The Oceantech Minibell system

Up until 1986, the air diver was still going to work as air divers had done for decades, i.e. jumping over the back of a boat. In the case of rigs or platforms, and DSV's , some companies used submersible basket systems, as a means to get in and out of the water. All these methods have an inherent danger. The Surface Interval.

Owing to the increase in incidents of decompression sickness in the late 70's early 80's, the Health and Safety Executive, (HSE) which governs all inshore and offshore diving activities, placed a restriction on bottom times, for all commercial air diving in the UK.

The Minibell air diving system was developed by Ocean Technical Services Ltd in the early 80's. The system was designed in modular form, allowing it to be mobilized on platforms, rig's and on board DSV's.

The system consisted of :- Bell winch module, TUP module, Twin Chamber module, all containerized, a Minibell and the Clump weight (secondary lift).

The Minibell system was first used operationally in 1986 in the North Sea, working for Conoco on the Viking field, platform complex. The Minibell system allowed two divers to enter the water, either sitting on the staging under the bell or in the bell with the door open, both divers dressed in ready to go to work.

Once the bell was within 33ft of the working depth, the decent was halted and diver1 went out to work, being tended by diver 2. Once diver 1 was at the work site, then diver 2 would blow all the water out of the bell and then proceed to the work site. Approximately 5 - 10 minutes before allowable bottom time was up, diver 1 would return to the bell, rack up his umbilical, and make ready to bring diver 2 back to the bell.

Both divers at the bell and umbilicals racked up on the staging, one diver would enter the bell remove his hat and hang it on the outside of the door, then assist the other diver into the bell and hang his hat on the outside of the door. The door was then closed, the bell lifted to get a seal on the door, the bell was then recovered to the system, the divers having vented the bell to the first stop pressure on route. The bell locked on and brought up to the transfer pressure. Both divers would lock through to the end chamber and begin decompression, leaving the bell and the first chamber free for the next dive.

The bell on its way to work. 2 divers sitting on the staging

As with all air diving, there was still a standby diver basket system, with the diver dressed in ready to go. But in waters where the visibility was poor, the second Minibell diver would stay at the bell and tend the other diver from the staging. The surface standby diver is required by law, and even when there was only one diver working away from the bell, the standby diver is always dressed in.

This system (although working on a dispensation from the HSE each year) was not governed by the bottom time limitations, as it dispensed with the surface interval, and allowed decompression to be controlled from start to finish.

the system installed on the CONOCO Viking platform. The system was moved three times during the season,
to different jackets on the complex, and completed the season without an incident of decompression
sickness. It's first location on the CONOCO 'A' platform was on the lower deck (spider deck) and for
insurance purposes the whole system had to be rigged to enable it to be winched up to allow an air gap of
around twenty feet between the deck and the underside of the system, quite a feat.

This system not only gave the client 100% more bottom time than conventional air diving methods, but it also gave the diver a much greater safety factor. I was privileged to take out the first Minibell system for Oceantech, and throughout the season, we did not have any problems with decompression sickness. Many visitors came to check out the Minibell and all were impressed, but this did not stop rival diving companies trying their very best to have this system banned.

I went to various seminars along with the management of Oceantech, to explain the workings of the system and the obvious safety advantage to the divers using the system, but the opposition was fierce. Basically it was all down to money, whilst the Minibell was picking up all the air diving work in the Southern sector of the North Sea, the companies using the conventional diving systems were governed by the restrictions laid down by the HSE.

The Minibell continued to work through till the early 90's, being further developed. Adding umbilical wheels on each side of the bell, which allowed both divers to stay on the work site for that little bit longer, and via a switch worn on the harness could operate the wheels to wind the umbilical back to the bell. It is a great pity that this system was not taken up by other diving companies, but I guess money will always be the deciding factor, not safety as it should be.

VJ

Courtesy: Vic Johns, Devon England