Abstract
This article thoroughly reviews the state-of-the-art methods for setting ALARP upper border as a straight line in logarithmic graph, which is the common practice in the risk assessments of nuclear, chemical plants and maritime facilities. It also reviews methods for setting ALARP upper border based on economic importance of a considered ship type. As a result, inconsistency related to ALARP upper border has been identified and new methods to resolve such inconsistency are developed. Here, firstly a method for approximating FN diagrams of existing major ship types is proposed and it is applied to ship types which consist of ships above 100 gross tonnage. After that the approximated FN diagrams were checked by goodness-of-fit test by 5 % significance level, and it was validated that those approximated FN diagrams well express corresponding FN diagrams made from IHSF casualty and ship databases. This method can extrapolate FN diagrams made from those databases to the area of severer accidents with more fatalities, which have not been occurred yet, rationally. Secondly, problems that accompany with an existing method for setting ALARP upper border are discussed and methods for resolving the problems using the approximated FN diagrams are proposed. The methods can set ALARP upper border keeping consistency of ALARP upper border between individual risk and FN diagram. Lastly, the new method for safety analysis of ships using approximated FN diagrams of major ship types is introduced. The method is used in order to find ships’ groups which should be considered preferentially. The method for approximating FN diagrams and the method for setting ALARP upper border proposed here is so general that they can be applied to risk analysis of the fields which have a lot of accident records like maritime field, such as aviation or automotive fields.
Highlights
Risk is an index to evaluate a safety level of a system under consideration
In order that allowance ratio between ALARP upper borders and approximated FN diagrams becomes smaller as numbers of fatalities are getting larger, values of which can be expressed by Eq 24, whose components are frequency of accidents and number of fatalities expressed by Eq 23
The approximated FN diagrams made here can be used as FN diagrams of existing major ship types, and they will be used in rule-making process or risk-based design effectively
Summary
Risk is an index to evaluate a safety level of a system under consideration. It is usually defined as a product of frequency and severity of consequences caused by an accident. Risk of sea pollution and property risk are major types of ship related risk. These types of risk are common to nuclear or chemical plants and aircraft, etc. The unit of individual risk is [1/year], etc This risk expression makes it possible to compare levels of safety between engineering systems, and industries because this expression is widely used in many industries.
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