Currently, the only route from Earth to the International Space Station for astronauts is by hitching a ride on the Soyuz spacecraft. But what happens if a fire breaks out en route to the station? Without fire extinguishers or normal firefighting tools, astronauts have special procedures to return them safely to Earth.

Like calling a rocket explosion a “rapid unscheduled disassembly,” a mid-flight disaster requiring an emergency landing is obliquely referred to as an “off-nominal situation.” During their training for upcoming missions, astronauts like ESA astronaut Andreas Mogensen and Russian cosmonaut Sergei Volkov undergo all sorts of worse-case scenarios to ensure that no matter how far from nominal a situation is, their odds of surviving it are as high as possible.

Mogensen, who is currently undergoing training for a mission in September 2015, explains fire suppression procedures for the Soyuz spacecraft:

When faced with smoke, the very first reaction is to close spacesuit helmets, putting astronauts in contained environments and avoiding smoke inhalation. That accomplished, they have three techniques to try to extinguish the fire:

  1. Switch off fans and ventilation. This stops forced convection, reducing easily-accessible oxygen to fuel the flames.
  2. Switch off all electronics. By switching off the electrical supply, astronauts kill possible ignition sources. This is a limited-time-only trick: they can only go so long before they need to restart everything for a safe voyage.
  3. Depressurize. This is the method of last-resort, yet undeniably effective: after checking their suits’ air supplies, astronauts can vent the spaceship of all oxygen. This instantly kills any fire, but also mandates a return-to-Earth within 125 minutes (1.5 orbits) to prevent heat exhaustion from debilitating the astronauts.