There are several reasons for sterilization failure:

Incorrect loading of the sterilizer - This is the #1 reason for sterilization failure.  Instruments should be placed in the sterilizer in a single layer or placed on edge and loosely loaded for complete circulation of the sterilant.   Items packed too tightly together will not allow complete penetration of the sterilant to the center of the load.  Sterilizer manufacturers' instructions should be strictly followed regarding the size of the load or number of instruments placed in the chamber.  It is far too easy to be tempted into saving time by putting in one more package. That one extra can cause the sterilization failure.

Inadequate cleaning of instruments - Both visible and invisible debris left on instruments will prevent complete surface contact with the sterilant.  This is the only cause of failure that cannot be detected by sterilization monitoring.  Therefore, decontamination procedures that include meticulous cleaning and inspection of instruments must be in place and strictly adhered to by everyone.

Improper packaging - Selecting a pouch that is too small for the number of instruments going into it will not allow complete circulation of the sterilant around the instruments.  Using packaging not compatible with the sterilization process will also impede penetration of the sterilant.  Solid metal containers should never be completely closed or the sterilant will not get inside the container and using too many layers of wrap may prevent the sterilant from penetrating to the instruments.

Processing instruments in a cold sterilizer - A cold sterilizer takes much longer to come up to temperature, since it must heat the chamber in addition to the contents, and may not adequately sterilize items.  Run a cycle with an empty chamber before the first load is processed.

Selecting the wrong sterilization cycle - Sterilizers with automatic cycle vs. manual time and temperature selection can sometimes be confusing.  If a load contains both wrapped and unwrapped items, the "wrapped" cycle should be chosen.  Always select the longer cycle when sterilizing mixed loads.

Selecting the wrong time or temperature - Sterilizers that require manual selection of time, temperature and/or pressure must be used according to manufacturers recommendations for optimal results.  The sterilant must have enough time for the sterilant to adequately penetrate items in the load and high enough temperature to kill all organisms.  Pressurized sterilizers must come up to the correct pressure in order for sterilization to occur.

Aborting the sterilization cycle - Aborting a cycle in order to use instruments more quickly or opening a sterilizer during a cycle to add instruments will likely result in sterilization failure.  Even through it may save time, DO NOT abort the sterilization cycle before it is complete, including drying time.  Remember, a wet instrument or package is contaminated as soon as it hits ambient air or is touched.  If extra instruments must be added to a load in process, restart the cycle.

Sterilization monitoring - The dials, gauges and printouts can indicate only instances of gross mechanical failure.  They cannot tell you what is happening within the load.  The use of chemical and biological indicators is recommended by several organizations such as CDC (Centers for Disease Control and Prevention), ADA (American Dental Association), OSAP (Office Safety and Asepsis Procedures Research Foundation), AAMI (Association for the Advancement of Medical Instrumentation), etc.  Their recommendations include: