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Class B autoclave

A class B autoclave is a pressurised steam steriliser that removes the air from its chamber by fractionated vacuum before every cycle. It is the most demanding class in the EN 13060 standard and the only one that guarantees steam reaches inside hollow instruments and pouched loads.

What does it actually do?

It places instruments in a sealed chamber and exposes them to saturated steam under pressure, typically at 134 °C for a few minutes. That combination of temperature, moisture and time destroys every form of microbial life, including spores, which are the most resistant form and the one that survives most disinfectants. The work is not done by heat alone: it is done by steam giving up its energy as it condenses on the metal surface.

The autoclave is step five of a chain of seven: cleaning, disinfection, drying, pouching, the autoclave cycle, logging the cycle and storage. The four before it decide whether the cycle can work at all; the two after it decide whether the result survives as far as the table.

Why class B specifically?

EN 13060 defines three classes of small steriliser: N, S and B. They differ in what they are capable of sterilising. Class N handles solid, unwrapped instruments only. Class S covers whatever the manufacturer specifies. Class B is the most demanding and the only one that takes on all three difficult cases at once: pouched loads, hollow or channelled instruments, and porous materials.

What is the vacuum for?

It is the defining feature of class B and the reason the other classes fall short. Air left inside the chamber forms pockets that steam does not displace, and where steam does not reach, nothing is sterilised. A class B machine removes that air in stages, alternating vacuum with pulses of steam before the cycle proper begins. That is what allows it to sterilise instruments inside a sealed pouch: the vacuum draws the air out of the pouch as well.

Why does the pouch matter?

Sterility is not a permanent property; it is a condition that holds only while the barrier holds. An instrument sterilised in the open is contaminated again as soon as it is handled, placed in a drawer or exposed to dust. The pouch, which is step four of the chain, holds that condition from the moment it is sealed until the moment it is opened.

What can be checked, in this order:

1. The pouch arrives sealed, with no tears and no dampness.
2. The chemical indicator printed on it has changed colour, which shows the pack went through the cycle.
3. The pouch carries a sterilisation or expiry date, within the window its manufacturer states.
4. It is opened in front of the person about to be treated, and the instruments are not set down on anything that is not sterile.
5. Files, buffers and sticks come out of a new pack.

How is a cycle verified?

Three ways, which complement each other. The chemical indicator printed on the pouch, that strip which changes colour, confirms the pack went through the process. The machine’s own log records pressure, temperature and duration for every cycle and can be reviewed afterwards. Periodic biological testing places a sample of resistant spores inside and verifies that nothing grows. The first is visible across the table; the other two are documentation a salon can show.

What does not replace an autoclave?

Not a glass bead steriliser, not an ultraviolet lamp, not a UV cabinet, not a disinfectant solution. Each of those has a legitimate role somewhere, but none sterilises a pouched load or reaches inside a hinged instrument. Nor does an ultrasonic cleaner, whose job comes earlier: lifting visible residue off before the instruments go into the pouch at all.

Sources: EN 13060, small steam sterilisers (CEN) · AEMPS · Cosmetic products (Spanish Medicines Agency)

Published: 12 October 2026 · Last reviewed: 12 October 2026