## 3 Results and Discussion
### QCA for Management Reasons: Combination Paths  
(1) Identify research questions and variables  
Research question: What combination of management-level factors can lead to poisoning and suffocation accidents in pre-treatment workshop? Outcome variables: poisoning and suffocation accidents (P) (1 = occurred, 0 = did not occur). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Symbol** & **Meaning** & **Symbol** & **Meaning** \\ \hline T & Biogas poisoning and suffocation in the & \(X_{9}\) & Not wearing protective equipment. \\ A\({}_{1}\) & Excessive harmful gases. & \(X_{10}\) & Failure of the protective equipment. \\ A\({}_{2}\) & The workers entered the workshop in violation & \(C_{1}\) & The harmful gases have not exceeded the standard. \\ A\({}_{3}\) & The workers failed to comply with the & \(C_{2}\) & Excessive harmful gases. \\ B\({}_{1}\) & Failure of forced ventilation system. & \(D_{1}\) & No forced ventilation system. \\ X\({}_{1}\) & Not setting up forced ventilation. & \(D_{2}\) & Installation of forced ventilation system. \\ X\({}_{2}\) & Failure of H\({}_{2}\)S gas detection alarm. & \(E_{1}\) & The workers enter the workshop in accordance with \\ X\({}_{3}\) & Failure of interlock between H\({}_{2}\)S gas detection alarm & \(E_{2}\) & The workers entered the workshop in violation \\  & and forced ventilation system. & \(F_{1}\) & The workers carry out the protective requirements. \\ X\({}_{4}\) & Failure of forced ventilation equipment. & \(F_{2}\) & The workers failed to comply with the \\ X\({}_{5}\) & Failure of gas detection equipment used in & \(F_{2}\) & protective requirements. \\ X\({}_{6}\) & Not conducting the environmental testing. & \(G_{1}\) & The effective ventilation system. \\ X\({}_{7}\) & Excessive gas levels were detected, but forced & \(G_{2}\) & Failure of ventilation system. \\  & ventilation was not performed. & & \\  & The gas exceeded the standard and forced & & \\ X\({}_{8}\) & ventilation was performed, but it was not diluted to & & \\  & a reasonable concentration. & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: List of causes of poisoning and suffocation accidents in the pre-treatment pool workshop. From the analysis results of the bow-tie model in Section 3.1, it can be seen that the causes of poisoning and suffocation accidents in the pre-treatment pool included: no forced ventilation system, forced ventilation failure, accident exhaust failure, no manual switch for accident exhaust, failure of the manual switch for accident exhaust, failure of the harmful gas detection alarm, failure of the interlock between the gas alarm and the ventilation system, operators failing to enter the factory building in accordance with the requirements for confined space operations, and operators failing to implement protection requirements, etc. From the perspective of management factors, the causes of the above accidents can be summarized into the following variables:  
Condition variables: system and procedure management (A), training and education management (B), equipment maintenance management (C), supervision and inspection management (D), safety facility investment (E), emergency and response management (F). (1 = in sufficient, 0 = sufficient)  
(2) Case selection and data collection  
Because poisoning and suffocation accidents in pre-treatment tanks cannot meet the sample size requirements, the selection of accidents needed to be expanded to cases of biogas poisoning and suffocation in septic tanks or sewage tanks. Therefore, this article selected a total of 45 biogas poisoning and suffocation accidents from 2021 to 2024, covering industries such as breeding, sewage treatment and environmental protection, thereby reflecting the commonalities and differences of management systems. (3) Data calibration. The data of 45 cases of biogas poisoning and suffocation accidents were converted into binary variables (i.e., 0 and 1). The data calibration is shown in Table 2.  
(4) Necessity Analysis.