After a conversation about whether or not diving bells were open or closed and whether or not a diver in a bell would need to follow the same rules for decompression as a scuba diver, I did a little more research and came to understand the concept of saturation diving.
From the beginning, diving bells can be either open or closed and, unless they remain inside a closed bell at one atmosphere, divers do breathe pressurized air so they do have the same decompression risks as scuba divers.
In the reading on the subject, saturation diving came up repeatedly, so I followed the train of thought and found out what that means. Divers who remain under water into a decompression dive are faced with long decompression times in order to safely return to the surface (this can be days). However, eventually, the diver’s tissues will reach a saturation point….the point at which the decompression times no longer increase. So, although the same decompression rules apply, a diver can stay at a given depth for longer periods.
This led to the development of larger diving bells that included space for multiple divers to remain for weeks at a time. These “habitats” are entered while on a boat and pressures are increased to match the depth at which the divers will be working. At that point, the entire habitat is lowered into the water to the defined depth and divers take turns outside the habitat until the task is complete. Then the habitat is raised back on to the boat and pressure is gradually reduced. This allows the divers to decompress with less risk and to only have to decompress once…saving a considerable amount of time.