Biological Indicators in Tabletop Sterilizers: Class B and Class N Cycles
A general practice often runs two tabletop steam sterilizers: in the decontamination area that takes pouched instrument sets, and a smaller unit beside the hygiene bay for a single unwrapped instrument that goes straight back into use. Both need monitoring records, but they do not take the same loads and a biological indicator is used differently in each.
The monitoring rule is written per cycle type, not per machine, and that detail decides how many tests a day cost and where the test device sits in the chamber.
What separates a Class B tabletop sterilizer from a Class N unit?
| Chamber and cycle | Class B | Class N |
|---|---|---|
| Air removal before steam enters | fractionated pre-vacuum: air pulled out in stages | gravity displacement: steam pushes air down and out through the drain |
| Loads the cycle is designed for | wrapped and pouched instruments, hollow items, porous loads | unwrapped solid instruments only |
| Porous or wrapped loads | processed when the cycle is validated for that load | not processed; no vacuum stage removes air from a wrap |
| Biological indicator placement | in a process challenge device in the load or chamber | in a process challenge device where air removal is slowest, per the unit's instructions |
| Monitoring obligation in Ontario | each day the sterilizer is used, one test per cycle type | same daily obligation; the cycle types differ |
Small steam sterilizers are labelled type B, type N or type S under EN 13060, the standard the cycle labelling on a bench-top unit refers back to. That label tells you which loads the chamber was designed to process.
Which loads can a Class N unit process?
Unwrapped, solid instruments. A wrapped set, a pouch, a lumen or a porous item depends on air being removed before steam arrives, and gravity displacement cannot do that dependably, so wrapped loads go to a vacuum-assisted unit.
How often must a clinic run a biological indicator?
Public Health Ontario's checklist for dental reprocessing requires a biological indicator in a process challenge device (item 7.13) each day the sterilizer is used, and with each type of cycle used that day. A control indicator from the same lot, unexposed to sterilant, is incubated with the routine test (item 7.14). Where implants are processed, an indicator goes into every load containing them and the devices are not released until the result is available (item 7.15).
Monitoring frequency is daily in Ontario, where the weekly schedule belongs to a different jurisdiction.
What has to be written down for each test?
A defensible record carries the date, the sterilizer identifier, the cycle type, the load reference, the indicator lot number and expiry, the control result, the incubation start and read time, the outcome, what was done about a failure, and who initialled it. Chemical monitoring sits alongside it: a Class 5 steam integrator in every package shows the load saw the cycle conditions, and indicator tape shows a pack went through a cycle at all, but neither proves spores were killed.
Daily testing consumes 24-hour rapid readout biological indicators, incubated at 57 to 60 degrees Celsius in a dry-block incubator with fifteen wells, so a unit with two cycle types does not run out mid-week.
Where does a small Class N unit leave the record?
Exactly where a Class B unit does. The cycle record is signed for each cycle, and where the practice cannot hold loads until a result is available, the checklist points to an evaluation of a Type 5 integrator instead of assuming the load was sterile.
Ordering for a clinic, lab or care home? Wholesale and multi-site ordering covers account setup and case pricing, and the B2B wholesale collection lists the lines stocked for institutional buyers. Clinics starting daily monitoring can begin with the biological indicator five-pack trial and the sterilization monitoring collection.
References
- Public Health Ontario - Infection prevention and control checklist for dental reprocessing (checked 24 September 2026)
- Royal College of Dental Surgeons of Ontario - Infection prevention and control in the dental office: some common questions (checked 24 September 2026)
- Public Health Ontario PIDAC - Cleaning, disinfection and sterilization in health care settings (guidance document) (checked 24 September 2026)
Related Reading
- How Often Should You Run a Spore Test? Sterilizer Monitoring Schedules
- What Is a Class B Autoclave? Chamber Design and Cycle Types
- When to Run a Biological Indicator: Ontario's Daily Rule vs the US Weekly Baseline
- printable sterilization log
Frequently Asked Questions
Can a Class N sterilizer process pouched or wrapped instruments?
No. A Class N cycle uses gravity displacement, so air is pushed out by steam rather than pulled out by a vacuum pump. A wrapped load or a hollow item holds air the cycle cannot displace reliably.
How many biological indicators does a tabletop sterilizer need in one day?
One for each cycle type used that day. The dental reprocessing checklist requires a biological indicator in a process challenge device each day the sterilizer is used, and with each type of cycle used that day.
Where does the biological indicator go in a tabletop sterilizer?
In a process challenge device, positioned as the sterilizer maker's instructions specify. In a Class B chamber the load can be built around it; in a small Class N chamber it goes in the position with the slowest air removal.
Is weekly spore testing acceptable for an Ontario clinic?
No. Weekly biological monitoring is the United States baseline in CDC guidance and AAMI ST79. Ontario's published expectation is a test on each day the sterilizer is used, which is what an inspector works from.
What has to happen when a biological indicator fails?
Stop releasing loads, quarantine everything sterilized since the last passing test, repeat the test with a control from the same lot, check the cycle record and load configuration, and document the investigation and the re-test.
Last updated: September 2026. CliniEco Medical is a licensed medical device establishment (MDEL #35334).
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