Fire restoration techs remove smoke odor by working through a sequence: remove the source, clean the smoke residues, recreate the penetration with fog or counteractant, then seal whatever cleaning could not reach.
Ozone generators, hydroxyl generators, thermal fogging and odor counteractants are tools inside that sequence.
This page explains how the methods fit together, the exposure limits that frame ozone work, and how techs verify the odor is gone.
Why source removal and cleaning come first
The logic of the sequence is practical: odor rides on smoke residue, and residue that stays in the building keeps feeding odor back into the air.
Source removal — pulling charred and smoke-damaged material out of the structure — comes before deodorization equipment runs.
Cleaning is the second half of the same idea.
Soot and smoke residues on surfaces, contents and systems hold odor with them, so washing and residue removal do the first round of deodorization before fog, ozone or counteractants are considered.
IICRC frames the work in ANSI/IICRC S700, the Standard for Professional Fire and Smoke Damage Restoration, which IICRC lists in its First Edition, 2025.
IICRC says the standard covers assessing the presence, intensity and boundaries of fire residues and odors in buildings, systems and contents — the assessment that decides what gets removed, what gets cleaned and what gets treated.
One scope limit sits before source removal: the S700 summary says that when regulated hazardous materials are suspected, restorers perform work consistent with the authority having jurisdiction's regulations.
The trade teaches this order deliberately.
IICRC's Fire and Smoke Restoration Technician (FSRT) certification covers scoping, mitigation, cleaning and deodorization of fire- and smoke-damaged structures and contents, and its Odor Control Technician (OCT) certification covers olfaction, odor sources, the detection process, odor-control theory, equipment and chemical options.
For the role around that odor work — hazards, certifications, hiring — see the fire restoration technician career guide.
How smoke odor penetrates materials
Smoke travels.
Heated air carries combustion gases and fine particles through a building, following air movement into rooms the fire itself never reached, and the residue it deposits settles on cool surfaces and works into porous ones.
That movement is why an odor assessment maps where smoke went, not just where flames burned.
Odor can persist in a closed bedroom or a distant office, and the assessment's job is to find the residue and the odor paths behind it.
HVAC is part of that map, not an afterthought.
IICRC scopes the S700 assessment to buildings, systems — the standard's own summary names HVAC — and contents, which is the trade's reminder that ductwork moves odor the same way it moves air.
Materials hold what smoke leaves differently.
Porous and semi-porous surfaces take residue deeper than hard, non-porous ones, which is why hard surfaces may come clean with washing while soft and porous materials need deeper treatment — or replacement, when residue cannot be pulled back out.
Penetration is also what the rest of the toolkit answers.
Treatment needs to reach the places the smoke reached — the gap thermal fogging tries to close, and the one sealing finishes when treatment is done.
Thermal fogging and counteractants
Thermal fogging recreates the smoke's own travel.
A fogging machine heats an odor counteractant and disperses it as a dense fog that drifts through the space the way smoke did, carrying the counteractant into voids, cavities and porous surfaces that surface cleaning cannot reach.
Odor counteractants are the chemical half of the toolkit, and the fogger is only one place they go.
Counteractants go into cleaning solutions during the wash stage, get applied to surfaces after it, and are matched to the residue type the assessment identified.
Fogging sits after cleaning in the sequence: the fog treats what cleaning left, but it does not remove char or lift heavy residue.
Fogging runs under the employer's safety procedures and the product's own directions for use, which is where the site-specific controls — clearing the space, timing, ventilation — get set.
Public documentation is thin across this whole technique cluster: our research found no primary source that lays out soot classification, fogging or sealing procedures in detail.
IICRC covers deodorization through the FSRT certification, and odor theory, equipment and chemical options through OCT.
Ozone vs hydroxyl generators
Ozone and hydroxyl generators are two equipment options for treating odor without a cleaning product or a fog, and they get grouped together in conversation because of it.
They differ in the site controls they demand and in how much independent evaluation stands behind them.
An ozone generator elevates ozone concentrations in the space being treated.
Ozone is regulated in workplaces: OSHA's permissible exposure limit is 0.1 ppm as an 8-hour time-weighted average under 29 CFR 1910.1000 Table Z-1.
NIOSH recommends a ceiling of 0.1 ppm — not to be exceeded at any time — and lists 5 ppm as immediately dangerous to life or health.
EPA's guidance frames the exposure side of the trade-off.
EPA says high ozone concentrations are sometimes used in unoccupied spaces — its own example is fire restoration — with conditions controlled so no person or pet is exposed, and it notes little is known about the chemical by-products left behind.
EPA also says no federal agency has approved ozone generators for use in occupied spaces.
EPA's effectiveness caution is the other half: at concentrations that do not exceed public health standards, EPA says ozone is not effective at removing many odor-causing chemicals, and in one test it cites, ozone had no effect on formaldehyde.
The concentrations EPA ties to unoccupied, controlled spaces are the high ones.
EPA also warns ozone can damage materials such as rubber, electrical wire coatings, fabrics and artwork with susceptible dyes and pigments, and can harm indoor plants.
On a contents-heavy loss, that warning is a scoping input: ozone and sensitive contents do not automatically mix.
Hydroxyl generators are the second equipment option.
Our research did not find an EPA, OSHA or NIOSH evaluation of hydroxyl generators for restoration odor control, so the performance and safety claims attached to them are the manufacturers' own.
On a job, the equipment choice follows what the space allows.
A space that can be cleared and controlled opens one set of options; an occupied building or a space with sensitive contents narrows them, and the company's own procedures set what runs and when.
The numbers above are where that conversation starts, not where it ends.
Exposure limits belong to the agencies
Sealing as the last step
Sealing closes out the surfaces cleaning could not finish.
An encapsulating coating goes over material that still holds odor — porous wood, framing in concealed cavities, subflooring — so what remains stays put instead of releasing into the room again.
It is late-sequence work on purpose.
Sealing too early covers residue that washing could have removed, and a sealed surface constrains what reconstruction and painting inherit on it.
Crews seal what assessment and cleaning passes have already answered.
Sealed areas are documented scope: what was sealed, with what, and why cleaning alone was not the answer.
The FSRT certification covers documentation of fire- and smoke-damaged structures and contents, and the seal belongs in that record.
Where the sealing line sits — which surfaces get cleaned further and which get encapsulated — is a judgment made from the assessment, the residue and what the surface is.
Testing that odor is gone
Verification closes the job, and the trade's first instrument is a trained nose.
IICRC's OCT certification covers olfaction and the detection process, which is the trade's own framing: odor is detected by people who know what they are smelling for.
The re-check recreates the conditions odor shows up in.
Crews close the space up, let it sit, and walk it fresh — cold air and a closed room give a remaining source the chance to announce itself that a busy, ventilated workday hides.
There is no published numeric odor threshold our research found that marks a fire loss finished.
Verification is sensory and documentary: the nose, the re-checks, and a record that shows what was removed, cleaned, treated and sealed.
The FSRT certification covers documentation of fire- and smoke-damaged structures and contents, and the close-out record is where the odor story lives for the project manager and the adjuster.
If odor returns after sign-off, the sequence's own logic says the source was not fully removed — the fix runs back through scoping and source removal, not more equipment hours.
Odor control is its own IICRC certification — OCT — and the FSRT certification covers deodorization alongside scoping, mitigation and cleaning.
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Career information for restoration technicians, not licensing, legal, insurance, health, safety or tax advice — confirm exposure limits and equipment procedures with OSHA, NIOSH, EPA and the equipment manufacturer.