Photograph of  .Ozone Toxicity & Ozone Gas Exposure Hazards

  • OZONE TOXICITY - CONTENTS: Ozone Toxicity Levels: How toxic is ozone, general background, levels of ozone gas toxicity, ozone gas applications. Is an indoor ozone generator harmful to family or pets? Properties and Actual Ozone Output of the OZN-jr ozone generator. What is the Legal Definition of "Up To" in Advertising Claims? What is the toxicity of Ozone Gas?
  • POST a QUESTION or READ FAQs about the toxicity of ozone gas & ozone gas exposure effects in enclosed spaces
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Toxicity of ozone gas:

This article discusses the toxicity of ozone gas in buildings, providing a summary of the hazards of indoor ozone levels & indoor ozone generators as well as the use of ozone generators for "mold remediation" - a popular but quite doubtful mold remedy. While there are some important uses of ozone (such as for medical disinfection under controlled conditions), in general this is an idea which ranges from bad to dangerous in the home.

This article explains the effects of using ozone in buildings for these purposes and warns consumers about misapplication of and health risks from ozone in buildings. Because at least some of these claims are based on marketing desire, not good science, and because ozone exposure can be both dangerous and ineffective indoors, I have collected some information and references on this topic.

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Ozone Toxicity Levels: How toxic is ozone, general background, levels of ozone gas toxicity, ozone gas applications

Article Contents

Reader Question: Is an indoor ozone generator harmful to family or pets?

Anonymous asked: A friend of ours gave us a ozone junior to use in our home it comes on for 10 minutes off for 10 minutes. We are happy with it as far as taking care of the pet odors or any odors but are concerned on whether it is safe to use as it had no paper work. I would just like to know whether this can be harmful to my family or pets? - N.A.

(Feb 17, 2015) Derik said:
Please evaluate the claims by Forever Ozone also selling on Amazon: 7000mg/hour (7g/hr). They use a 100 sq ft room.

Reply: It depends ... 

It might be. A competent onsite inspection or testing by an expert might find other unsafe conditions in your home or conditions that are affecting how your ozone air machine performs. That said, here are some things to consider:

Properties and Actual Ozone Output of the OZN-jr ozone generator

Reader Questions about ozone generators & their output:

Derik & Anon: here is an example calculation in which we show how you can calculate the cubic feet in a room and the ozone output of an ozone generator to obtain the actual ozone concentration in that space, assuming that the space is closed and air-tight. Certainly with doors or windows open or drafts the effects of the ozone generator will be different (and probably reduced).

Information about your "ozone junior" ozone generator: IF you are referring to the OZN-jr Ozone Generator that we noted is for sale at An Amazon advertisement viewed in March 2011 indicated that the OZN-jr ozone generator unit produces 200 mg of ozone per hour. The advertising material asserts that the product is "good for deodorizing up to 1000 cubic feet."

The product manufacturer, Sunlight Solutions, indicates that "Ozone output is 8 mg/hr."

How big is a 1000 cubic foot room? Figuring an 8-foot ceiling, that's about 125 square feet, or a 10 x 12 room.

Calculating ozone generator output concentration in a room: How much is 200 mg of ozone per hour seen in the [March 2011] Amazon Ad? We don't know because the 200 mg number looks incomplete. If that 200 mg of ozone is being produced over an hour in a 1000 cubic foot room, that would be a very low concentration of ozone. 1000 cubic feet = 23,317 liters. 200 mg of something distributed into 23,317 liters amounts to about 0.0085 mg per liter or about 0.0085 ppm. In other words, almost nothing.

How much is 8 mg/hour ozone output seen at the OZN-jr product web page [March 2011]? Following the calculation above, output is 0.0003 ppm - almost less than nothing.

In our OPINION, at those ozone output levels your machine would not be hurting anyone, but it also would not be doing much that you'll notice either. Our detailed text below states that " ... the odor of ozone can be detected and identified by most people at a concentration of from 0.02 to 0.05 ppm (parts ozone per million parts air + ozone)."

Watch out: there is a very wide range of ozone output from different types of ozone generating equipment, and some equipment can be used at output settings or in enclosed environments to produce levels of ozone gas dangerous to occupants and damaging to building contents.

What is the Legal Definition of "Up To" in Advertising Claims

With an advertising attorney we recently discussed the legal requirements for advertisers who make "up to" claims. She informs us that in the U.S. law on "up to" claims requires that the product meet the "up to" claim at least ten percent of the time. Translating this into plain language, in a given installation the OZN-jr can meet its advertising claims if in ten percent of cases it deodorizes 1000 cubic feet (that's a room that is about 8 feet by 15.6 feet or 125 square feet if the ceiling height is also 8 feet). And 90 percent of the time it can perform less well, or even not at all.

The ability to deodorize a space using just about any deodorizing method (other than complete removal of the odor source) depends on other variables that are certainly not under the product manufacturer's control, such as the level of odor or smell in the first place, the persistence and nature of the odor source, building air movement properties, space size, equipment location, and lots more.

Toxicity of Ozone Gas

The following information about Ozone is quoted from "Health Hazards of Some Gases" with minor edits and additions. See REFERENCES [8]

"Ozone is a kind (called an "allotrope") of oxygen . It is formed in the ionosphere by the action of ultraviolet radiation from sunlight on oxygen. Lightning strokes are another natural source of ozone and the characteristic odor of that material can often be noted during and after a thunderstorm.

When pollutants are emitted into the air either by man or nature, almost all are eventually removed by one or more of several processes including reaction under the influence of ultraviolet radiation. One series of such reactions results in the formation of ozone as a "secondary" (formed by reaction in the air) air pollutant, often in rather high concentrations (several tenths of a part per million).

"As ozone can be formed by nature's sparks (lightning), it can also be formed by man's. Whenever an electrical spark or corona occurs in air, some ozone is formed. This accounts for the characteristic odor noted near an operating electric motor such as an electric shaver.

"Because ozone is found in so many places, its toxicity (ability to injure a living organism by other than mechanical means) has been investigated extensively since the early 1900s. Experimentation has shown that the odor of ozone can be detected and identified by most people at a concentration of from 0.02 to 0.05 ppm (parts ozone per million parts air + ozone). As the concentration increases to a few tenths of a part per million, the first effect noted is likely to be a feeling of dryness in the back of the throat. If a concentration on the order of 0.2 or 0.3 ppm is inhaled more or less continuously for several hours to a few days some lung irritation may result.

"Higher concentrations can produce several kinds of toxic effects if exposures are sufficiently prolonged. Eye irritation (despite newspaper and TV accounts seemingly indicating otherwise) occurs only at concentrations high enough to result in other, more severe, toxic effects.

"Ozone is a very reactive substance. It will readily react with just about any material capable of being oxidized, and with many that are not. The material with which it reacts may be a gas or vapor, a particle floating in the air (a mold spore, for example), or a solid (or liquid) surface. For this reason, when ozone is present in most enclosed spaces its concentration declines quite rapidly with time. Of course, if ozone is being generated more rapidly than it is destroyed by reaction, its concentration can build up. This is the main reason why devices that produce relatively large amounts of ozone are safe only in relatively large enclosures and why the ozone generation rate should be reduced in small enclosures.

"Ozone is well known for its ability to eliminate certain odors. How this is accomplished is controversial. At concentrations just above the odor threshold, some odors do seem to vanish. The main reason for this may be ozone's ability to desensitize the olfactory apparatus so that the odors can no longer be perceived. Some evidence indicates that this may be the case at least occasionally. Other evidence indicates that ozone may react with the odor-causing substances, eliminating them from the air (this is probably the only mechanism that operates when concentrations are below the odor threshold).

"Finally, some people have insisted that even if ozone does not paralyze the olfactory sense, its odor is such that it "masks" other odors. Perhaps all three mechanisms operate, each in its own area of effectiveness.

"As with all other materials, ozone has a dose-effect relationship with a threshold. That is, once the threshold dose has been exceeded, toxic effects are proportional to dose. For inhaled gases, dose is proportional to both time and concentration. If the duration of exposures cannot be controlled (as is usually the case), then the concentration must be kept low enough so that no injury will occur even from prolonged and repeated exposures.

For ozone, that "threshold" concentration is 0.1 ppm. So long as concentrations are kept at or below that level, injury is not expected even in the most sensitive workers so long as their exposure durations coincide reasonably well with or are less than the 8 hr/day, 40 hr/wk regimen. This "threshold" level is accepted by the American Conference of Governmental Industrial Hygienists (and is called the Threshold Limit Value by that organization) and by the Occupational Safety and Health Administration, OSHA.

The TLV or OSHA's Permissible Exposure Level (PEL) is not a fine line between safe and non-safe. Instead, it represents the best judgment of a group of experts of the highest concentration that can be inhaled repeatedly by a population of workers with no resulting injury. Higher concentrations may or may not have any particular effect on a specific individual.

"Ozone is a highly toxic gas but even highly toxic substances can be encountered safely. The main concern with this material is that concentrations to which people are exposed do not average more than 0.1 ppm over an 8-hr day, and do not exceed that value by more than a factor of 2 or 3 during the exposure."


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