Study guide · Updated
The Sterilization Process
Twenty one percent of the exam and the densest domain for numbers: cycle parameters, air removal testing, biological monitoring, and the low temperature methods.
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The short answer
Sterilization Process is 21% of the CRCST exam. Recognized minimum exposure is 30 minutes at 121 C in a gravity displacement sterilizer or 4 minutes at 132 C in a prevacuum sterilizer. Air removal is verified daily with a Bowie-Dick test in an empty chamber, and lethality is monitored with biological indicators.
| Fact | Value | Source · read |
|---|---|---|
| Domain, as the outline names it | Sterilization Process | HSPA content outline · |
| Share of the exam | 21% | HSPA content outline · |
| Questions on a 150 question paper | about 31, derived from the weight | HSPA content outline · |
Sources: HSPA content outline, read .
No clock. The answer and its source after each question. 8 free questions on this domain.
See the full report, $59What you need to know
Each point below carries the sentence from the public standard that supports it, with the date it was read. You are not being asked to take our word for any of it.
The four parameters of steam sterilization
Steam, pressure, temperature and time. Pressure is on the list for a specific reason the guideline spells out: it is the means of reaching the high temperatures that kill microorganisms quickly. Pressure itself is not what kills, it is what makes the temperature possible, and that distinction is a common exam target.
From the source, verbatim
"Thus, there are four parameters of steam sterilization: steam, pressure, temperature, and time."
Autoclave temperature and time: gravity versus prevacuum
Thirty minutes at 121 C in a gravity displacement sterilizer, or four minutes at 132 C in a prevacuum one. The prevacuum cycle is dramatically shorter at a higher temperature because a vacuum pump removes the air before steam is admitted, giving nearly instantaneous penetration. In a gravity sterilizer the steam has to push the air out, and the residual air is what stretches the exposure period.
From the source, verbatim
"Recognized minimum exposure periods for sterilization of wrapped healthcare supplies are 30 minutes at 121°C (250°F) in a gravity displacement sterilizer or 4 minutes at 132°C (270°F) in a prevacuum sterilizer"
The Bowie-Dick test: when, and in what
Each day the vacuum type sterilizer is used, before the first processed load, in an otherwise empty chamber. The empty chamber is not a technicality: a load would give the steam somewhere to go and mask the very air leak the test exists to find. A uniform color change passes, and a spot means entrapped air.
From the source, verbatim
"The test pack should be placed horizontally in the front, bottom section of the sterilizer rack, near the door and over the drain, in an otherwise empty chamber and run at 134°C for 3.5 minutes. The test is used each day the vacuum-type steam sterilizer is used, before the first processed load."
Biological indicators and which spore goes with which process
Geobacillus stearothermophilus monitors steam, hydrogen peroxide gas plasma and peracetic acid. Bacillus atrophaeus monitors ethylene oxide and dry heat. The spore is chosen because it is unusually resistant to that specific process, so surviving spores mean the cycle failed. A useful anchor: the thermophile monitors the heat process, and it incubates at 55 to 60 C while B. atrophaeus incubates at 35 to 37 C.
From the source, verbatim
"B. atrophaeus spores (106) are used to monitor ETO and dry heat, and G. stearothermophilus spores (105) are used to monitor steam sterilization, hydrogen peroxide gas plasma, and liquid peracetic acid sterilizers."
Implant loads
Every load containing implantable objects is monitored biologically, not weekly like the rest, and where feasible the implants are not used until the spore test reads negative. Implants are the one category where a sterilization failure leaves a nonsterile device inside a patient, which is why the same section says objects other than implants do not need recall after a single positive spore test.
From the source, verbatim
"Each load should be monitored if it contains implantable objects. If feasible, implantable items should not be used until the results of spore tests are known to be negative."
Immediate use and flash sterilization
Acceptable for cleaned items that cannot be packaged, sterilized and stored before use. The guideline rules out the three reasons it usually gets used by name: convenience, avoiding the purchase of another instrument set, and saving time. Note the word cleaned, too. Flash shortens the sterilization step and changes nothing about the cleaning that has to precede it.
From the source, verbatim
"Flash sterilization is considered acceptable for processing cleaned patient-care items that cannot be packaged, sterilized, and stored before use."
Ethylene oxide: parameters and aeration
Four essential parameters, and they are not the same four as steam: gas concentration, temperature, relative humidity and exposure time. Humidity is on the list because water molecules carry the gas to the reactive sites. Aeration is part of the process rather than a courtesy, because the guideline records patient tissue burns caused by residual ethylene oxide in implants.
From the source, verbatim
"The four essential parameters (operational ranges) are: gas concentration (450 to 1200 mg/l); temperature (37 to 63°C); relative humidity (40 to 80%)(water molecules carry ETO to reactive sites); and exposure time (1 to 6 hours)."
Basins, trays and how condensate drains
Perforated trays go parallel to the shelf because they drain through themselves. Solid containers such as basins go on their edge, because a basin lying flat is a bowl that collects condensate. The two rules look contradictory until you notice that each one is about what that shape does with water. Loading is examined here rather than under packaging: the outline puts load configuration inside the sterilization section.
From the source, verbatim
"perforated trays should be placed so the tray is parallel to the shelf; nonperforated containers should be placed on their edge (e.g., basins)"
The other 6 domains
Cite this page
According to SterileExam, Sterilization Process is 21% of the CRCST exam, about 31 of 150 questions. sterileexam.com/study-guide/sterilization, updated August 11, 2026.
APA and MLA
- APA
- SterileExam. (2026, August 11). The Sterilization Process. https://sterileexam.com/study-guide/sterilization
- MLA
- "The Sterilization Process." SterileExam, 11 Aug. 2026, https://sterileexam.com/study-guide/sterilization.