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Short answer: an unwrapped (flash) steam cycle runs at 132 °C (270 °F), and the exposure time depends on the sterilizer type and on what is in the load. In the CDC’s example parameters, metal instruments with no lumens need 3 minutes in either a gravity-displacement or a prevacuum (dynamic-air-removal) sterilizer. A load that mixes in porous items such as rubber or plastic, or items with lumens, needs 10 minutes in a gravity sterilizer or 4 minutes in a prevacuum sterilizer. The familiar “121 °C for 15 to 30 minutes” figure belongs to wrapped loads, not to this case.
What counts as an unwrapped (flash) cycle?
“Flash” steam sterilization was originally defined as sterilizing an unwrapped object at 132 °C for 3 minutes at 27 to 28 lbs of pressure in a gravity-displacement sterilizer. Today it is a modification of conventional steam sterilization (gravity, prevacuum or steam-flush pressure-pulse) in which the item sits in an open tray, or in a specially designed, covered, rigid container that lets steam penetrate quickly. The CDC states that the time required now depends on the type of sterilizer and the type of item, porous or non-porous.
Who uses it: facilities that must process a cleaned item at the point of use because it cannot be packaged, sterilized and stored before it is needed. Lab and clinic staff who run a benchtop autoclave should read the sterilizer and container manufacturer’s instructions first. For a general introduction to the equipment, see what an autoclave is.
Unwrapped autoclave cycle times by sterilizer and load
These are the CDC’s “examples of flash steam sterilization parameters” (Table 8 of its Guideline for Disinfection and Sterilization in Healthcare Facilities, last updated June 2024), which the CDC credits as modified from the Association for the Advancement of Medical Instrumentation. Every row is 132 °C (270 °F).
| Sterilizer type | Load | Temperature | Time |
|---|---|---|---|
| Gravity displacement | Non-porous items only (routine metal instruments, no lumens) | 132 °C | 3 minutes |
| Gravity displacement | Non-porous and porous items sterilized together (rubber or plastic items, items with lumens) | 132 °C | 10 minutes |
| Dynamic-air-removal (for example, prevacuum) | Non-porous items only | 132 °C | 3 minutes |
| Dynamic-air-removal (for example, prevacuum) | Non-porous and porous items sterilized together | 132 °C | 4 minutes |
| Steam-flush pressure-pulse | Non-porous, or mixed non-porous and porous | 132 °C | Per the manufacturer’s instructions |
The CDC also notes that many facilities have extended the flash exposure time to give lethality comparable to wrapped items, for example 4 minutes at 132 °C. The CDC describes flash cycle parameters (time, temperature, pressure) as minimal, so 3 minutes is a floor for a non-porous load, not a target to shorten. The wrapped-load figures (121 °C and 132 °C hold times for packaged instruments) are covered in autoclave sterilization temperature and time.
Why do porous and lumened items need longer?
Steam has to reach every surface. The CDC’s table separates routine metal instruments with no lumens from rubber or plastic items and items with lumens, and in a gravity sterilizer that distinction moves the time from 3 to 10 minutes. The same guideline states that at constant temperature, sterilization times vary with the type of item (metal versus rubber, plastic or items with lumens), whether the item is wrapped or unwrapped, and the sterilizer type. How a sterilizer removes air is the reason the two cycle types differ; see gravity, pre-vacuum and liquid autoclave cycles.
What has to go with an unwrapped cycle?
- Clean first. The CDC recommends cleaning the item before it goes into the sterilizing container or tray.
- Use packaging designed for flash. Containers must be FDA-cleared for flash sterilization, and packaging or containers should not be used in flash cycles unless both the sterilizer and the container are designed for it.
- Protect it in transport. Open sterile items become contaminated over time in air, so the CDC advises preventing contamination between the sterilizer and the point of use, and using the item immediately.
- Monitor the cycle. Use mechanical, chemical and biological monitors. The CDC mentions biological indicators that give results in 1 hour for flash-sterilized items. See chemical indicators for sterilization.
- Mind the heat. Instruments straight from a flash cycle can be hot enough to burn; the CDC cites heat-protective gloves for transporting trays.
Common mistakes
Applying a wrapped-load time to an unwrapped load
Times are not interchangeable between wrapped and unwrapped loads, and the 121 °C hold times used for packaged items are not the flash parameters above.
Running porous and non-porous items on the 3-minute line
If rubber, plastic or lumened items share the load, the mixed-load row applies: 10 minutes in a gravity sterilizer, 4 minutes in a prevacuum sterilizer.
Using flash as a routine method
The CDC prefers the wrapped method and says flash sterilization should not be used for convenience, as an alternative to buying additional instrument sets, or to save time. It is acceptable for cleaned items that cannot be packaged, sterilized and stored before use, or when time is insufficient for the packaged method. Historically it was not routine because of the lack of timely biological indicators, no protective packaging afterwards, possible contamination in transport, and minimal cycle parameters.
Flashing implants
The CDC recommends against flash sterilizing implanted surgical devices unless it is unavoidable (Category IB). If it cannot be avoided, it advises keeping records: load identification, the patient identifier and the biological indicator result.
FAQ
How long should unwrapped items be sterilized in an autoclave?
At 132 °C, the CDC’s example parameters are 3 minutes for non-porous items in a gravity or prevacuum sterilizer, 10 minutes for mixed porous and non-porous loads in gravity, and 4 minutes for mixed loads in prevacuum. For steam-flush pressure-pulse cycles the CDC table gives 132 °C and refers to the manufacturer’s instructions for the time.
Is unwrapped sterilization the same as flash sterilization?
In this context, yes: flash sterilization is the steam process for items in an open tray or an approved rigid container rather than in wrapping. For how the term relates to immediate-use steam sterilization, see flash sterilization vs immediate-use steam sterilization. The CDC credits the Association for the Advancement of Medical Instrumentation (see ANSI/AAMI ST79) for the table it reproduces; follow the sterilizer manufacturer’s instructions for the exact cycle on your unit.
Sources
- Centers for Disease Control and Prevention, Guideline for Disinfection and Sterilization in Healthcare Facilities (2008), last update June 2024: Flash Sterilization section, Table 8 and Recommendation 13. cdc.gov guideline PDF. https://www.cdc.gov/infection-control/media/pdfs/Guideline-Disinfection-H.pdf. Checked 2026-10-29.
- Centers for Disease Control and Prevention, Steam Sterilization: https://www.cdc.gov/infection-control/hcp/disinfection-sterilization/steam-sterilization.html. Checked 2026-10-29.
