Seattle Tunnel Partners gave media a look at the high-pressure conditions crews will endure in the next phase of maintenance work Tuesday.
Project Manager Chris Dixon explained 5-person crews will have to go through a hyperbaric chamber and a series of man locks, which will prepare them to enter a pressurized excavation chamber behind the tunnel boring machine's cutter head.
Once they get there, they can assess what needs to be fixed or replaced.
Each crew will only spend a half hour inside. They will come out for an hour and a half of decompression before the next crew can go in.
Dixon says each worker can go in only once a day, and they need 18 hours between compressions.
The work is hot and humid, but Justin Costello from Ballard Marine Construction says it should feel like normal atmospheric pressure.
The worst part?
"Mostly your patience," Costello said. "You get pent up with a lot of people and it can wear on you a little bit."
In case something goes wrong a crane can lift an emergency shuttle to a hyperbaric clinic above ground, where staff can treat and evaluate up to twenty people.
STP won't know how long the routine maintenance work will take until they head 120 feet underground next week.