Hydroxyl vs Ozone for Smoke Odor Removal: Which and When

Reviewed by Tyler Bennett, Restoration Project Manager, IICRC WRT/ASD #291438, October 2026.

Short answer: Hydroxyl generators and ozone generators are both used for smoke odor removal, but they work on different chemistry. Hydroxyl is safe to run with people, pets, and plants present. Ozone requires the space to be unoccupied and is more aggressive. For most residential fire and smoke jobs in Spanish Fork, 4Sure uses hydroxyl so homeowners can stay in parts of the property during treatment.

The chemistry difference

Hydroxyl radicals (OH) are naturally formed in the atmosphere by UV light interacting with water vapor and oxygen. Hydroxyl generators use UV lamps to produce these radicals in a controlled chamber, then release them into the space. The radicals break down odor molecules (and some microbes) by stripping hydrogen atoms, after which they recombine back into water vapor and carbon dioxide. They are safe to breathe at the concentrations produced by residential-grade generators.

Ozone (O3) is an unstable molecule that oxidizes organic compounds aggressively. It is effective at eliminating odor but it is also harmful to breathe, damages rubber and some plastics, and can oxidize paints, wall coverings, and metal finishes. Treatment requires the space to be fully unoccupied, including by pets and plants, with ventilation for several hours after the treatment ends.

When we use each

Hydroxyl (default): most residential kitchen fires, wildfire smoke intrusion, cigarette-smoke decontamination of a purchased home, lingering odor after water damage. Homeowners can usually remain in unaffected rooms. Run time 24-72 hours typical.

Ozone (specific cases): severe commercial smoke restoration where the space is already unoccupied, remediation of extreme odor sources (dead-animal remediation, severe meth residue), situations where hydroxyl has been tried and residual odor persists. Space must be fully evacuated and sealed. Run time 12-48 hours followed by ventilation.

Why cheap foggers don’t work for lasting results

Chemical odor foggers mask smoke odor with a stronger scent. The underlying smoke molecules are still in the drywall, carpet pad, framing, and HVAC. Once the fogger scent dissipates in a few weeks, the smoke smell returns. This is why professional restoration uses hydroxyl or ozone (which actually destroy the odor molecules) combined with surface cleaning (which removes the residues feeding the odor) rather than a scented spray.

Related reading

• Smoke damage cleanup service
• Our equipment and process
• Fire damage restoration

Why cleaning comes before deodorizing

Smoke odor is not just in the air. It comes from residue on and inside materials: carpet and pad, upholstery, drywall, insulation, wood and ductwork. A deodorizer can neutralize odor molecules it reaches, but if the residue stays, it keeps releasing odor, especially when the heat comes on or the weather turns humid. That is why the IICRC S700 process removes and cleans residue first, then deodorizes.

The full odor-removal sequence

1. Remove materials that cannot be saved (charred drywall, insulation, carpet pad).
2. Clean soot from surfaces using the method that fits the residue type.
3. Clean or decontaminate the HVAC system so it does not redistribute odor.
4. Deodorize with hydroxyl generators.
5. Seal surfaces where needed before painting.
6. Verify the odor is gone before reconstruction finishes.

The four kinds of smoke residue

How soot is cleaned depends on what burned. Under the IICRC S700 standard, residue is identified before cleaning starts, because the wrong method can set a stain permanently:

• Dry smoke from fast, hot fires burning paper and wood. Powdery and easier to remove, but it gets into cracks and porous surfaces.
• Wet smoke from slow, smoldering fires burning plastic and rubber. Sticky, smeary and strong-smelling.
• Protein residue from kitchen fires where food burned. Nearly invisible, discolors paint and varnish, and has a strong odor.
• Fuel oil residue from furnace puff-backs. Dense and sticky, and it needs specialized cleaning.

Common questions

Is hydroxyl treatment safe while people are home?

Hydroxyl generators are designed to run in occupied spaces, which is one reason we use them. Ozone generators are different and require the space to be empty of people, pets and plants.

How long does hydroxyl deodorization take?

It depends on how much residue there is and how far it spread. Light smoke odor may take a few days; heavier jobs take longer. Deodorization works best after soot has been cleaned.

Will deodorizing alone fix smoke odor?

No. Odor comes from residue. If soot stays in the carpet, ductwork or wall cavities, the odor comes back. Cleaning first, then deodorizing, is the order that works.

Where can I see this used on a real job?

Our Payson smoke odor case study and Spanish Fork kitchen fire case study both used hydroxyl treatment.