ABSTRACT

The operation of deep diving bell systems (SDC's) onboard today's offshore drilling vessels has become a routine exploration tool. Virtually all diving support contracts specify system depth capability to at least 600 feet and, in many cases, to one thousand feet.

With well over one hundred such systems currently operating in the waters of the world, the inevitability of emergency situations that may require diver abandonment of the SDC is an alarming spectre. Entanglement of the SDC, toxic contamination of the SDC atmosphere and entrapment by structural failure are just' a few of the potential hazards that could cause an emergency abandonment situation or a prolonged bottom stay awaiting rescue.

This paper examines some DĀ£ the procedures programmed for use during a bottom emergency, the viability of commonly accepted but little used safeguards and briefly discusses the specific problems of recovering a disabled SDC or having the occupants leave an irretrievable SDC and ascend to the surface.

DIVING BELL ESCAPE SYSTEMS: SOME OBSERVATIONS AND TEST RESULTS

Under normal operations, the submersible diving chamber (SDC) or diving bell is lowered and raised from the work platform by means of a strength wire. Few, if any, of the SDC's operating around the world have any means to effect a controlled surfacing should the strength line become severed or otherwise detached or the SDC become entangled on the bottom. There are. a number of possible situations that could prevent the SDC from being raised to the surface station in the usual manner. A detailed examination of these potential situations may cause some reflection on the adequacy of existing emergency measures and the possible consideration of modifications and/or the formulation of additional measures.

The recent, well publicized tragedy involving the submersible "Sea Link" is a graphic illustration of the type of situation which may be encountered in the petroleum exploration support role. The SDC's usually operate under conditions where speedy outside assistance, in the event of an emergency, is logistically impossible and reliance must be placed on whatever self-contained measures are available or can be programmed.

There are at least five major factors to consider in programming emergency procedures:

  • Nature of the problem (e.g. is the SDC entrapped?

  • Depth of water (e.g. possible to use standby diver?

  • Umbilical condition (e.g. severed or intact?

  • Load line condition (e.g. severed or intact?

  • SDC pressure condition (e.g. pressurized or unpressurized?

If one fixed case is assumed for question "A" - the SDC is entrapped - the critical examination of the possible combinations of other factors will require a detailed analysis of at least sixteen possible situations and the calculation of the most effective emergency procedures to use in each case.

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