Is hydrogen peroxide a safe and effective way to make indoor air safe during a pandemic?

Summary: more or less.


Hydrogen peroxide is a commonly known disinfectant in its liquid form. In its gaseous form, it can disinfect the air and surfaces. Although immediately toxic and even lethal at high concentrations, levels well under OSHA exposure limits have been shown to reduce viruses and bacteria from indoor environments. The concentrations achieved from commercially available products meant for continuous use with humans present such as the Synexis machines ranges from 200 to 40 times lower than the 1 ppm (parts per million) OSHA 8-hour time-weighted maximum exposure. This value itself is 75 times less than the value established by U.S. NIOSH to be immediately dangerous to life and health. Moreover, unlike ozone, the byproducts of hydrogen peroxide decomposition or reactions are benign. From our survey data, we found that the overwhelming majority of people prefer entering a building that has UV air reflow system such as the one we build, despite being informed that our system does nothing for surfaces and that the levels are this low. However, it is our hope consumers will embrace any solution that is demonstrated to be safe. Presumably, the OSHA exposure limits have also taken into account that hydrogen peroxide has been classified as a "known animal carcinogen, with unknown relevance to humans" by the American Conference of Governmmental Industrial Hygienists.

[citation sources on wikipedia:]

Evidence for Efficacy

Of course, the key question is how effective hydrogen peroxide can be at such low levels that we can breath them without worry day in and day out. Synexis is one of the vendors in this space, having machines based on catalytically generated hydrogen peroxide. Most of the research available on the subject looks at much higher concentrations than Synexis 5-25 ppb (even "low concentrations" in research are much higher), but luckily they have done extensive at these levels against a broad number of pathogens. The overall results they show are fairly promising, looking at both closed systems and the actual levels of pathogens that are present in actual environments after a number of days. There is no question that the outcomes are much better wit hydrogen peroxide present than in the controls, but what is the exact level of efficacy on enveloped viruses such as SARS-CoV-2? With SARS-CoV-2, infected persons are continuously shedding the virus and contaminating the environment so the real time efficacy is critical.

We asked Synexis for some in-air data since most of their publicly available data we found relates to surfaces. They also informed us that the in-air efficacy is in fact 6 times higher (faster) than for surfaces. They sent us the following image about the in-air viral inactivation rate.

[to be added]

While this is for influenza rather than a coronavirus, both virons have a similar structure from a physical perspective -- a spiky lipid-enveloped ball, so it is similar to being confident that if one type of ammunition takes out a rhinoceros, it will probably also take out an elephant (note, please do not shoot at either). It appears to have about 96% percent viral inactivation at the 30 minute mark, which is a marked improvement given that aerosolized viruses can survive for at least a few hours. Moreover, it is not just the 99% or 99.9% point that matters since lower viral load both decreases infection risk and decreases severity upon infection. It is analog, not binary. However, with surfaces being disinfected 6 times slower, we'd be looking at a 2-3 hour wait. For surfaces that might be touched every few minutes, the benefit of this seems rather negligible. Anything that can be wiped down with a liquid disinfectant should be, and any surface for which this is impractical will require hand sanitization or washing. While gradual load reduction might be useful for the broad applicability against bacteria for which the Synexis machines were envisioned, for all intents and purposes during a viral pandemic, it should be thought of as an air treatment system only.

Since the only data we have on the effects of ultra-low hydrogen peroxide concentrations is the above image from one of the vendors, we can do a gut check on this data by looking at published research papers that have tested the closest concentrations. This is also critical to re-assuring your customers of the level of safety they can trust is present. A paper that looked at surface inactivation of influenza with concentrations as low as 10 ppm found a 99% reduction at the 2.5 minute mark. This is about 70 times faster than the 3 hour time that might be needed with Synexis with a concentration that is about nearly 1000 times higher. While this might seem to not line up, the inactivation is not linear. As the above image shows, the inactivation is faster at the start so a lower concentration means that each hydrogen peroxide has better odds of taking out an individual viron. That this effect could be a little over 10x seems plausible, though it would be good to see some peer-reviewed data to verify, as well as data on the effects in air that we actually care about.

Machines for Hydrogen Peroxide

The Synexis machines are extremely expensive, at $2,250 for their smaller unit that covers 500 sqft, and $3,750 for their larger machine that covers 1,250 sqft, plus $400 and $500 ongoing yearly expenses (respectively) with quarterly replacements of the catalytic material or they stop working. Compared to the Reflow Labs Airsafe, with Synexis you either pay several times more for similar performance, or you can pay the same amount and have a system that is several times faster. Hydrogen peroxide is an inexpensive material so if you are intrerested in hydrogen peroxide, you might want to evaluate whether there are other machines that offer a better value. Whereas Synexis uses a UV-initiated catalytic process to generate hydrogen peroxide, you can just as easily heat up hydrogen peroxide to vaporize it.

Synexis describes their machines as producing dry hydrogen peroxide and claims that they are producing a gas and not a vapor (mentioning that they own the many patents related to this). Sounds nice, until you realize those statements are in direct conflict with what any physicist (or high school chemistry student) will tell you a vapor is as compared to gas. A vapor is similar to a gas, but it exists below the critical temperature of the substance, which in the case of hydrogen peroxide is about 455 degrees celsius. It is only above the critical point that condensation into a liquid via compression at constant temperature cannot occur. So unless Synexis is turning your building into a furnace, they cannot provide hydrogen peroxide gas as they state, but hydrogen peroxide vapor. Their use of the word "dry" might give some indication of what they might be thinking, which would be the absence of water vapor. The level of water vapor, also known as humidity is fairly important as it can impact the efficacy of the hydrogen peroxide. Unfortunately, it seems to be the other way around with higher humidity levels improving the efficacy.

There might not be other good options that take advantage of the fact that liquids can be easily vaporized by heating them. We did not look extensively. We considered whether this might be a good machine to offer, but after comparing it to what we could achieve with UV air flow systems and customer preferences, we determined it would be an inferior solution. Not only is it challenging to pinpoint the efficacy with non-proprietary research data, but the concept is in opposition to all Goverment recommended practices that advise people to increase ventilation. In a well ventilated space, or even just a business where customers are regularly coming in through the front door, you will be decreasing your hydrogen peroxide concentration. Or if you own space in a building, but not the entire building, it will be difficult to maintain the concentration you want without having your HVAC system supressing it. The Reflow Labs Airsafe concept does not rely on putting something in the air so it works well in parallel to best practices such as opening windows when practical. However, the key advantage that hydrogen peroxide offers over the Airsafe is that less air needs to be moved so it can be quieter.

UPDATE: We may have been going a bit easy on Synexis in giving them the benefit of the doubt. In our references we are adding a key article that absolutely slams them. Brief excerpt from the editor responding to the CEO that didn't like the research published about their product: "We take exception with Mr Schlote’s claim that the dilute hydrogen peroxide system marketed by Synexis Biodefense Systems has been validated. Only a single abstract has been published,2 and no-peer reviewed, published studies have validated that use of this device can effectively provide continuous decontamination of the environment (eg, surfaces)."

See our other articles or take a look at our research paper summaries.

Learn more about the landscape of technologies marketed as making air safer: 1) Far UVC; 2) Ozone; 3) Violet and UVA

Read the Reflow Labs Airsafe White Paper

See the key FAQ pages provided by a team of scientists on COVID-19 transmission and preventive approaches:

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