Each crew of three launches in a Soyuz capsule. There are now six people on the ISS most of the time, which means there are two Soyuz capsules docked to the ISS. In an emergency situation, each three person crew can return to their assigned Soyuz. That Soyuz can be separated from the ISS within three minutes. Typical time from decision to leave until landing in Kazakhstan is just under 3.5 hours.

For a medical emergency we can just bring home one three person crew and leave the other onboard. For a vehicle emergency we can bring home all six and put the ISS into ASCR (Assured Safe Crew Return) mode, in which it can operate unattended, until we send up another crew.

Typically, when we have a fire alarm go off, there are crew assigned to fight the fire. The remaining crew sit in their Soyuz, prepared for evacuation. We also often put the crews in their Soyuz during red conjunctions of orbital debris.

When Dragon and the Boeing CST-100 capsules are man-rated and in use by US and ESA/JAXA astronauts, those vehicles will be used in the same ways.