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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 limites
• 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, I have collected some information and references on this topic. © Copyright 2008 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use the links at page left to navigate this document or to go to Other Website Topics. Green links at left show where you are in our document & 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]

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OZONE as a "CURE" for TOXIC INDOOR MOLD
WHAT IS OZONE- O₃
OZONE HAZARDS
TESTING FOR OZONE
OZONE TOXICITY
OZONE ODORS, MOLD, REFS

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

Use of ozone to "remove" or "kill" mold is ineffective, not recommended, and may be dangerous. Even if ozone were applied at a concentration and for a duration sufficient to "kill" every mold spore in a building (which is a very dubious claim), depending on the mold genera/species present there is a good chance that the process leaves toxic and allergenic particles in the building. A "dead" (or non-viable) mold spore may not grow but it can still be a health concern. The operative proper word for mold remediation is "clean" or "remove", not "kill." In 1997, Dr. Karin K. Foarde of Research Triangle Institute, tested the ability of ozone to decontaminate fungi on building materials. At ozone levels of 9 ppm for a 23-hour exposure, ozone was found to be ineffective. [5] (Notice that this is 90-times higher than permitted ozone exposure. Exposure at these "deodorizing" levels would be considered extremely toxic to humans.) This procedure is not recommended by the NY City Department of Health Guidelines on the Assessment and Remediation of Fungi in Indoor Environments. Jim Holland's article on Ozone as a "mold remediation step" is available online [6] �and is a good summary of this point. Jack E. Peterson's 1987 excellent work "Health Hazards of some Gases" also addresses ozone hazards but it may be harder to find so I have quoted from it at the end of this paper.

Deodorization and cleaning claims are questionable: The apparent deodorization at high ozone levels may be simply the effect of a general desensitization to odors in the nose of building occupants rather than actual removal of an odor source. Ozone has been used following building fires to "reduce" smoke odors but even in this application it does not remove soot.

If, for example, there is a persistent odor source (such as a dead animal, flood damage, mold in building wall and ceiling cavities), no amount of "air treatment" of any kind will remove the problem source. There is no substitute for the actual physical effort to find and remove the offending source. Cleaning or removing the problem source is proper and effective. Professional use of ozone, at concentrations and durations which the applicator guarantees will not damage building materials or cause other outgassing, may be helpful as one step in a cleaning procedure where mold is not involved.

Ozone has been used successfully in water treatment and in disinfection of cooling towers and possibly wastewater. However it is not a durable, reliable treatment in that O3 molecules are highly reactive and volatile and thus treated substances do not remain so.

Use of ozone may oxidize and damage materials and increase odor levels:>[7] If ozone is no longer being generated in a building the presence of ozone will diminish quite rapidly. However, other odors may remain or may even be increased. Because ozone is a very powerful oxidant, it may react with (oxidize) many materials found indoors, including carpets, carpet padding (especially rubber), other floor coverings, furniture, furniture cushion foam, and even surface paints and finishes. A common example is ozone-oxidized rubber carpet backing or padding. Weather research and other studies indicate that any material that will oxidize may be expected to react with ozone, especially cross-linked organic molecules, especially rubber.

Use of ozone may produce dangerous airborne byproducts: In other words, attempts to use high levels of ozone to "clean" or "deodorize" building interiors may in fact generate a second generation of unpleasant and even dangerous outgassing which may remain, persistent indoors, after the ozone "treatment."� Examples include increased levels of indoor formaldehyde, formic acid and other acid gases, toluene, or other toxic chemicals.

Use of ozone may increase sub micron particulates: Attempts to use high levels of ozone to "clean" or "deodorize" building interiors may also increase the level of extremely small sub-micron particles which themselves can be severe respiratory irritants.

TESTING FOR OZONE Contamination, Ozone Damage and Testing for Related Ozone-Related Outgassing Hazards

In exceptional circumstances I may test an indoor environment for ozone levels. Normally I do not, as this gas is so volatile and reactive that it would not be expected to remain in an environment. However, the byproducts of using this gas at high concentrations and durations indoors may oxidize and cause outgassing from other building products. When circumstances warrant, I would screen for a variety of common outgassing products such as formaldehyde, benzene, formic acid and other acid gases, toluene and related gases. My tests for these gases are described in my clients' sampling plan. I also may apply one or more of the three sets of multiple-gas hazard screen systems provided by Drager for the fire investigator profession.

At high or low levels (various test sensitivities are available) produced by popular indoor air "purifiers" and by commercial treatments for odors is a highly-reactive oxidizing gas which is dangerous to lung tissue itself. This gas may react with other building materials (as an oxidant) to produce secondary outgassing products which are also irritants or potentially unsafe. Ozone is highly reactive and volatile and may not be present in a building long after it was applied. Choice of use or omit this screen depends on the circumstances of the particular investigation. As a regular practice I include this screen where such equipment is in use (to detect dangerous current levels) or where commercial equipment has been recently in use. Sensidyne� #182SB 2.5-100 ppm / #182U 0.025 - 3.0 ppm.

Benzene 0.5/a: If there is a particular concern for Benzene I perform a test for this substance. I select a sampling tube which is not Benzene specific in order to also screen for other aromatic hydrocarbons including toluene, xylene (more likely to be in carpet out gassing than benzene) and ethel benzene. My test sensitivity is 0.4 to 10 ppm (40 to 2 strokes). +/30%.

Formaldehyde 0.2/a: because this gas is produced at virtually all house fires and because it is a well-known respiratory and eye irritant produced by many building materials even without combustion effects, if there are owner/occupant complaints, this test may be performed using the Gastec pump and tubes produced by Sensidyne or by the Draeger accuro pump and their tubes. Sensitivity 0.2 to 2.5 / 0.5 to 5 ppm at 10 / 20 strokes. Alternative: Sensidyne � Gastec� 91/L 0.1-40.0 ppm

Formic acid 1/a: because this gas screen addresses acid gases which can be expected to be produced by fire, heat, or oxidation (such as from ozone treatment) in commercial and residential properties it is an important screen for this topic. My test sensitivity 1 to 15 ppm, 20 strokes.

Toluene 5/b: because this is one of the most sensitive gas screens available to address gases which can be expected to be produced by fire, heat, or oxidation (such as from ozone treatment) in commercial and residential properties it is an important screen for this application. Toluol is a common contaminant produced by oxidized or burning carpets. My test sensitivity 5-300 ppm

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

More Information on Building Diagnostic Inspections and Repairs

Ozone Gas Hazards Description in our article "Effects of Toxic Gas Exposure to Ammonia, Arsine Arsenic Bromine Carbon Dioxide Carbon Monoxide Hydride Ozone & others"

Toxic Gas Exposure Hazards and Test Protocols including links to our toxic gas exposure screening and gas testing protocols.

Gases: Toxic gases, indoor exposure levels, testing, identification

• A Toxic Gas Testing Plan: A Gas Sampling Plan for Residential and Commercial Buildings lists some of the toxic indoor gases for which we test, depending on the building complaint and building conditions
• Gas Exposure Hazard Levels: for Toxic Gas Exposure to Ammonia, Arsine, Arsenic, Bromine, Carbon Dioxide, Carbon Monoxide, Hydride, Ozone - allowable exposure levels and hazard levels
• Carbon Dioxide Gas Toxicity hazard level, poisoning symptoms, & testing
• Carbon Monoxide Gas Toxicity hazard levels, poisoning symptoms, & testing
• Formaldehyde: US EPA. UFFI (Urea Formaldehyde Foam Insulation) was previously considered a hazard (formaldehyde outgassing). Subsequent research virtually closed concern regarding this material; however formaldehyde appears to remain a health concern for sensitive individuals.
• Ozone Warnings - Use of Ozone as a "mold" remedy is ineffective and may be dangerous.
• Sampling for gases in air such as VOC's, MVOC's, toxic chemicals, and combustion products.
  Unfortunately no single test or tool can detect all possible building contaminants. We use methods and equipment which can test for common contaminants. If the identity of a specific contaminant is known in advance we can also test for a very large number of specific contaminant gases in buildings.
  We use gas sampling equipment provided by the two most reliable companies in the world, Draeger-Safety's detector-tubes and Drager accuro� bellows pump, the Gastec� cylinder pump and detector-tube system produced by Gastec or Sensidyne, and we also use Sensidyne's Gilian air pump. For broad screening for combustibles and a number of other toxic gases and for leak tracing we also use Amprobe's Tif8850. All of these instruments, their applications, and sensitivities (minimum detectable limits) for specific gases are described in our Gas Sampling Plan online document.
• Radon Gas U.S. EPA Radon level maps

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