Sterilization Modalities: ISO 17665, ISO 11135 and ISO 11137

Quick Summary: Steam, ethylene oxide and radiation are the three modalities a Canadian clinic, lab or manufacturer is most likely to encounter, and each has its own standard covering validation and routine control. ISO 17665 covers moist heat, ISO 11135 covers ethylene oxide and ISO 11137 covers radiation. Knowing which standard belongs to which modality explains why some monitoring products work everywhere and others are cycle specific.

A clinic that owns one autoclave rarely thinks about modality. A distributor that ships to dental offices, veterinary clinics, laboratories and small manufacturers has to, because the same conversation about sterility assurance lands on three different standards depending on what equipment sits in the room.

The distinction is not academic. Monitoring consumables are qualified against a modality and a cycle type, and a chemical indicator built for a 132 °C steam cycle is not interchangeable with one built for an ethylene oxide cycle at 55 °C. Buying the wrong one produces a load record that looks complete and proves nothing.

Which sterilization modalities are actually used in Canadian settings?

Moist heat in an autoclave dominates clinic and laboratory practice. It is fast, non-toxic, inexpensive to run and compatible with the instrument loads a dental office or physician's clinic actually produces. Steam cycles vary by air removal method, which is why a Bowie-Dick style test exists for vacuum-assisted cycles and why gravity displacement cycles cannot be validated by the same test.

Ethylene oxide appears where heat and moisture would destroy the product: heat-sensitive polymers, complex instruments with long lumens, and devices assembled with adhesives. It is an industrial or centralized modality in practice, because the cycle is long, the gas is toxic and the aeration step is mandatory.

Radiation appears in manufacturing rather than in clinical reprocessing. Devices are sterilized in their final packaging by gamma or electron beam, which is why radiation-sterilized products arrive with a dose-based assurance argument rather than with a cycle record from your building.

Vapourised hydrogen peroxide, dry heat and nitrogen dioxide fill specific niches. Each has its own validation logic, and each changes the monitoring question slightly.

Low-temperature hydrogen peroxide systems exist because a growing share of instruments cannot take 134 °C. Flexible endoscopes, some camera systems and certain plastics are in that group, and the trade-off is throughput and cost per cycle rather than efficacy. Dry heat survives where moisture itself is the problem, such as powders and oils, and it needs longer exposure times and higher temperatures than steam for the same lethality. Nitrogen dioxide sits in the same low-temperature family and, like hydrogen peroxide, brings its own consumables and its own cycle-specific indicators.

The practical point for a purchasing decision is that modality determines the consumable list before it determines anything else. Two clinics buying the same instrument tray will buy different indicators, different packaging and different biological indicators if one runs steam and the other runs a low-temperature system. Getting that mapping wrong is one of the few ways a clinic can run a textbook cycle and still be unable to prove it worked.

What does ISO 17665 require for moist heat?

ISO 17665 is the standard for moist heat sterilization, structured around validation and routine control rather than around a machine setting. Its logic is familiar to anyone who has read a reprocessing guideline: establish that the process can deliver the required lethality to the load, demonstrate that it does so consistently, then monitor every cycle well enough to detect a drift.

Three practical consequences follow. First, load configuration is part of the process, which is why sterilizer loading diagrams and instrument tray weight limits are not optional details. Second, the combination of a physical parameter record, a chemical indicator and a biological indicator is the accepted monitoring stack, with the biological indicator providing the direct lethality check (ISO 11138-1). Third, routine control depends on records, which is why a clinic that logs cycles but cannot show what was in them is only half documented.

Steam quality is the parameter that quietly decides whether any of this holds. Wet steam carries entrained moisture that wets the pack and defeats the barrier; non-condensable gases such as air pockets in the chamber or dissolved in the condensate slow heat transfer. That is why sterilizer maintenance, water treatment and air removal testing belong in the same conversation as the monitoring log, and why a clinic that never checks its feed water can still pass a spore test and still produce wet, compromised packs.

Wrapping and pouching feed into the same logic. Packaging has to permit steam contact and air removal while maintaining the sterile barrier afterwards, which is the territory of the packaging standard (ISO 11607-1) and of the clinic-level workflows that public health guidance describes for reprocessing (Public Health Ontario, dental reprocessing checklist).

What does ISO 11135 cover for ethylene oxide?

ISO 11135 covers ethylene oxide sterilization, and its shape mirrors ISO 17665: validation, then routine monitoring, with additional attention to the parameters unique to EO. Gas concentration, humidity, temperature, pressure and exposure time all interact, and the residuals left in the product afterwards have to be addressed before release.

For a clinic the standard shows up indirectly. If a procedure pack, a heat-sensitive device or a lumen instrument arrives with an EO sterilized label, the reprocessing instructions will usually specify single use. Repackaging and re-sterilizing in-house is generally out of scope because a clinic cannot reproduce the validated cycle, and the residual limits cannot be met in a benchtop process.

For a distributor or a manufacturer's quality team, ISO 11135 is the reason EO-validated products carry cycle development documentation, and the reason a supplier questionnaire about sterilization method is a reasonable procurement step rather than a formality.

What does ISO 11137 cover for radiation?

ISO 11137 covers radiation sterilization and is unusual among the three because the critical variable is dose. The standard family covers the requirements for establishing a sterilization dose, including methods that let a manufacturer demonstrate that a lower dose achieves the required sterility assurance level, and the dose audits that keep the claim valid over time.

This is where the practical difference bites. A steam cycle is a machine process that a clinic can watch. A radiation dose is a manufacturing parameter whose verification is a laboratory activity. That is why radiation-sterilized single-use devices reach the clinic with a sterility assurance statement rather than with a cycle printout, and why no in-house reprocessing pathway substitutes for it.

How does modality choice change the monitoring you buy?

Monitoring consumables are modality specific, and the labels show it. Biological indicators are qualified against a modality and a resistance performance, which is why a steam indicator is not an EO indicator (ISO 11138-1). Chemical indicators are classified by what they measure and are similarly tied to a process (ISO 11140-1).

For a steam-based clinic the shopping list is short and consistent: external indicators on every pack, internal indicators where the instrument set warrants it, a Bowie-Dick cycle test for vacuum autoclaves, and biological indicators run on the schedule your province expects. Packaging has to match the modality as well, since paper and film laminates are qualified for steam and not for every low-temperature process.

Two of those items are worth stocking as a matched pair. CliniEco supplies a 24-hour biological indicator in a 25-pack for routine spore testing, a 24-well dry block incubator to run the incubation step, and a Class 5 integrating indicator for internal control of steam loads. The rest of the monitoring range is grouped in the sterilization monitoring collection, and a Bowie-Dick test pack for daily vacuum checks covers the air removal question separately.

Related reading

• ISO 11138 Series: Biological Indicator Standards for Steam, EO and VHP Explained — the indicator side of modality matching.
• ISO 11607-1 vs ISO 11607-2: Sterile Packaging Validation Roles — what each packaging part asks for.
• Does ISO Require a Sterilization Date on Packaging? ISO 11607 and ISO 11140 Explained — the marking question clinics raise most often.
• Steam Sterilization Science: How Autoclaves Destroy Microbes — the moist heat mechanism behind ISO 17665.
• diagnostic & research lab supplies
• free Ontario sterilization compliance log
• printable autoclave sterilization log sheet (free)

Reviewing your monitoring stack or setting up records for a new autoclave? Send a wholesale inquiry with your sterilizer model and weekly cycle volume, or start with the rapid reader seed trial to see how a fluorescence readout fits your existing routine.

Frequently Asked Questions

Do I need ISO 17665 compliance to run an autoclave in a dental office?

ISO 17665 describes the validation and routine control framework for moist heat sterilization. A dental office is expected to run its sterilizer according to the manufacturer's instructions and the monitoring expectations of its provincial regulator, which in practice means following the same logic: validate the process, monitor every cycle and keep records. The standard is the reference those expectations are built on.

Can a clinic use ethylene oxide sterilization?

Not in a benchtop format. EO cycles run in chamber-based industrial or centralized systems with gas handling, monitoring and mandatory aeration. Single-use devices that arrive EO sterilized are normally intended for single use, and the reprocessing instructions should be followed rather than substituted with an in-house process.

What is the difference between ISO 11135 and ISO 11137?

ISO 11135 covers ethylene oxide sterilization and ISO 11137 covers radiation sterilization. Both are validation and routine control standards, but the parameters they control are different: EO is driven by gas concentration, humidity, temperature, pressure and time, while radiation is driven by absorbed dose and dose distribution.

Why do biological indicators have to match the sterilization method?

Because resistance performance is established against a specific modality. An indicator qualified for steam is not qualified for EO or hydrogen peroxide, and using it in the wrong process produces a result that carries no assurance. The indicator's instructions for use state the modality and the cycle parameters it belongs to.

Is steam sterilization always the right choice?

For reusable instruments that tolerate heat and moisture, yes, it is the default because it is effective, non-toxic and quick. Where heat or moisture would damage the device, another modality is required, and that is usually handled at the manufacturing stage rather than in the clinic.

What records should accompany a sterilization modality change?

A change of modality, equipment or cycle type triggers a validation question. In practice the file should show the cycle parameters, the monitoring used, the results, and the basis for the parameters chosen. Adding a low-temperature system is not a like-for-like substitution for a steam process.

Does the packaging standard depend on the sterilization modality?

Yes. Packaging has to be compatible with the sterilization process, maintain the sterile barrier and be validated as a system for that process. Paper and film laminates are widely qualified for steam; other modalities require their own packaging qualification, which is part of why the packaging standard has a validation part as well as a materials part.

How does Health Canada fit into this?

Medical devices sold in Canada sit within the federal medical device framework, which is why importers and distributors hold establishment licences and maintain technical documentation for the products they place on the market. Sterilization standards are how manufacturers and reprocessors demonstrate the performance that framework expects, and the documentation chain runs from the validation report to the label on the pack. Workplace exposure questions sit alongside the device question rather than inside it, and the material published by CCOHS on biological hazards and by the World Health Organization on infection prevention is the neutral reference when a committee is writing its own procedure.

CliniEco Medical is a licensed medical device establishment (MDEL #35334).