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Hospital Sterilizers: Glossary of Terms
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Algorithm: The "logic" programmed into a computer that controls the process on the basis of inputs from sensors, switches, or other devices. A typical algorithm may control how many pumps can be operating or when a valve is turned on or off or is repositioned.

Back vent: A large-diameter valve and blower at the back of the sterilizer. The vent creates a high-volume evacuation of the sterilizer when the sterilizer entrance door is opened to reduce operator EtO exposure during unloading. Most back vents pull in air at a rate equal to one sterilizer volume per minute. Most back vents are automatically triggered when an operator opens or attempts to open the sterilizer door, regardless of conditions within the chamber.

Cycle: Treatment of a product with EtO in a sterilizer designed to render the product free of all forms of viable microorganisms. EtO concentrations in the sterilizer range between 100 and 800 mg/L or between 5.5% and 44.4%. The cycle includes removing air from the sterilizer, conditioning with temperature and humidity (if used), injecting EtO, exposing the product to EtO, removing EtO, and flushing the sterilizer. A diluent gas (such as nitrogen) is generally injected and evacuated as part of air removal at the beginning of the cycle and during flushing after EtO exposure. These diluent injections and evacuations have become prominent safety additions for OECD operation because they decrease the flammability of the environment within the sterilizer. After completion of the cycle, the back vent is run before unloading. (Note: Cycle parameters vary widely among facilities. Most facilities operate several different cycles, depending on customer needs.)

Emission control device: A device designed to reduce the EtO content in the exhaust stream (source).

Exhaust stream: The sum of all gases exiting from the facility (source) that is directed to the inlet of the emission control device or OECD.

Gas delivery system: The system that delivers EtO from its protective storage drum through automated valves into a vaporizer. The vaporizer converts the liquid EtO to gas as it is injected into the sterilizer. The correct amount of EtO injected may be determined by measuring the change in weight of the EtO tank, by measuring the change in pressure within the sterilizer, or both.

Interlock: A mechanical device or computer algorithm that ties one action into another action (response). An interlock may be as simple as a mechanical limit switch that is tied to a motor starter, or it may be a computer program that electrically or mechanically "locks out" a valve or motor until certain conditions have been met. Effective interlocks provide a safer, but not foolproof, method of assuring that an objective or procedure is met before an action is taken. A complete review of all normal and abnormal operating conditions (using a hazard analysis) is necessary when assessing an interlock's effectiveness. Startup and testing of safety-related interlocks is important and requires extreme caution.

Lower flammability limit: The lowest concentration of a substance in air that will sustain combustion when elevated to its ignition temperature. The lower flammability limit for EtO is about 3% or 30,000 ppm at standard conditions. This limit can be lower under elevated temperature or pressure. Note that EtO is also flammable at 100%, indicating that oxygen is not required to have a flammable event.

Manual intervention: The ability of an operator to manually override the sterilizer controller by (1) accessing the sterilizer controller and manually initiating an action before completion of a cycle step or (2) opening the sterilizer door (and thus triggering the operation of a back vent) before completion of the cycle.

Operator: A person who is responsible to initiate, monitor, and control a cycle. The operator may manually intervene and may also load and unload product from the sterilizer.

Overfeeding: Introducing EtO to an emission control device or OECD at a rate greater than the manufacturers design limitation.

Oxidizing emission control device (OECD): An oxidizing emission control device (catalytic or thermal) designed to reduce the EtO content in the exhaust stream (source).

Sterilizer: A sealed chamber in which a product is subjected to a cycle that renders it free of all forms of viable microorganisms. A sterilizer generally consists of a chamber with one or more doors, a vacuum pump, a back vent valve with a blower, a heating system, a gas delivery system, a sterilizer controller, and various parameter gauges and instruments.

Sterilizer controller: A computer system that controls and monitors the cycle. The system controls (1) the appropriate valves, pumps, blowers, and heaters according to a planned sequence (algorithm) and (2) rates of pressure changes to achieve the desired environment within the sterilizer. The system monitors sterilizer pressure, sterilizer temperature, possibly EtO cylinder weight and EtO temperature, evacuation rates, and vacuum depths. Redundant sensors or methods contribute to increased reliability of operating parameters.

Vacuum pump: A device that withdraws gases from a sealed sterilizer. It generally consists of a liquid ring pump capable of pulling a vacuum in a sealed sterilizer. Vacuum pumps are rated in cubic feet per minute at the pump inlet. Most pumps have a rated capacity between 0.1 and 0.25 sterilizer volumes per minute.


  • Sterilization - eliminates or destroys all forms of microbial life
  • High-level disinfection - should destroy all microorganisms, except for bacterial spores present in high numbers
  • Intermediate level disinfection - does not necessarily kill bacterial spores or some more resistant microbial forms
  • Low-level disinfection - kills most bacteria, some viruses, and some fungi, but does not have tuberculocidal activity
  • Cleaning - removal of all foreign material such as soil and organic materials and residues from objects


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Hub Last Updated: 5/21/2015