Sterilization Process is 21% of the scored CRCST exam. Answer 10 exam style questions on ethylene oxide sterilization and see exactly which concepts would cost you points on test day.
Start the 10 questions →Which item is the most appropriate candidate for ethylene oxide (EtO) sterilization?
These questions cover etO indications, etO critical parameters, etO mechanism, etO aeration purpose and etO aeration time. Each one shows the correct answer and why every other option is wrong, so a miss tells you exactly what to review before the CRCST.
Prefer to read first? Every question from the practice set above, with the correct answer and why each wrong option is wrong.
Answer: C. EtO is a low temperature gas method used for devices that cannot tolerate the heat and moisture of steam, and only when the device IFU lists EtO as a validated method. Heat stable items go to steam, which is faster, cheaper, and nontoxic.
Why not A: Stainless steel retractors tolerate steam, which is the preferred method for heat stable items.
Why not B: Stainless steel basins tolerate heat and moisture, so they go to steam, which is faster, cheaper, and nontoxic.
Why not D: Heat tolerant linen packs are sterilized by steam, not by a toxic gas that requires long aeration.
Exam tactic: Steam if it can take heat. EtO only when it can't and the IFU says so.
Answer: A. EtO effectiveness depends on four parameters working together: gas concentration, temperature, relative humidity, and exposure time. Changing one, such as raising concentration or temperature, can change the time needed.
Why not B: These are steam sterilization variables. EtO uses gas concentration and humidity instead of steam.
Why not C: These terms describe hydrogen peroxide plasma style systems, not EtO.
Why not D: These describe liquid chemical sterilant systems, not a gas sterilization process.
Exam tactic: EtO = gas, heat, humidity, time.
Answer: B. Ethylene oxide kills microorganisms by alkylation of proteins, DNA, and RNA, which blocks normal cell metabolism and reproduction. This chemical action works at low temperature, which is why EtO suits heat sensitive devices.
Why not A: Protein coagulation by moist heat is how steam sterilization works.
Why not C: Oxidation by free radicals describes hydrogen peroxide and other oxidizing sterilants.
Why not D: Dehydration and oxidation by high heat describes dry heat sterilization.
Exam tactic: EtO alkylates. Steam coagulates. Peroxide oxidizes.
Answer: C. Many materials, especially plastics and rubber, absorb EtO during the cycle. Aeration lets the residual gas desorb so the item does not cause chemical burns or tissue irritation in patients, or exposure for staff.
Why not A: Drying is not the purpose. Aeration removes toxic gas residues from the materials.
Why not B: Cooling happens anyway. The reason aeration is mandatory is toxic residue removal.
Why not D: Microbial kill is complete at the end of the exposure phase. Aeration is for safety, not lethality.
Exam tactic: Aeration = get the poison out.
Answer: D. CDC describes mechanical aeration as 8 to 12 hours at 50 to 60°C, and the commonly cited pairing is 12 hours at 50°C or 8 hours at 60°C. The lower end of the temperature range needs the longer time, and the device or aerator IFU always takes priority when it states different values.
Why not A: 2 hours is far too short to remove absorbed EtO residues at 50°C.
Why not B: 4 hours falls below the CDC mechanical aeration range of 8 to 12 hours and leaves residual gas in absorbent materials.
Why not C: 8 hours is the commonly cited time at 60°C. At the lower temperature of 50°C, the time is 12 hours.
Exam tactic: Aerate 12 at 50, 8 at 60. Hotter is faster.
Answer: B. Polyvinyl chloride readily absorbs ethylene oxide, and residual EtO can cause chemical burns and irritation of patient tissue. The item stays in the aerator for the full time required by the IFU, and the OR is offered an alternative.
Why not A: Sterility is achieved at exposure, but the item is not safe until aeration removes the residual gas.
Why not C: Rinsing does not remove gas absorbed into the plastic, and it would also contaminate the sterile item.
Why not D: An hour in open air is not validated aeration and releases EtO into the workroom where staff breathe it.
Exam tactic: Sterile is not safe until aeration ends.
Answer: B. Spores of Bacillus atrophaeus are the recommended biological indicator for EtO, and they are also used for dry heat. Geobacillus stearothermophilus is the BI organism for steam and hydrogen peroxide processes.
Why not A: Geobacillus stearothermophilus is used for steam and hydrogen peroxide, not EtO.
Why not C: Staphylococcus aureus is a common pathogen, not a resistant spore used in a BI.
Why not D: Clostridioides difficile is a pathogen and is not used as a sterilization BI.
Exam tactic: EtO and dry heat = atrophaeus. Steam and peroxide = stearothermophilus.
Answer: C. Personal monitoring badges, or dosimeters, measure the worker's exposure to ethylene oxide in the breathing zone over the shift or a short period. Results are compared with OSHA limits to verify that controls protect staff.
Why not A: EtO sterilizers do not emit radiation, and the badge measures gas exposure.
Why not B: Aerator temperature is shown by the equipment's own monitors, not by a worn badge.
Why not D: Room humidity is not measured by a personal badge worn near the collar.
Exam tactic: Badge at the collar = what you breathe.
Answer: A. Ethylene oxide is toxic, flammable, and associated with cancer from chronic exposure. Acute exposure causes respiratory irritation, headache, nausea, and vomiting, so OSHA requires exposure limits, monitoring, and training.
Why not B: Equipment damage is not the reason for exposure controls. The hazard is to human health.
Why not C: Water vapor and oxygen are the byproducts of hydrogen peroxide systems, not EtO.
Why not D: EtO is not known for rusting instruments. Its main danger is toxicity and cancer risk.
Exam tactic: EtO: toxic, flammable, carcinogenic.
Answer: C. Ethylene oxide is toxic, carcinogenic, and flammable. CDC notes that 100% EtO cartridges should be stored in a flammable liquid storage cabinet, which limits fire risk and accidental exposure.
Why not A: An open shelf next to the sterilizer gives no fire protection for a flammable chemical.
Why not B: A BI refrigerator is not designed for flammable chemicals and mixes a hazardous gas source with testing supplies.
Why not D: The decontamination sink area is wet, cluttered, and not a controlled storage location for a flammable chemical.
Exam tactic: Flammable gas cartridge, flammable cabinet.
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