Page 44 - Practical Design Ships and Floating Structures

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arrangements to insure tanks will not be over-pressurized. There are also safety concerns associated
with thejow through method in that it may be necessary to remove manhole covers or butterworth
openings to assure sufficient venting. This practice is labor intensive, and the overflow on deck is
prone to icing in cold environments. The safety concerns associated with Ballast Water Exchange is
representative of a case where regulations made to improve safety in one area - protection of the
marine environment, can possibly adversely affect safety in another area - structural safety.

11 FUTURE DIRECTIONS IN STRUCTURAL SAFETY

Looking back at developments in ship structural safety, one can conclude that structural safety has
been largely reactive, rather than pro-active. In some cases this is necessary because the types of
problems encountered were new and unexpected, such as the fatigue problems in VLCCs. Once the
causes of the problems were identified, appropriate changes were made to avoid those problems,
thereby increasing structural safety. Factors not relating at all to structural safety, such as the sudden
increase in size and number of tankers, led to an increase in the number of accidents and much larger
oil spills when an accident occurred. That led to increased awareness of tanker safety and
environmental protection that resulted in new regulations intended to reduce the frequency of
accidents and reduce their consequences. Those changes also produced an improvement in structural
safety.

11.1 Risk-Based Safety Standards
The definition of "risk" that is commonly used today is expressed mathematically as frequency (or
probability of occurrence) times consequence. Thus efforts to reduce the frequency of accidents and
reduce their consequence can be considered as efforts to reduce risk. Conversely, if safety is improved,
one can assume that risk is reduced. Certainly, structural safety is not the only aspect of shipping
which relates to risk, and in fact I believe it is a smaller part of the risk equation than many other
factors such as human error and operational issues. However, the concept of risk assessment and risk
management is something that enables us engineers to consider structural safety in the context of the
whole safety equation. Classification societies, regulatory bodies, and ship owners are now attempting
to place safety in the context of overall risk. This is a new way of looking at structural safety, and one
which I am sure will be both challenging and rewarding. It will be a gradual evolution in which new
technology, new methods and greater understanding of risk concepts, coupled with experience and
knowledge, will be used to refine and improve future standards of safety.