1·If hydrogen were used as a crack detector (it is not because of the fire hazard), it would escape four times faster.
如果把氢用来作裂缝检查(人们不这么做并是因为它们有火灾隐患)，他们逃逸的速度会比氦快四倍。
2·An ultrasonic detector for wall rock crack is introduced which is able to detect coal mine underground wall rock looseness range and cracks.
介绍了一种超声波围岩裂隙探测仪，可用于探测煤矿井下围岩松动范围及裂隙情况。