How many naval architects a have actually ever climbed into a large enclosed or semi-enclosed modern life boat or raft never mind being involved in a “fill to capacity” lifeboat drill embarkation test.
The IMO Life Saving Appliances (LSA) Code 220.127.116.11 states: “Every passenger ship lifeboat shall be so arranged that it can be boarded by its full complement of persons in not more than 10 minutes from the time the instruction to board is given.” The larger cruise ships will generally be fitted with 150 person capacity lifeboats, the largest allowed by the LSA code. This in essence gives an average of four second for each person to enter and be seated in the lifeboat. Quite understandably the lifeboat embarkation tests will generally be conducted in daylight in good weather conditions and with disciplined volunteers of reasonable health and mobility.
LSA Code 18.104.22.168 states: “No lifeboat shall be approved to accommodate more than 150 persons.” However, the codes do provide procedure for alternative design to demonstrating an equivalent level of safety for lifeboats with capacity beyond 150 persons. The lifeboat and davit manufacturer Schat-Harding has developed a 370-person mega lifeboat and davit system. The Oasis of the Seas cruise ship was the first vessel to be fitted with these new mega lifeboats.
Demonstrating compliance with evacuation requirements through full-scale evacuation exercise is expensive and difficult to organise, and the circumstances bear little resemblance to what would happen in a true emergency driven evacuation.
In a real emergency situation on a cruise ship lifeboat embarkation will of course take longer than the design idea of 10 minutes. A typical cruise contains a fair portion of passengers with impaired mobility. People will generally pass quickly through the doors to enter the enclosed or partially enclosed lifeboats. They will have had plenty of time to observe the doors and many will have watch their fellow passengers pass through, however, when they are actually inside it might well be quite a different matter. Many will be disorientated and stand still, some looking for the best seats, others will be looking for friend or family member to sit next. The rate of seating occupancy slows up progressively as the boat fills and random empty places become much harder to fill.
The current SOLAS rules for lifeboat design assumes an average mass of 75kgs per person on passenger ships and 82.5kgs per person on for cargo ships all wearing lifejackets, that can be seated in a normal position without interfering with the means of propulsion or the operation of any of the lifeboat's equipment with a minimum wide of 430mmm for seating areas.
Anthropometric data confirms that the human species is increasing in both stature and mass across the globe. For many years it has been apparent that the statue of most populations in the developing world is steadily increasing. In 2005 the US Centers for Disease Control in Atlanta quotes a figure of 86.6kg for adult men and 74.5kg for adult women.
Assuming an cruise ship would have a fairly even split between male and female passengers this would give an average of 80.6kgs. UK Civil Aviation Authority upped the weight allowance for offshore oil workers to 98kgs per man and 77kgs per women. ClassNK has already put forward a proposal to the IMO Marine Safety Committee (MSC) to amend the SOLAS regulations to assume that the average mass of 82.5kgs for liferafts.
It is not only the weight of peoples that is important but the people’s size that matters. The UK Health and Safety Executive produced in 2008 an information circular entitled ‘Big Persons in Lifeboats.’ This recommended that the offshore duty holder “select a small group of the largest members of the offshore workforce on the installation, and ask them to strap themselves in position on adjacent seats within the lifeboat, to confirm the ability of the seats and the seat belt/harness to accommodate them.” The International Association of Drilling Contractors has devised a ‘Gulf of Mexico Standard’ seating width of 530mm in place of the IMO minimum.
Evacuation simulation tools mainly dealing with the assembly process, lifeboat embarkation is not explicitly modelled, due mainly to a lack of operational feedback as well as in theoretical and experimental data.
Part of the FIRE EXIT research project funded under the European Union framework programme included a series of test undertaken at the Marine Institute (Marine Institute) of Memorial Universities Offshore Safety and Survival Centre measuring the performance of over 300 individuals through the various stages of the ship abandonment process. Test subjects used four different abandonment devices (davit launched life raft, davit launched lifeboat, inflatable slide and vertical chute).
You may also be interested in the next Design & Operation of Passenger Ships Conference, which is taking place in London on 20 - 21 November 2013.