# Cause Analysis of Coal Mine Gas Accidents in China Based on Association Rules
## 2 Methods
### Association Rule Statistics  
#### 3.2.1 Frequent Item Sets  
As mentioned above, the setting of the support threshold is crucial when calculating association rules. In order to ensure the reasonable setting of support, the paper first adjusts the calculation of the support threshold. When trying to set it to 0.5, 0.4, and 0.3, there is no frequent return of item set results, which will lose the value of subsequent research. When the support threshold is set to 0.2, two items are generated, so the paper conducts subsequent research from the support threshold of 0.2.  
According to Table 1, when the support threshold is set to 0.2, the mining result of the frequent item set of coal mine gas accident factors is \"habitual violation\", \"poor supervision of the safety supervision bureau\". This indicates that the support threshold is set too high and the frequent items are too few. It is not conducive to the generation of association rules.  
When the support threshold is set to 0.1, two factors, \"Illegally production\" and \"Gas accumulation\", are increased compared with the support threshold of 0.2, indicating that environmental factors will be returned after the support threshold is lowered.  
\begin{table}
\begin{tabular}{l c} \hline \hline
**Frequent Item Sets** & **Support** \\ \hline \(\left[\text{Habitual violation, Poor supervision of the safety supervision bureau}\right]\) & 0.24 \\ \(\left[\text{Habitual violation, Poor supervision of the safety supervision bureau, Illegal production}\right]\) & 0.14 \\ \(\left[\text{Habitual violation, Poor supervision of the safety supervision bureau, Gas accumulation}\right]\) & 0.12 \\ \(\left[\text{Habitual violation, Gas accumulation, Illegal production}\right]\) & 0.11 \\ \(\left[\text{Habitual violation, Poor supervision of the safety supervision bureau, Gas accumulation}\right]\) & 0.05 \\ \(\left[\text{Hlegally production, Ventilation system missing/imperfect}\right]\) & 0.05 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Results of frequent item sets.  
Figure 7: Statistics of accident grades and deaths.  
The support threshold is set to 0.05, meaning that the results of the frequent item in the equipment aspect is more reasonable. If the support threshold is lowered further, there will be too many causative factors, which means the coverage of the frequent item set in the transaction set is very small, therefore the occurrence of factors in frequent item set is very accidental, and the final result lacks feasibility. After synthesis, the support threshold is selected as 0.05 for subsequent analysis. The frequent item sets of coal mine gas accident factors are summarized as \"habitual violation\", \"poor supervision of the safety supervision bureau\", \"gas accumulation\", \"illegal production\", and \"ventilation system missing/imperfect\".  
In the analysis of frequent item set results, it can be found that it is difficult to return the results of environment factors and equipment factors of accidents and the number is small. The reasons may be as follows: Coal mine gas accidents are mostly liability accidents. At present, the investigation reports of coal mine gas accidents mainly focus on liability identification. The direct and indirect causes are generally analyzed for human and management reasons, and the analysis of equipment and environment is less commonly completed, and the records are not detailed enough.