The following paper about »The Development of Modelling Methods and Interface
Tools Supporting a Risk Based Approach to Fire Safety in Ship Design« by Richard Pawling
et alia has been recently honoured with the GL COMPIT Award 2012
1. Introduction
Recent decades have witnessed a continuous increase in the size and complexity of passenger ships, arising[ds_preview] from the popularity of cruise liners for leisure and holiday purposes, and the transportation efficiency of RoRo passenger ships. However, this trend has not been properly supported at the regulatory level with a rationalised fire safety framework, which would not penalise arrangements falling outside the constraint of past experience and nurtures innovation. The Probabilistic Framework for Onboard Fire Safety Project (»Fireproof«, www.fireproof-project.eu) has set out to change this situation by developing a Risk-based Design (RBD) assessment framework (Vassalos, 2009), at the heart of which lies the holistic performance assessment of the ship with respect to both fire occurrence and the ensuing societal consequences. This paper outlines the basis of the method under development, but primarily concentrates on the software development work involved to provide a demonstration implementation of the framework.
2. The »Fireproof« project
2.1 Background
Analysis of historical accident data for passenger ships has demonstrated that fire and flooding (due to collision and grounding) constitute 90% of accidents where ships had to be abandoned, with fire frequency is some eight times higher than flooding, (Nilsen, 2007). From a regulatory point of view, this evidence conflicts with the growing trend in the industry for more innovative arrangements, where size and complexity dominate the market expectations. That is, SOLAS Ch.II-2 pertaining to fire safety is largely based on past experience and the vulnerability analysis of a selected set of fire scenarios. Steps to improve this situation have been taken with the introduction of Regulation 17 (IMO, 2001) for alternative designs, but a holistic and comprehensive treatment of fire risk has yet to appear. This problem is addressed with the methodology developed in »Fireproof«.
2.2 The probabilistic framework
»Fireproof«was defined as a sequel to the »Safedor« project (www.safedor.org) in the area of fire risk analysis for passenger ships. Its aim is to build on the systems and methods developed within its precursor to develop a regulatory framework capable of ensuring fire safety of novel and existing designs through the application of the RBD methodology. That is, the rational assessment of fire risk, which pertains to events with catastrophic outcomes. In the context of »Fireproof«, the outcome of a fire accident is related to the societal consequen-
ces – the number of fatalities in the exposed passengers and crew onboard a ship.
»The increase in the size and complexity of passenger ships has not been properly supported at the regulatory level with a rationalised fire safety framework«
In line with concurrent developments in damage stability, »Fireproof« will condense its findings in a probabilistic framework in direct analogy to the one in SOLAS, Ch. II-1, which is currently under revision in the »Goalds« project (www.goalds.org). It is the intention of the »Fireproof« consortium to submit the project findings to IMO (FP sub-committee) for discussion and further consideration. Within the probabilistic damaged stability framework, survivability is represented by a subdivision index, which is a summation of the product of probabilities of flooding for a each compartment and the probability of surviving flooding of that compartment. Weighting factors are included to account for the effect of different loading conditions. Similarly the »Fireproof« framework will consider the probabilities of ignition within a given space, and a probability of »fire protection«, a concept that includes detection, suppression and spread. Weighting factors here are to represent space criticality, e.g. fire effluents, occupancy, space topology and proximity to staircases or fire mains.
2.3 Risk formulation
In the RBD methodology, risk is defined as the chance of a loss and for all practical purposes, risk is expressed as the frequency of occurrence of exactly N number of fatalities per ship-year (s-y) (Jasionowski and Vassalos, 2006):
[1]
where
hzi: a loss scenario (a series of events
with catastrophic outcome)
nhz: number of loss scenarios considered
frN: frequency of exactly N fatalities
per s-y
frhz: frequency of occurrence of loss
scenario hzi per s-y
prN: the probability of occurrence of
exactly N fatalities conditional on
the occurrence of hzi
In the context of the current development, care should be taken with respect to the following points, which signify the specific nature of the fire as a physical phenomenon, the compliance with concepts and definition in SOLAS Ch. II-2, and the introduction of new elements in the safety assessment process.
• The element of probability is associated with the ignition and escalation of fire outside the space of origin for each of the 14 types of spaces prescribed in SOLAS. The fire ignition is treated as an event that takes place at any time and in any space onboard without reference to its root causes. It is presented in the form of frequency of occurrence per s-y and SOLAS space type.
• The escalation of fire outside the space of origin is associated with failure to contain, control and suppress the fire by onboard means (mechanical or manual) and through human (passenger or crew) intervention. Fire escalation signifies the exposure of all passengers and crew located in the same fire zone to the fire effluents (poisonous gases, oxygen depletion, heat, and visibility impediment), which could result in injuries and fatalities.
• The consequences in the context of the current development correspond to loss of life, i.e. fatalities, which occur due to exposure to fire effects and delays in the evacuation process. The latter element signifies the importance of the topological arrangement of the accommodation area of passenger ships, the ease of reaching a place of safe refuge, and the blockage of the main escape routes due to fire (i.e. when the fire location is very close to an escape route).
• The fire risk is expressed as the frequency of a number of (statistical) fatalities that could occur due to the fire occurrence in a space per s-y. However, a holistic risk assessment process implies that the total fire risk should correspond to the summation of all risks due to fire occurrences in all spaces onboard.
The collation of the above elements in a single expression results in the following equation:
[2]
where
frN(N): number of exactly
N fatalities per s-y
frign(spacei): frequency of ignition
in spacei per s-y
presc(spacei): probability of fire escalation
outside the space of origin
prN(N
