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 clot
hes. (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 y
ield; 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.