美国煤矿的煤层平坦,一般倾角在2～8°顶底板稳定,瓦斯涌出量小。以1983年的灾害统计,死亡人数70名,伤休9730名,伤未休者2412名(井下总人数为88000名),且半数以上的灾害是因掉渣或冒顶 Coal mines in the United States are flat with a typical inclination of 2 to 8 °. The roof and floor are stable and the gas emission is small. According to the disaster statistics in 1983, there were 70 deaths, 9730 injuries and 2,412 wounded people (the total number of people underground is 88,000). More than half of the disasters were caused by dregs or roof fall