Danger on a space station is never farther away than the nearly perfect vacuum on the other side of a thin metal wall. Station inhabitants must be prepared for a wide range of emergencies, from fire to life support and power failures to decompression. Within the closed environment of a space station, emergencies tend to multiply. Fires can overload life support equipment with smoke, collisions can cause decompression and loss of power, and so on. Even an illness or injury that would be considered minor on Earth, where the victim can easily get to a doctor or hospital, might be considered an emergency on board a space station.

Emergencies can strike at any time. Space station crews cannot depend on any help from Earth reaching them in time if there is an emergency on board. Even if there were a rescue ship ready to launch from...