Steam Sterilization Cycles

Steam sterilizers have the capability to sterilize various types of loads through adjustments in time, temperature, and pressure at each cycle phase.  From glassware to redbag waste, Consolidated’s sterilizers can run the necessary cycles to accurately sterilize your specific loads.

Use the table and graphical information below to learn more about our basic and advanced cycle types, specific applications, sterilization cycle phases, and critical cycle parameters. Additionally, you will also find guidelines for optimum cycle types and even minimum recommended settings for various liquid volumes.

If you have a specific question you can’t find the answer to here, simply fill out the form below and our autoclave engineers will assist you.

There Are Four Standard Sterilization Cycles:

Basic Cycles Description Typical Application or Load Type
Gravity The most basic sterilization cycle. Steam displaces air in the chamber by gravity (i.e. without mechanical assistance) through a drain port. Glassware, unwrapped goods, waste, utensils, redbags.
Pre-Vacuum and/or Post-Vacuum Air is mechanically removed from the chamber and load through a series of vacuum and pressure pulses. This allows the steam to penetrate porous areas of the load that couldn’t otherwise be reached with simple gravity displacement. Wrapped goods, packs, animal cage bedding, cages, porous materials, redbags.
Liquids A gravity cycle with a slower exhaust rate to minimize boil-over. Media, LB broth, water, etc.
Flash (Healthcare sterilizers only) High temperature cycle (over 270F) for a shorter period of time. Unwrapped goods

Some loads, like small quantities of liquid or heat sensitive goods, cannot withstand the parameters of a standard sterilization cycle.  Advanced cycles alter parameters to sterilize the medium without destroying it.

Advanced Cycles Description Typical Application or Load Type
Effluent Decontamination All steam effluent is captured, filtered, and sterilized prior to discharging down the drain. BSL-3 contaminated goods such as waste, liquids, etc.
Low Temperature Sterilization near the boiling point of water (180-220F) Insippation or pasteurization of heat-sensitive goods.
Air-Over-Pressure Air maintains the pressure in chamber during exhaust phase until temperature of load drops below an adjustable value. Small quanitites of liquids (<10ml/vial) in danger of boiling over.
F0 Cycle Sterilization begins when temperature reaches a minimum of 212F and is completed when the F0 set-point is achieved. F0 is adjustable. Heat-sensitive media and liquids
Validation, Bowie-Dick Test Daily air removal test, typically for healthcare applications Validating the sterilizer.
Validation, Vacuum Leak Test Tests for air-tight integrity of chamber. Validating the sterilizer.
Pressure Ramping Steam pressure in the chamber can be ramped-up or ramped-down at an adjustable rate. Loads sensitive to rapid pressure change (e.g. heart valves)
Temperature Ramping Temperature in the chamber is ramped-up at an adjustable rate until exposure set-point temperature is achieved. Loads sensitive to rapid temperature change
Rapid Cool – Jacket During the cooling phase, cold water enters the jacket to speed up the cooling process. Customers looking to decrease cycle time
Rapid Cool – Spray During the cooling phase, cold water is sprayed into the chamber, showering the load, thereby speeding up the cooling process. Customers looking to decrease cycle time
Continuous Any sterilization cycle can be programmed to be continuously repeated (number of times is adjustable) without any input from the operator. Validation of product.
Steam-Air Mix Sterilization at an elevated pressure relative to temperature. Extra pressure is achieved using air. Liquid-filled syringes.
Tight Temp Control Utilizes an additonal, small chamber steam valve to tightly control temperature during sterilization. Also includes temperature ramp up. Customers with strict temperature tolerance.

The Steam Sterilization Cycles Article Series

To help you identify, create, and use the proper sterilization cycle for each load, CSS has introduced a new series of articles on steam sterilization cycles. This article series covers why, how, and when to use various different sterilization cycles.

Sterilization Cycles At-A-Glance

Sterilization cycles can be understood through a graphical expression of the change in pressure and temperature over time. Keep in mind, the frequency and duration phases will vary depending on sterilizer configuration, control selection and programming.

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

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

 

Have Your Sterilization Questions Answered
by Our Autoclave Experts

Do you have additional questions about sterilization cycles? Are you curious about how to program custom cycles? Simply fill out the form below with your sterilization cycle questions, and our engineers will contact you with a response.

Privacy Policy