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newSchoolWorks.com › VoTechWorks › Health & Personal Services › Surgical Technology › Sterilization: Principles and Practice in the Surgical Environment › Lesson 8
HLT-SURG65-05 · Lesson 8 · 30.5 clock hours · theory

Alternative Sterilization Methods: EO, Hydrogen Peroxide Plasma, and Dry Heat

Objective. Students will compare ethylene oxide (EO), hydrogen peroxide gas plasma, and dry-heat sterilization with respect to mechanism, compatible materials, cycle parameters, and safety requirements.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a licensed clinician in the field or by a certification or approval body. It is a study draft and may contain errors. Do not use it to make decisions about any patient or medication. Always follow your instructor, your supervising professional, and current official references and regulations.

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Why One Sterilization Method Is Not Enough

Steam sterilization is the workhorse of the central sterile department, but many surgical items cannot tolerate high heat or moisture. Flexible endoscopes, power equipment, implants with electronic components, and delicate optics would be damaged or destroyed in a steam autoclave. Three alternative methods fill that gap: ethylene oxide (EO) gas sterilization, hydrogen peroxide gas plasma sterilization, and dry-heat sterilization. Every surgical technologist must understand how each method works, what it can and cannot process, and the safety rules that protect patients and staff.

Ethylene Oxide (EO) Gas Sterilization

Mechanism of action. EO is an alkylating agent. It disrupts microbial DNA and proteins by adding alkyl groups to key molecular sites, preventing reproduction and killing all microbial life, including spores. This chemical action does not require high heat, which is why EO is ideal for heat-sensitive items.

Cycle parameters. EO sterilization takes place at relatively low temperatures, typically in the range of approximately 37–63 °C (98–145 °F), at controlled humidity and gas concentration. Because EO penetrates packaging slowly, cycle times are long—often several hours—and are followed by an aeration phase that removes residual gas from the load. Aeration may occur inside a dedicated aerator or within the sterilizer itself and commonly takes 8–12 hours or longer depending on the materials processed and the equipment used. Always follow the manufacturer's instructions for use (IFU) and facility policy for aeration times.

Materials compatibility. EO is compatible with a wide range of materials: rubber, plastics, metal, glass, and many electronic or battery-powered devices. It is one of the few methods capable of sterilizing long, narrow lumens. Check the device IFU to confirm EO compatibility before processing.

Safety requirements. EO is a known human carcinogen and mutagen. OSHA regulates occupational exposure to EO under a specific standard that establishes a permissible exposure limit (PEL) and an action level for airborne concentration. Engineering controls are mandatory: dedicated negative-pressure EO rooms or cabinets, local exhaust ventilation, continuous air monitoring, and personal monitoring badges for staff who work with EO regularly. EO must be stored and handled according to hazardous-material regulations. Proper aeration is a patient safety requirement as well—residual EO on devices can cause tissue irritation or burns. Staff must never open an EO sterilizer chamber door prematurely.

Hydrogen Peroxide Gas Plasma Sterilization

Mechanism of action. Hydrogen peroxide (H₂O₂) gas plasma works in two phases. First, vaporized hydrogen peroxide diffuses throughout the chamber and contacts microbial surfaces, disrupting cell membranes and enzymes through oxidation. Second, radiofrequency or microwave energy is applied to create a plasma state—an ionized cloud of highly reactive free radicals—that delivers an additional lethal oxidative assault on any remaining microorganisms. At the end of the cycle, the free radicals recombine into water vapor and oxygen, leaving no toxic residue.

Cycle parameters. H₂O₂ gas plasma cycles operate at low temperatures, typically below 50 °C (122 °F), and are relatively fast—many cycles complete in under 75 minutes with no separate aeration phase required. Items are ready for use immediately after the cycle ends. Packaging must be non-woven polypropylene pouches or trays approved by the sterilizer manufacturer; cellulose-based materials (paper wraps, cotton) absorb hydrogen peroxide and will cause a cycle abort.

Materials compatibility. H₂O₂ gas plasma is compatible with most metals, many plastics, cameras, powered instruments, and rigid endoscopes. It is not compatible with items that have long, narrow lumens below the manufacturer's specified diameter-to-length ratio, absorbent materials, cellulose, or liquids. Flexible gastrointestinal endoscopes generally require a liquid chemical sterilant or high-level disinfection process, not H₂O₂ plasma, unless the device IFU explicitly approves it. Always verify device compatibility in the IFU before use.

Safety requirements. Because the end-products are water and oxygen, H₂O₂ plasma poses far fewer occupational exposure hazards than EO. However, hydrogen peroxide in its concentrated liquid form (used to generate the vapor) is a strong oxidizer and irritant; it must be handled carefully and stored per the manufacturer's directions. The cassette or cartridge system used in most tabletop H₂O₂ plasma sterilizers simplifies safe handling.

Dry-Heat Sterilization

Mechanism of action. Dry heat kills microorganisms through oxidation and protein denaturation. Without moisture, higher temperatures and longer exposure times are required compared with steam.

Cycle parameters. Common dry-heat cycles operate at 160–170 °C (320–338 °F) for 1–2 hours, though specific time-temperature combinations are dictated by the load and the sterilizer's validated cycles. Items must reach the required temperature throughout before timing begins.

Materials compatibility. Dry heat is suitable for items that can withstand high temperatures but would be damaged by moisture: anhydrous oils, petroleum-based ointments, powders, glass syringes, and certain metal instruments. It is not suitable for rubber, plastics, or any material that melts, deforms, or degrades at high temperatures.

Safety requirements. Dry-heat sterilizers operate at temperatures that cause severe burns on contact. Items exiting the chamber are extremely hot; staff must use insulated gloves and allow items to cool before handling. Do not place items in packaging that cannot tolerate the temperatures required.

The IFU Is the Final Authority

For every sterilization decision, the device manufacturer's IFU must be consulted. AAMI ST79 provides comprehensive guidance for steam sterilization but also references the importance of following IFUs for all sterilization methods. Assigning a device to the wrong sterilization method can destroy the device, leave it non-sterile, or harm the patient. When in doubt, do not process the item until compatibility is confirmed.

Key terms9

AlkylationA chemical reaction in which an alkyl group is added to a molecule; the mechanism by which ethylene oxide disrupts microbial DNA and proteins to achieve sterilization.
Ethylene oxide (EO)A flammable, carcinogenic gas used as a low-temperature chemical sterilant that is effective on heat- and moisture-sensitive devices; requires controlled aeration after the cycle to remove toxic residue.
Hydrogen peroxide gas plasmaA low-temperature sterilization method that uses vaporized hydrogen peroxide followed by a plasma phase of reactive free radicals to kill microorganisms; leaves only water vapor and oxygen as byproducts.
AerationThe process of removing residual ethylene oxide from sterilized items and their packaging before use; a patient and staff safety requirement after every EO cycle.
Dry-heat sterilizationA sterilization method using high temperatures without moisture, relying on oxidation and protein denaturation; suitable for items that tolerate heat but would be damaged by steam.
Instructions for Use (IFU)Manufacturer-provided documentation specifying how a device must be cleaned, packaged, and sterilized; the authoritative reference for determining sterilization method compatibility.
Permissible Exposure Limit (PEL)An OSHA-established maximum allowable airborne concentration of a hazardous substance in the workplace over a defined time period; EO has both a PEL and a lower action level that triggers additional protective measures.
Free radicalsHighly reactive, short-lived chemical species generated during the plasma phase of H₂O₂ plasma sterilization that destroy microbial cell components through oxidation.
AAMI ST79A comprehensive guidance document from the Association for the Advancement of Medical Instrumentation covering best practices for steam sterilization and sterility assurance in healthcare facilities.
In class: Lecture and comparison matrix activity: students complete a side-by-side table for EO, H₂O₂ plasma, and dry heat covering mechanism of action, materials compatibility, aeration requirements, and primary safety hazard. · EO safety case study: students review OSHA permissible exposure limits for EO, identify engineering controls (ventilation, negative pressure rooms, monitoring badges), and write a brief summary of required protective measures. · Materials compatibility sorting exercise: students receive a list of 20 OR items (flexible endoscopes, rubber tubing, implants, power drill, glass syringes) and assign each to the appropriate sterilization method, citing compatibility data from manufacturer IFU cards.
Materials: Manufacturer IFU reference cards for EO sterilizer and H₂O₂ plasma sterilizer, OSHA EO standard reference, comparison matrix worksheet, AAMI ST79, course textbook
Check: Completed comparison matrix and materials sorting exercise reviewed by instructor; matrix must be fully accurate; sorting exercise scored against answer key with pass mark 80%.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Sterilization and Aseptic Technique
1. What is the primary mechanism by which ethylene oxide destroys microorganisms?
Sterilization and Aseptic Technique
2. A surgical technologist is preparing a load for hydrogen peroxide gas plasma sterilization. Which packaging material must be avoided?
Sterilization and Aseptic Technique
3. Which statement about aeration following ethylene oxide sterilization is correct?
Sterilization and Aseptic Technique
4. A flexible gastrointestinal endoscope must be processed after use. Which sterilization or high-level disinfection method is most likely appropriate, assuming no specific IFU guidance is available to the technologist?
Sterilization and Aseptic Technique
5. Which of the following items is best suited for dry-heat sterilization?
Sterilization and Aseptic Technique
6. What engineering control is most important for protecting staff who work routinely with ethylene oxide sterilizers?
Sterilization and Aseptic Technique
7. At the end of a hydrogen peroxide gas plasma cycle, the byproducts released into the environment are:
Sterilization and Aseptic Technique
8. A sterile processing technologist must determine which sterilization method to use for a newly received rigid laparoscope. What is the correct first step?
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