The UK MAIB analyzed an injury case during trials of marine evacuation system (MES) slides. The investigation highlighted that the MES design concept was to accommodate mass evacuation of passengers wearing normal clothing, but not survival suits.
The incident
A vessel was secured alongside in port undergoing scheduled maintenance. Part of the work included deployment of the marine evacuation system (MES) in the presence of an MCA surveyor, to satisfy a statutory certification requirement. In addition to the MCA survey, the vessel owners had arranged to carry out evacuation trials to evaluate the performance of a particular survival suit. The supplementary trials were hastily planned once the opportunity had been identified, and were intended to be carried out by shore staff.
The MES slide included two individual tracks that were open to the elements and separated by a non-rigid fabric partition. The slide inflation tubes and the centre partition were of dissimilar materials with differing coefficients of friction. Ship’s staff had expressed concerns relating to the trial as previous descents of the MES slide by personnel wearing survival suits had resulted in injuries.
This was believed to have been due to the lack of friction between the suit and the slide, leading to high speed descents and subsequent impact injuries as individuals hit the MES raft inflation cylinders. It was therefore agreed to use shock (coir) mats to mitigate against this risk as the trial participants entered the raft.
Environmental conditions at the time of the trial were light winds and dry. However, there had been an early morning frost followed by light rain, which had left residual moisture on the surface of the slide.
The MES was deployed to the satisfaction of the MCA surveyor and seven test subjects descended wearing normal working clothes using their feet and elbows to control their speed. One of the seven suffered a minor knee injury as he entered the raft, following which additional coir matting was added. All the test subjects reported that it was difficult to control the speed of descent.
The trial then moved to the second phase, with test subjects dressed in survival suits. Two subjects descended without incident, although they found they had very little control over speed due to the lack of friction. They also found that trying to control their speed by forcing feet and elbows into the inflation tubes and central divider caused them to twist as they were descending.
As the third test subject began his descent, pressure applied through one elbow, lifted him up, further reducing friction and causing a rapid increase in speed. As the subject entered the raft his feet became entangled in an overlap between the coir mats, causing him to flip forward and fall face-down into the raft. The force of his body turning against his trapped feet resulted in a fractured ankle. The trial was abandoned and the injured person transported to a local hospital.
Lessons learned
- The SOLAS regulations for an MES with an inclined slide state that it shall be installed such that the angle of the slide to the horizontal is within the range 30 to 35 degrees when the vessel is upright. On the day of this accident, the slide angle was measured between 41 and 43 degrees. The installation of the MES did not fully comply with SOLAS requirements as the vessel’s high freeboard resulted in the slide angle being too steep once the unit had been deployed.
- The MES design concept was to accommodate mass evacuation of passengers wearing normal clothing. While ‘normal clothing’ will have varying coefficients of friction, the survival suits being tested were known to have a low coefficient of friction. The late decision by the owners to supplement the statutory deployment with an in-house trial did not allow sufficient time to fully assess all of the hazards involved. Furthermore, they did not fully take into account the experiences of ship’s staff relating to previous accidents.
- The use of coir mats to mitigate the risk of injury was an unsatisfactory control measure that would have been unnecessary had the MES been deployed as required and used as designed.
