A Unique Approach to Enviroment Control in a 1000-Foot Commercial Saturation Diving System
Authors: Aaron A.L. 
Published: October 2008

A 1 OOO-foot saturation diving system was designed specifically for installation aboard a semisubmersible drilling vessel. Operational requirements and space restrictions made it necessary to develop modular explosion-proof external environmental control units for the deck chamber complex. These units use a special pumping system to circulate chamber breathing gas. Humidity is controlled without refrigeration equipment, and contaminants and odors are removed by means of regenerable chemicals.

HISTORY OF PROJECT DEVELOPMENT

In March of 1972 Oceaneering International started the construction of a saturation diving system designed to provide support for deep offshore drilling operations in the North Sea. The diving system was to have the capability of observation diving, limited duration ("bounce") diving, and saturation diving to depths of 1000 feet. It was to be entirely explosion proof in accordance with U. S. Coast Guard Class I, Division I, Group D requirements and was designed specifically for installation aboard the SEDCO 702 semisubmersible drilling vessel.

The Oceaneer 1000 diving complex is made up of four major equipment groups. The first group is deck-situated equipment and includes the deck chamber complex (two cylindrical 8-foot diameter vertical decompression chambers and one 7-foot diameter transfer chamber/entrance lock), two environmental control units, two water supply modules, a gas control van, an electrical system van, an air compressor unit, a bell/diver heating unit, a hydraulic power unit and a bell handling system. The second equipment group is made up of the diving bell, the bell umbilical and related equipment. The third group includes the divers' equipment (helmets, breathing gas heaters, suits, etc.). The fourth group is made up of miscellaneous items such as consumables, spare parts and tools.

Design considerations related to drilling vessel space limitations made it necessary to minimize the size of the deck chambers. On the other hand, it was desireable that the living area inside the chambers be maximized for personnel comfort during long-term saturation decompression. For these reasons it was necessary to locate the environmental control units outside of the deck chambers. In addition to affording the occupants more internal space, this configuration would allow ready access for reloading, preventative maintenance and repair. The design also made it possible to locate the electric driving motor outside of the pressurized recirculating environmental gas stream. The disadvantage of the design was that a sealing device had to be found which would allow the external electric motor to drive a recirculation pump situated in the high pressure gas stream. This sealing device had to be heliumleak-proof in a sustained 500 psig differential condition, and had to be virtually maintenance free in the field.

Operation requirements dictated that the deck chambers be capable of operating at different pressures simultaneously. For this reason two separate environmental control units were constructed.