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The Use of Ozone Generators Indoors for Control of Odors and Mold Removal in Buildings: A Summary of Hazards and False Claims
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• The effects of using ozone in buildings to "purify air" or to "kill mold"
• The toxicity of ozone gas and ozone gas exposure limits
• The hazards of ozone generators in buildings

Ozone is widely promoted by ozone generating equipment companies and cleaning services for use in indoor building environments to deodorize, disinfect, "kill" mold, and for "general health". Ozone generators are also promoted for use to reduce the level of airborne particles, pollen, animal dander, and allergens, ostensibly to improve indoor air quality for asthmatics and people with allergies.

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, we have collected some information and references on this topic. © Copyright 2010 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

WHAT IS OZONE: Ozone - O₃

"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." [1]

Using Ozone to Get Rid of Skunk or Mold Smells?

This quote from a reader's email pretty well sums up what happens if you overdo it when using an ozone generator indoors to try to "kill off" odors:

It's a long story, but I used a high powered ozone generator in our house, to get rid of skunk smell. Now I can't get rid of the left over nitric oxide, or whatever odor or gases, that linger in our house. I have been leaving the windows open every day, with running the heat on high (85 degrees) at night, to try to force off-gas the odors/gases.

We have investigated a number of cases of misapplication of ozone generating machines both to "kill mold" (no good, you're leaving toxic or allergenic particles, and you haven't corrected the reason for mold growth in the first place). We have also investigated several cases of excessive ozone-use to try to remove odors from buildings, including fire or fireplace smells, mold smells, pet or animal smells, skunk odors, smoking odors, etc.

Using Ozone Left a Smell in our Home - How do I Get Rid of It?

If you have aired out the building and days or more have passed and you still smell a "new" chemical or plastic or other odor that was not there before you tried using your ozone generator, you'll need to determine just what materials were oxidized by the high levels of ozone in the building.

It's been our experience that once you identify and dispose of the new-smelly material you'll probably be fine. Here are some examples of material we've found giving off horrible smells after misuse of an ozone generator. (Misuse means using the ozone generator to try to kill mold, or running an ozone generator too long at too high a setting in too small a space - overdoing it).

• Carpets, especially synthetic carpets
• Carpet padding
• Foam cushions
• Other plastic furnishings or furniture covers
• Rubber pads, padding

Try the Smell Capture Patch Test to Pin Down a Specific Indoor Odor Source

Our friend Jeff May suggested this procedure for pinning down a specific odor test in buildings - it has worked remarkably well for us where ozone had caused an indoor smell that could not be tracked down.

Details of this procedure to track down the source of indoor odrs is especially useful after an ozone treatmentprblem. Details of the smell source identification method are at SMELL PATCH TEST to Track Down Odors. We have had very good results with this procedure when used to narrow down odor sources in an ozone-treated building, and we had up to 95% repeatability when we used additional smell test patches.

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OZONE as a "CURE" for TOXIC INDOOR MOLD
WHAT IS OZONE- O₃
OZONE AIR PURIFIER WARNINGS
OZONE HAZARDS
SMELL PATCH TEST to Track Down Odors
STANDARDS FOR OZONE EXPOSURE
TESTING FOR OZONE
OZONE TOXICITY
OZONE ODORS, MOLD, REFS

• Jeff May - Jeffrey C May - May Indoor Air Investigations - Jeff is located in Tyngsborough, MA 01879 - Phone • 978.649.1055 • 800.686.1055
  

Ozone Hazards Overview

Exposure to a level you can smell or exposure to ozone over long periods at levels greater than 0.05 ppm for 24 hours at a time is likely to be dangerous: [2], [3] Health hazards to humans and animals occur and can be severe at ozone levels used for indoor cleaning purposes. At least some people can smell levels of ozone down to 0.05 ppm. This odor-detection level is already half-way to the recommended limit. If you are generating ozone indoors, even at "low" levels a problem may be present. People become desensitized to odors in a short time, perhaps 20 minutes. So if you do not smell it, the ozone level could still be hazardous. Problems include:[4]

• Lung irritation and infection. Breathing pain, coughing, wheezing, difficulty when exercising.
• Permanent lung damage.
• Aggravation of pre-existing asthma
• Increased risk of lung illnesses such as bronchitis and pneumonia
• Reduced breathing capacity

OZONE TOXICITY: - How toxic is ozone, general background, levels of ozone gas toxicity, ozone gas applications

The following information about Ozone is quoted from "Health Hazards of Some Gases" [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."

OZONE ODORS, MOLD, REFS: References on Ozone, Odors, and Mold

[8] "Health Hazards of some Gases" Jack E. Peterson, P.E., CIH, Ph.D., May, 1987

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