Class B is a European classification, from EN 13060, for a benchtop steam sterilizer that can draw a vacuum and therefore sterilise wrapped, porous and hollow loads, not just bare instruments on an open tray. Class N is the simpler machine without vacuum, and Class S covers a manufacturer-defined set of loads in between. The label tells you what the machine is built to handle; it does not replace the monitoring that proves a given cycle worked, which in practice means a 
Class 5 integrator in the load and a biological indicator on the clinic schedule.
What does the Class B vacuum stage actually do?
It removes air from the chamber and from inside the load before steam enters. Air is the enemy of steam sterilisation, because a pocket of air stays cooler than the saturated steam around it and shields the surfaces inside it. A vacuum stage, usually with several pulse cycles, replaces that air with steam so the whole load reaches temperature together.
That is exactly why a wrapped pouch or a hollow instrument needs it. Without air removal, the steam may never reach the inside of a pouch in the expected time, and the indicator on the outside will still look correct.
How do Class B, Class S and Class N differ in daily use?
Class N machines take unwrapped solid instruments and are common in small clinics that process a handful of items in open trays. Class S machines are validated by the manufacturer for specific load types, so the manual defines what is allowed. Class B machines are validated for wrapped, porous and hollow loads, which is the reason dental and medical clinics usually specify them.
Buying a Class B machine does not make every load valid. Loading a chamber past its stated capacity, using packaging that traps air, or selecting a cycle that does not match the load will still fail, and the class label will not save the pack.
| Class | Vacuum stage | Loads it is built for | Typical setting |
|---|---|---|---|
| Class N | None | Unwrapped solid instruments | Small clinics, open trays |
| Class S | Manufacturer-defined | Loads named in the manual | Specific procedure sets |
| Class B | Pulsed vacuum | Wrapped, porous and hollow loads | Dental and medical clinics |
Which monitoring does a Class B cycle still need?
Daily biological indicator testing in the challenge position, chemical indicators in the packs, and physical parameter checks recorded for each cycle. In Ontario, the regulatory expectation for dental sterilizers is a biological indicator for each sterilizer on every day it is used, not a weekly test; the weekly baseline familiar from the United States is the CDC and AAMI ST79 position, not the Ontario one.
Air removal also needs its own check. A Bowie-Dick type test in a pre-vacuum machine confirms that the vacuum stage worked; a failed air removal test shows up as a load that reads correctly on the pack indicator and fails in the load. The Bowie-Dick test packs, six per pack are the usual device for that check.
Does a Class B label satisfy an inspector?
No. Inspectors ask for records, not labels: cycle logs, indicator results, maintenance and the load release decision. A Class B machine with no monitoring record is a weaker position than a Class N machine with complete records, because the record is what demonstrates control.
The label does help in one way: it tells the reader whether wrapped loads were appropriate for that machine. A clinic processing pouches in a machine without a vacuum stage has a design mismatch that no amount of documentation fixes.
What should a clinic check before buying one?
Check the chamber size against the instrument sets you actually process, the cycle times against your turnaround, and the water quality requirement in the manual. Then check what documentation the supplier provides for validation, because a machine without a clear load specification leaves the clinic to define its own loads without a basis.
Finally, check the consumables the machine expects: pouch formats that fit the chamber, an indicator system that matches the cycles offered, and a sealer that produces a seal the pouch manufacturer recognises. Mismatched consumables are a common reason a well-specified machine produces failed packs.
Related reading
sterilization monitoring collection; what each indicator proves; reading mm and inch sizing on pouches; wholesale and multi-site ordering Reselling? become a distributor.
Take the paperwork with you: print the sterilization log sheet, pre-fill a week of cycles with the log generator, or ask a sterilization compliance specialist to review how the records line up with the load sheets.
Frequently Asked Questions
Is Class B better than Class N?
Class B handles wrapped and hollow loads that Class N cannot, so it is the right choice for a clinic processing pouches. It is not an upgrade in monitoring terms: both need the same records.
Does a Class B autoclave need a Bowie-Dick test?
A pre-vacuum machine needs an air removal check, and a Bowie-Dick type pack is the recognised device for it. How often it runs depends on the facility policy and the sterilizer manual.
Can I process pouches in a Class N machine?
Wrapped loads are outside what a machine without a vacuum stage is built for. If pouches are part of the workflow, the machine has to be specified for them.
CliniEco Medical is a licensed medical device establishment (MDEL #35334).
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