## 3 Results and Discussion
### QCA for Management Reasons: Combination Paths
The software fsQCA 4.0 was used to determine whether the six conditional variables were necessary conditions for biogas poisoning and suffocation \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Number** & **A** & **B** & **C** & **D** & **E** & **F** & **P** \\ \hline  
\hline \hline \end{tabular}
\end{table} 
Table 2: QCA calibration table for poisoning and suffocation accidents in pre-treatment pools. accidents in the pre-treatment pool. The consistency and coverage of each conditional variable are shown in Table 3.  
As can be seen from Table 3, the consistency of conditional variables B, D and F was greater than 0.9, which shows that the above three variables were necessary conditions for the occurrence of biogas poisoning and suffocation accidents. The consistency of variables B and D was one, which indicated that inadequate training and education management and inadequate supervision and inspection management existed in all accident cases. The consistency of the F variable was 0.93, which meant that the reason for inadequate emergency and response management existed in 93% of the accident cases. Variables A, C and E were not necessary conditions. For system and procedure management (A), even when the system is robust, non-compliance with established procedures by personnel may lead to accidents. For equipment maintenance management (C), despite well-maintained equipment, gas accumulation can still occur in the absence of properly installed ventilation facilities. For safety facility investment (E), even with adequate safety investments, staff members remain at risk of exposure to harmful gases if safety facilities are not utilized as intended. (5) Conditional configuration path analysis. In this paper, the consistency threshold was selected as 0.8 and the cutoff value was 1 to perform truth table analysis. The conditional combination path leading to the anaerobic tank explosion accident is shown in Table 4.  
It can be seen from Table 4 that the consistency scores of the above two groups of conditional combination paths were both one, which indicated that these two combination paths had a high degree of explanation for the 45 cases of biogas poisoning and suffocation accidents. Moreover, the consistency score of the solutions was greater than 0.8, and the coverage of the solutions was one, which meant that these two groups of solutions can well explain the path of the accident. In Path 1, if the three aspects of training and education management, supervision and inspection management, and emergency and response management were not in place, it would directly lead to the occurrence of biogas poisoning and suffocation accidents. The raw coverage of this path was 0.93, which indicated that this combined path could explain 93% of accident cases. The unique coverage of this path was 0.56, which meant that the accident cases with only these three conditional variables account for 56%, namely that 56% of the \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Conditional Combination Paths** & **Raw Coverage** & **Unique Coverage** & **Consistency** \\ \hline Path 1: B * D * F & 0.93 & 0.56 & 1 \\ Path 2: B *-C * D *-E & 0.44 & 0.07 & 1 \\ \cline{2-4} Solution coverage & & 1 & \\ Consistency of solution & & 1 & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Conditional combination paths. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Variable** & **Consistency** & **Coverage** \\ \hline A & 0.58 & 1 \\ B & 1.00 & 1 \\ C & 0.27 & 1 \\ D & 1.00 & 1 \\ E & 0.33 & 1 \\ F & 0.93 & 1 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The consistency and coverage of each conditional variable. biogas poisoning accidents were caused by inadequate training and education management, supervision and inspection management, and emergency and response management. In Path 2, even if equipment maintenance management and safety facility investment were in place, inadequate training and education management, supervision, and inspection management can also lead to accidents.