Steam sterilization temperature and time: 121 vs 134 °C

How steam kills microorganisms

Saturated steam under pressure transfers heat rapidly and, together with moisture, denatures proteins in microorganisms. The temperature of saturated steam depends on pressure, so autoclaves measure both. Sterilization only occurs where steam contacts the surface, which is why air removal is essential: trapped air forms cold spots where the process fails.

A complete cycle on a pre-vacuum sterilizer has phases: air removal by repeated vacuum and steam pulses, heating to the sterilization temperature, the holding (plateau) time, steam exhaust, drying under vacuum and return to atmospheric pressure. Looking only at temperature and holding time misses the phases that most often cause failures.

121 vs 134: typical autoclave temperature and time

Two temperature ranges are widely used. 134 °C is the standard for most surgical instruments in pre-vacuum sterilizers, with a short holding time (commonly a few minutes, such as 3 to 5, depending on the programme and standard). 121 °C is used for heat-sensitive materials, certain liquids and some textiles, and needs a much longer hold (commonly 15 to 20 minutes) because the lower temperature kills more slowly.

These figures are typical, not universal. The exact parameters are defined by the sterilizer's validated programme, the standard it follows (such as EN 285, EN 13060 or ISO 17665), the load type and the instrument manufacturer's IFU. Always apply the combination validated for your machine and load, as discussed in autoclave validation guidelines.

Why wrapped and container loads differ

Wrapped trays, pouches and rigid containers heat and dry differently. Wrap lets steam in through the whole surface and releases it again; a container admits steam through filter or valve openings and holds its own thermal mass in the base and lid. Heavy metal sets and containers heat more slowly and release moisture more slowly, so drying time is often the critical parameter.

REDA's containers use paper, textile or Teflon filters and Bio-Barrier valve models that the vacuum opens during the cycle and that close once the pressure is equalised; the Plasma model is described for both steam and low-temperature plasma (REDA sterilization containers). Container loads should be tested at their heaviest configuration, following the container's IFU. Choice of packaging is compared in rigid containers versus wrap.

Drying, cooling and special cases

Wet packs are not acceptable: moisture can carry microorganisms through packaging. Drying relies on vacuum and residual heat, so avoid overloading, nesting bowls and lining trays with absorbent material that holds condensate. Packs should cool in a draught-free area before handling and storage; see sterile storage and shelf life.

Special cases need their own programmes. Instruments with prion risk may require an extended 134 °C hold along with other measures, covered in CJD instrument reprocessing. Heat-sensitive instruments are sterilized by low-temperature methods, compared in types of sterilization in hospitals. Fast-cycle (flash) sterilization of unwrapped items is limited to urgent situations under local policy.

Monitoring and what to document

Local requirements for parameters and documentation in the UAE come from your licensing authority (DHA, DOH or MOHAP), so check them when you set programmes. Beckfinity's specialists can help you choose containers for your cycles; contact us.

• Review printout or electronic record for temperature, pressure and time in every cycle.
• Run a daily air-removal (Bowie-Dick or equivalent) test on pre-vacuum machines.
• Use chemical indicators in and on packs, and biological indicators as your policy specifies.
• Record load number, programme and operator.
• Investigate and quarantine any load with a deviation, wet packs or failed indicator.