Grey class | Drilling work (105 m) | Construction time (103) | investment (RMB 106) | Gas control cost (Yuan/t) | Prevention of secondary disasters (%) |
Best (I) | 7.5 | 8.9 | 15.9 | 33.2 | 126 |
Better (II) | 15 | 17.8 | 31.8 | 66.4 | 84 |
Bad (III) | 22.5 | 26.7 | 47.7 | 99.6 | 42 |