Sterilization cycles are broken down into different phases that are monitored during validation. The phases in chronological order are Conditioning, Heat Up, Exposure, Exhaust, and Drying.
The Conditioning phase is where the autoclave replaces the air inside the chamber with saturated steam. This is done through a series of vacuums and pressurizations and injection of steam.
The Heat Up phase begins at the point of the deepest vacuum on the last purge of the conditioning phase and ends when all parameters for exposure are met.
The Exposure phase begins when the chamber reaches a minimum of 270 degrees Fahrenheit with 97% to 100% saturated steam and less than 3 ½% non-condensable gasses. This must be held for at least 4 continuous minutes.
The Exhaust Phase begins when the exposure phase ends and is where the steam inside the chamber condenses back into water.
The Dry phase is where the remaining moisture is removed from the chamber and the instrumentation by use of a vacuum.
Each of these phases are intertwined and codependent on the others. If there is a failure in any of the phases, a Sterility Assuredness Level of 10-6 cannot be achieved.