Maritime University of Szczecin
Akademia Morska w Szczecinie
2008, 13(85) pp. 33‐39 2008, 13(85) s. 33‐39
Proposed approach to stability requirements based on goal
determination and risk analysis
Propozycja podejścia do wymagań stateczności opartego
na określeniu celu i analizie ryzyka
Lech Kobyliński
Fundacja Bezpieczeństwa Żeglugi i Ochrony Środowiska 80-278 Gdańsk, ul. Chrzanowskiego 36, tel. 058 341 59 19 e-mail: lechk@portilawa.com
Key words: ship stability, risk analysis, human factor Abstract
The paper describes the present state of the regulations concerning ship stability and it has been concluded that stability criteria including design requirements are insufficient for assuring safety. The main cause of the majority of stability casualties (about 80%) are operational factors that are related to human factor. The au-thor suggests applying a risk analysis adopting a holistic approach to stability safety as an alternative of the future stability requirements currently under development. This approach fits into the concept of goal-oriented approach to safety that is now recommended by the Marine Safety Committee. The author discusses also how human errors could be dealt with in risk analysis and he provides an example of risk contribution tree based on a casualty record.
Słowa kluczowe: stateczność statku, analiza ryzyka, czynnik ludzki Abstrakt
W artykule przedstawiono obecny stan w zakresie przepisów stateczności statku i stwierdzono, że projekto-wane wymagania obejmujące kryteria stateczności są niewystarczające dla zapewnienia bezpieczeństwa. Główną przyczyną większości wypadków statecznościowych (około 80%) są czynniki operacyjne związane bezpośrednio z czynnikiem ludzkim. Autor proponuje zastosowanie analizy ryzyka, przyjmując podejście ho-listyczne do bezpieczeństwa statecznościowego jako podejścia alternatywnego do opracowywanych obecnie przyszłych wymagań statecznościowych. Podejście to jest zgodne z lansowaną przez Komitet Bezpieczeń-stwa Morskiego IMO koncepcją podejścia opartego na „określeniu celu”. Autor omawia także sposób, w jaki czynnik ludzki – błędy operatora – mogą być uwzględniane w analizie ryzyka.
Introduction
Safety of a ship against capsizing at sea strongly depends on the way it is operated in the broad sense. Operation influences its behaviour at sea that depends also on external conditions, design charac-teristics and cargo distribution. The task of operator consists in taking proper decisions that assure safety. In order to assure safety against capsizing stability criteria have been developed.
Existing stability criteria applicable to all ships of 24 m in length and above are included in the International Code on Intact Stability, 2008. This
Code comprises a revised version of the Intact Sta-bility Code adopted originally as a recommendation in 1993 by IMO resolution A.749(18).
The task of revision of the Intact Stability Code was completed by the SLF Subcommittee at its 50th
session in 2007. The Code is now divided into two parts, the first of which, comprising basic stability criteria, will be made compulsory in 2009 by the reference in the SOLAS Convention, the other will remain as recommendation. With this decision, the first stage of work towards improved stability crite-ria has been completed. But from the point of view of ship safety this is not the final solution. From
time to time, stability casualties happen in spite of the fact that ships meet all IMO criteria. The exist-ing criteria may be also not applicable to some types of modern ships incorporating novel design features. There is no previous experience in relation to safety and stability of those ships and satisfying existing criteria may not assure required level of safety. Because of this, Maritime Safety Committee of IMO has recently included in its work pro-gramme the development of future improved crite-ria, mainly intended for ships incorporating novel features.
Existing criteria are, however, of prescriptive character and are virtually design-oriented. They are intended to be applied during the design stage of a ship. The future-improved stability criteria that are now under consideration by IMO SLF Sub-committee will certainly bear the same character. However, even the preliminary analysis of stability casualties shows that design features of the ship are not the most important nor are they the most often cause of casualty. Casualty – it will be in the fol-lowing called LOSA (loss of stability accident) [1], is usually the result of a sequence of events that involve environmental conditions, ship loading condition, ship handling aspects and human factor in general. Therefore, the author proposes to apply, instead or on top of prescriptive design-oriented criteria and goal-oriented risk analysis, at least when designing ships incorporating novel features, large ships or ships carrying great number of pas-sengers or dangerous cargo.
Risk analysis allows to take into consideration operational factors including human related factors, which are the main cause of stability accidents in a great majority of cases.
Prescriptive criteria, risk analysis and goal-oriented criteria
The essence of prescriptive criteria consists of specification of critical values of some stability parameters. Prescriptive regulations have many advantages. They are formulated in a simple lan-guage, which is easily understood by everybody, they are easy in application, they also make check-ing adherence to the requirements easy. The main shortcoming of prescriptive regulations is that they are bounding designers and that they do not allow introduction of novel design solutions. They also can not take into account operational aspects in a proper way. Usually they were amended after serious casualties happened. The risk involved in the application of prescriptive regulations is not known.
At the opposite of the prescriptive regulations, there is a risk-based approach. In this approach, the regulations do not require meeting certain specific measures, but they are based on assessment of the risk involved that may or may not be accepted. The advantages of the risk-based approach are obvious. They give the designer a free hand to develop new solutions, they actually allow taking optimal deci-sions from the point of view of economy and safety, and the risk to the public and to the envi-ronment is assessed and accepted. The risk-based approach allows taking into account all operational aspects including human factor.
The most recent concept of safety regulations is a goal-based approach. Goal-based regulations do not specify the means of achieving compliance but set goals that allow alternative ways of achieving compliance [2]. The goal-based approach is a con-cept that was introduced in IMO work at 89th
ses-sion of the Maritime Safety Committee. Goal-based standards are for some time considered at IMO and appraised by some authors [3], and they were intro-duced in some areas, albeit not in the systematic manner. Marine Safety Committee commenced in 2004 its work on goal-based standards in relation to ship construction adopting five-tier system (table 1).
Table 1. Five-tier system for goal-based requirements Tabela 1. Pięciowarstwowy system wymogów wynikających z zadania
Tier I Goals
Tier II Functional requirements
Tier III Verification criteria of compliance
Tier IV Technical procedures and guidelines, classification rules and industry standards
Tier V Codes of practice and safety and quality systems for shipbuilding, ship operation, maintenance, training etc.
The concept of the goal-based standard that in-cludes holistic approach involving risk analysis is an alternative to prescriptive standards widely used at present in regulatory work. IMO MSC committee has agreed on the following tier I goals to be met in order to build and operate safe and environmentally friendly ships: “Ships are to be designed and con-structed for a specific design life to be safe and environmentally friendly, when properly operated and maintained under specified operating and envi-ronmental conditions, in intact and specified dam-age conditions, throughout their life”.
Holistic and system approach to safety and stability
As mentioned above, existing criteria are design criteria intended to be applied during the design stage of a ship. However, even the preliminary analysis of stability casualties shows that design features of the ship are not the most important nor are they the most often cause of casualty.
Ship stability system is rather complicated. However, in most cases it could be considered as consisting of four basic elements: ship, environ-ment, cargo and operation [4]. The Venn diagram in this figure stresses strong interactions between the four elements. The use of the system approach to stability criteria had been proposed by the author quite a long time ago and it was partly applied in development of the Intact Stability Code [5], but in general, until this day, stability requirements re-main basically design oriented.
Analysis of LOSA casualties reveals that the causes of casualty may be attributed to [6, 7]:
– functional aspects resulting from reliability characteristics of the technical system, and therefore stability characteristics of the ship; – operational aspects resulting from action of the
personnel handling the system, and therefore crew members but also ship management, port authorities, marine administration and owners of company organisation;
– external causes resulting from factors independ-ent from designers, builders and operators of the technical system, and therefore ship environ-ment and climatology;
– cargo related aspect resulting from characteris-tics of cargo and its way of transporting.
In order to achieve sufficient level of safety with respect to stability, all elements creating stability system have to be taken into account. Taking into account the fact that less than 20% of all casualties are caused by faulty or bad design of the ship. The existing safety requirements that refer mainly to design features of the ship can not ensure sufficient level of safety, in particular with regard to ships having novel design features.
Risk analysis with application to stability It seems that there is some consensus on the need to apply holistic and risk-based approach to safety of ships at sea. The Marine Safety Commit-tee of IMO recommended this approach as Formal Safety Assessment (FSA) [8]. The possibilities to use this approach in the rule-making process are still under investigation and rather few trial
applica-tions of FSA have been attempted. This in particu-lar applies to stability problems, intact or damage, and existing IMO rules on stability, which do not include possibility to apply such methods. Few partial applications of risk analysis to stability prob-lems were published [7, 9, 10]. The risk approach is inherently involved in the total ship safety concept strategy proposed by Vassalos [3]. The author in-vestigated possibilities of application of the FSA methodology to intact stability criteria in several papers [1, 11].
First of all, hazards posed by seaway, as men-tioned above, are not the only ones. LOSA casualty is usually the end result of a sequence of events where various hazards play an important part. Fur-thermore, ship's behaviour in a seaway strongly depends on ship operation and in particular on deci-sions taken by the master in dangerous situations. There is no way to take account of those decisions in the design process of the ship. The author sees the only possibility to assure safety by applying risk analysis.
Risk-based approach according to IMO recom-mendation is formalized and includes the following steps:
1. Identification of hazards 2. Risk assessment 3. Risk control options 4. Cost-benefit assessment
5. Recommendations for decision-making It is rather obvious that application of FSA methodology is a tedious and time-consuming task, but in principle it is feasible. It would be not practi-cal to apply this method to conventional ships that are reasonably safe when conforming to the current IMO standards, but it could be effectively applied to important and large ships and ships incorporating non-conventional design features.
Table 2. Methods of safety assurance Tabela 2. Metody zapewnienia bezpieczeństwa
Ships Method of stability safety assessment Conventional, not
sophisticated Prescriptive criteria as in the IS Code Novel types, large
sophisticated ships
Risk analysis under the provision allowing application of alternative means of assuring safety
FSA may, therefore, be recommended as an al-ternative to existing prescriptive criteria subject to the discretion of the Maritime Administrations in-volved. This idea is presented in the table 2 and the general procedure for application of system and risk approach is shown in figure 1.
SHIP SAFETY SYSTEM STABILITY Generic ship and ship
operation model ANALYSIS
LEVEL Hazard identification Capsizing scenarios Hazard probabilities Risk assessment
Risk not accepted Risk accepted SYSTEM SUBSYSTEM ACCEPTANCE LEVEL Risk control options DESCRIPTION LEVEL
Fig. 1. General procedure of system and risk approach Rys. 1. Ogólna procedura podejścia do systemu i ryzyka
The role of operational aspects and human factor
From the operational point of view the most im-portant factor is human factor. Human and organ-isational errors (HOE), according to some authors, are responsible for about 80% of all accidents at sea [12], other sources definitely state that this percent-age is between 75% and 80% [13]. Analysis of the P&I Club [14] reveals that HOE are the main cause of 62% of all marine claims. Therefore, it may be concluded that operational aspects are the most important in assuring safety. Other data on the same subject:
According to the US Transportation Safety Board:
57% of all accidents at sea are caused by wrong organization of operation and er-rors of the crew members,
10% by technical errors of pilots,
33% by mechanical problems, weather and other factors.
According to the Swedish Marine Administration
71% of accidents result from errors of crew members and lack of understanding, 10% from lack of knowledge and training, 19% from other factors.
Figure 2 shows schematic classification of the influence of human factor according to Payer [15].
Accident
ENVIRONMENT HUMAN FACTOR 80%
DESIGNING CONSTRUCTION OPERATION
CULTURE HUMAN ERROR
ORGANIZATION SYSTEM
Fig. 2. Classification of human factor influences [15] Rys. 2. Klasyfikacja wpływów czynnika ludzkiego [15]
As may be seen from the above figure human factor in operation of ships depends mainly on four factors: direct human errors, culture of safety, or-ganization and system. The above four factors may be decomposed into several items each, for details see Bea [16] (also [17]).
It is however worth mentioning that the majority of participants of the RINA seminar on ship safety when asked in a questionnaire about the most im-portant factors contributing to safety singled out two factors: safety culture and training [18].
Identification of hazards related to human factor
There are many situations where human error contributes to LOSA. Therefore, there are also many capsizing scenarios where human factor is present. Practically in all scenarios, where the main cause of capsizing may be deficient stability, forces of the sea, shifting of cargo etc., human factor is also present.
Analysis of the influence of human factor that results from safety culture, organization and system is out of the scope of the present study. Focus of this paper is on the influence of human error. Cate-gorisation of the main elements that contribute to human error is shown in figure 3.
With more detailed analysis it may be found that the list of factors that contribute to the possibility of human error by the individual is quite a long one and may include the following: tiredness, negli-gence, ignorance, jealousy, arrogance, recklessness, wishful thinking, wrong assessment, wrong inten-tion, laziness, sluggishness, boredom, alcohol, drugs, lack of education and superciliousness. The list is in no way comprehensive.
HUMAN ERROR psychical predispositions
phisical predispositions character, morale, integrity knowledge and experience training degree
Fig. 3. Main contributions to human error Rys. 3. Główne przyczyny błędu ludzkiego
The crucial problem in safety assessment analy-sis is proper identification of various hazards to which a ship may be subjected. According to the definition, hazard is “a potential to threaten human
Hazard identification is carried out using hazard identification and ranking procedure (HAZID). Hazards could be identified using several different methods.
IMO resolution included general guidance on the methodology of hazard identification. With respect to stability, hazard identification could be achieved using standard methods involving evalua-tion of available data in the context of funcevalua-tions and systems relevant to the type of ship and mode of its operation. Stability is considered assuming that the ship is intact and accident evaluated is called LOSA. LOSA is a new definition covering capsiz-ing, that is taking by the ship position upside down, but also covering a situation where amplitudes of rolling motion or heel exceed a limit that makes operation or handling the ship impossible for vari-ous reasons – e.g. loss of power, loss of manoeu-vrability, necessity to abandon the ship etc. It does not necessary mean the total loss of the ship [1].
According to the general recommendation, HAZID comprises a mixture of creative and ana-lytical techniques. Creative element was necessary to prove that the process is proactive and is not limited to hazards that happened in past.
In general, HAZID involves several possibilities used separately or in combination:
− statistical data concerning causes of accidents, − historical data including detailed description of
accidents,
− conclusions resulting from model tests and computer simulations of ship capsizing in rough sea,
− application of event and fault trees method, − analysis of accidents using TRIPOD method, − opinions of experts organized according to
DELPHIC or any other method.
All the above possibilities could be used when assessing hazards related to human factor. How-ever, with regard to human errors some of the above methods may not provide satisfactory results. First of all, statistical data on causes of accidents applicable to risk analysis related to human factor are hardly available because ship owners are not willing to reveal data that may negatively affect their personnel.
Frequencies of hazards could be assessed on the basis of risk contribution trees (RCT) being a set and a combination of all fault trees and event trees as defined below.
A fault tree is a logic diagram showing the cas-ual relationship between events, which singly or in combination occur to cause the occurrence of a higher-level event. It is used to determine the
probability of the top event. Fault tree is a top- -down procedure systematically considering the causes and events at levels below the top event. An event tree is a logic diagram used to analyse the effect of an accident, a failure or an unintended event. An event tree is a down-top procedure start-ing from the undesired event and leadstart-ing to possi-ble consequences.
One or more events from the lower level must be present in order to cause the event in the upper level happens. Those events are then connected with the functor (gate) “AND”. If only one of the two or more events in the lower level is necessary to cause an upper event to happen, then those events are connected with the gate “OR”. Those functors or gates mean addition or multiplication of probabilities when calculating the probability of upper level event.
Assessment of risk of human error
Risk is defined as a product of hazard probabil-ity and hazard severprobabil-ity (consequences):
R = P · S
To facilitate the ranking and validation of rank-ing IMO [8] recommended definrank-ing consequence and probability indices on a logarithmic scale. A risk index may therefore be established by add-ing the probability (frequency) and consequence indices. We have then:
Log (risk) = Log (frequency) + Log (consequence) In order to assess risk index and construct risk matrix, IMO resolution recommended using haz-ards and operability study (HAZOP). For the method of constructing risk matrix and assessment of frequency and consequence indices reference is made to in [17]. Frequencies of hazards could be assessed on the basis of risk contribution trees (RCT) being a set and a combination of all fault trees and event trees. For identification of scenarios and construction of fault trees and event trees a team of experts has to be assembled. There are specific recommendations on how to organize work of such teams; especially, the difference between expert judgment and engineering judgement is stressed.
In the work of a team of experts the most advis-able is to take proactive approach including prob-abilistic modelling of failures and ship behaviour at sea. Historical data and statistics should also be used however statistics providing some information on the past cannot be used to predict hazards rele-vant to non-conventional ships of the future. In general, statistical data should no be overestimated.
Analytical methods and model tests could be used to evaluate rare events, such as encountering ex-treme or freak waves. However, those methods are hardly applicable for evaluation scenarios incorpo-rating human factor.
The difficulty with applying risk analysis lies in the multitude of scenarios possible. Capsizing sce-narios were discussed by the author [17, 19] and risk contribution trees for the hazard posed by dan-gerous icing are shown in [20]. Risk assessment due to hazards posed by forces of sea was consid-ered in [21].
In the risk analysis of stability safety a number of risk contribution trees (RCT) have to be con-structed, for each of the undesired event (hazard) in the first level hazard identification tree (fig. 4). Moreover, for some hazards more than one fault and event tree should be constructed, because of possibility of different capsizing scenarios. There-fore, before RCT are constructed, different modes or scenarios of capsizing must be identified.
and/or Critical stability Forces of the sea HOE Cargo
shifting External heelingmoments Icing and ballast Cargo
operations
Fire and explosion LOSA
Fig. 4. First-level hazard identification tree (HOE – human and organisation errors)
Rys. 4. Drzewo identyfikacji niebezpieczeństwa pierwszego stopnia (HOE – błędy ludzkie i organizacyjne)
With the identification of hazards related to hu-man factor all hazards resulting from huhu-man activ-ity (HOE) in all stages of ship’s life should be con-sidered, starting with design, construction, opera-tion and decomissioning. From the point of view the most important is however, ship operation in the broad sense, because at this stage there is greatest possibility that stability casualty caused by human fault happens. Operation is strictly connected with human activity.
Example of risk contribution trees
As mentioned above, hazards and their probabil-ity could be identified using several methods. How-ever, for identification of hazards related to human factor, the only practical method is experts' assess-ment and construction of risk contribution trees based on historical data on capsizing scenarios also using proactive approach. As there is a multitude of capsizing scenarios, where human factor plays an important part, there is also a great number of
pos-sible risk contribution trees that allow identification of hazards and their probabilities. Few examples of capsizing scenarios obviously relateing to human error are included in the following reports [22, 23, 24]. In those reports the following casualties were analysed:
DONGEDIJK: error in the calculation and as-sessment of initial stability,
SUN BREEZE: error in loading of cargo, JAN HEWELIUSZ (Ystad): error in ballast
op-erations,
SOPOT: error in ballast operation, order to drill holes in watertight bulkhead,
CYRANKA: error in ship handling in rough sea (in stormy weather sailing at full speed in following waves and making sharp 90° turn). The analysis of the above casualties leads to the conclusion that the main cause of casualty is human error resulting from various reasons, mainly from the lack of basic knowledge about stability and the lack of experience in ships’ behaviour at rough sea.
Examples of simplified fault and event trees for the casualty of CYRANKA fishing boat are shown in figures 5 and 6. In these examples, risky ma-noeuvre in following seas has been assumed as the primary event. Character and morale RISKY MANOEUVRE IN FOLLOWING SEAS Danger is not
recognized Wilful recklessness
Lack of knowledge and experience
Lack of instruction
Fig. 5. Fault tree for the event: risky manoeuvre in following seas
Rys. 5. Drzewo błędów dla zdarzenia: ryzykowny manewr na falach nadążających
Event tree showing possible consequences of risky manoeuvre in stormy following seas (90° or 180°turn) is shown in figure 6. This diagram could be used for assessment of frequencies and probabil-ity of occurring LOSA accident. For this purpose, however, it would be necessary to have available statistical data on the effect of training degree, character, morale and of other abilities of the master on the probability to perform such a risky
manoeuvre. Respective data are, however, hardly available in the literature, although one cannot ex-clude possibility of certain amount of such data collated by ship owner companies. Otherwise, the only possible method of frequencies assessment would be an assessment by the group of experts.
Risky manoeuvre in following seas
Speed reduced, careful turning Standard stability
Large excess of stability
Full ahead, sharp turn LOSA SURVIVAL
SURVIVAL Fig. 6. Event tree for consequences
Rys. 6. Drzewo zdarzeń dla konsekwencji
Risk control options
A detailed investigation of the influence of ju-man factor on the probability of stability accident and, in particular assessment of different options of risk control in relation to human factor is far be-yond the scope of this paper. Human element is present practically in all fault and event trees con-structed within various hazards as shown in figure 5. In general, risk options related to human factor could be, first of all, of preventive character and should affect all four elements of the human factor, i.e. safety culture, organization, system and indi-vidual.
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Recenzent: prof. dr hab. inż. Tadeusz Szelangiewicz Akademia Morska w Szczecinie
