22 Sterilization Methods Practice Questions & Answers

1. 1. A surgical instrument that will enter sterile tissue and the vascular system is classified under the Spaulding system as which category, and what is the minimum required level of processing?

   • A.Noncritical; the device requires intermediate-level disinfection
   • B.Semicritical; the device requires only intermediate-level disinfection
   • C.Critical; the device must be sterilized✓ Answer
   • D.Semicritical; the device requires a minimum of high-level disinfection

   Spaulding classifies devices by the infection risk of the tissue they contact. Anything entering sterile tissue or the vascular system bypasses the body's normal defenses, so any surviving microorganism could be introduced directly into a normally sterile site; such critical devices must therefore be sterilized. Semicritical items contact intact mucous membranes or non-intact skin and require at minimum high-level disinfection; noncritical items contact only intact skin.

   Source: CDC/HICPAC Guideline for Disinfection and Sterilization, Spaulding classification; HSPA CRCST Content Outline S2-VIReport a problem with this question

2. 2. In steam sterilization, what is the actual sterilizing agent, and what role does chamber pressure play?

   • A.The vacuum is the sterilizing agent; pressure returns the chamber to atmospheric conditions
   • B.Pressure is the sterilizing agent; the steam simply carries the pressure to the load
   • C.Dry superheated air is the sterilizing agent; pressure removes residual moisture from the load
   • D.Saturated steam is the sterilizing agent; pressure is only the means of raising steam to the required temperature✓ Answer

   Microbial kill in a steam sterilizer comes from moist heat, which denatures and coagulates cellular proteins; saturated steam is the vehicle that delivers that heat and the latent heat released as it condenses on cool surfaces. Raising pressure above atmospheric is simply how water vapor can be brought to 250 degrees F or 270 degrees F, since at atmospheric pressure steam cannot exceed 212 degrees F. Pressure alone kills nothing, which is why a chamber full of pressurized air at the same reading will not sterilize.

   Source: ANSI/AAMI ST79, steam sterilization principles; CDC/HICPAC Guideline, steam sterilization sectionReport a problem with this question

3. 3. How does a gravity-displacement steam cycle remove air from the chamber, and why is residual air the principal enemy of steam sterilization?

   • A.A vacuum pump evacuates the chamber; residual air raises the chamber pressure above the set point
   • B.Air is absorbed into the packaging material; residual air causes the load to dry too quickly
   • C.Incoming steam rises to the top and pushes the heavier air down and out through the chamber drain; trapped air forms cool pockets that steam cannot penetrate, so items in them never reach the required temperature✓ Answer
   • D.Steam flushes alternate with pressure pulses above atmospheric; residual air chemically neutralizes the steam

   In a gravity-displacement cycle there is no vacuum pump; steam is admitted at the top of the chamber and, because steam is lighter than air, it displaces the denser air downward and out through the drain. Any air that remains does not simply take up space, it insulates: an air pocket is a cool region where steam cannot condense and give up its latent heat, so the surfaces inside that pocket never reach the exposure temperature even though the gauge shows correct pressure and time.

   Source: ANSI/AAMI ST79 10.2.1, cycle types and air removalReport a problem with this question

4. 4. Which statement correctly distinguishes a steam-flush pressure-pulse (SFPP) cycle from a prevacuum cycle?

   • A.SFPP is a gravity cycle and therefore does not require any air-removal testing, unlike a prevacuum cycle
   • B.SFPP uses a deeper vacuum than a prevacuum cycle and is the only cycle able to process lumened devices
   • C.SFPP removes air using repeated steam flushes and pressure pulses that stay above atmospheric pressure, so it is less sensitive to small air leaks than a prevacuum cycle✓ Answer
   • D.SFPP sterilizes at a lower temperature than a prevacuum cycle because it never pressurizes the chamber

   SFPP achieves air removal with a series of steam flushes and pressure pulses that never drop below atmospheric pressure, whereas a prevacuum cycle pulls a vacuum. Because a prevacuum cycle draws below atmospheric pressure, a small leak in a gasket or line lets room air in during the vacuum phase; SFPP has no subatmospheric phase, so a comparable leak does not draw air into the chamber. Both are dynamic-air-removal cycles and both therefore require daily air-removal (Bowie-Dick type) testing.

   Source: ANSI/AAMI ST79 10.2.1, dynamic-air-removal cycle typesReport a problem with this question

5. 5. Per CDC minimum cycle parameters, what exposure time applies to a wrapped instrument tray processed in a gravity-displacement sterilizer at 250 degrees F (121 degrees C)?

   • A.3 minutes
   • B.4 minutes
   • C.15 minutes
   • D.30 minutes✓ Answer

   Time and temperature are inversely related in moist-heat sterilization: the lower the temperature, the longer the exposure needed for the same lethality. A wrapped instrument tray in a gravity cycle needs 30 minutes at 250 degrees F but only 15 minutes at 270 degrees F, and in a dynamic-air-removal cycle only 4 minutes at 270 degrees F because air is actively removed rather than displaced. This is why an exposure time is meaningless unless the sterilizer type, item type and temperature are all specified.

   Source: CDC/HICPAC Guideline for Disinfection and Sterilization, Table 7 minimum steam cycle timesReport a problem with this question

6. 6. A technician reads the total cycle time on the sterilizer printout as 47 minutes and records that as the exposure time. Why is this incorrect?

   • A.Exposure time includes drying but excludes the come-up phase
   • B.Exposure time is only the portion of the cycle during which the load is held at the required temperature; total cycle time also includes conditioning, exhaust and drying✓ Answer
   • C.Exposure time is always exactly half of the total cycle time on any sterilizer
   • D.Exposure time is measured from the moment the door is closed until the door is opened

   A steam cycle has distinct phases: conditioning (air removal and come-up to temperature), exposure (the sterilizing hold at temperature), and exhaust and drying. Only the exposure phase delivers the validated lethality, so only that segment can be compared against the required parameters. Confusing total cycle time with exposure time can mask a short exposure that failed to meet the device's requirement.

   Source: ANSI/AAMI ST79, steam sterilization cycle phases and monitoringReport a problem with this question

7. 7. A late-arriving loaner tray is needed for a case starting in 40 minutes, and the department is short on that instrument set. Is immediate-use steam sterilization (IUSS) appropriate?

   • A.Yes, IUSS is designed to handle loaner sets that arrive too late for a full cycle
   • B.Yes, provided the tray is wrapped and stored until the case begins
   • C.No; IUSS must not be used for convenience or to compensate for insufficient inventory, and a late loaner is not a justification✓ Answer
   • D.Yes, as long as a biological indicator is added to the load

   IUSS is reserved for urgent clinical situations, such as a dropped instrument with no replacement available during a procedure, and its use is to be kept to a minimum. Using it for scheduling convenience or to work around inadequate instrument inventory defeats the safeguards of a full terminal cycle, including packaging, drying and controlled storage, and shifts risk to the patient. Late loaner delivery is an inventory and logistics problem to be solved by requiring loaners to arrive with adequate processing time.

   Source: ANSI/AAMI ST79 10.2.3, immediate-use steam sterilizationReport a problem with this question

8. 8. Which handling requirement applies to an item processed by immediate-use steam sterilization?

   • A.It may be stored for up to 24 hours if kept in a closed rigid container
   • B.It should be wrapped after the cycle and placed on the sterile storage shelf
   • C.It must be transported in a validated containment device and used immediately, never stored or held over from one procedure to the next✓ Answer
   • D.It may be held for a second procedure on the same patient later that day

   IUSS cycles do not include the packaging and drying steps that maintain sterility over time, so the item leaves the sterilizer without a barrier system validated for storage. Sterility can only be assured at the moment of transfer to the sterile field, which is why the item must move in a validated containment device directly to the point of use and be used immediately. Holding or storing it eliminates any assurance that it remained sterile.

   Source: ANSI/AAMI ST79 10.2.3, IUSS containment and immediate useReport a problem with this question

9. 9. By what mechanism does ethylene oxide (EO) destroy microorganisms, and why is a mandatory aeration phase required after the cycle?

   • A.It coagulates protein by moist heat; aeration removes residual condensate from lumens
   • B.It alkylates proteins, DNA and RNA; aeration is required because EO residuals absorbed into the device are toxic to patients and staff✓ Answer
   • C.It oxidizes cell walls; aeration is needed only to cool the load before handling
   • D.It generates free radicals in a plasma phase; aeration converts the residue to water and oxygen

   EO kills by alkylation: it adds alkyl groups to protein, DNA and RNA, blocking normal cellular metabolism and reproduction. The same chemical reactivity means EO is absorbed into plastics, rubber and other porous device materials during the cycle, and EO is a known human carcinogen and irritant, so residuals must be driven off before the item can contact a patient or be handled. Mechanical aeration at elevated temperature accomplishes this in hours, whereas ambient-room aeration takes days.

   Source: CDC/HICPAC Guideline for Disinfection and Sterilization, ethylene oxide sterilization and aerationReport a problem with this question

10. 10. Why can paper-plastic peel pouches, cotton towels and gauze not be processed in a vaporized hydrogen peroxide (including gas plasma) sterilizer?

    • A.They generate static electricity that interferes with the plasma field
    • B.They cannot withstand the deep vacuum used during the conditioning phase
    • C.They melt at the process temperature of the cycle
    • D.They are cellulose-based and absorb the hydrogen peroxide, depleting the sterilant and causing the cycle to abort✓ Answer

    Cellulose fibers avidly absorb hydrogen peroxide vapor. When cellulose is present, it soaks up the sterilant before it can distribute through the chamber and reach device surfaces, so the concentration needed for lethality is never achieved and the sterilizer typically aborts the cycle. For this reason vaporized hydrogen peroxide loads require synthetic packaging such as polypropylene wrap, polyolefin pouches and validated container trays, and cannot include linens, paper, liquids or powders.

    Source: CDC/HICPAC Guideline for Disinfection and Sterilization, hydrogen peroxide gas plasma material restrictionsReport a problem with this question

11. 11. A cycle in a vaporized hydrogen peroxide sterilizer aborts repeatedly. Technicians confirm the packaging is polypropylene wrap and no cellulose is present. What is the next most likely cause?

    • A.The instruments were cleaned with an enzymatic detergent
    • B.Residual moisture remains on the instruments, preventing the sterilizer from achieving the required vacuum✓ Answer
    • C.The load is too light for the chamber sensors to register
    • D.The chamber temperature exceeded 50 degrees C

    Vaporized hydrogen peroxide cycles begin by pulling a deep vacuum. Water left on or in a device vaporizes under that vacuum and continues to outgas, so the sterilizer cannot reach or hold the required vacuum level and the cycle faults out; residual water also dilutes the peroxide. Items must therefore be completely dry, including lumens, before being loaded.

    Source: CDC/HICPAC Guideline for Disinfection and Sterilization, hydrogen peroxide sterilization moisture and vacuum requirementsReport a problem with this question

12. 12. Which description of ozone sterilization is correct?

    • A.Ozone sterilizes at 121 degrees C and is therefore unsuitable for heat-sensitive devices
    • B.Ozone cartridges are purchased pre-filled and must be aerated for 8 to 12 hours after the cycle
    • C.The sterilizer generates its own sterilant from oxygen, water and electricity, and the ozone reverts to oxygen and water vapor at the end of the cycle, so no aeration is needed✓ Answer
    • D.Ozone has no lumen restrictions and can process any flexible endoscope

    An ozone sterilizer makes ozone on demand from medical-grade oxygen, steam-quality water and electricity, so there is no toxic chemical to purchase, store or handle. At the end of the cycle the ozone is passed through a catalyst that converts it back to oxygen and water vapor, leaving no toxic residue and eliminating any aeration requirement. It operates at a low temperature suitable for heat-sensitive devices, but it does have published rigid-lumen diameter and length limits that must be checked against the device.

    Source: CDC/HICPAC Guideline for Disinfection and Sterilization, ozone sterilizationReport a problem with this question

13. 13. Dry-heat sterilization is selected for which category of items, and why does it require far longer exposure than steam?

    • A.Powders, oils and petroleum-based products that moist heat damages or cannot penetrate; dry heat kills by slow oxidation rather than the rapid protein coagulation produced by moist heat✓ Answer
    • B.Textile packs and linens; dry heat must first evaporate the moisture in the fabric
    • C.Heat-sensitive plastics and rubber; dry heat works at a lower temperature so it needs more time
    • D.Flexible endoscopes and lumened devices; dry heat needs more time to travel through long channels

    Dry heat is reserved for items that moist heat would damage or simply cannot penetrate, such as powders, oils, petroleum-based ointments and certain sharp instruments. Its lethal mechanism is oxidation of cell constituents, a much slower process than the protein coagulation caused by moist heat, and dry air transfers heat far less efficiently than condensing steam. Both factors force much higher temperatures and much longer exposure times, for example 170 degrees C for 60 minutes or 160 degrees C for 120 minutes.

    Source: CDC/HICPAC Guideline for Disinfection and Sterilization, dry-heat sterilizationReport a problem with this question

14. 14. Which limitation is characteristic of liquid peracetic acid chemical sterilization and distinguishes it from packaged terminal sterilization methods?

    • A.It can only be used on cellulose-based materials
    • B.It sterilizes only non-immersible electrical devices
    • C.Devices are processed unwrapped and immersed, so they cannot be packaged or stored and must be used immediately at the point of use✓ Answer
    • D.It requires an 8 to 12 hour aeration phase before the device can be handled

    Liquid peracetic acid is a just-in-time, point-of-use process: the device is fully immersed in dilute peracetic acid and rinsed with filtered water, which means no sterile barrier system encloses it at any stage. Without packaging there is nothing to maintain sterility after the cycle, so the device must go directly to the procedure. This also makes routine biological monitoring difficult, and it can only be used on devices that are fully immersible with correctly matched channel connectors.

    Source: CDC/HICPAC Guideline for Disinfection and Sterilization, liquid peracetic acid sterilizationReport a problem with this question

15. 15. The programmed cycle in the department's sterilizer specifies a shorter exposure time than the device manufacturer's written IFU for a particular tray, and the two cannot be reconciled. What must be done?

    • A.Use the sterilizer manufacturer's cycle, since the sterilizer is the equipment being validated
    • B.Average the two exposure times and document the decision
    • C.Use the shorter time and add a Type 5 integrating indicator to compensate
    • D.Investigate the discrepancy and, if it cannot be reconciled, follow the device manufacturer's written IFU✓ Answer

    The device manufacturer validated that specific device, with its mass, materials, lumens and assembly, at the parameters stated in its IFU; the sterilizer manufacturer validated only the chamber's ability to deliver a cycle. When the two conflict, the department must first investigate whether the difference can be resolved, and if not, the device IFU governs because only it accounts for what it actually takes to sterilize that item. Adding an indicator does not substitute for meeting validated parameters.

    Source: ANSI/AAMI ST79 10.2.2(a), reconciling sterilizer and device manufacturer instructionsReport a problem with this question

16. 16. A newly purchased heat- and moisture-sensitive device has no manufacturer reprocessing instructions available. What is the correct action before the device is used clinically?

    • A.Substitute the IFU from a similar device made by a different manufacturer
    • B.Obtain the manufacturer's written IFU and verify the facility has a validated, cleared cycle capable of processing it; do not process it until then✓ Answer
    • C.Process it in the lowest-temperature cycle available, since that is the most conservative choice
    • D.Process it by ethylene oxide, which is compatible with nearly all materials

    Reprocessing instructions are device-specific and are the only validated evidence that a given method and cycle will both sterilize the device and leave it functional and undamaged. Borrowing another manufacturer's IFU or guessing at a low-temperature method risks an ineffective cycle, material damage, or toxic residuals in a device whose materials were never tested against that sterilant. If the facility cannot obtain the IFU or lacks a cleared cycle that matches it, the device cannot be reprocessed there.

    Source: ANSI/AAMI ST79, manufacturer's written IFU as the authority for method selectionReport a problem with this question

17. 17. Why is steam the method of first choice whenever a device can tolerate heat and moisture?

    • A.Because it does not require biological or chemical monitoring
    • B.Because it removes any residual soil left after cleaning
    • C.Because it is the only method that achieves a sterility assurance level of 10 to the minus 6
    • D.Because it is nontoxic, rapid, inexpensive, penetrates packaging and lumens, and leaves no residue requiring aeration✓ Answer

    Steam is preferred because it combines the widest safety and practicality advantages: no toxic sterilant to handle or aerate, short cycles, low cost, and excellent penetration of wrapped sets and lumens. Every properly validated sterilization method, including the low-temperature ones, is designed to achieve a sterility assurance level of 10 to the minus 6, and every method still requires monitoring. Critically, no method can compensate for inadequate cleaning, since an item that is not clean cannot be sterilized.

    Source: CDC/HICPAC Guideline for Disinfection and Sterilization, steam sterilization advantages; ANSI/AAMI ST79 method selectionReport a problem with this question

18. 18. What does a Bowie-Dick (DART) test actually evaluate, and how must it be run?

    • A.It is an air-removal test using a Type 2 chemical indicator, run each day the dynamic-air-removal sterilizer is used, in an empty preheated chamber, before the first processed load✓ Answer
    • B.It is a biological test using Geobacillus stearothermophilus and is run weekly in any sterilizer type
    • C.It verifies sterility of the load and is run inside the first fully loaded cycle of the day
    • D.It is a dryness test and requires the cycle to be extended beyond the normal exposure time

    The Bowie-Dick test is a Type 2 chemical indicator designed for one purpose: to reveal whether the sterilizer's dynamic air-removal system evacuated air adequately, since residual air produces a distinctive non-uniform color change. It tells you nothing about sterility or lethality, which only biological indicators measure. It must be run in an empty, preheated chamber, on the bottom shelf over the drain, before the first processed load of the day, and at the normal exposure time, because extending the cycle can mask an air-removal deficiency and invalidates the test.

    Source: ANSI/AAMI ST79, air-removal (Bowie-Dick) testing of dynamic-air-removal sterilizersReport a problem with this question

19. 19. Which biological indicator organism is paired with which method?

    • A.Geobacillus stearothermophilus for ethylene oxide; Bacillus atrophaeus for steam and ozone
    • B.Bacillus atrophaeus for steam; Geobacillus stearothermophilus for dry heat
    • C.Clostridioides difficile spores for all low-temperature methods
    • D.Geobacillus stearothermophilus for steam and ozone; Bacillus atrophaeus for ethylene oxide and dry heat✓ Answer

    A biological indicator must contain spores that are highly resistant to the specific sterilizing agent being challenged, so that killing them proves adequate lethality for ordinary contaminants. Geobacillus stearothermophilus spores are the most resistant to moist heat and to oxidizing sterilants such as ozone, while Bacillus atrophaeus spores are the most resistant to ethylene oxide and to dry heat. Pairing the wrong organism with a method produces a test that is not a meaningful challenge.

    Source: CDC/HICPAC Guideline for Disinfection and Sterilization, biological indicators by sterilization methodReport a problem with this question

20. 20. An instrument tray containing an implant has completed a steam cycle. What is required before the implant may be released for use?

    • A.The load must contain a biological indicator with a Type 5 integrating indicator in a process challenge device, and the implant is quarantined until the BI result is known✓ Answer
    • B.The implant may be released as soon as the physical monitors show correct time and temperature
    • C.Only the external chemical indicator needs to be checked, since implants are terminally sterilized
    • D.A Bowie-Dick test result from that morning is sufficient release documentation

    Implants remain in the body, so an infection from a contaminated implant is severe and often requires surgical removal; this raised risk is why the release criteria are stricter. Only a biological indicator directly demonstrates that spores were killed, so every implant load is monitored with a BI plus a Type 5 integrating indicator inside a process challenge device, and the implant is quarantined until the BI is read. Release before the result is available is permitted only in a documented emergency, with follow-up on the BI outcome.

    Source: ANSI/AAMI ST79 13.5.3.2, monitoring and release of implant loadsReport a problem with this question

21. 21. Which loading practice is correct for a steam sterilizer load containing paper-plastic pouches, a solid-bottom basin, wrapped instrument trays and textile packs?

    • A.Stand pouches on edge with paper facing plastic, tilt the basin on its edge so condensate drains, lay wrapped trays flat, and place instrument trays below textiles✓ Answer
    • B.Lay pouches flat and stack them, place basins upright, and put textile packs on the bottom shelf under the instrument trays
    • C.Place instrument trays above textile packs so the heavier items heat first
    • D.Pack all items tightly against each other and against the chamber walls to maximize steam contact

    Load configuration is designed to let steam contact every surface and let condensate drain away rather than pool. Pouches on edge with paper facing plastic allow steam in through the porous side and prevent water from being trapped between two plastic faces; a basin tilted on edge sheds condensate instead of collecting a puddle; and metal instrument trays go below absorbent textiles so condensate dripping from metal does not soak the packs above. Tight packing and contact with chamber walls impede steam circulation and cause superheating and wet packs.

    Source: ANSI/AAMI ST79 10.1, sterilizer loadingReport a problem with this question

22. 22. A wrapped tray is removed from the sterilizer with visible moisture on the outside of the wrapper. Which of the following is both a recognized cause of wet packs and the correct disposition of the tray?

    • A.Excessive drying time; open the tray and use the instruments immediately
    • B.A clogged chamber drain or an overloaded chamber; the pack is considered contaminated and must be reprocessed, not used✓ Answer
    • C.Steam that is too dry; wipe the wrapper dry and place the tray in storage
    • D.Loading the tray flat on the shelf; allow the pack to air-dry on a cold metal shelf and then release it

    Wet packs arise when condensate cannot drain or evaporate, and recognized causes include wet steam, a clogged chamber drain or strainer, an overloaded or tightly packed chamber, stacked trays, insufficient dry time and removing the load too early. A wet wrapper is treated as contaminated because moisture wicks microorganisms from the outer surface through the barrier to the contents, so the pack cannot be used and must be reprocessed. Wiping it dry or air-drying it does not restore the sterile barrier.

    Source: ANSI/AAMI ST79, wet pack causes and handling of compromised packagingReport a problem with this question

Practice questions based on the HSPA CRCST Certification Exam Content Outline, ANSI/AAMI ST79 sterility-assurance practice, and CDC/HICPAC disinfection and sterilization guidance. CRCST is a mark of the Healthcare Sterile Processing Association; this site is not affiliated with or endorsed by HSPA. Always follow the device manufacturer's written instructions for use, your facility's policies, and the current edition of the applicable standards. About the CRCST exam →