## 5 Discussions  
A literature review of past studies shows that HFACS and FMEA had hardly been integrated to form a risk assessment [9]. However, it is one of the most significant studies of evaluating risk based on two main reasons. First, HFACS is very important analysis, which can be used to explore the potential risk of picking and material-handling accidents in warehouse facilities. In addition, FMEA is usually applied to evaluate risk factors and obtain the risk evaluation matrix. Therefore, an integrated analysis of HFACS and FMEA is a kind of comprehensive risk assessment and is a better mode for risk mitigation, which is applied by this paper to evaluate the risk of picking and material-handling accidents in warehouse facilities. In addition, for calculating the weights of the evaluation criteria for solving MCDM problems, some methods have been utilized, such as stepwise weight assessment ratio analysis (SWARA), the analytic hierarchy process (AHP), the analytic network process (ANP), the full consistency method (FUCOM), criteria importance through inter-criteria correlation (CRITIC), entropy, level-based weight assessment (LBWA), and so on [28]. A literature review shows that the developed BWM was the first to overcome some shortcomings of the analytic hierarchy process (AHP) in 2015 [27]. For example, BWM only needs to have 2n-3 comparisons while AHP needs n(n-1)/2 comparisons. Usually, the decision-makers prefer to have a unique optimal solution, but the min-max model may result in multiple optimal solutions. Therefore, the authors amended the mathematical calculation based on the same philosophy, but yielded a unique solution in 2016 [16]. Furthermore, the interval-valued intuitionistic uncertain linguistic set (IVIULSs) is used to improve the best-worst method (BWM) in the alternative evaluation [19; 30]. Not only can BWM be used to derive the weights independently, it can also be combined with other MCDM methods of simple additive weighting (SAW), the technique for order of preference by similarity to ideal solution (TOPSIS), ViseKriterijumska Optimizacija I Kompromisno Resenje (VIKOR), grey relational analysis (GRA), complex proportional assessment of alternatives (COPRAS), etc. [28]. In our real world, because of the actual system provides the message to the human being is not complete, mean it is under uncertainty grey. Hence, the article uses grey system theory as the core of mathematical to analyze the state. Since the invention of grey system theory in 1982, it has been a very important theory successfully applied in many fields and used more than three decades [17]. The essential contents and topics of the grey system theory encompass the following areas: grey relational space, grey generating space, grey forecasting, grey decision making, grey control, and grey mathematics [31]. The grey relational grade has been one of the very important chapters in the grey system theory, whose main function is to measure the norm of a discrete sequence. A literature review of past studies, especially on the applications of GRA, shows that there are many scholars proposing different GRA models for resolving MCDM problems. Focusing on the comparisons with past related studies, five different GRA methods [17] are directly cited by this paper for ranking 18 failure modes based on Table 8 of the assessment matrix of the average score by the eight experts. The calculation steps are explained in Appendix B, and Equations (A1)-(A4) are used for ranking, as shown in Figure A3. The results of the five different methods include [PERSON]'s GRA, [PERSON]'s GRA, [PERSON]'s GRA, [PERSON]'s GRA, and [PERSON]'s GRA [17], as shown in Table 10 and Figure 1.  
In the context of evaluation or selection, different GRA methods might generate different sorting results for the alternatives. In addition, as the number of criteria or alternatives in the problem increases, the ranking results obtained with the different MCDM methods become increasingly inconsistent [9].