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Hospital Healthcare Europe
Hospital Healthcare Europe

Ozone sterilisation of surgical devices

5 June, 2009  

The 125L Ozone Sterilizer has been designed to sterilise heat- and moisturesensitive reusable surgical devices and steam-compatible surgical devices. Rigid lumen devices 0.5 mm in diameter and 45 cm long can be safely processed in the 125L

Sylvie Dufresne
Director R&D, Section

Marc Chaunet
Director QA/RA

Simon Robitaille
VP Operation and Research

TSO3 inc.
Quebec, Canada

The 125L Ozone Sterilizer made by TSO3 inc. (Quebec, Canada) was cleared for market by Health Canada in 2002 and by the Food and Drug Administration (FDA) in the USA in autumn 2003. The steriliser’s chamber size is 125 litres with a capacity of 1.7 UST.[1] The sterilisation process of the 125L is compatible with most reusable medical items currently sterilised by other oxidative processes, ethylene oxide, peracetic acid or steam. Sterilisation of implants and flexible endoscopes is not, however, currently validated.[2]

Ozone has been recognised as a safe disinfectant for water and food.[3,4] It may be safely used in gaseous and aqueous phases as an antimicrobial agent for the treatment, storage and processing of foods, including meat and poultry.[5]

125L technology

TSO3’s 125L ozone technology uses an effective sterilisation agent, is safe for employees and patients, and does not harm the environment.

This steriliser produces its own sterilant from USP-grade oxygen, water and electricity. Ozone sterilisation does not require the handling of dangerous gas chemicals and poses no threat to the environment or the user’s health.

The 125L ozone cycle is composed of two identical half cycles. After the instruments have been loaded into the chamber, the door is closed and the cycle is started. A vacuum is drawn followed by a humidification phase. Ozone is then injected into the chamber and the sterilisation process begins. When the half cycle has been reached, the steps from the vacuum to the ozone injection phase are again repeated and followed by a final ventilation phase to remove ozone from the chamber and packaging. At the end of the sterilisation cycle, the ozone is transformed into oxygen. There are no toxic or hazardous residues or waste products associated with the process, only oxygen and purified water.


The 125L efficacy to sterilise surgical devices was performed according to ISO 14937:20006 and established by showing that the process can:

  • Demonstrate the lethal action of the sterilising agent (ozone) against a representative range of microorganisms.
  • Establish an empirical mathematical relationship defining the microbial inactivation kinetics and confirm the sterility assurance level (SAL6) predicted.
  • Select reference microorganisms, based on microbial inactivation kinetics, that have known high resistance to the sterilising agent.
  • Identify process variables that affect the lethal action of the sterilising agent.
  • Assess those factors that can adversely affect the delivery and/or distribution of the sterilising agent (eg, instrument configuration and material composition, packaging, loading).


Determination of the empirical mathematical relationship and of the most resistant microorganism
The biological lethality profile has been exhaustively evaluated for the test organisms identified in Table 1, which are recommended by the FDA[7] and by ISO 14937.[6] An overkill approach was used to determine the highly resistant organism, based upon the D-value calculated from the survivor curve and the fraction negative for each microorganism with no load, mixed with hard water 400 ppm or with serum 5%.

The TSO3 ozone sterilisation process follows Chick’s law. In the early 1900s, Dr Harriet Chick described a method for estimating the destruction of microorganisms by chemical disinfectants. Chick’s law has evolved into what is now referred to as D-value. This law works for all liquid disinfectants and for many sterilisation processes.[8]

The mortality of microorganisms is linear on a semi-logarithmic graph. However, the critical parameter for ozone is not time, as in steam or ethylene oxide sterilisation processes, but rather the ozone dose (expressed as concentration in mg/l) injected into the chamber. This process can be compared to the radiation process, where a minimal dose is needed to achieve the sterility assurance level.

For fraction negative, D-values were calculated using the Stumbo–Murphy–Cochran and Limited Holcomb–Spearman–Karber method by replacing the time parameter with the ozone dose.9 Based upon D-values, Geobacillus stearothermophilus is the most-resistant microorganism in the 125L Ozone Sterilizer with a D-value for spores mixed with serum of 11 mg/l.


Sterilisation of surgical medical instruments
The potential of the 125L Ozone Sterilizer to sterilise complex surgical devices has been demonstrated. Surgical devices were chosen due to their design rather than their material’s content and were inoculated with 106 spores of G stearothermophilus mixed with 5% serum. More than one site was selected on each instrument tested. After inoculation, the instruments were packaged and sterilised. Quantitative recovery methods were used to verify sterility.[9]

Furthermore, TSO3 has developed a Manufacturers’ Testing Programme (MTP) to offer medical device manufacturers and their suppliers a complete validation testing service for their reusable surgical devices. Within the scope of this programme, TSO3 performs material compatibility and sterilisation efficacy of medical devices. To date, more than 200 medical device manufacturers have participated in the programme, which translates into thousands of surgical MIS procedures achieved annually with devices sterilised in the 125L.

Rigid lumens

Furthermore, the TSO3 Ozone Sterilizer, Model 125L, was demonstrated to be effective in sterilising medical devices containing long and narrow rigid lumens.[10] Rigid medical devices with lumens compatible with the 125L Ozone Sterilizer have the lengths shown in Table 2.

Flexible lumens

The 125L Ozone Sterilizer has the potential to sterilise long flexible lumens. Using the same methodology as for rigid lumen devices, the 125L has shown its effectiveness in sterilising Teflon tubing measuring 1 mm in diameter by 240 cm in length.[11]


The demonstration of the 125L Ozone Sterilizer microbicidal efficacy is based on ISO 14937:2000. The tests show that ozone is an efficient and safe sterilising agent when used in the 125L Ozone Sterilizer. Moreover, the inactivation kinetics are a function of the ozone dose injected inside the chamber, and the sterility assurance level can be predicted.

1. EN868-8.
2. TSO3 white paper.
3. Adv Food Nutr Res 2003;45:167-218.
4. Langlais B, Reckhow DA, Brink DR, editors. Ozone in water treatment, application and engineering. Lewis Publishers: Chelsey, Michigan; 1991.
5. FDA. 21 CFR part 173, Section. 173.368 Ozone. 15 June 2001. www.fda. gov/OHRMS/Dockets/98fr/062601a.htm
6. ISO 14937:2000.
7. FDA-DSMA. Premarket Notification 510(k): Regulatory Requirements for Medical Devices; 1995.
8. Ozone Sci Eng 2000;22:227-39.
9. Pflug IJ. Microbiology and engineering of sterilization processes. 10th ed. Department of Food Science and Nutrition, University of Minnesota, Minneapolis. Environmental Sterilization Laboratory (Publisher); 1999; p.1.1-22.9.
10. AJIC 2008;36(4):291-7.
11. Data in preparation.