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Ozone vs hydroxyl
Ozone and hydroxyl generators both make reactive gases meant to break down odor molecules after a fire.
Get Help With Your Restoration Project What moves an odor bill
Written by HyreRestore Research Desk Primary-source research and fact checking
The short answer
Ozone and hydroxyl generators both make reactive gases meant to break down odor molecules after a fire.
The practical difference is occupancy: EPA says ozone can damage the lungs and that no federal agency has approved ozone devices for occupied spaces, while makers and a trade association say hydroxyl units can run with people present when instructions are followed.
EPA’s ash fact sheet advises avoiding both for smoke odor; cleaning the soot comes first either way.
What separates the two?
Ozone treatment requires an empty building; hydroxyl is marketed for occupied spaces.
The occupancy claim for hydroxyl comes from industry, not a regulator’s approval.
Neither removes soot. Odor returns if the residue stays on surfaces.
Ozone and hydroxyl, side by side
Government and industry sources disagree in places. Each row says whose claim it is.
| Ozone generator | Hydroxyl generator | |
|---|---|---|
| How it works | Makes ozone gas, which reacts with odor compounds | UV light on a catalytic surface makes hydroxyl radicals, per the maker |
| People and pets inside | No. EPA says exposure must be prevented | Industry says yes, when following the maker’s guidelines |
| EPA position | Lung irritant; little effect at levels that meet health standards; may form by-products | EPA’s ash fact sheet advises avoiding hydroxyl generators and other oxidizers for smoke odor |
| After treatment | The building is aired out before anyone returns | Industry says it can run during normal cleaning |
| Watch for | Units sold as household “air cleaners” | Combination units with an ozone mode, which the maker says is unsafe for occupied spaces |
HyreRestore found no independent test, in the sources reviewed, showing either method makes a building safe. Ask what a specific machine emits.
When a company proposes ozone
People, pets and plants out, as EPA requires.
Soot removal and surface cleaning come first.
When the machine stops and the building is aired.
When a company proposes hydroxyl
Hydroxyl is the method marketed for occupied spaces.
Confirm the model and setting in writing.
Not in place of it.
What to ask before any odor treatment
Model number, and whether it has an ozone mode.
In writing.
See soot removal.
After the machines are off.
Your inquiry
Tell us about the damage
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Questions
Is hydroxyl safer than ozone?
Can I run an ozone generator myself?
Do either of them remove smoke damage?
Written and audited by
HyreRestore Research Desk
Primary-source research and fact checking
We are a research desk, not a restoration company and not an insurance adjuster.
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