CRUISESHIP TECHNOLOGY
IN the first of two articles, S Deere, E R Galea, P Lawrence, L Filippidis and S Gwynne, of the University of Greenwich, UK highlight the problems with the current IMO response time distribution covering evacuation from large passenger ships. In next month’s issue, the same authors will present their proposed solution
H
OWEVER remote the possibility or difficult the task, passenger ship
evacuations do occur and they are usually the result of fire, collision, equipment failure, grounding or mal-operation. To arrive at coherent requirements for
passenger evacuation from passenger ships, the International Maritime Organization is re-evaluating its thinking on response time distribution among passengers in the case of evacuation from large passenger ships. In recognition of the development of sophisticated evacuation simulation techniques the IMO developed a set of Interim Guidelines that set out the standards on how evacuation simulation should be undertaken for certification applications. These guidelines define two benchmark scenarios (along with two variants) that must be simulated as part of the certification process. These are ‘night’ and ‘day’ scenarios, establishing a baseline performance for the vessel and crew allowing comparison with both the set target time and alternative designs. The scenarios only address the mustering or assembly phase of the evacuation and involve conditions of dead calm and do not explicitly take into consideration the impact of fire. To allow for these omissions a safety factor is added to the predicted muster time. The resulting analysis should allow
identification of areas of congestion that develop during an evacuation and demonstrate that escape arrangements are sufficiently flexible to account for the loss of particular parts of the evacuation system. The difference between the ‘night’ and ‘day’ scenarios consists of the starting locations of passengers and the simulated passenger response time distribution exhibited by the passengers. During an emergency, passengers will not
respond immediately to the call to assemble. Even when an individual decides to react to the call to evacuate, their situation often prohibits immediate flight. Individuals may decide to perform a number of tasks before actually evacuating, such as collecting belongings, reuniting family members, complete a financial transaction, finish a meal etc. Not everyone will react at the same time. As each passenger will have a unique response time it is necessary to define a response time distribution to represent this inherent variation. If the response time distribution is set to
zero or near zero, then all the passengers will react (almost) immediately and so considerable unrealistic congestion is likely to develop in many locations. If the response time
THE NAVAL ARCHITECT FEBRUARY 2007
Time to respond on ship evacuation Deck
6 7 8 9
10 Total
120 91 -
211
75 50 24
Fire Zone 1 Fire Zone 2 Fire Zone3 - -
210 225 584
Table 1 – Distribution of passengers for day Scenarios.
175 200 130 - -
505
Total 250 250 274 301 225
1300
Figure 1 – The three response time distributions, IMO (RTD1), modified retail (RTD3) and modified library (RTD4).
distribution is too wide then there will be a considerable gap between the starting times of passengers and so potential choke points in the geometry will not be detected. Furthermore, as the process is inherently non-linear, it is not possible simply to set a zero response time distribution and then apply a scaling factor to produce an estimation of the total evacuation time. Understanding and quantifying the response time is a key component of the entire evacuation process. In building applications, occupant
response time can in fact be longer than the actual evacuation travel time. As a result considerable effort has been expended in the building industry in attempts to quantify and understand occupant response time for particular situations. Unfortunately little or no data relating to passenger response time in maritime environments exists. Due to a lack of data, the passenger
response time distribution in MSC 1033 has been arbitrarily set to a uniform random distribution of 210–390 seconds with a mean of 300 seconds for the 'day' case scenario and 420–780 seconds with a mean of 600 seconds for the 'night' case scenario. This involves two key assumptions. The first
is that the response time distribution assumes the form of a random uniform distribution. Evidence from studies in the building industry suggests that this is not the case with response time distributions typically following a skewed or log-normal distribution. The second key assumption concerns the actual range of response times. The range
of response times adopted in the day case is 210 to 390 seconds. This range of numbers is not actually based on real measurements but represents values derived by committee. Evidence from the building industry suggests that typical response times in day situations range from 4 to 110 seconds in retail environments, 8 to 200 seconds in university library environments, 30 to 66 seconds in hospital waiting room applications, etc. The importance of the response time
distribution can be demonstrated by applying the MSC 1033 guidelines to a hypothetical vessel using the ship evacuation software maritimeEXODUS to compare simulation results generated using the arbitrary MSC 1033 response time distribution with what is arguably more plausible response time distributions generated from the building industry. A large hypothetical passenger ship consisting
of ten decks divided into three vertical fire zones has been defined within maritimeEXODUS using CAD drawings. The vessel has a capacity of 1734 passengers and a maximum berthing capacity of 950 passengers. Only the top five decks (Decks 6-10) are occupied by passengers. The assembly areas are located on Deck 8 and
there are two for each fire zone. The assembly deck also contains six LSA’s (Life Saving Appliances), each having a capacity of 400 passengers. Each deck of the first fire zone is serviced by
four staircases located within the far corner of the fire zone connecting each deck. The second fire zone possesses a single staircase centrally located within the fire zone. All the stairs are similar in construction and
are narrow, capable of allowing only a single lane of passengers to use the stairs. The only exception is the dual lane staircase in fire zone 2. Passenger cabins are located on both decks 6 and 7 in fire zones 1 and 2 and both decks 9 and 10 in fire zone 3.
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