109
Addressing Human Factors in Ship Design
( RMS) and 4.0° ( RMS) amplitude of roll motion. Observation on board during heavy
weather in the Norwegian Sea showed that it was impossible for anybody to stand
still on a vessel in 14 m wave height. Physical measurement at that time indicated that
the maximum vertical acceleration was 0.149 g ( RMS) and maximum roll amplitude
was 0.54° ( RMS). It is obvious that these standards need to be revised to induce comfort as well as to ensure safety. In real life, the seafarers adjust the way they operate
the vessel and their behavior on board. When the sea is high, the crew will try to find
an alternative route that may be further but calmer or they can reduce the speed of
the vessel and adjust the heading to reduce motion and slamming.
The quantitative survey confirms some aspects of human factors presented by
the LR like controllability, workability and habitability. Other aspects seem to be
weak. New dimensions appear: “ cargo facilities”, and “ reliability automation and
maintainability”.
HUMAN FACTORS IN SHIP AS A S AFETY-CRITICAL SYSTEM
A study was conducted to develop a model to examine how ship accidents can be analyzed from the human factors perspective, given that a critical incident has already
occurred ( Rumawas & Asbjørnslett, 2010b, 2011b, 2014b). The focus of the study is
on the operator’s role. The hardware reliability perspective was adopted where the
ship is considered as a safety-critical system to be protected by barriers. The crew is
modeled as active barriers with different functions: perception, decision and action.
A Markov model is utilized to describe different states of the crew on the ship. The
highest state is 4: the crew performs the task correctly. The lower states are: the crew
fails to monitor the situation ( 3), then fails to make the correct decision ( 2) and fails
to perform the proper action ( 1). Two conditions are defined: normal condition ( N)
and extreme condition ( E) 1 . Accidents usually happened in the latter, just as demonstrated in the section Lessons Learned above ( Figure 7.2).
In reliability engineering, safety instrumented system ( SIS) is defined as an independent protection layer that is installed to mitigate the risk associated with the operation of a hazardous system ( Rausand & Høyland, 2004). Most of the time, the system
is passive until a threatening situation takes place. The SIS model consists of a number
of sensors, a logic solver and actuators ( see Figure 7.3). The same logic is implemented
toward ship operation by putting the crew as the SIS, meaning that they should be able
to sense the hazard, to analyze the situation, to make a proper decision and to execute
the right action. A mathematical model to estimate the probability of failure in an
emergency situation is proposed ( PFE). A parameter is defined for the survivability of
a ship, given that a critical incident has taken place. Survivability, S(t), is defined as the
function of previous knowledge (S 0 ) combined with the accumulation of adaptation,
on board learning processes ( ) and formal trainings or assessment ( ).
γ
δ
S t S
i
i
∑
∑ γ τ δ
=
+
( )
0
( 7.1)
where τ is time between training or between assessments.
1 Refer to the original paper for detailed description of the model.
Addressing Human Factors in Ship Design
( RMS) and 4.0° ( RMS) amplitude of roll motion. Observation on board during heavy
weather in the Norwegian Sea showed that it was impossible for anybody to stand
still on a vessel in 14 m wave height. Physical measurement at that time indicated that
the maximum vertical acceleration was 0.149 g ( RMS) and maximum roll amplitude
was 0.54° ( RMS). It is obvious that these standards need to be revised to induce comfort as well as to ensure safety. In real life, the seafarers adjust the way they operate
the vessel and their behavior on board. When the sea is high, the crew will try to find
an alternative route that may be further but calmer or they can reduce the speed of
the vessel and adjust the heading to reduce motion and slamming.
The quantitative survey confirms some aspects of human factors presented by
the LR like controllability, workability and habitability. Other aspects seem to be
weak. New dimensions appear: “ cargo facilities”, and “ reliability automation and
maintainability”.
HUMAN FACTORS IN SHIP AS A S AFETY-CRITICAL SYSTEM
A study was conducted to develop a model to examine how ship accidents can be analyzed from the human factors perspective, given that a critical incident has already
occurred ( Rumawas & Asbjørnslett, 2010b, 2011b, 2014b). The focus of the study is
on the operator’s role. The hardware reliability perspective was adopted where the
ship is considered as a safety-critical system to be protected by barriers. The crew is
modeled as active barriers with different functions: perception, decision and action.
A Markov model is utilized to describe different states of the crew on the ship. The
highest state is 4: the crew performs the task correctly. The lower states are: the crew
fails to monitor the situation ( 3), then fails to make the correct decision ( 2) and fails
to perform the proper action ( 1). Two conditions are defined: normal condition ( N)
and extreme condition ( E) 1 . Accidents usually happened in the latter, just as demonstrated in the section Lessons Learned above ( Figure 7.2).
In reliability engineering, safety instrumented system ( SIS) is defined as an independent protection layer that is installed to mitigate the risk associated with the operation of a hazardous system ( Rausand & Høyland, 2004). Most of the time, the system
is passive until a threatening situation takes place. The SIS model consists of a number
of sensors, a logic solver and actuators ( see Figure 7.3). The same logic is implemented
toward ship operation by putting the crew as the SIS, meaning that they should be able
to sense the hazard, to analyze the situation, to make a proper decision and to execute
the right action. A mathematical model to estimate the probability of failure in an
emergency situation is proposed ( PFE). A parameter is defined for the survivability of
a ship, given that a critical incident has taken place. Survivability, S(t), is defined as the
function of previous knowledge (S 0 ) combined with the accumulation of adaptation,
on board learning processes ( ) and formal trainings or assessment ( ).
γ
δ
S t S
i
i
∑
∑ γ τ δ
=
+
( )
0
( 7.1)
where τ is time between training or between assessments.
1 Refer to the original paper for detailed description of the model.