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Also called: Steam sterilizer, Steam sterilisation

Steam Sterilizer: How Steam Sterilisation Works

Temperatures, pressures, air removal and the common reasons a steam sterilisation load fails — explained for clinic and CSSD buyers.

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Time, temperature and steam quality

Steam sterilisation depends on direct contact between saturated steam and every surface of the load for long enough at the right temperature.

TemperatureApprox. pressureMinimum holdTypical use
121 °C1.1 bar15 minHeat-sensitive but autoclavable items, liquids (lab)
134 °C2.1 bar3 minWrapped and unwrapped instruments
134 °C extended2.1 bar18 minPrion cycle where policy requires

Prevacuum vs gravity steam sterilizers

Prevacuum (dynamic air removal)

A vacuum pump removes air in pulses before sterilisation, so steam penetrates porous packs and hollow devices. This is how Class B and hospital sterilizers work.

Gravity displacement

Steam pushes air out through a drain. Simpler and cheaper, but air can stay trapped in lumens and packs, so it suits unwrapped solid items and lab liquids.

Why loads fail

  • Overloading or stacking that stops steam circulating.
  • Instruments not cleaned first — soil shields microorganisms from steam.
  • Air leaks or a failing door seal (caught by the vacuum and Bowie-Dick tests).
  • Poor feed water causing wet steam and wet packs.
  • Wrong cycle chosen for the load type.

Related guides

Autoclave Machine: Types, Sizes and How to ChooseA plain guide to the parts, cycles and sizes of a clinic or laboratory autoclave machine, written for buyers in Malaysia.Class B Autoclave vs Class N and Class SThe EN 13060 classes decide which loads your autoclave can legitimately sterilise. Here is what each class covers and how to tell them apart.Autoclave Testing: Bowie-Dick, Indicators and ValidationThe daily, weekly and yearly checks that prove your autoclave is sterilising — and what autoclave tape and pouches can and cannot tell you.

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Delivery, installation and training across Malaysia from Batu Caves, Kota Kinabalu and Kuching.

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Frequently asked questions

What pressure does a steam sterilizer run at?
About 1.1 bar above atmospheric at 121 °C and about 2.1 bar at 134 °C.
Why does a steam sterilizer need to remove air?
Air pockets insulate surfaces from steam, so those surfaces never reach sterilising conditions. Vacuum air removal is what makes hollow and wrapped loads sterilisable.
Is steam sterilisation safe for all instruments?
Only for instruments the manufacturer marks as autoclavable. Check each instrument’s reprocessing instructions.

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