What Is Plasma Sterilization? How H2O2 Plasma Works

Plasma sterilization is a low-temperature sterilization process that uses hydrogen peroxide, energized into plasma, to kill every form of microorganism including bacterial spores. It runs at roughly 45 to 55 degrees, well below the 134 degrees of a steam cycle, which is the whole point: it sterilizes heat-sensitive and moisture-sensitive devices that an autoclave would destroy, and it leaves no toxic residue behind, because the by-products are water vapour and oxygen.

Key takeaways

• Plasma sterilization sterilizes heat-sensitive devices at about 45 to 55 degrees using hydrogen peroxide vapour, far below steam temperatures.
• The cycle runs in fixed stages: evacuate the chamber, inject a metered dose from a single-use cassette, let the vapour diffuse, ignite the plasma, then vent with filtered air.
• There is no aeration step and no toxic residue, unlike ethylene oxide, which is the practical advantage in a busy department.
• It will not process liquids, powders or cellulose materials such as paper, cotton and gauze, and every device must appear on the machine’s load list.
• The governing international standard is ISO 22441:2022, which covers low-temperature vaporized hydrogen peroxide sterilization of medical devices.

What plasma means in this context

Plasma is the fourth state of matter: a gas energized until its molecules ionize into reactive ions, electrons and free radicals. Those reactive species are what do the work. When hydrogen peroxide vapour in the chamber is energized by an electric field, the radicals it produces attack microbial cells, and the same energy breaks down the remaining peroxide into water and oxygen once the cycle is done.

The load never gets hot and never gets wet. That is why the method suits items that cannot take steam: endoscopes and their delicate optics, camera heads and light cables, ophthalmic instruments, batteries, and certain powered surgical devices. It also means the machine has strict chemistry rules, which we come back to below.

The cycle, stage by stage

Every plasma sterilizer follows the same underlying sequence, with model-specific parameters on top:

1. Load preparation. Instruments are cleaned, dried and packaged in compatible materials. Moisture in the load is the most common cause of an aborted cycle, because the chamber cannot reach the vacuum the process needs.
2. Evacuation. The chamber is pulled down to sub-atmospheric pressure to remove air and condition the load.
3. Injection. A metered dose of hydrogen peroxide, supplied in a single-use cassette, is vaporized and introduced into the chamber.
4. Diffusion. The vapour spreads through the chamber and contacts every exposed surface. Penetration into narrow lumens depends on the cycle and the device geometry, which is why the load list matters.
5. Plasma phase. An electric field energizes the vapour into plasma. The reactive species complete the kill, and the plasma helps break down residual peroxide.
6. Vent and unload. The chamber returns to atmospheric pressure, commonly through a filtered air line, and the load comes out at room temperature, ready for the next case.

Cycle times depend on load and machine. In the Renosem low-temperature range we supply, the S20 unit (18 litres) runs an eco cycle in 21 minutes and an advanced cycle in 38 minutes, while the 90-litre S90 runs a non-lumen cycle in 28 minutes and an advanced cycle in 53 minutes. Those are the kind of figures a department plans around when it is deciding whether low-temperature capacity can sit in the daily rotation.

Why departments choose it over steam and over EtO

Against steam, the advantage is compatibility. Any device that cannot tolerate 134 degrees, or that cannot be fully dried before packing, has no place in an autoclave, and the alternative used to be sending it out or retiring it. A plasma sterilizer keeps that work in-house.

Against ethylene oxide, the advantage is the process itself. EtO cycles are long, the gas is toxic and carcinogenic, and absorbed residue has to be removed through an aeration step before the load is safe to handle. Hydrogen peroxide plasma has no such step: water vapour and oxygen are the breakdown products, and dedicated gas-room ventilation is not required for the process. EtO still has a role for devices that tolerate neither steam nor peroxide, but where a device is compatible, the peroxide route is simpler to run and simpler to house.

The relevant standard is ISO 22441:2022, which covers the development, validation and routine monitoring of low-temperature vaporized hydrogen peroxide sterilization for medical devices. It is the document a sterilology committee will ask about when a plasma sterilizer is proposed.

What cannot go through a plasma cycle

The exclusions are chemistry, not marketing. Absorbent cellulose materials soak up hydrogen peroxide and interfere with the process, so paper, cotton, gauze and cellulose-based wraps are out. Liquids and powders are out. Packaging has to be compatible synthetic material, and every instrument has to appear on the machine’s own load list, checked against the device manufacturer’s instructions for use. Long, narrow or complex lumens may exceed what a given cycle can validate, and no amount of wishful thinking changes that.

In practice this shapes what the machine is used for. Plasma sterilization sits next to the autoclave rather than replacing it: steam for the bulk of wrapped instruments and theatre loads, plasma for the heat-sensitive minority that would otherwise be the department’s bottleneck.

Choosing a plasma sterilizer

Four decisions do most of the work. Chamber size follows the daily heat-sensitive load, and the Renosem range covers it from the 18-litre S20 for small clinics and ophthalmology, through the 34-litre S30 and the dual-door D50 with two 30-litre chambers, up to the 90-litre S90 for midsize hospitals. Sterilizing agent delivery should be cassette-based and single-use, with automatic cassette disposal on larger models, because handling spent cassettes is where staff exposure risk lives. Power draw is modest by CSSD standards, at a maximum of 1.5 to 2.5 KVA across the range. And cycle documentation has to be exportable or printable, since a validated cycle without a record is an audit finding waiting to happen.

We supply the Renosem low-temperature H2O2 gas sterilizer range across South Africa, with DBD and corona plasma systems, single-use peroxide cassettes and full cycle documentation. The machines sit in our low-temperature sterilizers category alongside the rest of the low-temperature range, and alongside the steam autoclaves that cover the loads plasma cannot. Specifying low-temperature capacity for the first time, or replacing an ageing unit? Request a quote. A sales consultant replies within one business day, and our engineers handle installation and operator training nationwide.

Cover photo: Bakytzhan Baurzhanov on Pexels.

Frequently asked questions

Frequently asked questions