The dive bell is a glorified elevator used in saturation diving.
The bell houses 3 divers. Two divers actually do work outside the bell, while the 3rd is on standby in case of an emergency . All divers use their diving suits with their umbilical connected to the bell. The divers can typically reach 40 meters away from the bell. The umbilical feeds the divers with air (heliox), communication and hot water (it's only four degrees down there most of the time - and the divers are very sensitive to temperature due to the helium mix they are breathing).
Most bells are shaped slightly cylindrical, and has a minimum total volume of 6.3 m3. Things tend to get a bit cramped with all three divers inside.
The bell is pressurised at the working depth pressure whenever it is in use. This is to prevent the divers from experiencing rapid decompression and the bends. At depth the divers can close and open a sealed door, while at surface they dock to the life support tanks so that they can leave the bell.