IS TUP CLOSED BELL DIVING THE SAME AS “MINI BELL” DIVING?
In episode 3 we explained that a hard line should be drawn whilst comparing TUP diving with Saturation diving.
“Both techniques use a dry diving bell for getting the diver to and from the work location and that’s where all similarities end”
With that stated, we need to have a good understanding of what a proper closed bell entails, which brings us to the question “what is a mini bell?”. This is a phrase/name which is sometimes unrightfully introduced in conversations about the principle of TUP diving.
The mini bell was invented around 1983 and was first used commercially in 1985. The design of the system was not governed by guidelines or legislation. The typical mini bell was very small compared to our modern-day saturation diving bells and was built only to get the divers from depth to the surface chamber on deck. Safety features like survival packs, oxygen suppletion, castellating doors, trough water comms, on board gas etc. were often not or only partly available. In short, a mini bell was a dressed down Saturation diving bell operated without a bellman.
Although the principle of, and the motivation for the introduction of the mini bell was good it soon became clear that without the design criteria, now documented in the IMCA design document D024, closed bell diving, with a bell not built to incorporate all safety features and redundancies held a lot of risk as there were almost no mitigations for events that were not that unlikely to occur.
Mini bell diving was much more effective as the bottom time limitations were only given for normal air diving and dispensation was provided on this for mini bell diving. Later the HSE and afterwards IMCA in the D014 included bottom time limitations for TUP diving that are still considerably longer than normal air diving limitations, justification for that is clearly explained in episode 4 of this information bulletin.
To summarize, mini bell diving is a phrase from the past. Current design criteria for a closed bell detailed in the D024 is considered the only way to go when closed bell diving is conducted.
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