Small steam sterilisers, including the benchtop autoclaves used in dental practices, run cycles of three types set out in the European standard BS EN 13060. Suppliers call them Class B, Class S and Class N; the UK guidance documents call them Type B, S and N. The class tells you which instruments a machine is designed to sterilise.
The guidance depends on where your practice is: HTM 01-05 is England’s guidance, SHTM 01-05 is Scotland’s and WHTM 01-05 is Wales’. This page quotes all three.
Which classes suit which instruments
| Instruments | Class B | Class S | Class N | Source |
|---|---|---|---|---|
| Unwrapped solid instruments, such as mirrors, probes and forceps | Yes | Yes | Yes | SHTM 01-05, paragraph 4.21; HTM 01-05, paragraph 4.5 |
| Wrapped or pouched instruments | Yes | Only if its maker says so | No | HTM 01-05, note to paragraph 4.9; SHTM 01-05, table 4.1 and paragraph 4.23; WHTM 01-05, paragraph 4.11 |
| Hollow and lumened instruments | Yes | Only if its maker says so | No: can’t assure sterilisation inside | HTM 01-05, paragraph 4.5; SHTM 01-05, table 4.1; WHTM 01-05, paragraph 4.5 |
| Dental handpieces (follow the handpiece maker’s instructions) | Likely to be useful | Likely to be useful, if its maker lists them | Can’t assure sterilisation inside | HTM 01-05, paragraph 4.7; SHTM 01-05, paragraphs 4.11 and 4.21 |
“Likely to be useful” is HTM 01-05’s wording for Type B or S sterilizers and handpieces (paragraph 4.7). It adds that sterility is unlikely to be achieved whatever sterilizer is used, because of the lubricants in handpieces, and SHTM 01-05 (paragraph 4.11) says handpieces must still be steam sterilised.
How each class works
Class B (vacuum)
A vacuum pump actively removes air from the chamber, so steam can reach inside hollow instruments and through wrapping. HTM 01-05 says Type B sterilizers “are designed to reprocess load types such as hollow, air-retentive and packaged loads” (HTM 01-05, paragraph 4.5), and SHTM 01-05 says the Type B cycle “has the widest range of applications” (SHTM 01-05, table 4.1). Wrapped loads need a drying stage, which makes the cycle longer.
Class S (as specified by the maker)
Air is removed actively, for example by steam pulsing, but a Type S cycle is “only suitable for the types of loads specified by the sterilizer manufacturer” (SHTM 01-05, table 4.1). Some Class S models take wrapped or hollow loads and some don’t. SHTM 01-05 advises: “Care should be taken when considering the purchase of a type S sterilizer to make sure it will have wide applicability for the range of instruments which will need processing in the dental practice”.
Class N (non-vacuum)
Steam pushes the air out of the chamber by passive displacement; there is no vacuum pump. HTM 01-05 describes Type N machines as “non-vacuum sterilizers designed for non-wrapped solid instruments” (HTM 01-05, paragraph 4.5), and WHTM 01-05 adds that they “are not designed for reprocessing instruments with a lumen” (WHTM 01-05, paragraph 4.5).
What the UK guidance documents say
- England: HTM 01-05. Health Technical Memorandum 01-05: Decontamination in primary care dental practices, 2013 edition (Department of Health).
- Scotland: SHTM 01-05. SHTM 01-05 Part C: Management, equipment, and process of the decontamination of dental instruments in a Local Decontamination Unit (LDU) in NHSScotland, Version 1, April 2024 (Health Facilities Scotland, NHS National Services Scotland).
- Wales: WHTM 01-05. WHTM 01-05: Decontamination in primary care dental practices and community dental services, Revision 1, February 2014 (NHS Wales Shared Services Partnership).
All three say a non-vacuum steriliser is not for wrapped instruments:
“The use of a type N sterilizer is not appropriate for wrapped instruments.”
HTM 01-05, note to paragraph 4.9; the same words appear in WHTM 01-05, paragraph 4.11
Type N: “not suitable for wrapped loads (such as items in pouches)”.
SHTM 01-05, table 4.1
The documents differ in other details, such as how long processed instruments can be stored, so follow the one for your country.
Class B, S and N autoclaves on Vetted Index
Of the 46 autoclaves we list, 34 are Class B, 9 Class S and 3 Class N. Guide prices exclude VAT and count only models with a published UK price.
| Class | Models listed | Chamber sizes | Guide prices ex VAT |
|---|---|---|---|
| Class B | 34 | 5 to 38 L | £3,167 to £7,365 |
| Class S | 9 | 2 to 23 L | £3,250 to £6,850 |
| Class N | 3 | 11 to 18 L | £2,650 to £3,217 |
Questions and answers
What is the difference between Class B, Class S and Class N autoclaves?
They differ in how air is removed from the chamber and which loads they are designed for. Class B uses a vacuum pump and is designed for wrapped, hollow and solid instruments. Class S removes air actively, for example by steam pulsing, and is only suitable for the load types its manufacturer specifies. Class N has no vacuum and is designed for unwrapped solid instruments only.
Can I sterilise pouched instruments in a Class N autoclave?
No. HTM 01-05 (England) and WHTM 01-05 (Wales) both say the use of a type N sterilizer is not appropriate for wrapped instruments, and SHTM 01-05 (Scotland) says Type N cycles are not suitable for wrapped loads such as items in pouches.
Is a Class S autoclave enough for a dental practice?
It depends on the model. A Class S autoclave is only suitable for the load types its manufacturer specifies: some take wrapped or hollow loads and some don’t. SHTM 01-05 advises making sure a Type S steriliser will suit the full range of instruments your practice processes, so check the maker’s load list with your supplier and validation engineer.
Which decontamination guidance applies to my practice?
HTM 01-05 in England, SHTM 01-05 in Scotland and WHTM 01-05 in Wales. They describe Class (Type) B, S and N sterilisers in the same way, but differ in other details, such as how long processed instruments can be stored, so follow the document for your country.
This page summarises public guidance. It is not professional, engineering or clinical advice: confirm suitability with your supplier and validation engineer before buying.