Cargo hold bulkhead failure Giga 2

Summary

Early on 5 November 1996, the 140,086 tonnes deadweight Malaysian flag bulk carrier Giga 2 was nearing completion of discharge of a cargo of iron ore at No. 2 discharge berth, Port Kembla. Due to the vessel's light condition, the unloader could not be positioned over No. 1 hold, to remove the 1080 tonnes of cargo remaining in that particular hold. At the suggestion of the shift supervisor, ballast was pumped into No. 4 hold, which was permissible under the vessel's operations manual. Pumping of ballast into No. 4 hold commenced at 0530.

After the lunch break, two terminal workers descended into No. 5 hold, where the unloader was working, to clear iron ore from around the bottom of the forward spiral access ladder. The spiral ladder terminated at the top of the lower stool, six metres above the tank top. They had just completed this task and were about to climb the ladder when the bulkhead to the starboard side of the centre line, between No. 5 hold and the ballasted No. 4 hold, collapsed. Both workers were immediately engulfed by the deluge and, although one was able to haul himself clear, the other remained submerged.

The shift supervisor was working in his office ashore and, alerted by calls over the radio from the Hatchman, dashed on board and immediately descended the ladder into No. 5 hold. Up to his neck in the swirling water and guided by the Hatchman above, he was able to grab hold of the submerged worker. Assisted by another terminal worker, who had followed him into the hold, he was able to haul the unconscious and apparently lifeless worker clear of the water. The shift supervisor then administered cardio-pulmonary resuscitation (CPR), which was successful in restoring breathing in the worker. Very shortly afterwards an ambulance officer arrived on the scene and administered oxygen, before the worker was lifted from the hold and taken to hospital.

To identify the circumstances which led to the collapse of the bulkhead, the ship's procedures and documentation were examined. Also, a detailed examination of the bulkhead between holds 4 and 5 was undertaken, which included a metallurgical examination and a finite element analysis of the failed bulkhead.

Conclusions

These conclusions identify the different factors contributing to the collapse of the starboard side of the bulkhead at frame 193 aboard Giga 2 on 5 November 1996 and should not be read as apportioning liability or blame to any particular individual or organisation.

1. No. 4 hold was overfilled beyond its maximum allowable depth of water of 14 m.
2. The Mate relied totally on the remote gauging system for filling No. 4 hold, without physically checking on its accuracy.
3. An inaccurate reading was displayed in the ballast control room by the remote gauging system.
4. As the "high level" alarm was not independent of the gauging system, there were no effective defences, other than physical/visual checks, to ensure that the depth of water in No. 4 hold did not exceed the safe level.
5. There was no clear explanation as to the critical nature of the limit placed on the depth of ballast water in No. 4 hold. This was compounded by a lack of clear operating instructions, either in the native language of the ship's personnel or the working language of the ship.
6. The increase in depth of water from 14 m to 18 m resulted in more than doubling the maximum stresses within the bulkhead structure.
7. The specified size of the welds joining the lower stool shelf plate to the structure beneath it was insufficient to withstand the membrane forces developed at the bottom of the bulkhead with the excess water level in the hold.
8. The design and spacing of the webs within the lower stool, in relation to the corrugations of the bulkhead (and depending on the contribution made by the shedder plates), can result in high stress concentrations being formed within the area of failure at the stool shelf plate.
9. Buckling of the bulkhead, due to extensive wastage by corrosion, if not already started at the moment of failure of the welds, was imminent.
10. Extensive corrosion of the webs in the upper stool resulted in the bulkhead and the stool bottom plate being virtually detached from the upper stool. This would have facilitated detachment of the bulkhead along its upper edge during the failure but did not contribute to initiation of the collapse.
11. The quality of structural surveys of this vessel, over a period of time, was not effective in addressing the problem of substantial corrosion as defined and detailed in the International Association of Classification Societies requirements for enhanced surveys, or as recommended in the International Maritime Organisation's Assembly Resolution A.744(18).

It is further considered that:

1. detection of any deficiencies in the structure of the bulkhead was beyond the scope of Port State control inspections; and
2. based on the system for assessing applications for single voyage permits, there was no reason to refuse the application.