What Is Ozone Treatment for Smoke Odor, and Is It Safe?

What ozone treatment is

Ozone is a gas made of three oxygen atoms. It is a reactive molecule, which is why it can break apart some chemicals, and why it harms living tissue. An ozone generator is a machine that makes ozone on purpose.

In a smoke odor job, a generator runs in an empty building, the gas spreads through the rooms and reacts with odor compounds, and the building is then aired out.

Some versions are small. A University of Florida extension handbook notes that fire restorers and dry cleaners sometimes use an ozone treatment to break up smoke molecules, and says that, when it is done in a home, items are put under a tent while a generator operates ⁷.

The handbook is from 1998 and describes practice at that time. Current regulators are more cautious.

EPA describes ozone generators sold as air cleaners and explains the problem.

It says that, at concentrations that do not exceed health standards, ozone has little ability to remove indoor air contaminants, and that ozone can sometimes be used to decontaminate unoccupied spaces, such as after a fire, as long as exposure of people and pets is prevented ¹.

It also says little is known about the by-products that remain afterward ¹.

California’s Air Resources Board (CARB) is stricter in practice. It regulates the ozone emitted by indoor air cleaners, advises against in-home use of uncertified ozone generators and notes that ozone is used in industrial settings under controlled conditions ⁴³.

This page covers the smoke-odor use. It reports what these sources say and does not rate the method. The smoke odor removal entry covers the full order of work, and the fire and smoke damage restoration page shows how odor work fits a fire job.

How ozone treatment is described, and what the sources add

The steps below describe how a professional treatment is framed in the sources. They are not instructions. Ozone work is never a homeowner job, and the safety conditions come from the regulators.

1. Building cleared and emptied. The fire department must clear a fire-damaged building before anyone works inside ⁹. For ozone, EPA says exposure must be controlled so no person or pet is exposed ¹.
2. Cleaning and removal come first. UF/IFAS says soot must be removed before textiles are cleaned or deodorized, and FEMA’s homeowner ladder begins with ventilation, filtering, absorbing and cleaning ⁷⁸.
3. A generator runs in the sealed, empty space. A maker’s sheet for a combination unit says ozone mode is for unoccupied areas and that the area must be vacated during treatment ⁵. EPA says the concentration depends on device power, room size, door position and ventilation ¹.
4. The building is aired out. The same maker’s sheet says ozone requires the area to be vacated; EPA says concentrations can be high enough to exceed health limits even when the device is used as directed ⁵¹.
5. Odor is rechecked. EPA says ozone may only slow the growth of biological contaminants while it is present and may not affect contaminants embedded in porous materials, and that ozone may mask some odors rather than remove them ¹.

No source loaded here gives a safe re-entry concentration or a re-entry time for an ozone job. EPA says that exposure should be controlled so no one is exposed, and that is the standard to hold a contractor to.

What each source says about ozone, side by side

Example: comparing a generator reading with the published limits

The comparison below is plain arithmetic on figures EPA prints, not a measurement of any real machine.

EPA says tests found some ozone generators producing 0.20 to 0.80 ppm, and cites an FDA limit of 0.05 ppm for ozone from indoor medical devices and a NIOSH limit of 0.10 ppm that should never be exceeded ¹.

The point is not a precise exposure. Concentration depends on device power, room size, door position and ventilation, and EPA says some generators exceed health limits even when used as the manufacturer directs ¹.

The lesson is that an ozone job is a controlled, empty-building process, and no one should stand in the space. Compare any proposal with this reading, and use the estimate review tool to see what else is on the quote.

Where ozone shows up in a fire project

On an estimate. It appears as “ozone treatment,” “ozone machine” or “odor shock.” A line with a machine name and no cleaning plan is the thing to question.

In the work authorization. A careful authorization says the treated area is vacated and who controls access. Ask for that in writing.

In marketing for air purifiers. CARB notes that some companies call ozone “activated oxygen” and claim it is healthy; its consumer page does not support that claim ³⁴.

In the claim file. Adjusters may ask why equipment ran. Policies vary on odor scopes, so see the coverage guide.

Alongside other air treatments. The thermal fogging entry and the hydroxyl generators entry cover the common alternatives.

Why ozone is used, according to the sources

• Ozone reacts with some odor compounds. CARB says ozone is used in industrial settings because it can kill biological pathogens and neutralize odors, at very high concentrations under controlled conditions ⁴.
• It spreads through a space as a gas, which is why a generator can reach many surfaces. A maker’s sheet markets this for unoccupied areas ⁵.
• It is sometimes used on items in a closed tent. UF/IFAS describes that practice in older extension guidance ⁷.
• EPA allows that it can sometimes be used to decontaminate unoccupied spaces, such as after a fire, if people and pets are not exposed ¹.
• These points describe why it is used. They are not proof that it works on smoke odor in a home, and EPA’s own findings, below, limit them.

What EPA and CARB say it cannot or should not do

• Limited cleaning power at safe levels. At concentrations that do not exceed health standards, ozone has little ability to remove indoor contaminants, according to EPA ¹.
• It does not remove particles. EPA says ozone does not remove particles such as dust, pollen or allergens, and is not effective against carbon monoxide or formaldehyde ¹.
• It can create by-products. EPA says reactions with other indoor chemicals can form irritating by-products such as aldehydes and formic acid, and notes a carpet study in which total organic chemicals in the air increased after ozone was introduced ¹.
• It may not reach embedded contaminants. EPA says ozone may slow the growth of biological contaminants only while it is present and may not affect those embedded in porous materials ¹.
• It can mask odor. EPA says ozone may mask body odor rather than remove it ¹. CARB warns that smell is not a good way to tell if you are exposed ³.
• It can damage materials. EPA says ozone can damage rubber, electrical wire coatings, fabrics and artwork with sensitive dyes or pigments ¹.
• It is not a safety clearance. FEMA says cleanup can reduce but not eliminate contaminants and recommends environmental testing before long-term occupancy ⁸.

What drives the cost of an ozone service

The ozone treatment entry gives no prices. Ozone work may be billed inside a larger fire scope, and costs vary by region and contractor, so no figure here would meet our cost standard.

The drivers are the size of the space, how many machines run and for how long, how the building is sealed and aired out, and who carries the risk of damage. EPA notes that ozone can damage rubber, wire coatings, fabrics and artwork ¹, so a damage clause matters.

The larger cost question is what the treatment replaces. If ozone stands in for cleaning and removal, EPA’s findings suggest the odor and its cause may remain ¹⁷. Ask for the full scope in writing.

There is no warranty on an ozone result that a public source defines. Ask what is guaranteed and for how long. The cost guide explains what drives restoration totals.

Who does what, and who must stay out

After treatment: airing out and follow-up

Do not enter an ozone-treated building until the contractor says it is safe and the plan has been followed. EPA says ozone concentrations can exceed health limits and that conditions should be controlled so no one is exposed ¹.

Air the building out. EPA’s ash fact sheet advises opening windows and doors and using an air cleaner to capture fine particles during indoor cleanup ².

Check the odor again over several days. If it returns, a source was likely left behind. Residue in porous materials and cavities is a common cause, and the soot removal entry and the protein smoke residue entry explain it.

Look for material damage. EPA lists rubber, electrical wire coatings, fabrics and sensitive artwork ¹. Photograph anything that changes and tell the contractor.

Warning signs, and when to stop

• Anyone, including a child, pet or houseplant, is inside while a generator runs.
• A sharp smell, cough, chest tightness or throat irritation near a machine. EPA lists chest pain, coughing, shortness of breath and throat irritation as effects of ozone ¹.
• A plan that uses ozone in place of cleaning and removal.
• A claim that ozone is “natural,” “activated oxygen” or healthy to breathe. CARB says some companies make that claim and its page does not support it ³.
• A rented machine with no manual, no output information and no airing plan.
• A household member with asthma, heart or lung disease, who should ask a health professional first. EPA says vulnerable people, including those with asthma, face greater risk ¹.

Federal and state positions, and the standard

EPA. EPA’s page on ozone generators sold as air cleaners says no federal agency has approved ozone devices for use in occupied spaces and that EPA does not certify air cleaners.

It cites an FDA limit of 0.05 ppm for ozone from indoor medical devices, an OSHA worker limit of 0.10 ppm averaged over eight hours and a NIOSH recommended limit of 0.10 ppm that should never be exceeded ¹.

These are the figures EPA prints, and limits can change, so check current values before relying on a number.

EPA ash fact sheet. EPA-452/F-26-011 advises avoiding products that add chemicals to the air to neutralize smoke odors, such as ozone and hydroxyl generators or other oxidizers ².

California. CARB’s regulation requires certified indoor air cleaners to produce less than 0.050 ppm of ozone, and the consumer page lists industrial units that must carry the label “For industrial use only. Use only in unoccupied spaces. Health hazard: Emits ozone.” ³⁴. CARB’s fact sheet is dated January 1, 2010.

Industry standard. ANSI/IICRC S700 covers fire odor management in general terms; the first edition is dated 2025 ¹¹. It is a paid, voluntary standard, and this page does not describe its text.

Law versus advice. EPA guidance is advice. CARB’s rule is law for devices sold in California. Contracts and local rules set the rest.

Ozone compared with other odor treatments

See the entries on hydroxyl generators and thermal fogging for the details behind the other rows.

Common myths about ozone

Myth Ozone is just oxygen, so it is harmless.

Reality EPA says ozone can damage the lungs, and CARB says even low concentrations are harmful to people, plants and animals ¹⁴.

Myth You can tell by smell when it is safe.

Reality CARB says odor is not a good way to tell if you are exposed to ozone ³.

Myth An ozone machine removes any smell.

Reality EPA says at safe concentrations it has little ability to remove contaminants, may mask odors and can form by-products ¹.

Myth It is federally approved for homes.

Reality EPA says no federal agency has approved ozone devices for use in occupied spaces ¹.

Myth A short blast and a quick air-out is fine.

Reality EPA says generators have tested above health limits even when used as directed, and no source here gives a safe re-entry time ¹.

Where your state changes the picture

When this matters to you, and what to do next

Ozone treatment matters when a contractor, a rental shop or an online seller offers ozone for smoke odor. A safe default is to decline it and ask for a plan built on cleaning, removal, filtering and ventilation, which is where FEMA’s homeowner ladder starts ⁸.

If ozone is still proposed, ask for the written plan, the equipment, the airing-out method and the name of the person who decides when entry is allowed. The hiring guide and the scam avoidance guide help with that conversation.

If anyone in the home has lung disease, ask a health professional before returning to any treated space.

Related terms

Air Scrubber

An air scrubber is a portable filtration machine that draws room air through a series of filters, such as a pre-filter and a HEPA filter, and returns it to the room to remove airborne particles while restoration work is under way.

HEPA Filtration

HEPA filtration is air filtering with a high-efficiency particulate air filter, a pleated mechanical filter rated to remove at least 99.97% of airborne particles 0.3 microns across when tested under set conditions.

Negative Air Machine

A negative air machine is a portable fan unit with a HEPA filter that pulls air out of a sealed work area and sends it outside, so the area sits at lower air pressure than the rooms around it and dust and mold spores do not leak out.

Restoration Scope of Work

A restoration scope of work is the written description of the work a restoration company agrees to do, covering what, where, how much and when, so that you, the company and your insurer can compare the same plan.

Salvageable vs. Non-Salvageable Materials

Salvageable materials are building materials and belongings that can be cleaned and dried back to a safe, sound state after water damage, while non-salvageable materials are those that cannot and must be removed and replaced.

IICRC Standards in Restoration

IICRC standards in restoration are voluntary, consensus-based industry standards published by the Institute of Inspection, Cleaning and Restoration Certification, a nonprofit, that describe how professionals should carry out work such as water damage restoration, mold remediation and fire and smoke damage restoration.