This is my interpretation, and I may have some of the details off. I think it is going to be good enough to get you started, but I may have some errors, so if someone contradicts me, they may be closer to right than I am.
Because of the difficulties with pressure and decompression, deep sea divers will often work out of a diving tender platform kept at an elevated platform so that they don’t have to decompress to go off shift. Rather they’ll stay in a hyperbaric environment and eat and rest while still acclimated to the pressure.
The way I’m reading this incident, the diving platform was sealed and pressed up to 9 ATM pressure, to allow the divers to avoid decompression times while they kept going on and off shift during a job that was expected to take several shifts.
But, since the tender is basically a support platform, it’s easier to supply the needs of the divers in it, if it’s at the surface - it means less engineering requirements for getting air, water, food, power into the unit, and similarly makes taking waste out easier, too.
The diving bell was what would take the divers down from the platform to the job site, and was meant to be kept pressurized during the whole ascent and descent so that the divers were at a constant pressure environment. When the door was opened improperly the 9 ATM of pressure inside the tender was vented to the outside, and through the poor guy who got in the way.
The two divers mentioned as being dive tenders were outside the platform, and operating at surface conditions - taking care of everything outside the platform as the bell was raised and lowered.
I hope that this answers your question, torie.
