22 Sterilization Methods Practice Questions & Answers

1. 1. Saturated steam under pressure is used to sterilize surgical instrument sets. By what mechanism does moist heat actually destroy microorganisms, including spores?

   • A.Pressure inside the chamber physically ruptures the cell wall, so the organism collapses and cannot recover.
   • B.Moisture-laden heat coagulates and denatures the cell's proteins and enzymes, ending all metabolic activity.✓ Answer
   • C.Heated vapor draws the water out of the cell, and the resulting desiccation leaves the spore unable to germinate.
   • D.Steam chemically alkylates the organism's DNA, which blocks replication and leaves the cell unable to divide.

   Moist heat sterilizes by hydrating and then coagulating and denaturing cellular proteins and enzymes, which is why saturated steam, not hot air, is required. Pressure only raises the temperature at which the steam condenses and does not kill on its own; dry heat kills by oxidation and ethylene oxide by alkylation.

   Source: ANSI/AAMI ST79, principles of moist-heat steam sterilization; HSPA CRCST body of knowledge, Sterilization ProcessReport a problem with this question

2. 2. A wrapped instrument tray is opened in the operating room. The tape on the outside has changed, but the chemical indicator placed deep inside the tray has not. Which explanation best accounts for this?

   • A.External tape reacts at a lower temperature than an internal indicator, so a gap between them is expected.
   • B.A pocket of air stayed trapped in the center of the set, so steam never contacted that surface at cycle temperature.✓ Answer
   • C.Chamber pressure ran above the setting for the cycle, which pushed the internal indicator past its color endpoint.
   • D.The tray left the chamber before drying had finished, and the residual moisture bleached the indicator's ink.

   Air is heavier than steam and does not transfer heat the way condensing steam does, so a trapped pocket stays cooler and keeps steam off the instruments inside it. Trapped air is the most common cause of steam sterilization failure, and the set must be treated as unsterile and reprocessed; the external tape shows only that the package was exposed to a process.

   Source: ANSI/AAMI ST79, air removal and steam penetration; CDC Guideline for Disinfection and Sterilization, steam sterilizationReport a problem with this question

3. 3. The instructions for a rigid, nonporous instrument allow either a gravity-displacement or a dynamic-air-removal steam cycle. How do the two designs differ in the way air leaves the chamber?

   • A.In gravity, a pump evacuates the chamber first; dynamic cycles let the air rise and vent through a port in the door.
   • B.In gravity, repeated water sprays dilute the air; dynamic cycles heat the air until the steam supply absorbs it.
   • C.In gravity, the jacket absorbs chamber air before steam enters; dynamic cycles add gravity plus a longer exposure.
   • D.In gravity, entering steam pushes the heavier air down and out the drain; dynamic cycles remove air mechanically.✓ Answer

   Gravity displacement is passive: steam is lighter than air, so it enters at the top and pushes air out through the bottom drain. Because that removal is slower and less complete, gravity cycles need longer exposure and suit nonporous, non-lumened items, while dynamic air removal actively pulls or flushes air out and is used for porous and lumened loads.

   Source: ANSI/AAMI ST79, sterilizer cycle types: gravity-displacement and dynamic air removalReport a problem with this question

4. 4. A device's instructions for use specify a dynamic-air-removal steam cycle. Which sterilizer design satisfies that instruction?

   • A.A gravity-displacement sterilizer at the same exposure temperature, because the drain still carries chamber air away.
   • B.A steam-flush pressure-pulse sterilizer, which removes air with repeated flushes and pulses above atmospheric.✓ Answer
   • C.A tabletop gravity sterilizer set to its longest wrapped-goods cycle, because added exposure offsets residual air.
   • D.Any steam sterilizer at all, because dynamic air removal describes the drying phase rather than the air-removal method.

   Dynamic air removal covers both prevacuum and steam-flush pressure-pulse designs, so either satisfies an instruction that names it. The pressure-pulse design keeps chamber pressure above atmospheric instead of drawing a vacuum, so air cannot be sucked back in through a leak, and gravity displacement is not interchangeable with either one.

   Source: ANSI/AAMI ST79, dynamic air removal cycles (prevacuum and steam-flush pressure-pulse)Report a problem with this question

5. 5. A daily air-removal test pack of the Bowie-Dick type is run in a prevacuum sterilizer and passes. What does that result establish?

   • A.That the exposure phase reached and held the temperature needed to kill the resistant spores on the sheet.
   • B.That the air was removed well enough for steam to penetrate quickly, with no leak or non-condensable gas present.✓ Answer
   • C.That the sterilizer met every critical parameter for the load that follows, so no biological challenge is needed today.
   • D.That the chamber drain, the door gasket and the jacket passed the preventive maintenance scheduled for that week.

   The Bowie-Dick style test is a chemical indicator designed for one specific test: air removal and rapid steam penetration. It detects leaks, vacuum pump problems and non-condensable gases, contains no spores, says nothing about lethality, and never substitutes for biological monitoring.

   Source: ANSI/AAMI ST79, Bowie-Dick (air-removal) testing; ISO 11140 indicators for a specific testReport a problem with this question

6. 6. Under what conditions is the daily air-removal test of a dynamic-air-removal sterilizer performed?

   • A.In a fully loaded chamber at the end of the day, with the pack on the top shelf and away from the chamber door.
   • B.In an empty cold chamber at any convenient hour, with the pack placed at the geometric center of the chamber.
   • C.In an empty, prewarmed chamber before the first processed load, with the pack on the bottom shelf over the drain.✓ Answer
   • D.In the first patient-item load of the day, with the pack tucked inside the densest wrapped tray in that load.

   The chamber is empty so the test pack is the only challenge, and a warm-up cycle is run first so that a cold chamber does not itself generate condensate and a false failure. The pack sits over the drain because that is the coolest, hardest place for steam to reach, and the test is run each day the sterilizer is used, before the first processed load.

   Source: ANSI/AAMI ST79, daily air-removal (Bowie-Dick) test procedureReport a problem with this question

7. 7. The morning air-removal test sheet shows a pale, unchanged patch in the center while the edges changed uniformly. What is the correct next step?

   • A.Rerun the same pack through a second cycle, since the greater total exposure will finish the change and confirm it.
   • B.Release the sterilizer for use, since the edges responded and a pale central area is normal in a folded test pack.
   • C.Run the day's loads but add a second internal indicator to every tray, and report the pale center at the next service.
   • D.Repeat the test in an empty chamber; if the second pack also fails, hold the sterilizer out of service for repair.✓ Answer

   A lighter or unchanged center is the classic pattern of air trapped in the pack, caused by a leak, a vacuum pump fault or non-condensable gases in the steam. The test is repeated once to confirm, and a second failure means the sterilizer may not process patient items until the cause is found and corrected; extra indicators or a longer run do not fix air removal.

   Source: ANSI/AAMI ST79, interpretation of air-removal test results and removal of a sterilizer from serviceReport a problem with this question

8. 8. Physical, chemical and biological monitors are all applied to a steam load. Which statement describes what they can establish?

   • A.Only the biological indicator gives direct evidence of lethality; physical and chemical monitors show conditions.✓ Answer
   • B.Only the chemical indicator gives direct evidence of lethality, since its dye reacts to time, heat and moisture at once.
   • C.Only the printout gives direct evidence of lethality; indicators and spore tests are secondary checks on packaging.
   • D.All three give equally direct evidence of lethality, so a single passing result of any kind releases the load for use.

   Physical monitors report what the chamber actually did, and chemical indicators show that specified conditions were met where the indicator sat, but neither challenges the process with living organisms. The biological indicator carries a known population of highly resistant spores, so it is the only device that directly measures the lethality of the cycle.

   Source: ANSI/AAMI ST79, physical, chemical and biological monitoring of sterilization processesReport a problem with this question

9. 9. A supervisor proposes replacing the routine biological indicator challenge with an integrating (Type 5) chemical indicator, arguing that it responds to all the critical variables. Why is that unacceptable?

   • A.The integrator responds only to temperature, so it cannot confirm that steam and pressure were present in the chamber.
   • B.The integrator is a single-use device, and its result cannot be filed with the cycle records a recall investigation needs.
   • C.The integrator is calibrated to one named cycle only, so it would have to be replaced whenever the load contents change.
   • D.The integrator carries no living spores, so it can never show that a resistant microbial population was killed.✓ Answer

   An integrating indicator is calibrated against the performance of a biological indicator, but it is still a chemical reaction and contains no living organisms, so it cannot demonstrate spore kill. Biological monitoring at the required intervals, and in implant loads, cannot be satisfied by any chemical indicator.

   Source: ANSI/AAMI ST79, biological monitoring requirements; ISO 11140 integrating indicatorsReport a problem with this question

10. 10. A technician places an emulating (Type 6) indicator labeled for one specific exposure cycle into a tray that will be run in a different cycle. Why is that wrong?

    • A.An emulating indicator reacts to the variables of the one cycle it is labeled for, so its reading means nothing here.✓ Answer
    • B.An emulating indicator has to be paired with a spore strip in the same tray, and without that pairing it cannot be read.
    • C.An emulating indicator may be used only outside a package, so it cannot be placed inside a tray in any cycle at all.
    • D.An emulating indicator outranks an integrator, so using one in a routine tray wastes the highest grade made anywhere.

    An emulating indicator is a cycle-verification device: it is designed and labeled for the stated variables of one named cycle, so in a different cycle its endpoint no longer corresponds to anything meaningful. The numbering of indicator types describes what an indicator responds to and is not a quality ranking.

    Source: ISO 11140 emulating (cycle-verification) indicators; ANSI/AAMI ST79, selection and use of chemical indicatorsReport a problem with this question

11. 11. A technician incubates the day's processed biological indicator together with an unprocessed control from the same lot. The processed indicator shows no growth, and the control also shows no growth. How is this interpreted?

    • A.The run fails: no growth in the control means the sterilizer contaminated that vial, so the load is recalled.
    • B.The run passes: no growth in either vial confirms the spores were killed and that the incubator was right.
    • C.The run is invalid: with no growth in the control, neither the spores nor the incubator can be trusted at all.✓ Answer
    • D.The run is unresolved for implants only: other items are released and the control is repeated the next day.

    The unprocessed control from the same lot proves two things at once: that the spore population was viable and that the incubator was working. If the control does not grow, nothing can be concluded from the processed indicator, so acceptance requires the processed indicator negative and the control positive.

    Source: ANSI/AAMI ST79, biological indicator controls and interpretation of resultsReport a problem with this question

12. 12. A full-size dynamic-air-removal sterilizer is monitored with a process challenge device holding a biological indicator. Where and under what chamber condition is that device placed?

    • A.In the part of a fully loaded chamber that steam reaches last, low and toward the front near the drain.✓ Answer
    • B.On the top shelf of an empty chamber, so that nothing else takes up steam and the device gets the full flow.
    • C.Inside the heaviest tray of the load and wrapped with the instruments, so it shares that tray's exact conditions.
    • D.Anywhere in the chamber provided the load is light, since the device itself is the challenge rather than its position.

    A process challenge device has to present a challenge at least equal to the most difficult item routinely processed, and it only does that where the sterilant arrives last. For a full-size chamber that means a chamber loaded as it is for routine work, with the device low and near the door over the drain.

    Source: ANSI/AAMI ST79, process challenge devices and placement for routine biological monitoringReport a problem with this question

13. 13. A steam sterilizer has just undergone a major repair to its vacuum system. What must happen before it processes items for patient use again?

    • A.It is requalified with challenge cycles monitored by a biological indicator, and stays out of service until they pass.✓ Answer
    • B.It is returned to use and waits for the next scheduled spore test, with earlier loads simply noted in the cycle log.
    • C.It is released once the service report is filed, since the repair company has already verified the unit's function.
    • D.It is run through one empty warm-up cycle, and the first load is released on the strength of its chemical indicators.

    Qualification testing with biological indicator challenge devices, plus air-removal testing on a dynamic-air-removal unit, is required after installation, relocation, a malfunction, a major repair, a process failure or a change in utilities. Consecutive passing cycles are needed, and the sterilizer may not process patient items until they pass; a vendor's report does not release it.

    Source: ANSI/AAMI ST79, qualification testing after installation, relocation, malfunction or major repairReport a problem with this question

14. 14. An implant was processed in a load monitored with a process challenge device holding both a biological indicator and an integrating indicator. The biological indicator is still incubating and the implant is needed for a documented emergency. What does the standard allow?

    • A.Release on the passing integrator alone and discard the biological indicator, since the load has gone to the operating room.
    • B.Release on the passing integrator and physical monitors, record the early release on an exception form, and still read it.✓ Answer
    • C.Release the implant and log it as a routine issue, because an emergency case adds no further documentation duty at all.
    • D.Release the implant only once the biological indicator has been read out, even if the procedure has to wait until then.

    Implant loads are quarantined until the biological indicator has been read, and that remains the default. Only in a documented emergency may the implant be released early on the strength of the integrating indicator and the cycle record, and even then the biological indicator is still incubated, the result documented, and the early release recorded on an exception form with follow-up.

    Source: ANSI/AAMI ST79, monitoring of implant loads and documented emergency releaseReport a problem with this question

15. 15. A department owns a single set of a frequently needed instrument and runs it through an immediate-use steam cycle between cases every day. How should this practice be judged?

    • A.It is acceptable because the set is cleaned and decontaminated the same way before each immediate-use cycle is run.
    • B.It is a misuse of immediate-use sterilization, which exists for an urgent item and not to cover an inventory shortage.✓ Answer
    • C.It is acceptable as long as every cycle is logged and the set travels to the operating room in a closed container.
    • D.It is acceptable because an immediate-use cycle reaches the same exposure temperature as a terminal wrapped cycle.

    Immediate-use steam sterilization is reserved for a situation where an item is needed right away and no sterile replacement is available. Using it day after day to work around a permanent shortage of instruments is exactly the convenience use the standard prohibits, and correct cleaning or good record keeping does not make it acceptable.

    Source: ANSI/AAMI ST79, immediate-use steam sterilization; AORN Guideline for SterilizationReport a problem with this question

16. 16. What must the record of an immediate-use steam cycle make possible?

    • A.Tracing the load contents and cycle data to the individual patient on whom the items were used, and to the operator.✓ Answer
    • B.Showing that the items were placed into sterile storage and were rotated with the rest of the department's stock.
    • C.Proving that the set carried an expiration date and a shelf-life statement before it went to the operating room.
    • D.Confirming that the set was wrapped in a validated barrier so it could be held for the next case on that day's list.

    An immediate-use item is transported aseptically and used at once rather than stored, so there is no quarantine period and no shelf life to record. The record therefore has to support traceability to the patient, along with the load contents, the cycle parameters, the operator and the reason the cycle was run.

    Source: ANSI/AAMI ST79, immediate-use steam sterilization documentation and traceabilityReport a problem with this question

17. 17. A mixed steam load holds wrapped metal instrument trays, textile packs, basins and peel pouches. How should the chamber be loaded?

    • A.Textile packs low, metal trays above them, basins flat on the shelf, and pouches laid flat and stacked to save room.
    • B.Everything packed tightly so nothing shifts, with the pouches placed inside the wrapped trays so they cannot slide.
    • C.Metal trays low, textiles above them, basins tilted on edge and pouches on edge, with space between every item.✓ Answer
    • D.Metal trays and textiles side by side and touching on one shelf, with basins upright so they can hold the condensate.

    Condensate runs downward, so metal placed above porous goods drips onto them and soaks the barrier. Basins and solid-bottom containers are tilted on edge so water runs out, pouches stand on edge so steam enters and the paper can dry, and space between items lets steam circulate and reach every surface.

    Source: ANSI/AAMI ST79, sterilizer loading and load configurationReport a problem with this question

18. 18. Wrapped trays come out damp from one steam sterilizer, while the same trays run dry in another sterilizer in the same department. Which cause best explains this?

    • A.That chamber runs hotter than the cycle calls for, and the superheated steam lays a film of water on the wrapper.
    • B.The internal indicators in the trays take up steam during exposure and then give the moisture back during drying.
    • C.The trays are cooling too slowly on the cart, so the warm air around them keeps the wrappers from drying off.
    • D.The steam reaching that chamber carries too much water, so condensate forms faster than the drying phase removes it.✓ Answer

    Steam that carries excess water, typically from boiler carryover or a supply problem serving that one machine, deposits more condensate than the drying phase can drive off, which is a classic wet-pack cause. A wet pack is considered contaminated: it cannot be dried, re-taped or used, and the contents must be fully reprocessed.

    Source: ANSI/AAMI ST79, steam quality and causes of wet packsReport a problem with this question

19. 19. A staging rack used for cooling sits directly under a ceiling air diffuser, and packages are unloaded onto it straight from the chamber. What is the problem?

    • A.Moving air dries the wrappers faster than the sterilizer's own drying phase, which makes the barrier brittle and easy to tear.
    • B.The diffuser keeps the packages warm for longer, so the indicators inside them go on reacting and overshoot the endpoint.
    • C.Cold air blowing onto hot packages drives condensation inside the wrapper, and that moisture carries contamination in.✓ Answer
    • D.Air from a diffuser is unfiltered, so airborne dust settles on the wrappers and has to be wiped off before they are stored.

    Cooling a hot package too quickly makes water condense on and within the barrier, and a damp wrapper wicks organisms from the outside to the contents. Loads are cooled undisturbed on a rack away from vents, drafts and cold surfaces, are never set hot onto a cold solid counter, and are not handled or transferred until they are cool.

    Source: ANSI/AAMI ST79, cooling and post-sterilization handling of sterilized itemsReport a problem with this question

20. 20. A heat-sensitive device is processed with ethylene oxide. Why must the aeration phase be completed before the item is handled or issued?

    • A.Aeration allows the external indicator to finish changing color, and the load is not released before that change is read.
    • B.Aeration is the phase in which the gas finishes killing the spores, so an early removal leaves the process incomplete.
    • C.Aeration restores the humidity the device lost inside the chamber, without which its plastic parts grow brittle and crack.
    • D.Aeration lets the gas taken up by the device and its packaging dissipate, since that residue harms patients and staff.✓ Answer

    Ethylene oxide is absorbed by polymers and packaging materials, and residual gas is toxic, so aeration is a mandatory phase that drives the residue off before anyone handles the item. Sterilization itself occurs by alkylation during the exposure phase, and it is the long aeration requirement that gives ethylene oxide the longest turnaround of the low-temperature methods.

    Source: ANSI/AAMI ST41, ethylene oxide sterilization and aeration; OSHA ethylene oxide standard, 29 CFR 1910.1047Report a problem with this question

21. 21. A rigid device with a long, narrow lumen is being considered for a hydrogen peroxide cycle. What determines whether it may be processed that way?

    • A.Whether the lumen can be flushed with sterile water first, because a wetted channel helps carry vapor along its length.
    • B.Whether a longer exposure can be selected, since added time will move the vapor through any channel a device may have.
    • C.Whether the device and sterilizer instructions accept a lumen of that bore and length, since the vapor must reach its end.✓ Answer
    • D.Whether the device is metal, because a metal channel conducts the vapor while a polymer channel absorbs and stops it.

    Hydrogen peroxide sterilizes by diffusing to every surface, and a long narrow channel limits how far the vapor penetrates, so the lumen claims validated in the device and sterilizer instructions decide the question. The item must also be completely dry, because residual moisture will cancel the cycle.

    Source: ANSI/AAMI ST58, low-temperature chemical sterilization; device and sterilizer instructions for use, lumen claimsReport a problem with this question

22. 22. An instrument's instructions for use call for one steam exposure, while the rigid container's instructions call for a longer one. What should the department do?

    • A.Follow the more demanding of the two instructions, and contact both manufacturers to settle the difference in writing.✓ Answer
    • B.Follow whichever instruction the sterilizer's own manual comes closest to, because the chamber sets what is achievable.
    • C.Follow the shorter instruction and add one more internal indicator, since the indicator would reveal any shortfall.
    • D.Follow the instrument's instructions, since the device that touches the patient always outranks its packaging system.

    Reprocessing is governed by the manufacturers' validated written instructions, and when the device, the container and the sterilizer instructions disagree the department follows the more stringent requirement and contacts the manufacturers to resolve the conflict. A chemical indicator cannot be used to justify a shorter exposure, because it only reports conditions at its own location.

    Source: ANSI/AAMI ST79, following device, container and sterilizer manufacturers' written instructionsReport 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 →