7.3 Ozone & Liquid Peracetic Acid Sterilization Systems
Key Takeaways
- Ozone (O3) sterilization generates sterilant gas from medical-grade oxygen via electrical corona discharge, requiring high humidity (>85% RH) and operating at 86°F to 95°F.
- Liquid Peracetic Acid (LPA) system (e.g., STERIS SYSTEM 1E) provides automated point-of-use liquid sterilization for immersible endoscopes and microsurgical instruments using a 0.2% concentration at 50°C to 56°C.
- Instruments processed in liquid peracetic acid emerge WET and UNBAGGED; they cannot be stored and MUST be used immediately for a patient procedure.
- Ozone sterilizers convert residual gas back into oxygen and water vapor through catalytic converters, requiring no chemical consumables or external aeration.
- Geobacillus stearothermophilus is the biological indicator used to monitor both Ozone and Liquid Peracetic Acid sterilization systems.
7.3 Ozone & Liquid Peracetic Acid Sterilization Systems
Exam Tip: Liquid Peracetic Acid (LPA) and Ozone represent specialized low-temperature technologies. For the CSPDT exam, remember that liquid peracetic acid processed items are wet upon completion and CANNOT be stored—they are for immediate point-of-use only. Ozone requires high humidity (>85% RH) and generates its gas from oxygen.
In addition to Ethylene Oxide and Hydrogen Peroxide, healthcare facilities utilize Ozone ($O_3$) gas sterilization and Liquid Peracetic Acid (LPA) automated immersion systems to process specialized surgical devices. Each technology occupies a specific operational niche in sterile processing, especially regarding scope re-processing and environmental sustainability.
1. Ozone ($O_3$) Sterilization Systems
Ozone is an allotropic form of oxygen containing three oxygen atoms ($O_3$). It is an extremely powerful oxidizing gas that destroys microorganisms by attacking cell walls, membrane lipids, and intracellular enzymes.
Ozone Generation & Cycle Parameters
Unlike EtO or hydrogen peroxide, which require chemical cartridges or cassettes, Ozone sterilizers generate their own sterilant gas on-site from medical-grade oxygen ($O_2$) and water via electrical corona discharge.
| Process Parameter | Operating Range / Condition |
|---|---|
| Sterilant Source | Medical-grade oxygen ($O_2$) converted to Ozone ($O_3$) gas via high-voltage generator |
| Temperature | Low temperature: 86°F to 95°F (30°C to 35°C) |
| Relative Humidity | High Humidity: 85% to 90%+ RH (Moisture is mandatory to form reactive hydroxyl radicals) |
| Cycle Duration | Approximately 4.5 hours (consisting of two identical pulses of vacuum, humidification, ozone injection, and exposure) |
| Aeration / Residuals | No aeration required. Ozone passes through a manganese dioxide catalyst that converts $O_3$ back into $O_2$ and water vapor. |
Material Compatibility & Advantages
- Compatible: Stainless steel, titanium, silicone, rubber, rigid lumens, and specialized polymers.
- Incompatible: Natural rubber, latex, neoprene, copper alloys, and cellulose/paper packaging.
- Packaging: Requires Tyvek® pouches or anodized aluminum containers with synthetic filters.
- Biological Indicator: Geobacillus stearothermophilus incubated at 55°C to 60°C.
2. Liquid Peracetic Acid (LPA) Sterilization Systems
Liquid Peracetic Acid (LPA) is a liquid chemical sterilant used in automated, table-top processor units (such as the STERIS SYSTEM 1E®) designed primarily for point-of-use sterilization of fully immersible surgical instruments, including flexible and rigid endoscopes, video laryngoscopes, and microsurgical tools.
Chemical Mechanism & Cycle Parameters
Peracetic acid ($CH_3CO_3H$) is a potent mixture of acetic acid and hydrogen peroxide. It denatures proteins, disrupts cell wall permeability, and oxidizes sulfhydryl and sulfur bonds in enzymes and proteins.
- Sterilant Concentration: Concentrated liquid peracetic acid diluted with warmed, filtered water to approximately 0.2% peracetic acid solution (pH ~6.4).
- Processing Temperature: Controlled warmth between 50°C and 56°C (122°F to 133°F).
- Cycle Duration: Rapid, total cycle time is approximately 23 to 30 minutes.
- Water Rinsing: The processor performs automated rinses using internal UV-treated, sterile-filtered water to strip all chemical residues from instrument channels.
CRITICAL RULE: Immediate Use Only (No Storage)
WARNING (Exam Essential): Items sterilized in a liquid peracetic acid processor are wet and unbagged at the end of the cycle. Because the instruments are not wrapped in a sterile barrier pouch and remain wet, THEY CANNOT BE STORED. They must be transported in a covered, sterile tray directly to the operating room for immediate patient use ("just-in-time" processing). Storing wet, unsealed instruments leads to immediate recontamination and bacterial growth.
Quality Assurance for LPA Systems
- Diagnostic Test Cycle: Performed daily prior to processing the first clinical load to verify hydraulic pressure, temperature, and filter integrity.
- Chemical Concentration Monitoring: Technicians must test the peracetic acid solution using chemical test strips to verify the Minimum Effective Concentration (MEC) before starting a cycle.
- Biological Indicator: Geobacillus stearothermophilus spore strips contained in a specialized challenge tray, incubated at 55°C–60°C.
Comprehensive Low-Temperature Sterilization Technology Comparison Matrix
| Sterilization Technology | Primary Sterilant | Operating Temp | Aeration Required? | Biological Indicator | Packaging Compatibility | Storage Status |
|---|---|---|---|---|---|---|
| Ethylene Oxide (EtO) | 100% EtO Gas | 100°F - 140°F | YES (8-12 Hours) | Bacillus atrophaeus | Tyvek, Paper-Plastic, Non-woven | Terminal (Can store) |
| H2O2 Gas Plasma / VHP | Vaporized H2O2 | 113°F - 131°F | NO (0 Hours) | Geobacillus stearothermophilus | Tyvek, Polyolefin wrap (NO cellulose) | Terminal (Can store) |
| Ozone (O3) | Ozone Gas (from O2) | 86°F - 95°F | NO (0 Hours) | Geobacillus stearothermophilus | Tyvek, Rigid synthetic containers | Terminal (Can store) |
| Liquid Peracetic Acid | 0.2% Peracetic Acid Solution | 122°F - 133°F | NO (Rinsed with sterile H2O) | Geobacillus stearothermophilus | None (Bare trays immersed in liquid) | IMMEDIATE USE ONLY (Cannot store) |
Summary Comparison of Low-Temperature Sterilization Technologies
When evaluating low-temperature options for fragile medical instrumentation, sterile processing professionals balance processing time, material compatibility, worker safety, and packaging requirements:
- Ethylene Oxide: Widely compatible with complex instruments and deep lumens, but carries significant worker hazards, long cycle times, and mandatory 8–12 hour aeration.
- Hydrogen Peroxide (VHP / Gas Plasma): Rapid, non-toxic, and widely used, but strictly prohibited from contacting cellulose (paper/linen) or wet/liquid items.
- Ozone: Generated on-site from oxygen with zero chemical consumables, but requires high humidity and a longer 4.5-hour cycle time.
- Liquid Peracetic Acid: Unmatched turnaround speed (30 minutes) for flexible endoscopes at point-of-use, but items emerge wet and unbagged, prohibiting shelf storage.
What is the most critical operational constraint regarding items sterilized in a Liquid Peracetic Acid (LPA) processor?
Which relative humidity (RH) level is required during the exposure phase of an Ozone sterilization cycle?
Which liquid chemical sterilant solution is diluted with sterile water to a 0.2% concentration at 122°F to 133°F (50°C to 56°C) for point-of-use endoscope processing?