why can you get decompression sickness in engineering caissons, even thought they are not underwater?

Answer 1

Caisson disease is so named since it appeared in construction workers when they left the caisson and had rapid decompression. It is caused by the same processes as decompression sickness in divers. The Brooklyn Bridge was constructed with the help of caissons, and several workers died of caisson disease.
Dysbarism refers to medical conditions resulting from changes in ambient pressure. Various activities are associated with pressure changes. Scuba diving is the most frequently cited example, but pressure changes also affect people who work in pressurized environments (for example, caisson workers), and people who move between different altitudes.

Effects of pressure on the body
Air spaces
Air is very compressible. Humans have many air spaces: sinuses, middle ears, gas in our bowels, cavities in our teeth, and largest of all, our lungs. On land in our daily lives, the pressure in our air spaces is usually exactly the same as the pressure outside, because our air spaces are connected to the outside world. If there was a pressure difference between the outside world and one of our air spaces, then we experience painful pressure on the walls of that air space, as air “tries” to get from the higher-pressure side to the lower-pressure side. This is why we sometimes get painful ears on air trips.


Dissolved gas
A percentage of the gas we breathe (air) is always dissolved in our blood, like the gas dissolved in a soda bottle with the lid on. If we move to a higher ambient pressure, then the gas we breathe is at a higher pressure, and more of it dissolves in our blood and body tissues. If we move back to a lower pressure, and we move slowly, then the extra gas comes out slowly until we are back to our normal amount of dissolved gas. But if we move quickly to a lower ambient pressure, then the gas comes out of our blood and tissues violently, in large bubbles, like to the difference between slowly opening a bottle of soda (dropping the pressure in the bottle slowly down to sea level), versus ripping the cap off quickly.

Answer 2

Players answer covers it but to put it more simply:

decompression sickness is caused by the rapid release of nitrogen into the bloodstream which is caused by moving quickly from a high air pressure to a lower air pressure.

Answer 3

Simply because the air inside is at the same pressure as the water outside to stop the walls collapsing inwards, same as your lungs when diving. hope this answers your question.