CRCST Sterilization Study Guide: Steam, BIs and Bowie‑Dick

Why this domain matters

Sterilization Process is about 21% of the CRCST exam, tied with two other domains for the largest share. The weight comes from the HSPA content outline, and most steam rules here come from AAMI ST79. Many of its questions are short scenarios. You may read a cycle printout or decide what to do after a failed test. If you know why each step exists, you can answer scenarios that don't match a memorized rule.

Steam sterilization basics

Steam is the method of choice for items that can take heat and moisture. It kills by moist heat. When saturated steam touches a cooler surface it condenses and releases its latent heat. That heat coagulates the proteins in microorganisms.

• Steam quality: saturated steam that is at least 97% dry. Wet steam causes wet packs. Superheated steam acts like hot dry air and kills less well.
• Air removal: any air left in the chamber or a pack keeps steam from touching the surface.
• Gravity displacement: steam enters and pushes the heavier air down and out the chamber drain.
• Dynamic air removal: vacuum pulses (prevacuum) or steam-flush pressure pulses actively remove air, so steam reaches pack interiors and lumens faster.

The chamber drain line is the coolest point, so that is where temperature is usually sensed. Exposure timing starts when the drain reaches the set temperature. The steam jacket around the chamber keeps the walls hot and limits condensation, and the door gasket seals the chamber.

Cycle phases

Every steam cycle runs in the same order: conditioning (air removal and heat-up), exposure (the timed kill phase), exhaust, and drying.

Typical minimum exposure times (wrapped instruments, per ST79 tables)

Drying times vary. The device's instructions for use (IFU) always govern. Some loaner and specialty trays call for extended cycles, and those must be run exactly as written.

Immediate-use steam sterilization (IUSS)

IUSS is for urgent situations when there is no time to process an item the normal way. A dropped instrument needed for a case in progress is one example. It is never used for convenience or to make up for too few sets. Implants are not processed by IUSS except in a documented emergency.

The item is cleaned exactly as it would be for terminal sterilization (see the cleaning and decontamination guide). It is then moved to the point of use in a way that keeps it sterile. It is logged so it can be traced to the patient.

Other methods

• Dry heat: for oils, powders and items moisture would damage. It is slow: 340 F (171 C) for 1 hour or 320 F (160 C) for 2 hours.
• Ethylene oxide (EO): a low-temperature alkylating gas. It needs humidity and a long cycle. Aeration then removes toxic residues (often about 12 hours at 50 C, per IFU). EO is toxic and carcinogenic. OSHA limits worker exposure to 1 ppm as an 8-hour time-weighted average. The excursion limit is 5 ppm over 15 minutes. Exposure is checked with personal monitoring badges.
• Hydrogen peroxide (gas plasma or vaporized): short, low-temperature cycles with no aeration. No cellulose (paper, linen, cotton), no liquids or powders, and items must be completely dry or the cycle may cancel. Lumen length and diameter limits come from the sterilizer and device IFUs. Use Tyvek-type pouches, polypropylene wrap or validated containers. Handle sterilant cartridges with chemical-resistant gloves.
• Liquid chemical sterilant (peracetic acid) systems: items come out wet and unwrapped, so they are used immediately and never stored.

Quality tests and when to run them

Bowie-Dick / dynamic air removal test (DART): run daily in dynamic-air-removal sterilizers only. It is the first cycle after a warm-up, in an empty chamber. It checks air removal and steam penetration, not sterility. The sheet must change color evenly. A pale center means trapped air, and the sterilizer comes out of service.

Vacuum leak test: checks whether air leaks into the chamber under vacuum. Run it as the manufacturer recommends, commonly weekly.

Biological indicators (BIs): the only monitors that directly show microbial kill. Use only BIs labeled for the specific process and sterilizer.

• Steam: at least weekly, preferably daily, for each type of cycle used, and in every load that contains an implant.
• EO: every load.
• A control BI from the same lot, not processed, is incubated with every test and must grow. If the control does not grow, the test is invalid and must be repeated.

Process challenge device (PCD) placement: for routine steam monitoring in a large sterilizer, use a full load. The BI PCD goes on the bottom shelf, near the front, over the drain. In a table-top sterilizer it goes in the coldest spot the manufacturer identifies.

After installation, relocation or major repair: run three consecutive BI PCD cycles in an otherwise empty chamber. Table-top sterilizers are tested with a full load instead. Dynamic-air-removal sterilizers also need three consecutive Bowie-Dick tests. All must pass before patient loads are run.

Chemical indicators show that a package was exposed to the process, but they do not prove sterility. The indicator classes are covered in the preparation and packaging guide.

Loading the sterilizer

• Check package integrity first. A torn wrap means repackaging, never tape.
• Leave space for steam to circulate; items do not touch the chamber walls.
• Peel pouches stand on edge in baskets.
• Basins and containers sit on edge or tipped so condensate drains.
• In mixed loads, textiles go on top and metal on the bottom.
• Stack rigid containers only if their IFU allows it.
• Choose the cycle the device IFU lists, and confirm the sterilizer can run it.

After the cycle

Printout review. At the end of every cycle the operator checks the printout against the required cycle. Check the cycle type, temperature, exposure time and drying time. If everything was met, the operator initials it. "Cycle complete" only means the program finished. It does not prove the right cycle was chosen. For example, a 10-minute gravity exposure at 270 F is too short. Wrapped sets need 15 minutes.

Cooling and staging. Loads cool on the cart in a low-traffic area away from cold-air vents. Cooling commonly takes 30 minutes to 2 hours, depending on contents and IFU. Packs are not touched while warm, because damp wraps can wick microorganisms through to the contents. After cooling, check each pack for moisture, damage and indicator changes.

Tip from Andrew Hector Smith: When you review a printout, first read the cycle name and exposure time against the tray's IFU. A wrong cycle is easy to miss at the sterilizer door. The printout is where you catch it.

Implants: quarantine and early release

Implant loads are monitored with a BI PCD and held until the BI result is known. Early release is allowed only in a documented emergency. It needs a PCD containing a BI and a Class 5 integrating indicator. It also needs an exception form and follow-up on the BI result. If that BI turns positive, the surgeon and infection prevention are notified promptly.

Process failures and recalls

• Wet packs are considered contaminated and are reprocessed. Common causes are basins placed flat, overloading, dense sets, poor steam quality, short drying and cooling on cold surfaces.
• Failed chemical indicator: do not release that pack. Report it so the load can be evaluated.
• Positive BI: remove the sterilizer from service and notify the supervisor and infection prevention. Quarantine or recall every load back to the last negative BI, then retest and document.

Load documentation and traceability

Every package carries a load control (lot) number made up of the sterilizer number, the date and the cycle number. The same number goes in the sterilization log with the load contents and the physical, chemical and biological monitoring results.

That link is what makes a recall possible. It lets the department find every item from a suspect load. Patient records then show the patients those items were used on. If a pack's load number does not match its printout, hold it until the mismatch is resolved. The sterile storage and inventory guide covers how recalled items are pulled from the shelves.

Quick review

• Remove the air; use saturated steam that is at least 97% dry.
• Bowie-Dick: daily, empty chamber, first cycle after warm-up, dynamic-air-removal sterilizers only.
• BIs: weekly minimum (daily preferred) for steam, every implant load, every EO load, always with a control.
• Implants wait for the BI unless a documented emergency allows early release.
• Positive BI: out of service, notify, recall back to the last negative BI.

Related: Bowie-Dick test vs biological indicator, compared side by side.

Test yourself with the free sterilization practice questions, each with the answer explained. To see which domain to study first, take the free CRCST diagnostic test.

Sources

The Sterilization Process questions cite these documents, by document and, where we can confirm it, chapter or section. We never reproduce them.

1. HSPA Sterile Processing Technical Manual (61 questions)
2. ANSI/AAMI ST79 (34 questions)
3. ANSI/AAMI ST41 (5 questions)
4. OSHA 29 CFR 1910.1047 (2 questions)
5. ANSI/AAMI ST58 (1 question)

Found a mistake? Use "Report a problem" under any question, and Andrew Hector Smith checks it.

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