A recent incident has been reported in which there was a failure of both the primary and back up slings of a ‘Frog’ personnel transfer capsule, which was under low load conditions (a single passenger). The personnel capsule with its passenger was dropped on to the deck of the vessel. The occupant received injuries to his back and neck resulting in a medical evacuation.
The Frog sling set comprises a primary and a back-up sling, each constructed of non-rotating steel wire rope. A high visibility sling cover, closed by a Velcro fastening, is fitted, to
- keep both legs of the sling set together; and
- assist both crane driver and deck crews in monitoring the position of the sling set during Frog operations.
Subsequent investigations conducted by the operator indicated that the slings failed due to corrosion. The manufacturer was unable to confirm the age of the sling set. This corrosion may have been accelerated due to the hot and humid tropical operating environment in which the equipment was deployed, causing condensation to collect inside the high visibility cover.
The incident further highlights the importance of adhering to a rigorous inspection and maintenance procedure, particularly regular inspections of sling sets by a competent person, and periodic replacement of sling sets.
The manufacturer has noted the following:
- The lifting sling set’s high visibility cover is closed by means of a Velcro seam, to allow convenient opening for sling inspection. This cover should always be opened to allow a full visual inspection prior to use of the unit. Plastic cable ties or other securing devices which prevent convenient opening of the cover should not be used;
- Users of the Frog sling sets should conduct a one-off inspection to check the condition of the slings and their maintenance and inspection records, in order to ensure that preventative measures are being carried out and any sling sets showing signs of significant deterioration are replaced;
- Frog sling sets should now be replaced every 12 months (the previous recommended interval was up to 24 months);
- The specifications of the standard sling set were changed earlier in 2007 to a more corrosion resistant material;
- Users in tropical environments (or environments which may cause accelerated corrosion) should change their sling sets to the new specification at the earliest opportunity.
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