For the purposes of this discussion, we are using definitions that emphasize the functional behavior of each technology rather than adhering strictly to formal scientific classifications.
In a recent conversation, an infectious disease physician asked about dry hydrogen peroxide. His questions assumed a familiar picture: a sealed room, the air handler shut off, a generator running a cycle, and nobody allowed back in until a meter indicated it’s clear.
That picture fits vaporized hydrogen peroxide. It doesn’t correlate to dry hydrogen peroxide. His view changed the moment he learned that patients could stay in the room while DHP technology runs.
It’s an easy mix-up. Several technologies use hydrogen peroxide, and the chemistry is shared. However, the delivery model is not, and the delivery model determines whether a room must be vacated.
This guide explains the same six criteria from our bipolar ionization comparison and our ultraviolet germicidal irradiation (UVGI) comparison to show how vaporized hydrogen peroxide and Synexis DHP® technology each perform in an occupied space.
Key Takeaways
|
Six Criteria to Judge Any Hydrogen Peroxide Technology in an Occupied Space
Our bipolar ionization and UVGI pieces used the same six questions, so all three articles line up criterion by criterion. Here, each one is framed around what happens to the room while treatment runs.
1. Does it operate while people are in the room?
For hydrogen peroxide, this is the deciding question. Some methods need the room vacated and sealed for the full cycle. Others are designed to run with people present.
2. Does it treat surfaces as well as air?
A vapor or gas that fills a room reaches both. The more pertinent question is when.
3.Does it run continuously or in cycles?
A cycle treats a room at a single point in time. The next patient, shift, or production run starts adding bioburden back as soon as the door opens.
4. Does it depend on staff labor and uptime?
Sealing vents, running a generator, monitoring concentrations, and clearing the room for re-entry all take trained people and time.
5. Does it reach enclosed and shadowed areas?
Unlike light, a vapor or gas doesn’t need line of sight. The difference is whether the room must be empty while it moves through.
6.What is the depth of the evidence?
Ask where each result was measured: in a sealed test room against biological indicators, or across a room the way people use it.
The Hydrogen Peroxide Family: Shared Chemistry, Different Delivery
Every technology in this family relies on hydrogen peroxide. What separates them is the starting strength, the form they deliver it in, and whether anyone can be in the room.
| Approach | How it’s delivered | Starting strength | The room during treatment |
|---|---|---|---|
| Vaporized hydrogen peroxide (VHP or HPV) | Liquid hydrogen peroxide heated into a vapor, with particles under 1 micron | 30 to 35% hydrogen peroxide | Vacated and sealed, with ventilation sealed off |
| Aerosolized hydrogen peroxide (aHP) | A fine mist of electrically charged droplets | 5 to 8% hydrogen peroxide | Vacated and sealed |
| Ionized hydrogen peroxide (iHP) | A mist passed through a plasma arc, which converts it into hydroxyl radicals | 7.8% hydrogen peroxide | Sealed, with re-entry after hydrogen peroxide falls below 1 ppm |
| DHP technology | Dry hydrogen peroxide, a pure gas form of hydrogen peroxide, generated from ambient oxygen and humidity | Not applicable | Occupied because it’s designed for continuous operation with people present |
Sources: ARHAI Scotland, 2022 (VHP and aHP). Cramer et al., Scientific Reports, 2021 (iHP).
Vaporized Hydrogen Peroxide
VHP generators heat 30% to 35% hydrogen peroxide into a vapor, according to a 2022 literature review from ARHAI Scotland. The vapor fills the sealed room and is broken down into water and oxygen during an aeration phase. Unfortunately, this can make it corrosive and it’s possible that it damages equipment. Dry hydrogen peroxide doesn’t do this.
VHP decontamination is common in hospital rooms, laboratories, and pharmaceutical clean rooms. The terms VHP sterilization and hydrogen peroxide sterilization usually describe something else: closed chambers that process heat-sensitive medical devices.
Aerosolized Hydrogen Peroxide
Aerosolized systems, often called fogging systems, spray weaker hydrogen peroxide as a fine mist of charged droplets, also in a vacated, sealed room. A 2011 head-to-head study in Infection Control & Hospital Epidemiology ran both in a 136-cubic-meter test room. A full cycle, including aeration, took about three hours for vapor and about three and a half hours for aerosol.
What Is Ionized Hydrogen Peroxide?
Ionized hydrogen peroxide passes a 7.8% hydrogen peroxide mist through a plasma arc, according to a 2021 analysis in Scientific Reports. The room is sealed during treatment, and staff confirm hydrogen peroxide is below 1 ppm before anyone is allowed to return.
Dry Hydrogen Peroxide
Dry hydrogen peroxide is a pure gas form of hydrogen peroxide. It isn’t aqueous, and it isn’t vaporized. Synexis devices convert ambient oxygen and humidity into dry hydrogen peroxide, which flows freely and continuously through indoor spaces to reduce microbes in the air and on surfaces. There’s no cycle to start, which is why the room can stay in use.
Room Clearance Is the Dividing Line
The ARHAI Scotland review is direct about clearing rooms. Airborne hydrogen peroxide systems “can only be used in areas which have been vacated of people and properly sealed.” Ventilation systems also must be sealed off before use.
Here’s what a typical cycle requires from a facility:
- Perform a manual cleaning first. The same review recommends running airborne hydrogen peroxide only after a manual cleaning, because residual soiling reduces how well it works.
- Conduct a materials check. The review notes that certain materials are incompatible with hydrogen peroxide and recommends assessing a room’s building materials and contents before treatment. One study it cites found that aerosolized hydrogen peroxide caused damage or corrosion to bronze plating and steel, as well as damage to some plastic coatings.
- Ensure the room is empty and sealed. Doors and gaps should be sealed, and the HVAC supply to the space must be shut off or sealed off. Ireland’s Health Service Executive also asks teams to check how the process will interact with the fire alarm system.
- Verify the cycle itself. ARHAI Scotland defines a full cycle as “from over an hour to several hours, or overnight,” depending on room size.
- Conduct aeration before re-entry. Aeration is the longest phase. People must stay out until hydrogen peroxide falls below 1 ppm, which is the OSHA-permissible exposure limit as an eight-hour time-weighted average.
- Have trained operators. Ensure someone runs the generator, monitors concentrations, and confirms the room can reopen.
Every hour a room is sealed is an hour it isn’t available for patients, workers, customers, production runs, or animals. That’s why whole-room disinfection systems tend to run after discharge or during an outbreak rather than every day.
Vaporized Hydrogen Peroxide vs. DHP Technology Against the Six Criteria
VHP treats a room while it’s empty. Synexis DHP technology works while the room is in use. Here’s how that plays out across the same six criteria.
| Criterion | Vaporized hydrogen peroxide | Synexis DHP technology |
|---|---|---|
| Operates in occupied space | No. The room is vacated and sealed for the full cycle, including aeration. | Yes. Designed for safe, continuous operation in occupied spaces. Safe for use around people, products, animals and equipment. |
| Treats surfaces as well as air | Vapor fills the sealed room and reaches air and exposed surfaces during the cycle. | Yes. Reduces pathogens both in the air and on surfaces. |
| Continuous or cyclical | Episodic. Each cycle treats the room at a single point in time. | 24/7/365 touchless and automated technology, with no disruption of operations. |
| Staff labor and uptime | Trained operators seal the room, run the cycle, and confirm re-entry. The room is out of service until aeration ends. | Minimal routine, low-cost maintenance. |
| Enclosed and shadowed areas | Vapor moves beyond line of sight within the sealed space. | Moves with room air into enclosed and hard-to-reach areas, reducing pathogens in the air and on surfaces. |
| Depth of evidence | Long research history, including testing against biological indicators in sealed rooms. | The efficacy of Synexis DHP technology is backed by independent peer-reviewed published studies, including research in occupied patient rooms. |
Operates in occupied space. The room is vacated and sealed for the full cycle, including aeration.
Want to see how the six criteria apply to your building? A Synexis walk-through and application assessment looks at your space and its airflow, then sizes a deployment to fit. Request an assessment.
1. Working with People in the Room
This is the widest gap between the two approaches. VHP is built to run in an empty room. Synexis DHP technology is designed for safe, continuous operation in occupied spaces, and that statement rests on specific documentation:
- Meets requirements for OSHA safety, 29 CFR 1910.1000 Table Z-1
- Certified to meet UL 2998 for zero ozone emissions
- Meets California ozone emissions limit: CARB certified
- Designed for continuous use in sensitive environments like NICUs and oncology units
For a closer look, watch Synexis DHP® technology: Safe for Occupied Spaces.
2. Air and Surfaces During the Day, Not Just Overnight
A VHP cycle reaches air and surfaces while the room is sealed. Synexis DHP technology treats air and surfaces while the room is open, and each surface result is published with the conditions under which it was measured:
- Candida auris: 89.0% reduction on surfaces within occupied patient rooms (Sutton et al., OFID).
- Klebsiella pneumoniae: 99.5% reduction on surfaces during the first 24 hours of exposure, achieved in a simulated hospital suite (Data on File, SYN-0013).
- Staph. aureus (MRSA): >99.99% reduction on surfaces at 2 hours vs. control (Data on File, SYN-0006).
- *Salmonella enterica: 91.62% reduction on surfaces at 6 hours vs. control.
These figures come from different test conditions than the hydrogen peroxide studies above, so they are not directly comparable. Each one stands on its own terms. Every published figure, with its source, is on the pathogens page.
3. A Cycle vs. a Continuous Layer
A VHP cycle resets a room right before it reopens. Then the next admission, shift, or production run begins, and bioburden starts building again.
Synexis DHP technology works continuously, whether the room is occupied or not. The devices run around the clock, through shift changes, overnight, and during the busiest hours. It’s 24/7/365 touchless, automated technology with no disruption to operations.
4. What It Asks of Your Team
VHP needs trained operators for every cycle, plus a room out of service until aeration ends. Synexis devices require only minimal routine, low-cost maintenance, with consumables replaced periodically. There’s no room to seal and no re-entry reading to wait on.
5. Reach Without Clearing the Room
To be fair to VHP, a vapor reaches well beyond line of sight. Dry hydrogen peroxide also moves with the room’s own air into enclosed and hard-to-reach areas, such as under equipment and behind furniture, reducing pathogens in the air and on surfaces there. The difference is that it does so with the room open.
That reach depends on the space being enclosed. Results vary with air movement and microbial load, so we size every installation to the specific space.
6. Where the Evidence Comes From
VHP has a long research record, much of it built on biological indicators in sealed test rooms, which is the right test for a validated decontamination step. The efficacy of Synexis DHP technology is backed by independent peer-reviewed published studies. That includes the Candida auris research above, which measured surfaces within occupied patient rooms.
Where Vaporized Hydrogen Peroxide Still Has a Legitimate Role
VHP is a proven tool with clear strengths, and a fair comparison should name them:
- Terminal decontamination after a known outbreak. ARHAI Scotland supports using airborne hydrogen peroxide as an adjunct to manual cleaning for terminal room decontamination, and for specific outbreak situations.
- Validated decontamination in life sciences. Isolators, clean rooms, and laboratories that need a documented result against biological indicators rely on VHP decontamination for that step.
- Device sterilization in closed chambers. Low-temperature hydrogen peroxide sterilization of heat-sensitive instruments happens in a dedicated chamber, not in a room.
How a Continuous Layer and an Episodic Tool Work Together
These methods answer different questions. An episodic vapor cycle resets an empty room at a single point in time. A continuous layer keeps working on the air and surfaces in the hours and days the room is in use.
Synexis DHP technology complements the tools a facility already uses, VHP included. Each one keeps its place in the routine.
How the Criteria Apply by Facility Type
Healthcare
Infection prevention and environmental services (EVS) teams may run VHP after an isolation patient is discharged. Then the next admission arrives. Synexis technology can help support infection prevention strategies by treating air and surfaces while the room is occupied. More information is on the healthcare page.
Food processing
Lines rarely stop long enough to seal a room and wait out aeration. The technology runs during production and is USDA Organic permitted, with no chemical residues, 7 CFR 205.605. More details can be found on the food page.
Life sciences
VHP often handles validated decontamination of isolators and clean rooms. Labs and support spaces remain in use between those steps. Learn more on the life sciences page.
Poultry and hatcheries
Dry hydrogen peroxide has been evaluated as a replacement for formaldehyde in commercial hatcheries (USPOULTRY PROJ_727). Find out more on the poultry page.
Animal health
Exam rooms and kennels are seldom empty long enough for a sealed cycle. The technology helps create a sanitary and welcoming atmosphere for clients and animals. More information is on the animal health page.
What Should a Facility Ask Before Choosing a Hydrogen Peroxide System?
Bring these questions to any vendor, including Synexis:
- Does the room need to be vacated and sealed while the system runs?
- What hydrogen peroxide strength does it start with, and in what form is it delivered?
- How long is a full cycle, including aeration, for a room our size?
- Does the HVAC need to be shut off or sealed off, and how does the process interact with our fire alarm system?
- Which materials, finishes, and electronics in our space are compatible with it?
- How is re-entry confirmed, and who signs off?
- Who operates it, and what training do they need?
- For each result, what organism, medium, time frame, and comparator sit behind it, and was it measured in a sealed room or during normal use?
- What happens to the room between cycles?
- How does the system fit alongside our existing cleaning protocol without changing it?
Frequently Asked Questions
What is the difference between vaporized, aerosolized, ionized, and dry hydrogen peroxide?
All four rely on hydrogen peroxide but deliver it differently. Vaporized systems heat 30 to 35% hydrogen peroxide into a vapor. Aerosolized systems spray 5 to 8% hydrogen peroxide as a charged mist. Ionized systems pass a 7.8% mist through a plasma arc. Dry hydrogen peroxide is a pure gas form of hydrogen peroxide that DHP technology produces from ambient oxygen and humidity.
Which hydrogen peroxide methods require clearing the room?
Vaporized, aerosolized, and ionized hydrogen peroxide all require a vacated, sealed room, with ventilation sealed off. Synexis DHP technology is designed for safe, continuous operation in occupied spaces, so the room stays in use.
How long must a room stay empty during a treatment cycle?
It depends on the system and the room size. ARHAI Scotland estimates a full airborne hydrogen peroxide cycle at over an hour to several hours, or overnight, including aeration.
Can people remain in the space while treatment runs?
Not with vaporized, aerosolized, or ionized hydrogen peroxide. People must stay out until hydrogen peroxide falls below 1 ppm. But with Synexis DHP technology, no one needs to vacate the rooms. It’s designed for safe, continuous operation in occupied spaces and runs 24/7/365.
What is ionized hydrogen peroxide and how does it differ?
Ionized hydrogen peroxide passes a 7.8% hydrogen peroxide mist through a plasma arc, which converts it into hydroxyl radicals. Like vapor and aerosol systems, it treats a sealed room in cycles, and re-entry waits until hydrogen peroxide falls below 1 ppm.
When is an episodic vapor system still the right choice?
When a vacated room requires a high-dose reset, such as terminal decontamination after a known outbreak, or a life sciences space needs a validated result against biological indicators.
Is vaporized hydrogen peroxide the same as hydrogen peroxide sterilization?
Not quite. Room VHP fills a sealed space. VHP sterilization and hydrogen peroxide sterilization usually refer to closed chambers that process heat-sensitive medical devices.
Does Synexis DHP technology replace existing cleaning and sanitation programs?
No. It supports existing cleaning protocols with an additional layer of continuous microbial control. A facility that runs terminal cleans and periodic vapor cycles keeps doing both. The technology fills the hours in between.
Fill the Hours Between Vaporized Hydrogen Peroxide Cycles
Every facility already runs a cleaning and sanitation program. Synexis DHP technology is what keeps working on the air and the surfaces after that program ends: continuously, in occupied spaces, without clearing the room.
A Synexis walk-through and application assessment consider how your space is laid out and used, and how air moves through it. Then it sizes a deployment to fit.
Request a walk-through and application assessment.
Synexis is a pathogen control technology company. Synexis Systems are regulated by the US Environmental Protection Agency and state governments as devices. Accordingly, our Systems are produced in an EPA-registered facility and packaged and labeled in accordance with EPA regulations appearing at 40 CFR 152.500.
Product claims, regulatory status, and approved uses may vary by region. Please contact Synexis for information specific to your country.
*(Data on File, SYN-0009)
