Free-fall drill danger
Standing unsecured in a lifeboat is one of the many concerns raised by Canada’s Transportation Safety Board (TSB) following its investigation of a bulk-carrier accident.
Sadly, the occurrence of accidents during lifeboat drills is all too frequent. One recent case involving two crew members in a free-fall lifeboat drill aboard the 78,819-tonne deadweight bulker Blue Bosphorus resulted in serious injury requiring hospital transfer.
The 25-seat lifeboat was stowed aft about 6m above the vessel’s main deck on a raised launching structure. It is secured to the launching platform by a release hook and can be free-fall launched by activating a release handle inside the lifeboat. It can also be lowered and retrieved using a davit during drills and tests.
Before lowering the lifeboat using the davit, it must first be attached to the davit using four wire rope slings. The lower end of each sling is attached to the lifeboat with a shackle while the upper end is permanently coupled to an oval ring; the oval ring is then connected to a hook on the spreader bar.
The slings in use at the time consisted of wire ropes with an eye at either end. The eye was formed by threading the wire rope around a thimble and then securing the wire in place using a crimp sleeve.
Stern section of Blue Bosporus showing its lifeboat launching platform (Credit: TSB)
On 1st December 2020 a lifeboat drill was planned during which the lifeboat was to be lowered to the water using the davit and taken for a test run.
The drill entailed the Third Officer and a seaman entering the lifeboat – the former operating the release gear while the seaman watched. Both remained standing as had happened in previous drills. When the release hook was unlatched, the lifeboat slid forward approximately 25cm. Suddenly the aft starboard sling failed, followed by the two forward slings. The bracket holding the aft port sling onto the lifeboat broke off as well. The lifeboat then fell about 14m into the water.
The launch crew had unknowingly deviated from the instructions outlined in the manufacturer’s manual when they placed both the oval ring and the eye of the aft starboard sling onto the starboard hook. This caused the aft starboard sling to be shorter than the others, and when the lifeboat was released, the shock load concentrated entirely on it. It was held together by a weakened crimp sleeve which, in combination with the concentrated load, caused the sling to fail. The load then shifted to the other slings, causing the crimp sleeves on the two forward slings to also fail. It then shifted to the remaining aft port sling and its sleeve which, although cracked, remained intact. However, the bolts and the aft port bracket could not withstand the load and were pulled off the lifeboat.
Moored at a local terminal in Vancouver, BC (Credit: TSB)
The TSB laboratory examined the slings and recovered crimp sleeves, as well as the brackets and bolts used to secure the aft slings to the lifeboat. The four wire ropes of the slings were in good condition, with no broken wires, wear or corrosion observed. A close visual examination identified that the crimp sleeves on the aft port sling had small cracks, the largest of which was approximately 1cm in length. Similar cracks were visible on the broken portion of the aft starboard crimp sleeve.
TSB investigators taking pertinent measurements of the occurrence lifeboat (Credit: TSB)
The laboratory also examined the inner fracture surface of the aft starboard crimp sleeve. Over 90% of the fracture surface on the upper side of the sleeve had an aged, corroded appearance. The surface on the lower side of the crimp sleeve also had an aged, corroded appearance. The examination indicated that the crimp sleeve failure was due to intergranular stress-corrosion cracking.
Findings and outcome
The TSB investigation report noted:
- Without a complete procedure for conducting a drill that involved launching the lifeboat using the davit, the crew had developed an informal practice that did not address the risk of standing unsecured in the lifeboat.
- In the absence of any international guidance requiring free-fall lifeboat slings to be verified periodically, inspected before use, and marked with a safe working load, there is a risk that this critical equipment will be overlooked during inspections or its safe limits will be exceeded, leading to an accident.
- There was no additional restraining device in use to protect the lifeboat from falling when the slings failed.
The vessel’s owner took immediate remedial action by replacing the failed slings with new tested ones and circulating information to its other vessels as to the correct procedures for lifeboat drills. It has also established that the slings and wires associated with the lifeboats be replaced during the five-year dynamic load testing regardless of their condition; and established an annual safe working test of the slings by an authorised lifeboat technician.
Finally, the TSB report also identified several other occurrences involving lifeboat launching appliances and is aware of others that have occurred internationally.
Read the full TSB safety investigation report into the accidental release of a free-fall lifeboat from Blue Bosphorus.
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John Barnes is a journalist and author and former editor of Marine Engineers Review.