Draeger gas pum and test tube for ozone (C) D FriedmanOzone Generator Ozone Treatment FAQs

  • OZONE ODOR TREATMENT FAQs - CONTENTS: questions & answers along with warnings About Using Ozone for Treatment of indoor air, car or other vehicle smells, or for mold treatments.
  • POST a QUESTION or READ FAQs about using ozone generators to kill odors or mold: dangers & false claims & about how to get rid of odors caused by ozone overdosing
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Ozone air, odor, car or mold treatment FAQs:

Questions & answers about using ozone to treat indoor or car smells or mold. This article provides questions and answers about the use of ozone generators or ozone treatments for odors, smells, or mold in buildings, cars, or other vehicles.

This article series provides government and other authoritative warnings about using ozone generators and ozone air purifiers in buildings to "purify" indoor air or to "kill mold" in buildings. We give a definition of ozone or O3, we explain what problems can arise when using ozone generators to try to get rid of odors indoors or to try to kill mold.

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FAQs About Using Ozone for Treatment of Indoor Air: Respiratory System

This quote from a reader's email pretty well sums up what happens if you overdo it when using an ozone generator indoors to try to "kill off" odors:

It's a long story, but I used a high powered ozone generator in our house, to get rid of skunk smell. Now I can't get rid of the left over nitric oxide, or whatever odor or gases, that linger in our house. I have been leaving the windows open every day, with running the heat on high (85 degrees) at night, to try to force off-gas the odors/gases.

We have investigated a number of cases of misapplication of ozone generating machines both to "kill mold" (no good, you're leaving toxic or allergenic particles, and you haven't corrected the reason for mold growth in the first place). We have also investigated several cases of excessive ozone-use to try to remove odors from buildings, including fire or fireplace smells, mold smells, pet or animal smells, skunk odors, smoking odors, etc.

Here is another similar case:

Dan, Our dog was sprayed by a skunk and then ran through our house. The skunk smell was terrible. We hired servpro to get rid of the odor. They used the ozone machine and although is helped to get rid of the skunk smell, we now have a lingering chemical smell.

We have had our walls, ceiling, furniture, rugs, clothes, bedding all professionally washed but the smell still remains. What do you recommend? BTW, we live in eastern massachusetts. Thanks for your time and for this service you provide. - S.M.

Reader Question: We also have had a very bad experience with use of Ozone generators.

5/18/2014 Sandy said:

We also have had a very bad experience with use of Ozone generators. We purchased a new condo last May and from the time we did our walk thru we noticed a faint odor as we entered. The builder blew it off as construction odors. After two months we shipped clothing to our second home and noticed a musty smell on everything. We then noticed that our luggage and other personal belongings had also picked up an odor. We hired a company to do mold testing and they found no elevated mold spores. The builder hired a remediation company to investigate the source of the odor.

They did thermal imaging, checked air handlers and checked all plumbing and could not determine the source so they tried to get rid of the odor by putting two ozone generators in our home for 4 days! This altered the odor and significantly increased it. Air testing after this showed high levels of VOCS in the house which we think was caused by the ozone oxidizing all the new carpet and furnishings in the home.

As recommended by and industrial hygienist we removed the carpet and all furnishings and tried 6 air purifiers with charcoal filters being changed every two days for a week and two weeks of a flush out process and the odor still remained. We determined that the odor had permeated into the drywall so we have just had all the drywall sealed with a special primer and two coats of paint applied and we're hoping that this is the final solution after 6 months of dealing with this mess.

My husband has been bothered with severe eye irritations which we also believe is the result of this ozone treatment. We now have to determine how much of our furniture can be salvaged. We've been told that it will continue to off gas. Do you think this is possible and do you have any suggestions for eliminating any remaining odors from mattresses, upholstered and leather pieces. This is all new furniture valued at about $40,000.

Reply: stunning incompetence in mold remediation

Regrettably the procedure you describe as used by your remediation company is packed with improper and ineffective methods, providing a compelling example of in my opinion incompetence that wasted everyone's time and your money. These include:

The solution at this point is

Reader Question: We left the ozone machine running and are now left with a strong chemical smell

(May 6, 2014) L.K. said:

We purchased second hand furniture for my sons room that smelled like smoke. A friend gave us an ozone generator to eliminate the smell. Unfortunately, we did not know much about ozone. We left it running on high in his room for many hours and now are left with a strong chemical smell. Upon doing research, we now realize that ozone is unsafe and have sealed off the room and had windows open and fan running for a week. However, the smell still lingers and gives us a headache to even walk into the room.

I am concerned for my 8 year old son to move back into that room and he is concerned for all his belongings! We have small children as well as a newborn. How do we keep them all safe once this toxic gas is already in the house? How do we eliminate it? No one seems to know much about ozone or how to get rid of it once it is present. Please help! We are very concerned. - L.K. [reader anonymity protected]


Sorry to read you're another victim of over-dosing a room with ozone.

The ozone itself is very volatile and will be long gone if you turned off the equipment and aired out the room.

The smell that remains is probably from oxidized materials, possibly carpeting, padding, foam cushions or something else. That outgassing odor tends to continue for a long time. The solution is usually to identify exactly what is giving off the odor and dispose of it.

See our SMELL PATCH TEST procedure linked to throughout this article.

for an inexpensive and easy way to track down the offending material.

Keep us posted.

Reader Follow-up:

Thank you so much for your response! We had contacted home inspectors, EMT, Poison Control, doctors etc and no one knew anything about ozone! I am glad we found someone who is knowledgeable in the area, as I have been very concerned.

Here are the circumstances of our situation.

The ozone generator was left on high in a small bedroom for aprox 6 hours. The door was sealed, the AC vent closed, the window opened and ceiling fan on. Upon turning off the machine, there was a terrible smell and we had to run out of the room. We got headaches instantly. We then left the ceiling fan on, door sealed, windows opened and box fan blowing out the window, for a week.

However, the room still has a sweet – like, artificial smell to it. There is no carpet in the room. Just a bed, dresser, closet full of spare pillows and blankets, and lots of stuffed animals and toys. The clothing that I retrieved from the room continue to have the same artificially sweet smell even after washing them several times. I got a headache once again from just entering for a moment even after a week of airing out, and every morning I now wake up with a sore throat.

We have small children including a newborn and I worry for their health. I keep all the bedroom windows cracked open every night.

The website was very helpful. However, after reading I am a bit confused. I have several questions.

You mentioned in your response that the ozone would be gone by now.

· Is that “sweet” smell the smell of ozone?

· If the ozone doesn’t stay around, why do I still smell it? And why do I still get a headache?

· Are the dangers of exposure only referring to the actual time when the generator is on, or are there dangers in the lingering smells from the ozone machine? Is that smell toxic as well? Why did people say they had to throw out all their belongings or leave their home, if there was no danger once the machine is off?

· How do I know the ozone level in that room? Is there a way to measure it? Is there a machine/purifier to take ozone out of the air or a way to detox the room and belongings?

· Do I need to throw out everything in the room if it continues to have this smell? Is it safe for my son to sleep in there? Safe for infant to be exposed to?

· What department does this topic fall under and why doesn’t anyone else seem to know anything about it?!


My intention suggesting the smell patch test was to try and focus on what is the source of the horrible odors ensuing from overdosing with ozone - the oxidized materials. If you can relate one or more of your smell patch tests to the odor that was bothering you in the first place you know what needs to be tossed out (as oxidized materials usually won't be much deodorized by washing or dry cleaning).

Other odor sources can usually be cleaned successfully, or cleaned then sealed.

Reader follow-up:

Is the odor caused by oxidized materials toxic as well?

At this point, the smell left behind in the pillows, blankets and clothing don't seem to bother anyone (or be noticeable to anyone) but me. So I am wondering if it would be harmful to keep my sons clothing etc once I've washed them several times and the smell is very faint - L.K.


Possibly, the odors you smell are harmful in any of a variety of ways: respiratory irritant, or even toxic. One can't say what's toxic or not with not any idea of what was oxidized.

L.K. as people vary in their sensitivity to odors and chemicals and as we're talking vague generalities here "clothing" and "faint smells" niether I nor anyone can by e-texting reliably assess risks to your family.

I would agree that if you are confident that a noxious odor remains and that you can't get rid of it by laundering or cleaning, and if by comparison with other non-ozone-exposed items made of the same material you can confirm that the odor of the offending items truly is due to the ozone treatment, then your choices are to tolerate the odor or dispose of those items.

Question: how do I get rid of high ozone concentrations produced by a spark generator

How do you rid a room of highly concentrated ozone produced by a spark generator?? 400sq ft, various items of wood furniture, paneling, bed with foam mattress, etc?? - Charles 12/2/11

Reply: if you smell ozone it's probably unsafe; if you smell something else later it may be due to an ozone treatment "overdose"

Charles, in the article above we make suggestions for getting rid of ozone smells indoors. If you are inside of an enclosed space while ozone is being generated at levels that you can smell, it is unsafe.

And ozone is ozone. It doesn't matter how it's produced: by spark generator or any other means, the molecules are the same. What does vary among ozone treatments and the people who use them, are

Actually unless you are smelling ozine while you are in an enclosed space while ozone is being generated (something that is most likely unsafe), you are not smelling ozone - it's very volatile and doesn't hang around. So the ozone itself, and its characteristic odor, will dissipate rapidly, minutes to hours, of fresh air ventilating of the space where ozone was produced.

Most complaints we receive are from lingering odors after an ozone overdose of an indoor area in an attempt to remove smells.

An "ozone treatment overdose" is my general term for applying ozone at levels or at a duration long enough to cause chemical changes, probably oxidation, of other indoor materials (carpets, curtains, foam cushions, plastics) that in turn leaves a lingering, obnoxious odor that just doesn't go away satisfactorily. Please review the article above and you'll see an outline of how we suggest you proceed.

Question: I have asthma and was exposed to ozone in an enclosed space for a few minutes.Will that cause health problems?

I have asthma and was in a closed room with the ozone machine working for a few minutes, would that cause me health problems in the future? - Sandy 10/26/11

Reply: a brief exposure to low levels of ozone should not cause lasting health problems for most people, but some are at extra risk


No one give a "for sure answer" to your question about ozone exposure based on a text note; your doctor would have to do that based on an examination.

At 3 STEPS to ASSESS POSSIBLE HARM from OZONE GAS O3 EXPOSURE we summarize a reasonable approach to assessing possible complaints ascribed to ozone exposure, starting with a consult with your doctor and we describe the TLV point for ozone below which no expert expects there to be an injury or ozone-related complaint (given certain exposure duration assumptions).

At OZONE TOXICITY we report that

Exposure to a level you can smell or exposure to ozone over long periods at levels greater than 0.05 ppm for 24 hours at a time is likely to be dangerous: [3] Health hazards to humans and animals occur and can be severe at ozone levels used for indoor cleaning purposes.

At least some people can smell levels of ozone down to 0.05 ppm. This odor-detection level is already half-way to the recommended limit. If you are generating ozone indoors, even at "low" levels a problem may be present.

People become desensitized to odors in a short time, perhaps 20 minutes. So if you do not smell it, the ozone level could still be hazardous.

As with any potentially harmful or irritating substance exposure, the risk is a function of several variables including

This means that even a brief exposure to very high levels of ozone could injure someone. Of course now, after the fact, you will most likely have no idea of what the actual level of your ozone exposure was.

But in general, a brief exposure to a closed room "for a few minutes" is very very unlikely to produce a measurable future health problem provided

Ultimately this is a question you need to discuss with your doctor or with a pulmonologist who knows your medical history.

Thanks for the question. Keep us posted on what your doctor says - that will surely assist other readers. .

Question: Spark generated ozone is not the same as UV generated ozone and my ozone is safe

This article represents spark generated Ozone. Long doses of this method can be detrimental with nitros oxide. UV generated ozone in high levels "DOES NOT" cause collateral damage and it would have to be left at super high levels for a over a week to have an affect on carpet or building materials. In ranges near 150PPM it is 100% effective on killing mold with exposure times over 6 hours and 99.996% of all bacteria.

When the treatment is over the ozone converts back to oxygen 'O2' and the clean smell is gone within 2 days. I have independent test results to prove it and detailed personal and business experience using it. Most articles I have read have been by mold remediation contractors that would take a major blow to their profits because they would not be able to rent their equipment to insurance companies. If a building is wet of course it needs to be dried and sheetrock removed.

There is no need however to tear a house apart because there is mold present on dry sheetrock. I challenge anyone to a significant 'bet' that can prove otherwise. Brent - 9/29/11

Ditto- DCW.


Thanks for your comment, Brent. We note that you appear to disagree with the U.S. EPA as well as the fundamentals of chemistry, science, and other authoritative sources cited above and below as well as with our own extensive field experience with severe odors and damaged building materials following over-use of ozone as a cure all for building smells or mold.

Brent, there is almost nothing correct in what you say in claiming that how ozone is generated affects the potential toxicity or volatility of the ozone molecules.

Ozone is O3 , a molecule that is identical regardless of how it was generated. At this point with so many years of expert research on this topic, there isn't much room for arm-waving challenges, bets, and assertions.

We agree that ozone is highly volatile and does not stay around in buildings. We also agree that ozone, precisely because of that extra oxygen molecule, is highly volatile and can oxidize other molecules. It is precisely that volatility that can result in overdosing a building or car or other enclosed space and its contents, apparently oxidizing materials and causing related problems.

And please compare your 150PPM concentration of ozone with the recommended industry standards, limits, exposure limits, etc. See OZONE EXPOSURE STANDARDS where you will see that your recommended dosage levels are enormously higher than any recommended human exposure.

DCW: in the most elementary chemistry class one learns that an ozone molecule is identical regardless of how it is generated. What may vary is the ozone level reached in an enclosed space, and the duration of exposure of the space to that gas.

Ozone or O3, or "trioxygen" is a molecule made of three oxygen atoms. In this form, and referred to as an "allotrope" of oxygen, ozone is an unstable gas - that means it breaks down into oxygen molecules.

While ozone is helpful in the upper atmosphere (filtering out UV light rays), in lower atmosphere, or in buildings, it is an air pollutant that is harmful to humans and other animals, and a gas that can oxidize or "burn" plants or various materials found indoors.

Ozone is widely used in industry in a variety of applications and can be of significant benefit and use when applied properly. Improper use of ozone is a topic of discussion in this and related articles for which we provide citations.

Question: who says Ozone can be dangerous?

I think these claims about the hazards of ozone are made-up. Tim / 2011

8/11/2014 Anonymous said:

I am a 72 year old white male. I have no significant health problem. I have had an ozone machine running in my 1300 ft.sq home for 30 years, 24/7. I live in a humid southern climate next to a river and a large swamp. In the beginning, it killed a small patch of mold next to a window and it has never come back.

There is no mold elsewhere in my house. If these machines were dangerous I would be dead by now. I dont see how an odor can linger because it completely dissipates in about 15 minutes after you turn it off which I have done just to see the effects. Once the third electron comes in contact with anything, dust, mold, virus, bacteria, it reverts back to O2, regular oxygen. I know it is very dangerous to the bottom like of Big Pharma.

They have convinced the FDA to indicate in papers that it is dangerous. I have a friend who bought one. He has asthma. He didnt have an attack for eight months of using the machine.

Then he read about the FDA's report on the 'dangers'. He quit using the machine and is back to seeing the doctor for his asthma attacks. I am not a doctor but I am reporting my own experience and condition. After 30 years of ozone machine use, I am probably the youngest looking, healthiest guy you ever saw at my age. So how do we know that most or all of these conditions listed here arent from other causes or other conditions?

If you took me for an example it would certainly blow all these contradictions out of the water. Furthermore, my wife is from Charleston, WV and I used to tell her she had terminal allergies. That is chemical city down in a valley with Union Carbide and other chemical plants blowing alarms and releasing chemicals on a regular basis. After moving south she continued to have the allergies. After the ozone machine, none.

She had tried everything, over the counter and homeopathic,nothing had helped. You say what you want and people can do what they want but I stand firm in my beliefs on this issue.


Tim and Anonymous: please read again with more care, including the US EPA and other citations at the end of this and each Ozone-related article at this website. While anonymous is certainly entitled to his beliefs, they are just that, beliefs, not credible science.

This article includes fourteen citations regarding ozone hazards. And above in the FAQs we refer readers to OSHA and other sources who set standards for allowable ozone exposure. Those articles contain hundreds of additional source citations.

And like the US EPA, InspectAPedia is an independent publisher of building, environmental, and forensic inspection, diagnosis, and repair information provided free to the public - we have no business nor financial connection with any manufacturer or service provider discussed at our website.

Question: How to treat a person [who] inhaled ozone? ... chest pain

(May 8, 2014) Jorge said: Bought an imported portable generator ozone, a concentration of 400mg / h of ozone as equals in ppm? How to treat a person inhaled ozone? And this with chest pain and lack of air 2 weeks?



The treatment question you ask required consulting with a physician who has expertise in environmental medicine and will e
Surely involve a medical examination and some diagnosis before any treatment is discussed. No one should prescribe treatment in a Q&A forum.

To address your other question, I don't thnk one can immediately translate mg. of a substance into ppm in air. That's because the concentration of a substance in air that results from release of a quantity of that substance depends o.

Where it is released, or more specifically, the volume of the space and the fresh air intake or air exchange rate of the space. Releasing 400 mg of a substance into a closed shoebox produces a much higher ppm concentration in air in the shoebox than releasing the same quantity into an auditorium.

Question: What machine or service would be effective in removing toxicity left behind by an ozone generator?

(May 15, 2014) Jeff said:

What machine or service would be effective in removing toxicity left behind by an ozone generator? How to test the air and materials for toxicity if no smell is obvious? At what point is it safe to reuse materials and room? Thank you.



I can't name such a machine and don't know one and doubt that such a machine exists, considering the possible causes, effects, & sources of over-dosing an area with ozone treatment.

You can
- clean surfaces that are washable
- dry clean or launder soft goods
- use our Smell Patch Test Kit procedure to identify the prime offending materials that need to be removed completely like oxidized carpet or carpet padding or upholstered furniture -

There is no machine one would put into the room that would "make it safe"

The ozone itself is gone quickly once the machine is off and removed. The odors that remain are from oxidized materials.

Reader Question: Smell from burned pot of baked beans, carpets cleaned, used an ozone machine, now the house smells horrible: I can't find the problem

8/19/2014 Michelle wrote:

Hi My name is Michelle and I just got off with you. The carpet person agreed to come out and only use steam water. I am happy about this and hopefully it takes care of the smell.


Super, Michelle. Do let me know how that works. Your complaint was that after the carpets were cleaned there was a bad smell that got worse when you ozone-d the house. You added that because of high outdoor humidity and temperatures (South Texas) you didn't want to ventilate with outdoor air.

If he will tell you the brand and product that was used that included a scent I'd be interested in taking a look at that as well.

Reader follow-up:

I returned the ozone generator and I bought some activated carbon. Have you heard of that? A restoration company told me to try it. I put them in Styrofoam cups fill about 3/4 and put them all over the house. One in each bedroom and 2 in the larger rooms. Let me know what you think. I will keep you posted so someday you can pass the word to others.

The incident happened 2 months ago and due to the humidity, I feel as if it's working against me. Once October is here, the windows will be open all day and night. Hopefully that solves the problem.


Unlike the ozone, the activated charcoal won't hurt a thing (unless you spill it and make a mess) and it will absorb SOME odors. However more likely if you observe a reduction in odor it will be from a combination of dissipation and ventilation. I'm doubtful that activated charcoal in cups on floors can possibly remove any substantial odor source any more than waving the vacuum cleaner wand in the air in the kitchen can pull out dust bunnies from under the couch.

It wont' hurt though. Keep me posted.

Reader follow-up:

Do you think the smell will go away eventually with time?


I just don't know. I would expect the odor to dissipate - that is diminish with airing out and fresh air.

But I've had complaints from folks who ozone-oxidized synthetics or foam that smelled for months until the material was tossed.

If we're not sure we've identified all of the odor sources we're flying blind - or holding our noses.


Have some good news. I noticed my kids rooms smell worst and the odors are coming from their room. I just walked into their closets and found that socks, formal clothes and anything with that polyester or padded texture was the source. I am washing all their clothes and will steam the carpets with hot water. I can't believe it, You are so right about trying to identify the items. I walked outside and clear my nose and then went into each room. I am happy and working on this at the moment.


nice going. And thanks for the follow-up.

Question: odors remain after thermal fogging and ionization treatments

(Jan 10, 2015) Anonymous said:
After using servpro to cleanup after smoke damage to our home , the thermal fogging and ionization odor still remain strong ? Is this dangerous to my Family ?



Ionization treatments, in concept related to ozone treatments, attempt to remove some airborne particles or possibly molecules by causing them to retain an electrical charge that in turn causes them to plate out on building surfaces. This procedure cannot remove an odor source however.

I'd start by asking the company what treatments they used and then I'd take a look at the MSDS for those chemicals.

I'd continue by determining if the treatments were applied in accordance with the manufacturer's instructions.

Question: ozone to remove protein smoke odor, now strange odor remains

(Feb 21, 2015) Michael said:
My house was cleaned with ozone in order to remove the protein smoke odor. It was cleaned and re-painted as well: ceiling and walls. Now I have strange odor, which is not a smoke. I suspect the oxidants odors coming from surfaces. It is clear how to remove the odor from the carpet - replace the carpet. However, I do not really understand how to remove it from the walls. Should I re-seal and re-paint the walls? If yes, what paint should I use?

Reply: what is in smoke & why odors remain after an odor-treatment program


Really? "Protein smoke odors" ?

Since you describe an odor complaint that remains after a post-fire treatment it is most likely that the odor is coming from one or more building surfaces. People's complaints of odors that remain or that are "new" after post-fire odor-treatments typically come from one of two underlying sources:

Surfaces or materials that have received deposits of burned materials have not been adequately cleaned, sealed, or removed and are continuing to release molecules (or even particles) that smell.

The treatment itself, if it was not properly conducted, can produce new odors and smells from a sealant coating or from over-dosing with ozone as is discussed in this article series.

Therefore, before using an odor sealant (such as is used after a fire) and before repainting, you might have better and more economical success by identifying the odor source. Try the easy smell patch test kit described at


When you've identified where the odors are coming-from you have a much better chance at a successful odor-cure.

(Feb 23, 2015) Michael said:
In fact, what I have done is a kind of partitioning test. I removed my loveseat and chair from the room, which was affected by smoke and further ozone and a chemical cleaning treatment done by professionals, and put inside of the garage. Garage is a cold place that was not affected by smoke. After 1 week I have smelled this furniture and discovered that I have similar smell in the rooms (specifically where carpet is.

I believe that I need to really push my insurance adjuster to cover the carpet replacement. This way, one of the major suspicious factors will go away. My air ducts were sealed by ServPro. I hope this will take care of another factor that could potentially affect the air. What is weird is that kitchen cabinets are producing a unique odor, which is probably a combination of cleaning chemicals with ozone that is still doing outgassing.


Michael: I'd still do some further smell-patch testing work as you may find that treatment either left some surprising surfaces smelling from inadequate cleaning or sealing, or if ozone was used it may have oxicized materials causing new odors to emanate.

Question: reader warns against ozone generating devices

Janine said:

Ozone's Impact on Public Health by Charles Weschler. specifically pages 7,8,9, and Table 1 for reaction products of household materials and ozone.

Our home was treated with hydroxyl and ozone generators for smoke odour. Rubbers, plastics, items with skin or cooking oils, among others, were visibly and materially degraded ("melted",embrittled,discoloured,)

On contact with items,surfaces and air in our home,we suffered irritative symptoms,and became ill and chemically sensitized,eventually having to abandon it and all our belongings. The restoration industry is decades behind the current and available science - in 21 months have not been able to produce a damage assessment and restoration plan that addresses all the issues of material degradation due to indoor ozone chemistry, leaving us owning a house we cannot live in.

We have no assurance that the sources of our health problems will be removed and the house be restored to pre-loss, un-ozoned condition. All scientific, government and health organization information confirms the damage and health issues, even industry organizations. The insurance industry does not want to acknowledge these credible sources. We have a lot more information -and pictures - anyone who has had this type of experience needs to speak out.

The use of these machines has to stop, especially as their use is endorsed by the insurance industry, homeowners are not warned of the potential for material damage(some is non-visible) and the toxic by-products left behind, and considering there are no guidelines for the restoration industry to remedy the damages their machines cause.

The "certified" restoration professional treating our home for smoke odour had no knowledge of harmful by-products from the ozone reactions he was promoting to "clean" the air.



While we have published various reader complaints about mis-application and over-dosing of ozone treatments that result in further IAQ or odor or even health complaints, there are valid and effective uses of ozone, provided that the process is properly applied and monitored by people who know what they are doing and providfed ozone is used where and how it works. Ozone is not a panacea for odors and smells in buildings and unfortunately too often it seems that people think that if some is good, more is better, overdosing and oxicizing and creating more trouble than before. In my OPINION.

[The reader cited the following]

We do not completely share Weschler's conclusions because ozone itself is so highly volatile that ozone molecules don't tend to hang around long in buildings - unless an ozone generator is left turned on in the building itself. It would seem that a significant number of complaints about "ozone" may in fact be generated by odors emanating from oxicized materials that were exposed to an overdose of ozone during building "treatment" for odors. - OPNION - DF.

Also see more complete research at

Question: the car we want to buy smells, the dealer says get used to it and says will use their ozone generator to fix the smell

(May 19, 2015) R. C said:
Firstly, thanks so much for providing this an excellent resource, there seems to be a lot of misinformation out there on the web on this topic. Your website, is the first that I feel I can trust.

I'm hoping that you can help advise. There is a car that I am interested in buying second-hand, and I was basically almost ready to hand over my cash. I tested the air-conditioning, and discovered a very strong source of mould smell. The car dealer said no problem, every car has its own odour and is just something that you can get used to, and that in any case he'd use his ozone generator and that would fix it. Also, some anti-mould spray was sprayed down the air vents. However, after reading several of your articles it seems like neither of these approaches is appropriate.

I'm still considering whether to buy this car or not. The car is about $2000 cheaper than a comparable used car which does not have a mould smell in the ventilation system.

Therefore my thoughts are: if I could say just take the car to a company that could guarantee complete mould and odour removal for say less than $1000, then I should buy the car. Otherwise, I should just walk away and pay more for a car which doesn't have this problem in the first place.

What I've had difficulty working out from my reading so far is the likely commercial costs, and success probability in any removal attempt.

Would you buy the car?

Thanks in advance.


Thank you for the vote of confidence R.C. We work hard to provide researched, authoritative and unbiased information, and we are strict about having no financial relationships that could jeapordize your trust. To that end, we also much welcome questions, suggestions, or critique.

About mold smells in cars, indeed that can be tough to get rid of, and it is in my opinion NOT something to ignore or just "get used to". We had a client, an audiologist who knew that they had mold in their offices at a problematic level - but no one working there was much bothered until a customer, a teenager who was asthmatic, came in for a hearing test.

Shut into the hearing test booth he went into anaphylactic shock in response to the MVOCs that were present at a high level. And even people who are not bothered by mold can become sensitized to it by exposure.

At we illustrate a worst case moldy car, while
at you'll find a less scary recounting of finding and fixing mold smells in vehicles.

I would be *very* careful about relying on ozone treatments - that can sometimes create a worse hazard, as you'll see warned in the article above. Best is to find and remove the moldy material - such as carpeting.

I am also a little cautious about "guarantees" to remove "mold smell" which itself is a claim that is a bit of a red flag since we need to remove the mold (the source) not the "smell".

I suggest the following: invite the seller to cure the mold problem for themselves - which also relieves them of the liability of selling a car that could be a problem for some users. The price can be adjusted upwards for the actual cost of the cure.

I would not buy the car without either having it satisfactorily cleaned or with the assumption that I might spend $1000. only to find that I was going to abandon the vehicle if that treatment was not successful. It can take weeks or longer to be sure that a treatment is successful. Changes in humidity, temperature, and ventilation can mask or renew a mold smell if the moldy source was not removed.

Question: car dealer used ozone to remove smoking odor. Is there a lasting effect or hazard?

I am considering purchasing a used vehicle from a dealer. It came to them with horrendous odor from the previous owner that smoked heavily in it. They used on ozonator in it for 3 days. Should I be concerned about the lasting negative effects of that? - by private email, Anonymouos, 22 July 2015


Yes if the vehicle interior has a plastic or chemical odor. You have not said whether or not the car interior smells. Check by sitting in the car with windows all closed. Note that changes in temperature or humidity may also affect odor levels in any inclosed space.

Perhaps not if the ozone treatment was not over-done (which is often the case)

Reader follow-up:

Would you mind elaborating, or directing me to a website that could help me understand the ramifications, so I can make a clear decision?


Sure see CAR SMELL - Mold DEODORIZING - though the discussion is about mold odors the same issues remain for deodorizing other smells inside a vehicle.

Basically ozone is a highly reactive oxygen molecule that interacts with (oxidizes) most substances with which it comes in contact. If you over-dose a car interior, which is very easy to do as it's a small, enclosed space, with ozone, you may oxdize the interior fabrics, headliners, upholstery, carpets. If that has happened you'll know because even if the original odor (say cigarettes) is no longer noticeable you'll smell a strong, pungent chemical odor.

Unfortunately once we've oxidized such materials the only effective fix is to replace them. This problem comes up in car deodorizing as well as building odors where carpets or other furnishings can be affected by over-dosing.

and see


Let me know if after reading those articles you have more questions.

Question: using ozone treatment to clean up heating oil smell / fumes after a spill indoors

I have been googling to try to find a question to a problem I have.

Someone broke into my cabin and stole a toyo stove I had in there.
Whoever it was left the fuel line on and about 250 gallons of home fuel flooded the area.

Insurance will handle the ground fuel clean-up. (Fuel ran through the floor and into the crawlspace-- and through the ground soil, pad.

As for the cabin itself, Insurance has said it will pay to replace everything touched by fuel.
However, they will be using ozone-hydroxyl treatment on the walls.
It has taken 7 months to settle this issue with insurance and so the vapors have set in the cabin all this time..

Can you tell me how effective you think the ozone-hydroxyl treatment would be?
The upstairs was not touched by fuel, however it did have vapor exposure all this time.

I would very much appreciate any comments you can offer.

Mary - by private email, kept private, 22 March 2016


You or I would have to do further research, but I suggest you start by searching for OZONE WARNINGS where you'll see that very often contractors over-dose a building interior with ozone in the hope of eliminating a smell that has deeper roots - causing a serious new odor problem and greater costs than ever.

Question: my son put an ozone generator in the room for 6 hrs now a week later EVERYTHING smells horribly

(Dec 15, 2015) sharon kopple said:
My daughter painted her nursery with 5!!! coats of paint. my son put an ozone generator in the room for 6 hrs now a week later EVERYTHING smells horribly and gives us a sore throat. The windows are open .
We have had the clothes outside for 3 days, washed some. Nothing has helped. Please we are desperate to find a solution.


Sharon, air out the room, use the smell patch test we describe to confirm the odor soyrce, and then you'll know if you need to remover oxidized carpet / padding, I'c repaint with a post fire sealant.

Don't do the ozone trick again.


Question: run gas heaters whike running an ozone air purifier?

(Mar 1, 2016) Thomas sapp said:
Can you run gas heaters whike running an ozone air purifier?


"Can" meaning physically possible, of course. But, then, I don't run ozone purifiers, for reasons discussed in this article series.

Comment: ozone shock treatment done for smoke odor problem - now a burnt smell remains

(Apr 25, 2016) Robert said:
I had a smoke odor problem in garage that wouldn't go away after weeks of airing area. Local restoration company recommended ozone shock treatment for a minimum of 24 hour Garage was detached from house but ozone odor (which is almost as offensive to me as smoke) permeated my entire house.

Now I have a smell(sweet,acidic,burnt electronics) that has affected all of my possession: clothes, furniture, pictures, CD's and videos, counter tops, media equipment, everything. A few things can be salvaged by washing but basically the ozone smell is the most resilient and pervasive I have ever experienced. For me, ozone treatment was a huge mistake and I would never recommend to anyone.

Question: how high will ozone gas concentrations be under these conditions ... ?

2016/06/19 Bill said:

Here's a good question. In an apartment building, if there are three ozone generators that max out at 57 grams per hour (designed for 1500 sq foot usage) shock treating three 700 square foot completely unventilated suites on the same floor, with fan in suite, taped off while concentrating but untaped when the machines were removed (but fans left running in suites), then moved to 2-3 other suites on the same floor and started again... How high do you think the concentration of gas could reach in the hallway, ballpark?

The easiest evacuation point for the gas must be under the front door into the hall, given the seals on doors+windows in suite. Unsure of hallway square footage, likely 2-3000 sq/ft. Assuming that the generators were designed to maintain 6ppm+ in a 1500 sq/ft room, could they potentially reach 12ppm+ in a 700 sq/foot room?

How dangerous would such a hallway be, then? I realize there are a lot of unknown variables that make it difficult to judge, but I ask because I was made to set up these machines and was exposed to this hallway for 45-60 minutes, experienced confusion, stinging eyes, and now have lung irritation. I could smell the gas in varying levels in the halls but was told it was normal. Confusion didn't help in stopping me from working in the halls. Employer screwed me really, really bad, I just don't know how much gas might have built up in the hall or how much I was exposed to.

Based on research, 1.5ppm for 2 hrs is confusion onset. Myself and a coworker experienced confusion, forgetting where we were going, what we had just done etc after 20-30 mins. I can't help but think that given the circumstances there must have been at minimum 1.5ppm in the halls in certain areas, more likely 3ppm+ if there were particularly bad areas?

Any information is helpful, thank you. I do have moderate lung irritation right now, constant fatigue, and was prescribed a long term puffer, something I've never had to use before. I had inflamed bronchi 4-5 days later when I visited a doc (Honestly did not understand the severity of the incident until then).

Thank you

For claritys sake, the front doors to suites were taped off from the hallway. The gas could be smelled as soon as the door was closed and I was taping them. Neither me nor a co-worker were told to open doors/windows to ventilate the rooms, or replace tape after removing the generators, so after concentration the space under the doors to the hallway was wide open (and again, the easiest evacuation point), approximately 3/4 of an inch, maybe a full inch high space between door and floor.



The questions you raise and potential hazards you note are not something that can be honestly, accurately, professionally assessed from an e-text. One would need to be on-site, making visual observations, interviewing occupants, considering building history, construction details, layout, air movement - many factors - to reach any credible opinion. Even claims of output of an ozone generator cannot be generalized to guess at the actual ozone concentration in air without more data.

I agree with more general observations such as your ability to smell "ozone" indoors. If someone can smell ozone then it's certainly plausible that they're being exposed to a too-high concentration of that gas to be safe.

Bill said:
Thanks for the answer. I expected that kind of reply, I know there's so many variables at play there. I figured the situation would need to be recreated in order to know for sure, it's truly impossible for any of us to know how much gas we were exposed to other than general observation on symptoms and the experience..

Appreciate it though, thanks again.

(mod) said:

If you had actual quantitative measurements - (the dose makes the poison) you'd want to see OZONE EXPOSURE STANDARDS at

Ozone is volatile - it doesn't stay around, but my point about being able to smell it remains worth considering. If you or people with whom you work are experiencing respiratory distress, lung complaints or similar worries it's worth mentioning the possible ozone exposure when consulting with your/their doctor.

Bill said:

I did contact my doctor. He didn't seem to be very knowledgeable about it. I was prescribed a long term corticosteroid inhaler, it must be helping because my lungs still feel awful and I've been using it for a week.

At the very least - there should be nobody walking the halls in which 3 unventilated suites are running commercial generators, without proper equipment, right?

Bit of background here. It made national news in Canada. After having done some research all week for mine and co-workers benefit, I still have few answers. Seems like ozone is a pretty grey area in general.


(June 21, 2016) Bill said:

I will definitely be booking your pages for future reference as well. This site has some of the best info available online, thank you for collecting it.


For space and to permit live links I moved our discussion to the current end of


in a section titled
Question: how high will ozone gas concentrations be under these conditions:

Your questions are helpful. Thanks back to you.

Question: house ozoned to rid the odor neutralizing powder that was put INTO the furnace - smells remain

(July 19, 2016) Katherine Lyons said:
we had our house ozoned to rid the odor neutralizing powder that was put INTO the furnace and should not have been...what is the average time to ozone a 900 square foot house?


Katherine I can't answer your question. I do not believe that "time" and "square feet" is enough to specify a treatment time, since we don't know the ozone generating equipment being used, the concentration of ozone that is being produced in the indoor air, the building air change rate per hour, the building layout, floors, and air movement patterns, nor the placement of the equipment, nor the problem that the ozone treatment was supposed to solve.

But as you will read in this article series, common problems with ozone treatments in buildings include

- mis-use of the ozone generating process: using ozone is not generally appropriate for building odor problems; finding and removing the odor source is more effective, reliable, and safer.

- over-dosing with ozone, resulting in oxidation of building materials and severe ongoing odors after treatment

It would be helpful if you could tell me what furnace problem was being solved and what "odor neutralizing powder" was put into the furnace, where and how it was applied, and what the product was.

You can also use the page top or bottom CONTACT link to send details or photos.

Question: 3 large machines used to ozone the house

(Aug 14, 2016) Anonymous said:
Hello, Our house is 900 square ft and there were 3 large machines to ozone the house.....the ozone started on friday night at 5:00 and ended sunday afternoon at around 3:00...the machines ran all of the time without stopping.


OK Anon, but other than raising the concern of ozone over-treatment discussed in the article above, and the concern of mis-use of ozone to "cure" house problems such as mold or an odor source that's not been found, I don't see a question here.

Question: How do you protect electronics during ozone treatment?

(Oct 23, 2016) Jack said: How do you protect electronics during ozone treatment?

Reply: research on effectives of & control of corrosive gases on electrical equipment

Good question, Jack. Below I'll cite some research pertinent to the effects of ozone on electrical and electronic equipment. If you have additional citations and research or specific field experience with this problem, let me know.

IMO you'd need to either remove the equipment from the ozone treatment area or you'd need to wrap it in mylar (best) or heavy poly and seal it against gas intrusion.

Question: mattress smells after ozone treatment for mold

(Oct 12, 2015) Marlene said:
A ozone machine was used as part of a mold clean up in my master. Mold is gone, but the ozone machine has interacted with my mattress which is releasing a toxic byproduct that is nauseating.

Everything is removed from the room except four hard wood pieces of furniture, wood bamboo flooring and a flat screen TV.

Walls washed down and floors steam cleaned. Nauseating smell still exist. It's been one month that we have been unable to sleep in our room. Any further suggestions of how to get rid smell?


You may need to apply a sealant coating such as those used after a building fire, sealing walls, trim, floor.


Question: powdery substance found after ozone treatment for smoke odors

(Nov 6, 2015) Jean said:
An ozone machine was used in my apartment to remove the smoke odor left from previous tenant. The maintenance man set the machine up in a small bathroom, shut the door and left running for 8 hours.

I returned and their is white powdery substance everywhere. Is this substance toxic or dangerous? Should we take any special precautions?


Jean I have no idea what the white material is - that'd be tough to guess from an e-text. Certainly it's unusual. Perhaps something else was going on.

Ozone itself will be long-gone the machine has been removed.

Damp mop or HEPA vac up the mess.


General Use of Ozone Generators nor Ozone Shock Treatments as a "Cure" for Building Mold or Other Smells & Odors is Not Recommended

Watch out: Ozone is a highly toxic, oxidizing gas. It can be absorbed into the body via inhalation, skin or the eyes. It can also oxidize building materials. See the Ozone hazard and use warning articles listed at the end of this article.

Watch out: In-Home or "portable" ozone generators and industrial or "shock treatment" ozone generators not only fail to find and remove the source of mold or building odors, in addition ozone concentrations generated by ionic air purifiers can exceed (industrial) levels permitted by U.S. Environmental Protection Agency.


Continue reading at OZONE MOLD / ODOR TREATMENT WARNINGS - home, or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see OZONE HAZARDS - home



Or see this

Article Series Contents

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OZONE ODOR TREATMENT FAQs at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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