THE BRIDGE IS ON FIRE!

What bridge?
The Brooklyn bridge, although it's not called that yet. In fact it's not even a bridge, indeed it's hardly visible above the waterline of the East River at this stage.

Wait, what?
Most of what you see above is stone and steel. What could have possible caught fire?
And thereby hangs a tale.
Of the two granite towers, the Brooklyn and the Manhattan, the Brooklyn side was started first because the river bottom on that side was rockier and harder digging. The thinking being: If this is going to fizzle due to the unworkability of digging tower foundations, it would be best to find out early.

As you may recall from your school days, the foundations beneath the river were dug in caissons.
When first developed, these were just tubes that kept the water out of the work area and sank as they were undermined - like a self-contained cofferdam. Easy-peasy.
Illustration to the left is from 1846 and shows a very simple and shallow example.
The water in the scenario pictured isn't deep - three feet or so. Different problems arise when the water is deep, said problem being; keeping the water out - it being heavy and liquid.
The Eads Bridge, built across the Mississippi at St. Louis, was one of the first to use "pneumatic caissons" which, as the name implies, keeps the water from intruding by filling the space with compressed air of a pressure sufficient to counterbalance the weight .
Of course, the caisson will need a roof now, unlike our pictured example.
With me so far?
The Eads Bridge was one of the first times that "caisson disease" was noticed. Now we call it "the bends" or decompression sickness.
Official Brooklyn Bridge genius,  Washington Roebling, often consulted with Eads concerning his project, happening at the same time, the projected "East River Bridge", which would use the deepest caissons ever sunk.
On top of that, Roebling's caissons were to serve not only as work chambers but later, as the ultimate foundation of the tower.
And these were big items.

Launching Size and weight of Brooklyn Caisson: 168 x 102 x 14.5 feet; 3000 tons

Of course, upon launching still more courses of timber were laid until the total over the heads of the workers in the caisson totaled fifteen feet. Apologies for the shitty quality of the next image. I had to scan it from a book since all the Internet shitheads have taken these public domain prints and are monetizing them to sell prints.
The book: "The Great Bridge". Excellent read but don't buy it from Amazon. Fuck that guy.
The upper of the two shows the completed caisson before it was floated down to its new home.
So, since a granite tower was to be erected topside, Roebling's caissons had to be closed at the top. Rather like a big, thick, wooden box open at the bottom.
The lower picture: The layout of the caisson. I'll dispense with any description of the multitude of details relative to the how of things and just say this: What you see above the heads of the happy workmen toiling at the bottom - and below the masonry a'building above - represents fifteen feet of solid, southern yellow pine. Twelve-inch square timbers laid in alternating directions until the full height was reached.
Yellow pine was chosen due to its high resin content, in fact the sticks Roebling used would hardly float due to their density.
Movie break!

 

Dave Matthews was going to provide the soundtrack but bailed at the last minute. 

As the riveting footage above illustrates, the other side of the rot inhibiting character of such resinous wood was...  Anyone?

Now Roebling was no idiot and was well aware of the dangers of a compressed-air work area and the need to be careful with open flames.

The work progressed apace and on December 2, 1870 the Brooklyn caisson was almost forty-three feet below the river bed and very near to where it was going to be for the rest of eternity.

But, whadya know, fire.

It seems that, in spite of the diligent pointing of all the joints between the timbers, one area in the roof of the caisson was missing an inch of two of mortar so the oakum caulking was exposed.

Probably no biggie except that just below this spot a fella had nailed a box to the partition  to keep his lunch in. In looking into said box, he would put his candle on top of the box and...

A most unspectacular catastrophe indeed. There was no smoke, no flames, nothing but a hole a few inches across through which was visible an inferno of glowing coals a foot or more wide and possibly seven feet long.

Up in that fifteen feet of criss-crossed yellow-pine timber with a huge fuel supply and all the combustion air a fire could want. Compressed even.

Short version: This fire wasn't going away on its own.

Assholes were jumped through and bricks were shat.

They stuffed rags and mud into the hole. They threw buckets of water up into it and they shot steam into it for fifteen or twenty minutes. Then two big cylinders of CO2.

None of it worked. It would work well enough - until it didn't. When the steam was shut off or the gas ran out, the fire was back.

This was a serious problem being that there was now approximately 28,000 tons of stone piled on the ceiling of this structure which now had a supercharged fire burning the guts out of it.

Roebling had been there since half an hour after the fire was discovered and was by now exhausted. He was on his way home, feeling sick to begin with but then got word that the drilling that had been going on into the roof of the caisson had discovered more fire.

Back he came and the monumental decision to flood the caisson was slowly but finally arrived at.

This wasn't as easy as it sounded. There were odd parts of the interior that were lower than the outside rim and the interior partitions. These were the water shafts which served as an air-lock for the clam shell buckets to pick up material from.

A few problematic boulders beneath the water shafts and the perimeter had to be dealt with and even then it was a gamble.

Prior to this, the caisson had never rested anywhere with none if its weight unsupported. Ever since it was launched it had been full of air and buoyant. It was only supposed to be down settled on the bottom after the bedrock had been reached.

The short version is: There was nothing else for it. The compressors were shut down and water was pumped into the caisson. 

It was left flooded for two days and survived with some minor damage.

With the water gone, the gamble was deemed a success being that no traces of the fire were evident. The only indication that there had even been a fire was the small opening in the roof, just above the partition.

That was such a nothing-burger that everyone immediately assumed that the damage would be minor, probably just sticking to the edges of the timbers leaving lots of meat there to support this half of the bridge.

Good news indeed, especially since during and after this drama played out, the preparations for finally settling the caisson into its new home were nearing completion. Brick piers were built to support the weight above for the time ahead when the air pressure will be shut off so the remaining space could be filled with concrete.

About this time, strong smell of turpentine is detected at the top of the caisson along with a frothy brown liquid.

Back to panic mode. Roebling and his chief mechanic took another look at the fire damage and realized that it may reach farther than they'd expected. In any case, it was obvious that lots of compressed air was being lost through the timbers.

The thought was this: They'd pump concrete (a grout really) into the main hole as well as the two-hundred holes that had been drilled up into things over the past few weeks.

Roebling devised a pump with a cylinder and a piston that, when a screw jack applied pressure, the grout would be forced through a 1/4" pipe and into the void.

Slow going as you may imagine. When all was said and done, they'd pumped six-hundred cubic feet of concrete. Those in the trades would refer to this by cubic yards, in this case, twenty two and change. 

Another way to look at it: It's just a little shy of four mix-trucks worth - or forty-five tons

Trucks like this one.
A giant, collective sigh of relief was expressed and, since the caisson was finally at its destination and the brick piers were in place, Roebling decided to cut off the compressed air so they could all bask in their handiwork.
He then ordered that a six-foot hole be cut into the ceiling of the caisson so that the effects of the fire and its brilliant repair could be examined.
Turned out - the concrete had been very effective. It had completely filled-in all the labyrinthine passages that the fire had eaten - but it'd left a nice, crunchy, structurally-unsound, charcoal layer an inch of two thick around it all.
Out came those forty-five tons of mud and the task then became "gigantic dentistry".
All the charcoal had to be scraped out and the voids filled.
For three full months, eighteen carpenters worked 'round the clock clearing away the charcoal and filling in the gaps.
Small spaces would be filled - again - with concrete while the larger were filled with timber.
The ragged edges were chiseled square and new sticks - again southern yellow pine, 12"x12",  in lengths of eight to ten feet - were snaked up into the mess above and bolted in place.
So, even though the caisson was virtually in its home since December, the final repairs weren't  finished until March 6, 1871.
Five days later, the caisson was filled with concrete and that end of the great bridge was settled.
Apparently, it's still there. But, as they used to say: "I ain't never lost nothing in New York" so I can't personally verify.