Home > Education/ Resources > Sterilization Cycles
Sterilization Cycles

There are four general types of sterilization cycles or "standard" cycles.
 
Cycle Type
Typical Application or Load Type
Gravity
Glassware, unwrapped goods, waste, utensils, redbags.
Pre-Vacuum and/or Post-Vacuum
Wrapped goods, packs, animal cage bedding, cages, porous materials.
Liquids
Media, LB broth, water.
Flash (Healthcare sterilizers only)
Unwrapped goods
 
 
Advanced Cycles
 
Effluent Decontamination
BSL-3 contaminated goods such as waste, liquids and other.
Low Temperature  
Insippation or Pasteurization of heat-sensitive goods (180°F - 220°F)
Air-Over-Pressure
Small quantities of liquids (<10ml/vial)
F0 Cycle
Heat-sensitive media and liquids.
Validation, Bowie-Dick Test
Daily air removal test, typically for healthcare applications.
Validation, Vacuum Leak Test
Tests for air-tight integrity of chamber.
Pressure Ramping
Loads sensitive to rapid pressure change.
Manual
Non-controlled; manual opening and closing of valves as desired.
 
Sterilization Cycles At-A-Glance
 
Sterilizer performance can be effectively understood through a graphical expression of cycle function. The frequency and duration of vacuum and purge (conditioning), ramp-up, dwell and cool-down functions is not literally expressed herein, and depends on sterilizer configuration, control selection and programming.
 
 
Typical Sterilization Cycles
 
 
Gravity

 
 
Gravity with Post Vacuum

 
 
Liquid

 
 
Pulse

 
 
Air Over Pressure

 
Sterilization Cycle Phases
  • Purge
    • Steam enters the chamber and displaces ambient air by expelling it through the chamber drain. This displacement can occur by gravity or with use of a vacuum system.
    • All outlet valves are OPEN during this phase.
    • Discussion
      • Air in the chamber acts as a barrier to adequate steam penetration and will negatively affect the sterilization process. A heavily loaded sterilizer will contain many "pockets" where air may become trapped. "Conditioning" aids in the removal of this air, helping to prevent stratification of the functional steam/air mixture.
      • Conditioning times can be programmed by the operator and can last from 30 seconds to several minutes.
      • The overall length of the Conditioning phase will depend on the following factors:
        • Quantity and pressure of the supplied steam.
        • Density of the goods in the chamber.
        • Chamber size.
  • Pre-Vacuum (Vacuum System Required)
    • Ambient air is efficiently removed from the chamber and the load. This allows steam to completely penetrate the products being sterilized.
    • This phase is useful for porous instruments or wrapped goods.
    • Alternative steam and vacuum phases creates pressure/vacuum "pulses".
  • Sterilization (Dwell)
    • Interior temperature and pressure are maintained at setpoint for a time specified by the controller or manual protocol.
  • Drying (Cool Down)
    • The interior load returns to ambient temperature and pressure in any of three typical methods.
      • Gravity (Fast Exhaust)
        • This method allows the steam and condensate to exit through the chamber drain with no mechanical assistance. As the effluent discharges, the pressure and temperature in the chamber decrease. When the chamber pressure is near zero, the door can be opened and the goods may be removed. This method is simple, but not the fastest.
      • Gravity (Slow Exhaust)
        • For liquids. The cool down is gradual to permit dissolved gases in the liquid media to reach equilibrium; this avoids boilover until ambient temperature and pressure are restored.
        • Liquid, air-over-pressure. The cool down is gradual as pressurized air is injected to replace steam, thereby lowering the interior temperature under pressure and preventing smaller media samples from evaporating. Once temperature is reduced, air pressure is gradually equalized and ambient temperature and pressure are achieved.
      • Vacuum Drying (Post Vacuum)
        • A vacuum system pulls the steam and condensate through the drain port. The longer the vacuum system runs during the dry phase, the cooler and dryer the goods will be when removed from the chamber.
        • The Vacuum exhaust is programmed to run for a settable amount of time.
        • Vacuum exhaust should not be used on sterilized liquid because a quick reduction in pressure will cause the liquid to boil over.
Sterilization Cycle Parameters
Many first-time sterilizer users want to know how to select the best cycle parameters for their applications. The answer depends on at least four factors:
  • Size of load
  • Type of load (waste, media, glassware, or other)
  • Time and throughput constraints
  • Steam source (house steam, integral steam generation or other)
Guidelines for optimum cycle types are suggested in the chart below.
 
Cycle Type
Application/Load 
Temperature
Sterilization Time
(minutes)
Pre-Vac Pulses
psi - in/Hg
Dry Time
(minutes)
Gravity
Glassware, unwrapped goods, waste, utensils, redbags
250°F (121°C)
30-90
none
0-30
Pre-vacuum and/or post-vacuum
Wrapped goods, packs, animal bedding, cages, porous materials
250°F (121°C)
20-90
18 psi, 20in/Hg
0-6 pulses
0-30
Liquids
Media, LB broth, water
250°F (121°C)
20-90
-
0.5 psi/minute
Flash
Unwrapped goods
270°F (132°C)
3-10
-
0-10
 
Minimum Recommended Settings for Various Liquid Volumes
 
The following chart suggests minimum exposure times. Additional time may be required if flasks are placed in a plastic container. Best practice suggests using smaller volumes whenever possible. Larger liquid volumes will take longer to achieve temperature.
 
Temperature Setting
Liquid Quantity (ml)
Time Setting (minutes)
250°F (121°C)
75
25
250°F (121°C)
250
30
250°F (121°C)
500
40
250°F (121°C)
1000
45
250°F (121°C)
1500
50
250°F (121°C)
2000
55