Ozone generators sold as air cleaners: why to avoid them

An ozone generator is a machine built to release ozone gas into the air, and for a home where people are present EPA and California’s air board give the same answer: do not run one. EPA says inhaled ozone can damage the lungs, that “NO agency of the federal government has approved these devices for use in occupied spaces,” and that at concentrations within public health standards ozone “has little potential to remove indoor air contaminants.” That is the whole problem: at levels low enough to meet health standards the gas does very little, and EPA’s figure for decontaminating air of organisms, set out below, is far above those standards.

What an ozone generator does, and what it is not

EPA’s opening description is short: “Ozone generators that are sold as air cleaners intentionally produce the gas ozone.” That word, intentionally, separates these machines from other electronic air cleaners. An ionizer air purifier or an electrostatic unit can release some ozone as a side effect of high voltage. An ozone generator makes it as its method of working.

The difference matters when reading a product page, because the word “ozone” may not appear. EPA warns that sellers use terms such as “energized oxygen” or “pure air” that suggest ozone is a healthy form of oxygen, and answers that “Ozone is a toxic gas with vastly different chemical and toxicological properties from oxygen.”

What ozone does to the body

EPA states that “Relatively low amounts can cause chest pain, coughing, shortness of breath and throat irritation,” and that ozone “may also worsen chronic respiratory diseases such as asthma and compromise the ability of the body to fight respiratory infections.” Those are statements about what the gas does when breathed. Anyone with symptoms or a lung condition should take the question to a clinician rather than to a product label.

Your nose is not a meter. EPA cautions that “lack of odor does not guarantee that levels are safe,” and the FDA’s regulation adds that “Since olfactory fatigue develops readily, the odor of ozone is not a reliable index of atmospheric ozone concentration.” The smell can fade for the person in the room while the gas remains.

What the machines were measured doing in rooms

EPA’s page summarizes tests that are more useful than any advertising claim, because they report concentrations:

Two limits on that table. These are air concentrations from particular devices in particular rooms, not measurements of anyone’s health. And the fourth row does not rescue the devices: EPA’s point elsewhere is that at those lower concentrations the ozone is not doing much cleaning. EPA also reports that concentrations from these devices can exceed health standards even when the maker’s instructions are followed.

Why it fails as an air cleaner

EPA goes through the pollutants one at a time, and the list is longer than most sellers would like:

• Particles. EPA says “ozone does not remove particles (e.g., dust and pollen) from the air, including the particles that cause most allergies.”
• Viruses, bacteria and mold. Used at concentrations within public health standards, ozone “does not effectively remove viruses, bacteria, mold, or other biological pollutants.” EPA adds that concentrations would have to be 5 - 10 times higher than public health standards allow before ozone could decontaminate the air enough to stop organisms surviving and regenerating afterward.
• Carbon monoxide. EPA says “ozone generators are not effective in removing carbon monoxide.”
• Odors. At concentrations within public health standards, ozone “is not effective at removing many odor-causing chemicals.” For a smell problem, the guide to odors and VOCs covers the methods with better support.

There is also a chemical cost. In one experiment EPA describes, ozone reacting with chemicals in the air “produced a variety of aldehydes, and the total concentration of organic chemicals in the air increased rather than decreased.” The gas does not simply disappear after doing its job; it can leave different pollutants behind.

The FDA’s regulation at 21 CFR 801.415 takes a similar view of ozone as a germ-killing agent. It calls ozone “a toxic gas with no known useful medical application,” and says that to work as a germicide “it must be present in a concentration far greater than that which can be safely tolerated by man and animals.”

The limits that apply, and to whom

Several ozone numbers circulate online, and they are frequently confused because each was written for a different setting.

None of these figures is a promise that a lower level is harmless, and a workplace limit should not be read as a target for a bedroom.

California’s text deserves its exact wording. Section 94802(a) says that, except as section 94803 provides, “no person shall manufacture for use in California, or sell, supply, offer for sale, or introduce into commerce, any indoor air cleaning device unless the device is certified by CARB to produce an ozone emission concentration not exceeding 0.050 ppm.” What CARB certification does and does not tell you has its own page, since the listing covers ozone emissions and electrical safety, not cleaning performance.

The regulation also has an industrial door. Under section 94803(a), devices “manufactured, advertised, marketed, labeled, and used solely for industrial use” fall outside the article if they display: “For industrial use only. Use only in unoccupied spaces. Health hazard: emits ozone.” CARB’s FAQ limits those uses to specified applications, several of them conditioned on no one being physically present, and states: “Ozone generators are not permitted for use in other applications because of the risk of exposure to unhealthy levels of ozone.” CARB’s FAQ also says that non-certified devices that “show up in commerce and for sale in California” would be in violation, and that fines could be imposed or other enforcement actions taken.

Outside California, the state rule does not apply. That does not change what EPA says about the devices. EPA does not certify air cleaners, and it adds that an EPA number displayed on a product “does not imply EPA endorsement or suggest in any way that EPA has found the product to be either safe or effective.”

If one is already in your home

1. Turn it off and unplug it if it runs in a space where people or pets spend time. EPA’s and CARB’s texts give no reason to keep it running while the room is in use.
2. Open windows if outdoor air is reasonably clean, and leave the room if you notice irritation.
3. Get medical help promptly if anyone has chest pain or trouble breathing, see a clinician about a persistent cough, and mention the exposure.
4. Find what you were trying to fix. EPA’s advice is “to use proven methods of controlling indoor air pollution,” which it lists as “eliminating or controlling pollutant sources, increasing outdoor air ventilation and using proven methods of air cleaning.”
5. Choose the replacement by the problem: a filter for particles and an adsorbent such as activated carbon for gases, with a California certification check on anything electronic.

This page gives no re-entry time after running a machine, because a figure would have to be specific to the device, room and ventilation, and a general number would be invented.

Reading a product page skeptically

Two patterns deserve distrust. One is the language of oxygen: CARB lists “activated oxygen” and “super oxygenated” among the terms that give the impression ozone is healthy. The other is a very large coverage claim. EPA’s own example of a generator recommended for a very large area is the top row of the table above, and the result was a very high reading in a small room. A marketing number for coverage tells you nothing about what the air in your room will contain.