What Is Sterrad Sterilization and How Does It Work?

Sterrad sterilization is a low-temperature method used in hospitals and surgical centers to sterilize heat-sensitive medical instruments using hydrogen peroxide gas plasma. Developed by Advanced Sterilization Products (a Johnson & Johnson subsidiary), the system kills bacteria, viruses, fungi, and bacterial spores without the high temperatures of steam autoclaving or the toxic residues of ethylene oxide gas. The technology was one of the first hydrogen peroxide gas plasma (HPGP) systems approved by the U.S. Food and Drug Administration, and it has become a mainstay in sterile processing departments worldwide, particularly for delicate devices like endoscopes, powered surgical tools, and fiber-optic cables that would be damaged by heat or moisture.

How a Sterrad Cycle Actually Works

A Sterrad cycle begins with a vacuum. The sterilization chamber is sealed and air is drawn out, dropping the pressure low enough that hydrogen peroxide can transition from liquid to vapor at a relatively low temperature, typically around 45–55 °C. Liquid hydrogen peroxide is stored in a sealed cassette that is punctured only after the sterilizer door closes, so operators never handle the chemical directly under normal conditions.

Once the chamber is under vacuum, a measured dose of hydrogen peroxide is injected and allowed to vaporize and diffuse throughout the chamber, contacting all exposed surfaces of the instruments inside. This diffusion phase is where the actual killing of microorganisms happens. The concentrated hydrogen peroxide vapor is a potent oxidizer that attacks and destroys cell membranes, proteins, and DNA in bacteria and spores. In the Sterrad 100S model, the system runs two complete diffusion-and-plasma stages per cycle to improve reliability.¹

After the diffusion phase, a radio-frequency electrical field is applied to the remaining hydrogen peroxide gas, creating a low-temperature plasma. This plasma phase breaks down the leftover hydrogen peroxide into water vapor and oxygen, which are then vented from the chamber. The entire cycle, from door-close to door-open, takes about 75 minutes in many configurations.²

The Plasma Does Not Do What Most People Think

Here is one of the most common misconceptions about Sterrad: many people assume the “gas plasma” in the name is what kills the microorganisms. It is not. Research has demonstrated that the plasma generated by the radio-frequency discharge primarily serves to break down residual hydrogen peroxide gas, not to sterilize. Studies have shown that the sterilization outcome was not affected by the presence or absence of the RF gas plasma phase, confirming that the hydrogen peroxide vapor itself is the sterilizing agent.³

The plasma stage is better understood as a cleanup step. By converting leftover hydrogen peroxide into water and oxygen, it ensures that instruments come out of the sterilizer dry and free of chemical residues. This matters for patient safety, since residual hydrogen peroxide on a surgical instrument could irritate tissue, and it matters for the instruments themselves, since prolonged chemical exposure could degrade certain materials over time. The byproducts of this breakdown, water and oxygen, are completely nontoxic and require no special aeration or off-gassing period before instruments can be used.²

That said, research on oxygen-based gas plasmas in general has identified mechanisms like an etching effect on microbial structures, particularly bacterial spores, causing visible shrinkage of their outer layers.⁴ This etching may contribute something in broader plasma-based sterilization research, but in the specific context of a Sterrad system, the evidence points to hydrogen peroxide vapor doing the heavy lifting.

What Sterrad Can and Cannot Process

The low operating temperature is the whole point of the system: it handles instruments that would melt, warp, or degrade in a steam autoclave running at 121–134 °C. Flexible endoscopes, laparoscopic instruments, battery-operated drills, fiber-optic light cables, and certain implantable devices are all commonly processed in Sterrad systems. Most metals and many plastics tolerate the process well.

But Sterrad has clear material restrictions. Cellulose-based materials are the biggest limitation. Cotton wraps, paper-plastic pouches, linen, and materials that absorb hydrogen peroxide should not be placed in the chamber. These materials soak up the vapor before it can reach instrument surfaces, effectively starving the sterilization process. Packaging must use Tyvek pouches or appropriately sized nonwoven fabric wraps instead.⁵ This packaging constraint catches many sterile processing departments off guard, especially those transitioning from steam-based workflows where cotton wraps are standard.

Liquids and powders also cannot be sterilized in the Sterrad. The vacuum would cause liquids to boil off, and powders would absorb the hydrogen peroxide. Any instrument with sealed internal cavities that trap air can also interfere with the process, since the vapor needs direct contact with contaminated surfaces to work.

The Lumen Problem

Long, narrow lumens, the hollow channels inside instruments like endoscopes and catheters, present the most persistent challenge for hydrogen peroxide gas plasma sterilization. The vapor must travel the full length of the lumen and make contact with every interior surface. The narrower and longer the channel, the harder this becomes.

Newer Sterrad models like the 100NX include a dedicated lumen cycle and booster attachments designed to force hydrogen peroxide vapor through narrow channels. Under ideal conditions with clean carriers, testing of the 100NX achieved a reduction of bacterial spores exceeding five log steps (meaning it killed more than 99.999% of test organisms) inside lumens. However, any additional contamination, whether organic material like dried blood or inorganic residue like mineral deposits, significantly impaired the sterilization outcome.⁶

This is a critical practical point. The system works well on lumens that have been thoroughly cleaned beforehand, but it does not compensate for poor cleaning. If dried biological material is left inside a channel, the hydrogen peroxide reacts with that debris instead of reaching the underlying microorganisms. Sterrad, more than steam autoclaving, is unforgiving of shortcuts in the pre-cleaning process.

Why Pre-Cleaning Matters More Than You Might Expect

With steam sterilization, the combination of high temperature and saturated steam is aggressive enough to penetrate some degree of residual soil on instruments. Hydrogen peroxide vapor does not have this luxury. It works by chemical oxidation, and any organic or inorganic material sitting on a surface will consume the oxidizing agent before it reaches the microorganisms underneath.

Testing with the Sterrad 100NX showed this clearly: under clean conditions, the system achieved a spore reduction of six log steps or more on all three carrier materials tested, regardless of how many wrapping layers were used. But when organic or inorganic challenges were introduced to simulate insufficient cleaning or crystalline residues, the sterilization outcome was significantly impaired.⁷ The takeaway for anyone working in sterile processing is straightforward: meticulous manual and automated cleaning before loading instruments into the Sterrad is not optional. It is the single most important variable in whether the cycle will succeed.

How Sterrad Compares to Ethylene Oxide

Before hydrogen peroxide gas plasma arrived, ethylene oxide (EtO) was the main option for sterilizing heat-sensitive devices. EtO is effective and compatible with a very wide range of materials, but it comes with serious drawbacks. Ethylene oxide is a known human carcinogen and a reproductive toxin. Workers must be protected from exposure, and sterilized items require a lengthy aeration period, sometimes 8 to 12 hours, to allow the toxic gas to dissipate from the materials before they can safely contact a patient.

Sterrad largely eliminates these concerns. Operator contact with hydrogen peroxide under normal conditions is negligible, since the liquid is contained in a sealed cassette that opens only inside the closed chamber. The byproducts are water and oxygen, so there is no aeration step and no need for dedicated exhaust ventilation to the building exterior.² That 75-minute cycle time compared to the hours-long EtO process (including aeration) also means faster instrument turnaround, which in a busy hospital translates directly into fewer backup instrument sets needed.

The tradeoff is compatibility range. EtO can penetrate materials and long, narrow lumens more effectively than hydrogen peroxide vapor. Some devices that can be sterilized with EtO still cannot be reliably processed in a Sterrad, particularly instruments with very long and narrow internal channels or components that absorb hydrogen peroxide. Many hospitals keep an EtO sterilizer on hand specifically for these edge cases, even after adopting Sterrad as their primary low-temperature system.

How Sterrad Compares to Steam

Steam autoclaving remains the gold standard for sterilization. It is fast, inexpensive per cycle, deeply penetrating, and effective against essentially all microorganisms including prions (misfolded proteins that cause diseases like Creutzfeldt-Jakob disease). For any instrument that can withstand the heat, steam is generally the first choice.

The problem is that a growing share of modern surgical instruments cannot withstand it. Powered devices, flexible endoscopes, cameras, light guides, and many specialized orthopedic instruments contain components, such as plastics, adhesives, optics, or electronics, that degrade rapidly at autoclave temperatures. Switching these instruments from steam to low-temperature sterilization not only preserves their functionality but reduces repair costs. An economic analysis found that moving instruments from steam to low-temperature sterilization cut the repair rate by roughly 35–40%, with one dataset showing repairs dropping from about 0.028 per instrument use to 0.016, and another showing a drop from 0.036 to 0.024.⁸

Over time, those repair savings add up considerably, which brings us to the cost picture.

The Economics of Running a Sterrad System

A Sterrad 100NX unit costs around $130,000 to purchase, with annual maintenance running about $19,000. The per-cycle consumable cost (mainly the hydrogen peroxide cassettes) is also higher than the per-cycle cost of steam, which essentially uses only water and energy. On paper, this makes Sterrad look expensive.

But the full economic picture looks different when instrument damage is factored in. The same economic analysis that tracked repair rates found that the savings from fewer instrument repairs more than offset the higher sterilization costs. Over a 10-year period, the net savings were estimated at roughly $739,000, with an internal rate of return above 60%.⁸ The math depends on the specific mix of instruments a facility processes, but for departments handling large volumes of expensive, heat-sensitive surgical tools, the investment tends to pay for itself relatively quickly.

Safety for Workers and the Environment

Hydrogen peroxide at the concentrations used in Sterrad (typically 58–59% solution) is a strong oxidizer and can cause burns on direct skin contact. Under normal operation, this risk is minimal because the cassette system keeps the liquid sealed until the chamber is closed. The vapor inside the chamber is converted to water and oxygen by the end of the cycle, so opening the door exposes the operator to nothing harmful.

That said, real-world practice does not always match the ideal. A cross-sectional survey of hospitals in Sichuan, China found that hydrogen peroxide leaks were reported by about 8.5% of facilities, and signs of hydrogen peroxide residue were noted by over 80% of surveyed hospitals. Hazardous gas alarms were present in only about 69% of hospitals surveyed.⁹ These numbers suggest that while the technology itself is designed for safety, gaps in maintenance, training, and facility setup can introduce risks that the engineering controls were meant to prevent.

Environmentally, Sterrad is far friendlier than EtO. There are no toxic emissions, no regulated waste byproducts, and no need for external venting systems. Spent cassettes contain only trace amounts of hydrogen peroxide and are typically disposed of as regular waste. For hospitals under regulatory pressure to reduce their use of ethylene oxide, a scenario becoming more common as the EPA tightens emissions standards around EtO sterilization plants, Sterrad offers a practical alternative for most (though not all) of their low-temperature sterilization needs.

Cycle Interruptions and Failure Modes

One operational frustration with Sterrad systems is cycle cancellations. The sterilizer monitors chamber conditions throughout the process and will abort the cycle if it detects anything that might compromise sterilization, such as a pressure leak, a humidity spike from improperly dried instruments, or excessive absorption of hydrogen peroxide by packaging materials. While these safeguards exist for good reason, frequent cancellations waste time and consumables.

Common causes of cycle failures include loading instruments that are not fully dry, using the wrong packaging materials, overloading the chamber so that vapor cannot circulate freely, and failing to properly connect lumen booster adapters. The failure-mode analysis behind updated packaging guidance, such as the mandate to use Tyvek or nonwoven wraps rather than paper or cotton, was driven in part by the need to reduce these preventable interruptions.⁵ For sterile processing departments switching to Sterrad from steam, there is a real learning curve, and training on proper loading, drying, and packaging makes a measurable difference in how often cycles run to completion.

What Sterrad Cannot Handle

Beyond the cellulose and lumen limitations already discussed, a few other categories of items fall outside Sterrad’s reach. Prions, the infectious proteins responsible for conditions like Creutzfeldt-Jakob disease, are extremely resistant to most sterilization methods, and hydrogen peroxide gas plasma has not been shown to reliably inactivate them. Instruments suspected of prion contamination typically require specialized reprocessing involving high-concentration sodium hydroxide or extended high-temperature autoclaving, not Sterrad.

Implantable devices also require careful consideration. While some implants are validated for Sterrad processing, others are not, and the manufacturer’s instructions for use (IFU) must be followed for each specific device. The FDA clearance of Sterrad covers particular device categories and configurations, not a blanket approval for all medical devices. Processing an implant that has not been validated for hydrogen peroxide gas plasma sterilization could leave the patient at risk.

Instruments with long, dead-end lumens (channels that are sealed at one end) are another problem category. Hydrogen peroxide vapor needs a path to flow through; a sealed tube traps air and prevents the vapor from reaching the closed end. Devices with this geometry may need to be processed by EtO or by an alternative validated method instead.

Biological Indicators and Monitoring

Like any sterilization process, Sterrad cycles are monitored using biological indicators (BIs), which are small vials or strips containing a known population of highly resistant bacterial spores. For hydrogen peroxide gas plasma systems, the standard test organism is Geobacillus stearothermophilus, the same species used to challenge steam autoclaves, though the specific BI products are designed for the lower temperatures and chemical environment of the Sterrad process.

After a cycle completes, the BI is incubated to check whether any spores survived. A negative result (no growth) confirms the cycle achieved sterilization conditions. Most Sterrad models also include chemical indicators that change color when exposed to hydrogen peroxide vapor, providing an immediate visual check that the sterilant reached the indicator’s location inside the load. Neither type of indicator alone is sufficient. Biological indicators are the definitive test, but they take hours to incubate, so chemical indicators serve as a real-time screening tool while the BI results are pending.

Facilities typically run BIs with every load that contains implantable devices and at least daily for routine loads, though institutional policies vary. The system also records cycle parameters electronically, creating a traceable record of temperature, pressure, and hydrogen peroxide concentration for each run. If any parameter falls outside the validated range, the system flags the cycle as a failure, and the load must be reprocessed.