How to choose an autoclave: classes B, N, S and chamber size
Class B, N or S, chamber volume, cycles and routine testing: how to choose a compliant autoclave sized for the work you actually do.
Choosing an autoclave comes down to one point many buyers discover too late: the class. A class N machine does not sterilise wrapped or hollow instruments. If your work involves any, the machine is unusable whatever its price.
The three classes, and which one applies to you
EN 13060 defines three classes for small steam sterilisers:
- Class N (naked): solid, unwrapped instruments with no lumen. No pre-vacuum. The cheapest, and the most limited.
- Class S (specified): loads defined by the manufacturer. Only worth considering after reading the authorised load list carefully.
- Class B (big small steriliser): fractionated vacuum. Sterilises wrapped, porous and hollow instruments — including dental turbines and cannulated instruments.
In practice: a dental practice, an operating theatre, a minor surgery room, or any department that wraps instruments for storage needs a class B. Class N suits only a very narrow use.
Sizing the chamber
Common volumes run from 8 to 29 litres for small sterilisers, and higher for large sterilisers covered by EN 285. Size for your peak, not your average: if you have to run three consecutive cycles on a Tuesday morning, you will lose half a day of production.
A full class B cycle typically takes 30 to 50 minutes including drying. Multiply by your daily cycle count to confirm the machine keeps up.
Cycles and temperatures
Two temperature/time combinations structure daily use:
- 134 °C for at least 3 minutes 30: the standard cycle for metal instruments.
- 121 °C for 15 to 20 minutes: the cycle for heat-sensitive materials (some plastics, rubbers).
Check for a prion cycle if your activity requires one, and a rapid cycle for urgent turnaround.
The tests you will run, every day
An autoclave without traceability is worth nothing in an inspection or a dispute. Plan for these from the purchase:
- Bowie-Dick test: steam penetration check, daily on class B machines.
- Helix test: specific check for hollow loads.
- Biological indicators: periodic validation of actual efficacy.
- Printer or data export: archiving of cycle curves. A USB port or network output is a minimum today, not an option.
Ask the supplier for the annual cost of test consumables: it is a recurring budget line that never appears in the initial quotation.
Water quality: the leading cause of failure
Autoclaves require demineralised or distilled water. Mains water scales the chamber and the generator, and destroys the machine within months. Two options: buy distilled water in containers, or install a reverse osmosis unit. Under heavy use, the RO unit pays for itself in under two years.
Put the question to the supplier: what maximum conductivity does the machine accept?
Installation and environment
An autoclave releases heat and humidity. It needs proper ventilation, a dedicated and correctly rated electrical supply (some 23-litre and larger models require their own line), and a worktop able to carry its weight empty and loaded.
Your checklist
- Does the class match my real loads (wrapped? hollow?)
- Does the chamber volume absorb my peak workload?
- Is the machine EN 13060 compliant, and is the certificate supplied?
- How are cycles archived?
- What is the annual cost of test consumables and water?
- Who services it in my country, and within what response time?
Compare the autoclaves and sterilisation equipment listed on MedicalExpo Africa, by supplier and by country. For a complete theatre fit-out, see the operating theatre category too.