the place wore rubber boots and got about on planks laid from one section to another and between the planks the muck and water were sometimes a foot deep or more. Most days the work force would be concentrated in a few locations, leaving some of the huge chambers as dark and silent as subterranean caves.
Where there was light it came from calcium lamps, limelights as they were also called, which threw steaming, blue-white, luminous jets into the corners where the men worked, or from squat sperm candles that blazed like torches at the end of iron rods planted alongside the plank walkways. “The subject of illuminating a caisson in a satisfactory manner is rather a difficult problem to solve,” Roebling remarked in his report to the directors of the Bridge Company. At first the candles had burned with such vigor in the compressed air and sent up such clouds of smoke that the air had become intolerable. This had been overcome somewhat by reducing the size of the wick and of the candle and by mixing alum with the tallow and drenching the wicks in vinegar. Even so Roebling worried about the quantities of floating carbon the men were breathing into their lungs.
Kerosene lamps had to be ruled out from the start. They smoked even worse than candles, and with fire a constant hazard in such a charged atmosphere, Roebling did not want the risk of spilled oil. So he had hit upon the idea of limelights, of the kind ordinarily used for stage lighting or nighttime political rallies. He had the gas—a combination of compressed oxygen and coal gas—piped into the caisson, put burners in every chamber, and found two lamps per chamber would do the job. One small explosion had singed the beard off an attendant, but other than that the system had worked most satisfactorily. Ordinary street gas would have been about five times less expensive, but when that had been tried, the heat inside the caisson had built up to the point where no one was able to take it.
The air as it was, besides being heavy and dank, was uncomfortably warm. On the way from the compressors it passed through a cooling spray of water. Even so, winter or summer, regardless of the time of day or the weather outside, the temperature inside stayed at 80 degrees or more and the air was so saturated with water that under the best conditions the chambers seemed continuously shrouded in mist. Visitors who did not have to exert themselves in any way soon found they were wringing-wet with perspiration.
Most of the people who visited the caisson—newspapermen, local politicians, an artist from Harper’s Weekly, editors from some of the professional journals—came out with their clothes thoroughly mud spattered and quite relieved to have the experience behind them. Many of them also expressed open amazement that men could actually work in such a place day after day.
The first load of rock and mud was hauled out of the caisson by clamshell dredge buckets on July 5. Most of the effort inside was spent removing the sharp-edged boulders that threatened to damage the frames and shoe as the caisson began to come down on them with crushing force. Boulders under the water shafts were the most serious initial problem, for if the caisson were to settle suddenly, the shafts might be blocked shut or badly damaged. And there was no way to get the boulders out of there except to chip away laboriously hour by hour, by hand, with long steel bars and sledge hammers.
In the middle chambers the ground was nearly all traprock, packed like gravel and joined by what Roebling described as a natural cement made of decomposed fragments of green serpentine rock. Every boulder was coated with this unyielding substance, upon which a steel-pointed pick had virtually no effect. Only by driving in steel-pointed crowbars with heavy sledges were the men able to make the slightest headway.
In chambers No. 1 and 2, those nearest the ferry slip, there was clay and gravel between the rocks, which made the going easier, while in Nos. 5 and 6, those at the upstream end of the caisson, there was a gummy blue clay that extended down forty feet, just as indicated by earlier soundings. This made the digging there relatively easy, of course, but it also meant that the caisson would have to go down at least forty feet—or beyond the clay. As Roebling said, no better foundation could have been wished for than what they were finding in chambers No. 3 and 4, but only if it had extended all over. And with the nature of the material so vastly irregular from one chamber to the other, lowering the caisson uniformly seemed practically an impossibility.
Roebling kept careful track of the rock uncovered. Nine-tenths of it, he found, was of Hudson River Palisades origin, transported, like all of Long Island, millions of years before by the glaciers. This traprock, as it was commonly called, was basalt, an igneous rock, like granite, and nearly as hard. As the men dug into the caisson floor, the traprock emerged in chunks the size of paving blocks or in monstrous boulders, but when a shovel or pick first struck one of them, with a sharp metallic clink, there was no telling which size it would turn out to be.
Boulders of quartz and gneiss occurred here and there, but rarely. Two big boulders of red sandstone were also found. But a collection made by Roebling of all the different varieties of smaller rocks uncovered, most of which had been worn down to pebble size, presented a complete series of the rocks to be found for a hundred miles to the north and northeast of Brooklyn.
The idea of driving the cutting edge of the caisson through such material by building weight overhead had to be abandoned at the start. The pressure needed to do that would crush the cast-iron shoe and smash the bearing frames. So the cutting edge would simply not cut. Instead, every boulder, every rock of any size, had to be removed before the shoe or frames began bearing down on them. And all such work had to be done by probing underwater since there were trenches along the inside edge of the shoe, clear around, and these were nearly always brimful of water that seeped in from the outside. (This water flowed in turn into cross trenches at the foot of the frames, which supplied the big pools under the water shafts.)
Just finding the boulders under the shoe, let alone removing them, was an unbelievably tough and disagreeable task. The full perimeter of the cutting edge was 540 feet. This added to the five frames, each 102 feet long, brought the caisson’s full bearing surface to 1,050 lineal feet, or a distance greater than the length of three football fields, every inch of which had to be probed beneath with a steel sounding bar twice daily with each shift. Whenever a new shift came down, the work accomplished in the preceding eight hours had to be carefully explained; and since most of the trouble spots discovered would be underwater, there was no way simply to point them out—the information had to be written down or memorized. “Moreover,” as Roebling wrote, “a settling of the caisson of six inches or a foot would bring to light an entirely fresh crop of boulders in new positions, and very often half without and half within the caisson.”
To keep weight off the shoe, and so off any such boulders protruding under the shoe, it was necessary that the frames, or chamber partitions, take up that part of the load not balanced off by the compressed air. And with the frames thus the prime structural supports of the whole enormous burden, there had to be a way to lower them as the caisson descended.
The system used at first seemed the simplest solution, but it did not work well at all. Small pillars of earth were left under the frames, each one about three feet square and from six to eight feet apart. These pillars were then to be dug away systematically and the caisson lowered in that fashion. But the earth pillars often concealed a boulder that had to be removed, or they would be eroded away by water, or still more often, the workers in adjacent chambers, not working in unison, would undermine them and destroy their usefulness.
The system next adopted worked extremely well and was used until the end. Beneath each partition, every eight feet or so, two wooden blocks, a foot square and two feet long, were placed, one on top of the other, with oak wedges jammed between them and the bottom edge of the partition. Whenever the shoe had been cleared of all obstructions to a depth of several inches the entire way around the caisson, the wedges were knocked loose with sledge hammers, one by one, frame by frame, until the whole caisson settled. New blocks were then put in beside the old ones, which, if the descent of the caisson had been sudden, were split in two or crushed to a pulp. “The noise made by splitting blocks and posts was rather ominous,” Roebling commented dryly, “and inclined to make the reflecting mind nervous in view of the impending mass of thirty thousand tons overhead.”
Collingwood and Paine were in charge of clearing boulders from beneath the shoe and seeing that the caisson settled properly. “Levels were taken every morning on the masonry above,” Collingwood wrote later, “and a copy furnished the general foreman…. If the caisson were level, the usual method followed in lowering was to begin at the central frame, and loosen the wedges regularly from the center towards the ends. The two frames next to these were then treated in like manner, and finally the outer two. When no obstructions occurred, the blocks would all be gone over several times in the course of a day, and the caisson would settle easily, at the rate of three or four inches in 24 hours.”
At first, however, things had not gone that way at all. Through July and on into early August, the rate of descent had been less than six inches a week, and the boulders, instead of diminishing in number, as had been expected, became more plentiful. It was a hopeless rate of progress Roebling reported to his directors. At this rate it would take nearly two years to sink just the one caisson.
Boulders within the work chambers were the lesser evil. Before they could be hauled up the water shaft, they had to be split into manageable pieces, never an easy job, but at least they could be dealt with under comparatively reasonable conditions. Boulders under the shoe, however, or those found beneath the frames, were each a major undertaking. The removal of a boulder from under the shoe, for example, went as follows.
The ground around the inner side of the boulder had to be dug away with pick and shovel, with the excavation filling with water as fast as the men worked. Then the boulder had to be drilled by hand, underwater, and a lewis inserted, a dovetailed iron eyebolt to which a hoisting rig of some kind could be attached. In the early days of the work, double sets of block and tackle were tried, with a gang of thirty or forty men hauling at the ropes, while others worked furiously with winches and crowbars. But very often the boulder refused to budge. So Roebling had hydraulic jacks lowered through the supply shafts. These were of a kind designed for pulling instead of lifting and had a capacity of two to three tons. The water chamber on such a jack was above, not below, the piston, and the piston rod had a big hook at the end instead of a lifting shoulder. This hook was attached to the iron eye in the boulder, while the opposite end of the jack was chained fast to the nearest substantial timber or, better still, to the ceiling. The jack pump was then set in motion and, as Roebling said, it would prove itself a “very effective instrument.” There would be an immense momentary strain, then the boulder would give way and come sliding into the caisson, where it would be broken up..
When a boulder appeared to extend several feet outside the caisson, no attempt was made to haul it in. Rather the part inside was slowly split up until enough had been removed for the caisson edge to clear.
But whichever way they were handled, a few good-sized boulders beneath the shoe could hold up everything for three or four days. Such delays were maddening, and there were more and more of them as time passed and equipment began to break down or the water shafts failed to function as they were supposed to. The big clamshell buckets, armed with seven-inch teeth, were formidable-looking affairs and under normal conditions one of them could dredge up more than a thousand yards a day. This, in theory at least, meant that the equipment in use should have been able to haul out the whole volume of material that had to be removed for the tower foundation in about a month’s time. But the buckets kept breaking down or getting caught under the bottom edges of the water shafts. As it was, the job would take five months, and these, as Roebling wrote, were “five months of incessant toil and worry, everlasting breaking down and repairing, and constant study to make improvements wherever possible.” Bucket teeth that worked well for scooping would not last a day at grappling with stones. For every two buckets in working order, three were being repaired. “There was, indeed, one period,” Roebling said, “when we were almost tempted to throw the buckets overboard…”
One of the greatest early disappointments was to find that the buckets were unable even to dig their own hole under the water shafts, as they were supposed to. Much of the time the buckets failed even to bite into the material dumped into the hole unless a couple of men were kept constantly stirring the pool, “to keep the stuff alive,” as Roebling said. But even then the bottom of the pool kept filling in and had to be dug out by hand repeatedly.
Stone and clay would pack solid and actually fill the hole in a few hours, such was the incredible nature of the material being excavated. So it became necessary to feed all the stones into the pool at one time, separately, then the clay by itself. The kind of bucket in use could lift any stone it could catch hold of, but such a stone, or a chunk of split boulder, had to be placed just so in the hole for the bucket to get a proper hold, and the stones could only be taken out one at a time. Whenever a badly placed stone got wedged under a shaft, which happened fairly regularly, somebody had to dive under to see what could be done. “When the lungs are filled with compressed air,” Roebling wrote, “a person can remain under water from three to four minutes.” He knew this, it seems, from personal experience.
Any material fed into the pools from other parts of the caisson could be properly prepared, as it were, for the dredges to handle, but when the trouble was inside the water-shaft pools, as often happened, or when the pool had filled in, one to two days would be lost while the shaft was sealed off on top, with an iron cap, the water forced out by compressed air, the pool pumped dry, and the pit dug out by hand to a depth of six to eight feet. And the whole time this was going on (about two days on the average), the other shaft had to handle all the work. There were, in fact, so many occasions when the pools had to be cleared in just this fashion, so many repairs needed on the buckets, that most of the time only one water shaft was in operation.
Furthermore, whenever the work was held up a day or two, and the caisson stopped settling, its movement immediately afterward could be quite erratic, coming in sudden, unpredictable, uncontrollable starts. This, Collingwood explained, was due to the earth compacting around the caisson, as it does around a pile when driven slowly. “At such times it would seem impossible to get it started, and when once movement began, it was almost sure to split a set of blocks before it was arrested.”
Once, after the caisson had been at rest for several days because of breakdowns in equipment, all the usual steps were taken to get it started again, but to no avail. The blocking was eased, the shoe was cleared of obstructions, and still the caisson just hung there, motionless, with nothing holding it. The men did not know quite what to make of this. The only real significance of the episode, however, was that it gave the engineers a chance to compute roughly how much side friction the caisson had to overcome during its descent. As Collingwood figured it and reported later to a meeting of the American Society of Civil Engineers, the average pressure in the chamber at the time was seventeen pounds per square inch, giving a lifting force from the compressed air only of 20,400 tons. The bearing surface (posts and frames) was carrying about 625 tons and estimates were that the whole outer edge was probably carrying about that much again, which gave a total upholding force of somewhere near 21,650 tons. But the total weight of the caisson then, including the stonework on top, was judged to be 27,500 tons. Therefore, when it failed to move, the weight being carried by side friction alone was 5,850 tons. So this meant that along with everything else that had to be overcome to get the caisson down even a single inch, there was about 900 pounds of friction working against every square foot of the exterior surface.
To add to the over-all physical discomfort of everyone involved, blowouts continued and with greater frequency than Roebling had figured on. After each initial rush of air out one side or other, a returning wave would follow, inflowing river water that would stand knee-deep over the work surface until the air pressure eventually forced it out. Blowouts were usually caused by changes in the tide, which in the early stages affected the balance of pressures inside and out and which apparently Roebling had anticipated. But even the wake of a passing steamer could cause enough of a change in the water level to bring on a blowout, and this came as quite a surprise.
To build up additional weight on the caisson, some of the excavated material was dumped on top, in the spaces not taken up by the masonry. The rest of the material was dumped into carts that ran on inclined tracks down to big scows tied up on the riverside. (Once the caisson was in position this side had been closed in with a cofferdam, as the others were, and docks and tracks and turnarounds for the stone carts had been built.)
Eventually, when the caisson got down about ten feet below the river bottom, water ceased to come in at all, so tightly was the ground packed about the outer sides. Now, much to their amazement, the boulder crews encountered a new phenomenon. As Collingwood wrote, “It was not an uncommon occurrence in removing a large boulder, that an opening would be made entirely outside the caisson, for three or four feet.” Sometimes when this happened a man might crawl inside, beyond the limits of the caisson, that is, to dramatize the uncanny nature of such a space, not to mention his own nerve.
To step up the pace, Roebling organized a special force of forty men who worked at boulders exclusively, from eleven at night until six in the morning, when the regular shift came on. In time everybody grew more accustomed to the work. Roebling, in the words of William Kingsley, gave “the work his unremitting attention at all times,” but especially at critical points was he “conspicuous for his presence and exertions.” Like his father, he demanded much of every man under him, and even more of himself.
As the weeks passed he found that a slight lowering of the air pressure inside the chamber could work wonders whenever added weight was advantageous. The compressors would be slowed a little and the caisson would immediately bear down harder. It was a ready, effortless way to apply an additional twelve hundred tons or so any time that was needed, and for only as long as needed.
But when the caisson had reached a depth of some twenty feet, or approximately half the distance Roebling intended to sink it, the boulders became so large and numerous that there was no choice left but to begin blasting.
The idea of using powder on the boulders had, of course, been considered from the start. It would have saved all kinds of time and effort obviously, and as things grew increasingly difficult and frustrating inside the caisson, the men were more than ready to give it a try, whatever the supposed risks involved. But Roebling had held off. In such a dense atmosphere, he reasoned, a violent concussion might rupture the eardrums of every man inside. Smoke from the explosions might make the air even more noxious and certainly more unpleasant than it already was. The doors and valves of the air locks might be damaged.
His greatest fear, however, was the possible effect on the water shafts. The two immense columns of water that stood above the work chambers and every man in the caisson were held there in a critical balance only by the pressure inside the chambers. The margin of safety was just two feet of water—the distance from the surface of each pool and the bottom edge of each shaft. An explosion inside the caisson, Roebling explained, might suddenly depress the level of the pool and allow the air to escape underneath. A water shaft might blow out, in other words. All the compressed air would escape in one sudden blast and almost certainly with the following immediate consequences: with the work chambers instantly deflated, so to speak, the full weight of the caisson would come down all at once, smashing blocks and frames and outer edges. The impact might be so great as to crush every interior support and everyone inside; and in the early stages of the work, the river would have rushed in and drowned everyone. What the effect might be on top was anybody’s guess, but it was realistic to assume that all that water bursting out of a shaft would be about the same as a major explosion.
Still, Roebling knew, such prospects, however sobering, were all hypothetical. There was no past experience to go by. So whether he was right or not remained to be seen. With luck, he might be wrong. He decided to find out.
He began by firing a revolver with successively heavier charges in various parts of the caisson. When it was clear this was perfectly safe and causing no adverse effects, he set off small charges of blasting powder, fired by a fuse, gradually working these up in magnitude until they were on the order of what was needed to get on with the work. The concussions bothered no one especially, nor did they have any noticeable effect on the air locks or water shafts. “The powder smoke was a decided nuisance,” Roebling said. “It would fill the chambers for half an hour or more with a thick cloud, obscuring all the lights.” But this he alleviated greatly by switching to fine rifle powder.
The results were spectacular. With a little practice the work moved ahead as never before. A long steel drill would be hammered into the rock to make a hole for the blasting charge and the charge would be tamped in and set off. * “As many as twenty blasts were fired in one watch,” Roebling reported, “the men merely stepping into an adjacent chamber to escape the flying fragments.” The hard crystalline traprock split more easily than the tough gneiss or rotten quartz boulders. Invariably the traprock broke neatly into three equal-sized boulders. The caisson now began descending twelve to eighteen inches a week, instead of six.
Care was taken to guard against fires igniting in the yellow-pine roof and the men did their best not to injure the shoe with the charges they set off beneath it. But the shoe by this time was in such shape that a little more damage hardly mattered. The armor plating was bent and torn, the shoe itself cracked or badly crushed in dozens of places.
One convenient method for disposing of a boulder lodged beneath the shoe was to drill straight through to the other side, plant a charge at the far end, then shoot the boulder bodily into the caisson. Some boulders encountered now were up to fourteen feet in length and five feet in diameter.
For the people of New York and Brooklyn all such activity was considered somehow removed from reality. The whole concept of an enormous wooden chamber descending below the river was a little difficult for many to understand and the men who went in and out of it seemed a breed apart. There was simply something quite unnatural about all this. “For night is turned into day and day into night in one of these bridge caissons,” wrote the Herald; “and when the steam tugs, with their red and blue lights burning from their wooden turrets go creeping along the bosom of the river like monstrous fireflies, then do these submarine giants delve and dig and ditch and drill and blast…The work of the buried bridgebuilder is like the onward flow of eternity; it does not cease for the sun at noonday or the silent stars at night. Gangs are relieved and replaced, and swart, perspiring companies of men follow each other up and down the iron locks, with a dim quiet purpose…”
The sheer physical exertion inside the caisson was as great as ever, the work every bit as unnerving as it had been. And the deeper they went, the more the men felt the discomforts of the compressed air.
The work went on around the clock, except for Sundays, with three shifts of eight hours each. The first shift went down at six in the morning, the second shift at three in the afternoon, the third, the special night gang, went down about eleven. Most men stayed in the caisson the full eight hours, taking their dinner pails down with them. Work in such an atmosphere brought on an uncommonly fierce appetite, they said, and the standard meal consisted of great slabs of bread and cheese or beef, washed down with beer.
The two day shifts were composed of 112 men each, while the night shift Roebling kept to roughly forty picked men. So the full force working inside the caisson came to about 264. Up on the surface there were two shifts to operate the dredging gear and two shifts to dispose of the material brought up from below. In addition, there were people to run the compressors and hoisting engines, blacksmiths, mechanics, men to look after the gas for the lighting below, a carpenter’s force of some twenty-five men, and thirty men working on the masonry, bringing the total force aboveground to something like a hundred.
But the number of those inside the caisson who had been with the work from the start was quite small comparatively. According to the time books, a total of 2,500 different individuals worked in the Brooklyn caisson from start to finish. This means then that men were quitting in droves—at a rate of about a hundred a week on the average, or, to put it another way, every week about one man in three decided he had had enough of building the Great Bridge and walked off the job, never to return again..
There were notable exceptions, of course. One man named Mike Lynch went down with the very first shift to go into the caisson and would be the last man to come out. He not only never lost an hour’s time during the ten months he worked in the caisson, but he made a day’s extra pay in overtime. “He is strictly temperate and regular in all his habits,” William Kingsley noted, “and is none the worse for his long service in compressed air.”
That the turnover was so great is not surprising.
Amenities provided by the management were very few—about what was customary. Two unpainted frame sheds had been put up in the yard, with rows of pegs and hooks inside for the men to hang their clothes. (The temperature inside the caisson was such that most men went down wearing nothing but pants and a pair of company boots.) In front of the sheds were sets of washtubs, with hot and cold water. And that was about the sum of the comforts provided aboveground.
Inside the caisson itself there were generally a few dry spots where a man could eat his midday meal. And against one wall stood what was considered by all the world’s most extraordinary toilet. It was described in one of Roebling’s official reports as a pneumatic water closet and consisted of a wooden box with a lid and a large iron pipe that passed up through the timber roof. The box was kept about half full of water, and whenever its contents were to be discharged, a valve was opened and the pressure from within the caisson would blast everything instantly overhead in the form of a fine mist. This particular device was not installed until the work had progressed some little time, however, and until then the pools beneath the water shafts, or any convenient corner, had sufficed for the same purpose. When he came to describe the general working conditions, Roebling would note that the sense of smell was almost entirely lost in the “made air,” as he called it. “This,” he said, “is a wise provision of nature, because foul odors certainly have their home in a caisson.”
For an ordinary laborer the pay was two dollars a day. But after the caisson reached a depth of twenty-eight feet, it was decided to revise that. The bad air, the increased unpleasantness over all, and the widespread feeling that the deeper down they went the more hazardous the work, all called for a commensurate hike in wages, the management decided. So from that point on the pay was $2.25 a day.
Men kept quitting just the same, but for every one who did, there were at least a dozen anxious to take his place, most of them Irish, German, or Italian immigrants who were desperate for work of any kind, and many of them, like those who had gone into the Eads caisson, were thinly clothed and undernourished.
But for all the talk and worry there had been over caisson sickness, and for all the growing fear of it as pressure inside the caisson increased steadily, only a few so far had experienced any ill effects.
One pound of air pressure equals two feet of tidewater, so for every two feet the caisson was lowered, one pound had to be added to the pressure. Gauges in the engine room indicated the height of the tide and the pressure of the air. The greatest the pressure would ever be in the Brooklyn caisson was twenty-three pounds per square inch above normal atmospheric pressure, or nearly ten pounds less than it had been inside the Eads caisson the day James Riley fell dead. In St. Louis several more had died miserably, but there had been only mild symptoms in Brooklyn. A little paralysis in the legs was all. Only three or four men had been bothered in the slightest and none of the engineering staff so far.
Like Eads, Roebling noted that the ones who did have trouble were all new to the job. His way of alleviating their discomfort was to send them right out of the caisson. Now that he had seen something of the problem first hand and had spent as much time under compression as anyone on the job, Roebling was convinced that Eads’s system of shortening the hours was the best possible prevention and said he would follow that same system in the New York caisson. The thing to do, he said, was to “reduce the period that the human system is in contact with the exciting cause.” The increased quantity of oxygen inhaled under pressure was what did the damage, he thought. “That the system struggles against this abnormal state of affairs,” he said, “is shown by the fact that the number of inhalations per minute is involuntarily reduced from thirty to fifty per cent. It follows, therefore, that the shorter the period of exposure to compressed air the less the risk.”
But any change in the schedule would wait until the New York side, since the Brooklyn caisson was not going deep enough to produce anything like what was happening in St. Louis, where Eads had had a special hospital ship fitted up and had hired a full-time physician who prescribed special diets and set down strict rules about rest. Eads’s men by this time were permitted to work in the caisson only an hour at a time.
But the men in the Brooklyn caisson were having their troubles all the same. The work was a hazard to the health, it was agreed, and far more exhausting than anything any of them had ever done before. Collingwood said a full day inside would leave him feeling worn-out and in ill temper for days. And when the weather turned cold in the late fall, dozens of men began coming down with severe colds and bronchitis, caused by the abrupt drop in temperature inside the air lock. Every time they “locked out” at the end of the day, hot, tired, and dripping wet, the men would experience a sudden temperature drop, from at least 80 to 40 degrees. Roebling had steam coils installed in the air locks to keep the temperature the same as in the chambers below, but the men still had to face the chill open air once they emerged from the locks.
A hacking cough also became common among those who had been on the job any time. Candle smoke and the blasting were said to be the cause. Those who had been going down the longest could spit black and would still be able to do so several months after the work was finished.
But what plagued everyone most was the thought of all that weight bearing down overhead and the river outside and the unspoken fear that sometime, sooner or later, something was going to go wrong and they would all be drowned like rats or suffocate or be crushed to death. And then just to confirm how very tenuous was the balance upon which they were all trusting their lives, there occurred what would afterward be called “The Great Blowout.”
It happened at about six in the morning and on a Sunday, when only a few men were about, a fact the pious took to be more than a matter of coincidence. Eads had his men working seven days a week, it was noted, while Roebling kept the Sabbath. This was a sign, it was said, and thanks were given through Brooklyn and nowhere more fervently than in the Irish neighborhoods near the Navy Yard. Heaven only knew how many would have been left widows, people were saying, had it happened any other day of the week.
All at once in the very still early morning there had been a terrific roar. The few who actually saw the thing go off said it looked more like a volcano than anything else. It was as though the river had exploded, sending a column of water, mud, and stones five hundred feet into the air and showering yellow water and mud over ships and wharves and houses for blocks around. The column was seen from a mile off and the noise was so frightful that people began pouring out of their front doors and rushing pell-mell up Fulton Street. The whole neighborhood was on the run. Roebling described it as a stampede. “Even the toll-collectors at the ferry abandoned their tills,” he said.
Nobody was inside the caisson at the time and only three men were on top of it. One of them, a yard watchman, said later that the current of air rushing toward the blowing water shaft was so powerful it knocked him off his feet, ruining his Sunday suit. He had been struck by a stone after that and could remember no more. One of the other men leaped into the river, while the third tried to bury himself in a coal pile.
Then in an instant it was all over and everything was as silent as before. Both doors of the air locks fell open and for the first and only time the submerged caisson was flooded with daylight. The quiet lasted but briefly. Within minutes there was another rush of people heading down Fulton to see what had happened.
Roebling, Collingwood, and one or two of the others from the work force were on the scene almost immediately. They turned hoses into the open water shaft, closed the air locks, and in about an hour had a head thirty-one feet high back in the shaft and fifteen pounds of pressure back in the shaft and fifteen pounds of pressure back in the work chambers. When it was time to go down to take a look at the damage, Roebling led the way. “The first entry into the caisson was made with considerable misgiving,” he wrote. But incredibly none of the disastrous consequences he had feared had occured, as he reported later to the Board of Directors:
The total settling that took place amount to ten inches in all. Every block under the frames and posts was absolutely crushed, the ground being too compact to yield; none of the frames, however, were injured or out of line. The brunt of the blow was, of course, taken by the shoe and sides of the caisson. One sharp boulder in No. 2 chamber had cut the armor plate, crushed through the shoe casting, and buried itself a foot deep into the heavy oak sill, at the same time forcing in the sides some six inches. In a number of places the sides were forced outward. The marvel is that the airtightness was not impaired in the least.
His caisson had withstood the staggering blow of 17,675 tones dropped ten inches. By the way certain boltheads were sheared off, he could tell that the sides of the caisson—nine solid courses of timber—had been compressed two inches, such had been the impact. In the roof, however, there was not a sign of damage except for the slightest sag near the water shaft, where the support from the frames was the least.
With a little figuring Roebling concluded that once all the settling had stopped and before the compressed air was build up again inside the chambers, the caisson was carrying a total weight of twenty-three tons per square foot. This was an astonishing revelation. As never-racking as the whole episode had been, it had demonstrated just how large a margin of safety Roebling had built into the structure, since its ultimate load, once the bridge was built, would be only five tones per square foot. So he had built the caisson at least four times as strong as it needed to be.
Why the water shaft blew out was, needless, to say, a question of the gravest concern and the answer takes a little explaining.
The problem was that the weight of the columns of water in the shafts was not always the same. Particles of rock and earth were constantly washing out of the clamshell buckets as they were hauled up through the water shafts, and as a result a fine silt was held in suspension and this, in a column of water seven feet square by, say, thirty-five feet high, could and did increase the specific gravity of that column to a remarkable degree. But when the shaft was not in use for some reason or other, the silt would settle, the water would become less thick and weight less. So great would be the difference in the weight between a nearly cleared column of water and one still in use that the difference in the levels of the two (both of which were, of course, being supported by the same air pressure) would be about ten feet.
Outside, on the top of the caisson, such a disparity, in the level of the water in the shafts could be an alarming sight for anyone on duty who did not understand the reason for it. The impression would be that the lower of the two shafts was getting close to the danger level-that it might may blow out at any instant-and the immediate response would be to feed more water into the shaft as quickly as possible.
This is precisely what happened on more than one occasion and effect inside, naturally, was that the pool beneath one shaft would begin overflowing rapidly, which led those in charge below to assume the air pressure in the chamber was giving out. And since there was no direct communication between those above and those below, somebody had to scramble up through the air lock and find out what had gone wrong. On one such occasion it was discovered that the water in one shaft was above twelve feet from the top while the water in the other shaft was twenty-one feet from the top and despite the fact that a heavy stream of the water was pouring into the shallower shaft. The water was immediately shut off when it was known what was happening below and samples of water were taken from each shaft. Water from lower shaft was found to weight eighty-five pounds per cubic foot, which was twenty-one pounds more than the water from the other shaft.
On the Sunday of the blowout, apparently the sediment in one shaft had settled to such an extent that the water no longer weighed enough to contain the pressure inside. The normal precaution had been to keep a small stream of the water playing into the shaft to make up for just a likelihood during the days when the work was halted and no dredging was going on. But this time had not been done. Sounding very much like his father, Roebling said “To say that his occurrence was an accident would certainly be wrong, because not one accident in a hundred deserves the name. In this case it was simply the legitimate result of carelessness, brought about by an overconfidence in supposing matters would take care of themselves”
Trusting matters to take care of themselves was something this extremely competent young man had seldom done in his life. He had had the contrary attitude drummed into him since childhood and from here on more than ever, he would insist on the strictest attention to every detail and to safety precautions especially, and he would come down hard on anyone caught taking such matters lightly. The thing to fight against, he told the men, was the kind of carelessness that comes from familiarity with the job.