ISO 25424: Low Temperature Steam and Formaldehyde Sterilization
A flexible endoscope that cannot survive 134 degrees Celsius still has to reach a defined sterility assurance level, and for some facilities the cycle that gets it there uses low temperature steam with formaldehyde. ISO 25424 is the standard that describes how such a process is developed, validated and then controlled once it is in routine use.
Knowing what the standard covers helps a reprocessing lead ask the right questions of an equipment supplier.
What does ISO 25424 cover?
ISO 25424 sets out requirements for a sterilization process that uses steam together with formaldehyde vapour at temperatures well below a normal autoclave cycle. It addresses process development, validation and routine control. It is written for devices that would be damaged by moist heat at 134 degrees Celsius, such as flexible scopes and bonded optical assemblies.
The standard does not decide which devices must be processed this way. That comes from the device manufacturer's reprocessing instructions and from the infection prevention policy your facility follows.
Where does a low temperature cycle fit in Canada?
Most Canadian dental offices and small clinics run steam cycles and never need this method. It appears where a facility reprocesses heat-sensitive instruments, or in a hospital or veterinary setting with flexible endoscopes. | Stage | What is documented | Who reviews it |
| Process definition | Temperature, formaldehyde concentration, exposure and evacuation phases | Reprocessing lead |
|---|---|---|
| Performance qualification | Biological indicator results with the full load configuration | Infection control lead |
| Routine release | Chemical indicator in every load, plus biological indicators at defined intervals | Operator on shift |
| Records | Cycle logs, indicator results, service and calibration dates | Inspector on request |
How is the cycle validated?
Validation follows the same logic as any sterilizing process. You establish the bioburden and the required sterility assurance level, define the process, then demonstrate with biological indicators that the load reached the required conditions. Cycle phases and tolerances live in the standard, and your sterilizer supplier should be able to map their programme to it in writing.
Which supplies does the monitoring programme need?
Packaging has to match the process. Class 4 sterilization pouches and heat-sealable sterilization roll are available with dual indicators, but the indicator chemistry is validated for defined cycle types, so confirm compatibility rather than assuming steam performance carries over.
For load release you need a spore test. A 24-hour readout biological indicator gives a same-next-day answer without a separate laboratory, and indicator tape still has a place on the outside of the pack as a processing marker, not as a release test.
What changes in daily practice?
Do not change the monitoring routine in the same week you change the cycle. Run the new process, keep every record, and compare biological indicator results across several cycles before you retire the old one. Keep indicator lot numbers and expiry dates in the log, because anyone reviewing a cycle from two months ago will want to see which lot released that load.
If you are building a monitoring baseline for a low temperature cycle, the five-pack biological indicator trial is CA $12.99 with shipping included, which is enough to establish a starting point before committing to a case. For multi-site or mixed orders, our team can build a quote around your loads.
References
- ISO 25424:2018 - Sterilization of health care products - Low temperature steam and formaldehyde (checked 19 September 2026)
- Public Health Ontario - infection prevention and control guidance for clinical settings (checked 19 September 2026)
- ASTM F1980 - Accelerated aging of sterile barrier systems (checked 19 September 2026)
Related Reading
- Sterilization monitoring supplies for Canadian clinics
- Learning Hub - clinical and procurement guides
- Wholesale and multi-site ordering
- Sterilization modalities: ISO 17665, ISO 11135 and ISO 11137
- Sterile packaging alternatives: paper, film and reusable options
- Which BI works with your autoclave brand?
- dental clinic sterilization supplies
- free Ontario sterilization compliance log
- printable autoclave sterilization log sheet (free)
Frequently Asked Questions
What is low temperature steam and formaldehyde sterilization?
A process that combines steam with formaldehyde vapour at temperatures well below a standard autoclave cycle, so instruments that cannot survive moist heat at 134 degrees Celsius can still be processed to a defined sterility assurance level. The whole method, from process definition to routine control, is described in ISO 25424.
Does ISO 25424 replace ISO 17665?
No. ISO 17665 covers moist heat sterilization. ISO 25424 covers the low temperature steam and formaldehyde process, which uses a different sterilant mix and a different cycle profile. A facility can use both standards side by side for different loads.
Can I use ordinary autoclave tape with a low temperature cycle?
Tape and chemical indicators are validated for particular cycle types. A strip validated for 134 degrees Celsius steam is not automatically valid for a low temperature formaldehyde cycle, so ask the supplier what cycle type the indicator was tested against and file that answer with your records.
How often should a biological indicator be run on this cycle?
Frequency is set by your facility policy and by the reprocessing expectations you are inspected against. A common shape is a chemical indicator in every load for release, with biological indicators on a defined schedule and after any equipment service or failed cycle.
Last updated: September 2026. CliniEco Medical holds MDEL #35334 issued by Health Canada, and supplies clinics, long-term care homes and home-care programs across Canada.
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