If the group becomes too tightly packed, you could run out of air by compressional asphyxiation.

如果人群变得过于拥挤，您可能会因压迫而窒息。

The information will travel like the compressional wave ahead of an earthquake, detectable only by special equipment.

这些信息将像地震前的纵波一样传播，只有特殊设备才能检测到。