Published
article:Liwång, H.
(2016). Conditions for risk based ship survivability approach: a study on the
analysis of fire risk. Naval Engineers Journal, 128(3), 31-45.
Some
comments from the article
The purpose
for introducing a risk-based approach is to identify risks in the intended
operation of the ship and use this information to guide the concept development
and ship design using a risk-based ship design approach. The uncertainty in the
design decision making is generally high when novel concepts are developed.
Therefore, a rational ship design support process is necessary to avoid
erroneous assumptions that affect design choices. Risk analysis is a knowledge model
that may reduce this uncertainty. Based on this need, the proposed analysis
models are in this paper used to identify critical aspects and gaps in the
analysis process, specifically for naval ships.
Risk
controls must be analyzed with respect to susceptibility, vulnerability and
recoverability; the total effect of these aspects must be understood to
evaluate survivability. The fire risk cannot be analyzed without a general
analysis of a ship’s susceptibility and vulnerability with respect to relevant
threats, which indicates that the analysis depends on relevant multiple operational
scenarios.
Physical
descriptions of fire depend on the ship specifications, and for the same
operational scenario, the ship design concept will vary due to differences in
the ship tactics, susceptibility and vulnerability. The example in this paper
demonstrates that the ignition frequency for weapon-ignited fires depends on
the location of the compartment; this is not the case for accidental fires.
Different design concepts will also require different passive and active fire
protection depending on the differences in the design and how it is manned. For
example, if an FRP concept is considered, the combustible nature of FRPs can
contribute to the fire in extreme fires; in other cases, with higher expected
frequencies, the thermal insulation of FRP will yield a smaller fire zone and
contribute to survivability.
The
critical systems must be identified to analyze the ship kill levels. These
critical components and systems depend on the ship design and assumed tasks after
a hit (often described as the ship survivability levels). Typical critical
systems include the propulsion system and power supply.
The
importance of firefighting on naval ships is highlighted in the study which
show that firefighting is the most important aspect for reducing the
probability of catastrophic consequences from complicated ignition cases because
the built-in protection is insufficient for stopping the fire escalation. The
reaction times and effectiveness with respect to firefighting onboard naval
vessels are difficult to compare with other firefighting conditions thanks to
extensive training, a high level of readiness, high number of crew members relative
to the ship size and good firefighting equipment availability.
Certain
problems have been raised for risk-based approaches, especially for defining
the scenario, such as limited research and perceptions. However, these problems
are consistent among most analysis approaches, but heavy use of complicated
tools may hide these aspects and make validation more complicated. Further, uncertainties
are particularly challenging, especially for analyzing antagonistic threats. On
the other hand, a probabilistic approach offers a framework that is consistent
from theory to the first principle tools, which has been found to improve the
decision-making process when selecting among candidate survivability design
principles.
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