# Estimating the Human Error Probability during Lifeboat Drills
## 3 Results
This confirms that using the BN-SLIM in addition to the SLIM is beneficial because specific tasks that are identified with the highest probability of operator failure could be additionally analysed, and better insight could be obtained. Sensitivity analysis in the GeNle Modeler was performed to identify which nodes are the most sensitive regarding the overall task HEP (Figure A3). According to the obtained results, PSF1--Crew Competence is the most sensitive node, followed by PSF2--Design and condition of equipment. It can be concluded that for the recovery of the lifeboat (part of the lifeboat drill), the greatest effect on safety would be obtained by acting on these two factors. It has to be mentioned that, when weighting PSFs for SLIM, the experts gave higher importance to PSF2 than PSF1. Consequently, the result obtained is also one of the advantages of using the BN-SLIM over the SLIM since the PSFs with the largest effect on HEP can be identified for each phase of the lifeboat drill. Therefore, if effective measures to improve Crew Competence (PSF1) and the Design and condition of equipment (PSF2) are introduced onboard ships, the HEP for tasks included in lifeboat recovery would be as presented in Table 11.  
As presented in Table 11, just acting on PSF1 would reduce the HEP during lifeboat recovery from 4% to 2.2%. If PSF1 and PSF2 are acted upon and improved, the HEP would be reduced to 1.4%. In addition, there is a need to show the change in HEPs if all PSF probabilities change. Table 12 presents changes in the HEP of lifeboat recovery T4 (tasks T4.1-T4.5) when changing the probabilities of PSFs. However, in practise, it might be difficult to implement measures that could improve all of the PSFs identified in this study. The optimal solution would be to implement measures that would improve the effect of PSF1 and PSF2 on lifeboat drill tasks and subtasks. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Method/Task** & **T4.1** & **T4.2** & **T4.3** & **T4.4** & **T4.5** \\ \hline HEP obtained by SLIM & 3.4\% & 4.1\% & 2.8\% & 1.8\% & 4.1\% \\ HEP obtained by & 2.6\% & 2.6\% & 3.8\% & 4.5\% & 3.8\% \\ BN-SLIM & & & & & \\ Difference & 0.8\% & 1.5\% & 1.0\% & 2.7\% & 0.3\% \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Comparison of HEPs obtained by SLIM and BN-SLIM. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Tasks** & **Estimated HEP** & **Estimated HEP** & **Value of _a_** & **Value of _b_** \\  & **for the Best Case** & **for the Worst Case** & **Constant** & **Constant** \\ \hline T4.1 & \(1.00\times 10^{-3}\) & \(1.00\times 10^{-1}\) & 0.000453 & \(-0.04576\) \\ T4.2 & \(1.25\times 10^{-3}\) & \(1.00\times 10^{-1}\) & 0.000452 & \(-0.04576\) \\ T4.3 & \(1.33\times 10^{-3}\) & \(1.43\times 10^{-1}\) & 0.000664 & \(-0.06695\) \\ T4.4 & \(2.00\times 10^{-3}\) & \(1.67\times 10^{-1}\) & 0.000783 & \(-0.07918\) \\ T4.5 & \(1.33\times 10^{-3}\) & \(1.43\times 10^{-1}\) & 0.000664 & \(-0.06695\) \\ \hline \hline \end{tabular}
\end{table} 
Table 9: The experts’ estimates of HEP for the task T4—Recovery of the lifeboat. Furthermore, the BN-SLIM model needs to be validated; therefore, a real-life lifeboat drill accident investigation report was used. The short details of the accident are as follows: the bulk carrier was at anchor, and the abandon ship drill was carried out. During the lifeboat recovery, the aft hook-release gear mechanism opened. Because the forward mechanism was unable to take the full load, it also opened. The lifeboat then fell from a height of 11 m into the sea, fatally injuring one of the five lifeboat crew members [37]. The accident investigation report lists the following as the causes of the accident [37]:  
* \"The aft release mechanism opened when the floating blocks impacted the davit arms. The load was then transferred to the forward hook, which, due to improper resetting, was released and caused the lifeboat to fall\". * \"The hooks were improperly reset because they were not held in their proper position during the reset of the release mechanism\".