What are the two most common steam sterilization temperatures?

121°C (250°F) and 132°C (270°F). CDC gives recognized minimum exposure periods for wrapped supplies of 30 minutes at 121°C in a gravity displacement sterilizer, or 4 minutes at 132°C in a prevacuum sterilizer.

Why are prevacuum cycles so much shorter?

A dynamic-air-removal sterilizer pulls air out of the chamber and packs with a vacuum before steam is admitted, so steam reaches every surface quickly. A gravity sterilizer relies on steam pushing the air out through a drain, which is slower and less reliable, so exposure times are longer.

Are these the times to set on our sterilizer?

No. They are minimums from CDC’s guideline for exam study. Always use the cycle validated by the sterilizer manufacturer and the device’s instructions for use (IFU); many devices and containers specify extended cycles.

What is immediate-use steam sterilization (IUSS)?

A shorter cycle, formerly called “flash” sterilization, for items needed right away that cannot be packaged, sterilized and stored first. It is not meant for convenience or to replace adequate instrument inventory, and items should not be stored after IUSS.

Free tool · CRCST exam topic

Steam sterilization cycle times

Pick the sterilizer type and what is in the load to see CDC’s minimum exposure time at 250°F (121°C) and 270°F (132°C), and the drying time.

Gravity displacement · Wrapped instruments

Exposure at 270°F (132°C): 15 min
Exposure at 250°F (121°C): 30 min
Drying time: 15–30 min

Minimum cycle times for wrapped items

CDC’s Table 7, adapted from AAMI standards, lists these minimum exposure and drying times:

Sterilizer	Item	250°F (121°C)	270°F (132°C)	Drying
Gravity displacement	Wrapped instruments	30 min	15 min	15–30 min
Gravity displacement	Textile packs	30 min	25 min	15 min
Gravity displacement	Wrapped utensils	30 min	15 min	15–30 min
Dynamic-air-removal (prevacuum)	Wrapped instruments	Not applicable	4 min	20–30 min
Dynamic-air-removal (prevacuum)	Textile packs	Not applicable	4 min	5–20 min
Dynamic-air-removal (prevacuum)	Wrapped utensils	Not applicable	4 min	20 min

Immediate-use steam sterilization (IUSS)

CDC’s Table 8 gives examples of cycles at 270°F (132°C) for unwrapped items used immediately:

Sterilizer	Load	Time at 132°C
Gravity displacement	Nonporous items only	3 min
Gravity displacement	Mixed nonporous and porous items	10 min
Prevacuum (dynamic-air-removal)	Nonporous items only	3 min
Prevacuum (dynamic-air-removal)	Mixed nonporous and porous items	4 min
Steam-flush pressure-pulse	Nonporous or mixed items	4 min (and the manufacturer’s instructions)

The four parameters of steam sterilization

CDC names four: steam, pressure, temperature and time.

Steam: ideally dry saturated steam that contacts every surface. Trapped air blocks that contact, which is why air removal matters.
Pressure: raising the pressure is what lets steam reach sterilizing temperatures.
Temperature: 121°C (250°F) and 132°C (270°F) are the two common set points.
Time: the exposure time at temperature, which does not include come-up or drying time.

Each load is checked with mechanical, chemical and biological monitoring; see thesterilization indicators guide.

Steam sterilization on the CRCST exam

Sterilization Process is 21% of the CRCST exam in HSPA’s content outline. Cycle types, loading, cycle parameters, drying, wet packs and process failures all come up, alongside low-temperature methods such as ethylene oxide and hydrogen peroxide.

Test yourself: a CRCST-style question

According to CDC, what is the minimum exposure time for wrapped instruments in a dynamic-air-removal (prevacuum) steam sterilizer at 270°F (132°C)?

3 minutes
4 minutes
10 minutes
15 minutes

Show answer

B. 4 minutes

CDC Table 7 lists 4 minutes at 132°C for wrapped instruments in a prevacuum sterilizer, with 20–30 minutes of drying. A gravity displacement sterilizer needs 15 minutes at 132°C (or 30 minutes at 121°C).

Questions like this come up in the Sterilization Process section of the CRCST exam. The 901 questions in the app each come with a written explanation.

FAQ

What are the two most common steam sterilization temperatures?: 121°C (250°F) and 132°C (270°F). CDC gives recognized minimum exposure periods for wrapped supplies of 30 minutes at 121°C in a gravity displacement sterilizer, or 4 minutes at 132°C in a prevacuum sterilizer.
Why are prevacuum cycles so much shorter?: A dynamic-air-removal sterilizer pulls air out of the chamber and packs with a vacuum before steam is admitted, so steam reaches every surface quickly. A gravity sterilizer relies on steam pushing the air out through a drain, which is slower and less reliable, so exposure times are longer.
Are these the times to set on our sterilizer?: No. They are minimums from CDC’s guideline for exam study. Always use the cycle validated by the sterilizer manufacturer and the device’s instructions for use (IFU); many devices and containers specify extended cycles.
What is immediate-use steam sterilization (IUSS)?: A shorter cycle, formerly called “flash” sterilization, for items needed right away that cannot be packaged, sterilized and stored first. It is not meant for convenience or to replace adequate instrument inventory, and items should not be stored after IUSS.

Sources

Checked against CDC on November 13, 2026. Minimum times from CDC’s 2008 guideline, for CRCST exam study only. Always follow the sterilizer manufacturer’s validated cycles and each device’s instructions for use (IFU), your facility’s policy and ANSI/AAMI ST79.