Thermal Fogging and Ozone Treatment for Fire Odor Elimination

Persistent smoke odor after a fire is one of the most technically challenging aspects of the restoration process, driven by microscopic particulates and volatile organic compounds that penetrate porous building materials far beyond the reach of surface cleaning alone. This page covers two specialized deodorization technologies — thermal fogging and ozone treatment — explaining how each works, where each is appropriately applied, and the professional and safety standards that govern their use. Understanding the distinction between these methods is essential for property owners, adjusters, and contractors evaluating odor removal after fire damage and the broader fire damage restoration process.

Definition and scope

Thermal fogging is a deodorization technique in which a petroleum- or water-based deodorant solvent is heated and atomized into a dense fog of sub-micron droplets, typically ranging from 0.5 to 15 microns in diameter. These droplets mimic the behavior of smoke particles, allowing the deodorant to penetrate the same porous surfaces — wood framing, drywall, upholstery, insulation — that absorbed odor-causing compounds during the fire event.

Ozone treatment uses an ozone generator to produce ozone (O₃), an unstable molecule that reacts chemically with odor-causing compounds — including phenols, aldehydes, and sulfur-based gases — oxidizing them into odorless byproducts. Unlike thermal fogging, ozone treatment leaves no residue and does not rely on a masking agent.

Both methods fall under the deodorization phase of a complete restoration scope. The Institute of Inspection, Cleaning and Restoration Certification (IICRC S700) and the IICRC S500 standard address odor control as a structured remediation category. Neither method is classified as a standalone solution; the IICRC standards for fire damage restoration position deodorization as a post-cleaning phase, meaning gross soot and residue removal must precede either treatment.

How it works

Thermal Fogging — Process Breakdown

1. Pre-treatment preparation. The structure is cleaned of visible soot and smoke residue. Surfaces are wiped, HEPA-vacuumed, and neutralized. All occupants, pets, and plants are removed.
2. Sealing the space. HVAC systems are shut down. Windows and doors are sealed to prevent fog dissipation and maximize dwell time.
3. Fogging application. A thermal fogger heats the deodorant solution to a temperature that causes rapid vaporization and atomization. The operator moves through the space, allowing the fog to permeate cavities, subflooring, wall voids, and ceiling spaces.
4. Dwell and ventilation. The fog is allowed to dwell — typically 1 to 4 hours depending on product specification. The structure is then ventilated thoroughly before re-entry.

The mechanism relies on pairing — the deodorant molecules bond with odor molecules rather than simply masking them, neutralizing the volatile compounds at the molecular level.

Ozone Treatment — Process Breakdown

1. Source removal first. Charred materials, heavily contaminated contents, and residual soot must be removed prior to ozone treatment.
2. Generator placement. Industrial ozone generators, rated in milligrams per hour (mg/h) or grams per hour (g/h), are placed within the affected zone. Larger spaces require higher-output units or multiple placements.
3. Sealed operation. The space is sealed and the generator runs for a calculated period — from 3 to 24+ hours depending on ozone concentration targets and space volume.
4. Off-gassing and clearance. The ozone off-gasses naturally after the generator is turned off. Re-entry is prohibited until ozone levels fall below 0.1 parts per million (ppm), the permissible exposure limit (PEL) established by the Occupational Safety and Health Administration (OSHA) for occupational settings (OSHA PEL: 0.1 ppm ceiling, 29 CFR 1910.1000 Table Z-1).

Common scenarios

Thermal fogging is most effective in structural smoke penetration cases — kitchen fires with grease-laden smoke, bedroom fires involving synthetic materials, and post-wildfire scenarios where smoke infiltrates wall cavities and subfloor assemblies. It is a standard component of smoke and soot damage restoration when odor persists after HEPA cleaning.

Ozone treatment is preferred in scenarios involving:

• Vehicles, storage units, and enclosed spaces where fog residue is problematic
• Protein fire odors from cooking fires, where organic compounds require oxidation rather than pairing
• Final odor clearance verification in residential or commercial fire damage restoration after all other treatments are complete

Air quality testing after fire damage is recommended both before and after either treatment to establish baseline odor compound levels and confirm post-treatment clearance. Testing may detect residual volatile organic compounds (VOCs) that indicate incomplete treatment.

Decision boundaries

The choice between thermal fogging and ozone treatment is not arbitrary — each method has structural limitations.

Ozone is classified by the U.S. Environmental Protection Agency (EPA) as a lung irritant at concentrations above health thresholds. The EPA explicitly states that ozone generators used in occupied spaces at concentrations sufficient to affect odors would also exceed safe exposure levels. This makes proper sequencing — treatment in unoccupied, sealed spaces with measured clearance — non-negotiable.

Thermal fogging solvents vary in chemical composition; petroleum-based formulations carry flammability ratings that require compliance with National Fire Protection Association (NFPA 30) Flammable and Combustible Liquids Code storage and handling requirements.

Professional contractors evaluate both methods as complementary tools within a tiered deodorization protocol. The fire damage restoration equipment and technology used for deodorization is subject to manufacturer calibration requirements and technician certification under IICRC training tracks.

References

• IICRC S700 — Standard for Professional Odor Control
• IICRC S500 — Standard and Reference Guide for Professional Water Damage Restoration (referenced for deodorization sequencing principles)
• OSHA — Chemical Sampling Information: Ozone, 29 CFR 1910.1000 Table Z-1
• U.S. EPA — Ozone Generators Sold as Air Purifiers (Indoor Air Quality)
• NFPA 30 — Flammable and Combustible Liquids Code