Caisson Disease | Prairie Public Broadcasting

Caisson Disease

Feb 27, 2021

The self-taught engineering genius behind the construction of the Northern Pacific Railroad Bridge (completed 1882) spanning the Missouri River at Bismarck was George Shattuck Morison. “At the time of his death on July 1, 1903, at the age of sixty-one,” the geologist and historian Edward C. Murphy writes, “Morison was regarded by many to be the leading bridge engineer in America, if not the entire world.”

Read Murphy’s article in North Dakota History; study Morison’s own report to the NPRR, which you can find online or browse in person at the state archives; examine his signed drawings of the design and details incorporated into the report; go out and have a look yourself at the elegant and durable structure still in service at the heart of North Dakota; and you have to agree with Murphy’s assessment, perhaps even drop the qualifiers: Morison is the greatest bridge-builder in American engineering history.

Perhaps I ought not to mention this, since I serve a university that trains engineers in droves, but here it is: Morison never studied structural engineering formally. He learned it on the job. He was a liberal-arts grad with a law degree from Harvard. He could read and write, he could execute drawings, he could see the big picture, and he could reason out problems and solve them. He was the perfect exemplar of Gilded-Age engineering.

And we have the perfect example of his genius and craft right here in the middle of the Flickertail State. If we can keep it.

As one of those fuzzy-headed liberal-arts grads who lacks the free-ranging acuity of a guy like Morison, I can understand just enough of his exhaustive report to see what he is trying to do, and I confess, I really like the pictures. The most gripping image he renders is Plate 10, “Showing process of sinking the caisson.”

When you look at the bridge today, your eye is drawn to the great stone piers on which the iron and steel elements rest. They are impressive stone work, but the granite sits atop massive concrete foundations that were poured deep underwater. This was accomplished--the river gravel vacuumed out, forms emplaced, concrete inserted--through the use of pneumatic caissons, pressurized chambers in which men worked at, or below, the bottom of the Missouri River!

This was a fairly new technology, and there were hazards, so now perhaps we should shift our attention from the engineering genius to the situation of the poor blokes laboring at the bottom of these caissons--as graphically depicted by Plate 10. The Tribune described their situation: “The workmen will descend to the working chamber through cylinders of iron, provided with iron ladder rounds. Before entering these, two iron doors have to be passed through, which fit their casings of iron and rubber air tight. A chamber separates these, and one door cannot be opened until the other is closed.”

The air pressure in the caissons had to be raised and lowered for the convenience of handling materials, and laborers had to descend and ascend, so that they were subject to what was known as “caisson disease”--what deep-sea divers call “the bends.”

Morison does not deal with this difficulty, leaving us to think there were no such problems on his project--but Murphy the historian and I are skeptical. The genius of Gilded-Age engineering did not extend much into the realm of worker safety or any other kind of concern for workers. Instead, Morison disparaged the quality of his workmen and wondered in print why they kept quitting the project.

There is historic engineering to view, and there are blood and tears to remember, too, at the site of this bridge. We should keep it.

-Tom Isern