A number of industrial hygienists have expressed opinions that the use of ozone by restoration contractors is unsafe and should not be used. The issue is that many fire and smoke restoration companies use ozone to remove odors, even though they have been warned about these problems in their own trade magazine.

A 2022 article published by Restoration & Remediation Magazine, Using Ozone in Fire Restoration: Is It a Friend or a Foe?, states:

Are There Health Risks Associated With Using Ozone?

Most of my colleagues in the restoration industry feel that ozone is natural to our environment and relatively harmless. To illustrate this, here are some comments made by a manufacturer of ozone generators: ‘Ozone is a highly effective natural sterilizer that can inactivate practically any organic contaminant on contact. As it is a highly reactive gas, ozone continually reverts back to its most stable form by releasing one of its atoms to turn back into oxygen (from O3 to O2). As ozone is a gas composed entirely of oxygen, it leaves no chemical residue whatsoever. The only by-product remaining is fresh, clean air.’

That sounds pretty amazing, right? Let’s take a closer look and see what scientists and government agencies have to say about ozone.

The Canadian Centre for Occupational Health and Safety reports that: ‘Even very low concentrations of ozone can be harmful to the upper respiratory tract and the lungs. The severity of injury depends on both the concentration of ozone and the duration of exposure. Severe and permanent lung injury or death could result from even a very short-term exposure to relatively low concentrations.’

The U.S. Environmental Protection Agency states that ozone exposure can be especially hazardous for people that have respiratory ailments such as asthma and COPD. People with asthma are likely affected by ozone in two ways: (1) They might be more sensitive to ozone than other people, and experience lung function changes and respiratory symptoms at lower concentrations or with greater magnitude; and (2) the injury, inflammation and increased airway reactivity induced by ozone exposure may worsen a person’s underlying asthma.

The National Institutes of Health has identified the following health effects associated with ozone exposure: 

  • Nervous system disturbances: Nervous system effects other than narcosis
  • Respiratory effects other than irritation: Cumulative lung damage
  • Respiratory effects: Acute lung damage/edema or other
  • Irritation: Eyes, nose, throat, skin

The article concludes with the following warning:

If you are going to use ozone generators in indoor environments, take the necessary precautions to protect workers and occupants. Consider the following:

  1. Provide occupants and workers with a safety data sheet on ozone so everyone is informed.
  2. Remove or protect any items or materials that may be adversely affected by ozone exposure.
  3. Set up proper environmental controls and place warning signs around the area where ozone will be used.
  4. Provide workers with proper PPE and avoid working in areas where ozone is being generated.
  5. When the ozone treatment is complete, thoroughly ventilate the area before allowing workers to reenter.

Conduct air sampling after ozone use to verify that ozone levels are safe and that no toxic chemicals or byproducts remain.

The real question is whether fire and smoke restoration companies should be doing this at all. The science suggests that the levels of ozone needed to effectively remove odors creates an unsafe structure during and after the process is completed.   

The United States Environmental Protection Agency raised this point by stating in a study, Ozone Generators that are Sold as Air Cleaners:  

Are Ozone Generators Effective in Controlling Indoor Air Pollution?

Available scientific evidence shows that at concentrations that do not exceed public health standards, ozone has little potential to remove indoor air contaminants.

Some manufacturers or vendors suggest that ozone will render almost every chemical contaminant harmless by producing a chemical reaction whose only by-products are carbon dioxide, oxygen and water. This is misleading.

  • First, a review of scientific research shows that, for many of the chemicals commonly found in indoor environments, the reaction process with ozone may take months or years (Boeniger, 1995). For all practical purposes, ozone does not react at all with such chemicals. And contrary to specific claims by some vendors, ozone generators are not effective in removing carbon monoxide (Salls, 1927; Shaughnessy et al., 1994) or formaldehyde (Esswein and Boeniger, 1994).
  • Second, for many of the chemicals with which ozone does readily react, the reaction can form a variety of harmful or irritating by-products (Weschler et al., 1992a, 1992b, 1996; Zhang and Lioy, 1994). For example, in a laboratory experiment that mixed ozone with chemicals from new carpet, ozone reduced many of these chemicals, including those which can produce new carpet odor. However, in the process, the reaction produced a variety of aldehydes, and the total concentration of organic chemicals in the air increased rather than decreased after the introduction of ozone (Weschler, et. al., 1992b). In addition to aldehydes, ozone may also increase indoor concentrations of formic acid (Zhang and Lioy, 1994), both of which can irritate the lungs if produced in sufficient amounts. Some of the potential by-products produced by ozone’s reactions with other chemicals are themselves very reactive and capable of producing irritating and corrosive by-products (Weschler and Shields, 1996, 1997a, 1997b). Given the complexity of the chemical reactions that occur, additional research is needed to more completely understand the complex interactions of indoor chemicals in the presence of ozone.
  • Third, ozone does not remove particles (e.g., dust and pollen) from the air, including the particles that cause most allergies. However, some ozone generators are manufactured with an ‘ion generator’ or ‘ionizer’ in the same unit. An ionizer is a device that disperses negatively (and/or positively) charged ions into the air. These ions attach to particles in the air giving them a negative (or positive) charge so that the particles may attach to nearby surfaces such as walls or furniture, or attach to one another and settle out of the air. In recent experiments, ionizers were found to be less effective in removing particles of dust, tobacco smoke, pollen or fungal spores than either high efficiency particle filters or electrostatic precipitators. (Shaughnessy et al., 1994; Pierce, et al., 1996). However, it is apparent from other experiments that the effectiveness of particle air cleaners, including electrostatic precipitators, ion generators, or pleated filters varies widely (U.S. EPA, 1995).

There is evidence to show that at concentrations that do not exceed public health standards, ozone is not effective at removing many odor-causing chemicals.

The bottom line is that many in the fire and smoke remediation industry are using these machines that use ozone to remove the smoke odor. The manufacturers selling those ozone machines want to keep selling them. The trend is that industrial hygienists are stating opinions that we should stop using this method because it is not safe and citing to scientific papers for proof of their opinions.   

Where are the scientific papers supporting smoke removal by these ozone machines is safe? I could not find them.    

Thought For The Day      

It takes leadership to improve safety.

—Jackie Stewart