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Odor Removal

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Good examples of indoor air nuisance odors are:

1: Houses where the previous occupant had pets and the subsequent odors have soaked into the floors and walls. 

2: And previous homeowners/occupants that smoked and the odor has soaked into the walls, ducts, floors, etc.

The three most common approaches to reducing indoor air pollution, in order of effectiveness, are:

  1. Source Control: Eliminate or control the sources of pollution;

  2. Ventilation: Dilute and exhaust pollutants through outdoor air ventilation and

  3. Air Cleaning: Remove pollutants through proven air cleaning methods.

Of the three, the first approach — source control — is the most effective. This involves minimizing the use of products and materials that cause indoor pollution, employing good hygiene practices to minimize biological contaminants (including the control of humidity and moisture, and occasional cleaning and disinfection of wet or moist surfaces), and using good housekeeping practices to control particles.

The second approach — outdoor air ventilation — is also effective and commonly employed. Ventilation methods include installing an exhaust fan close to the source of contaminants, increasing outdoor air flows in mechanical ventilation systems, and opening windows, especially when pollutant sources are in use.

The third approach — air cleaning — is not generally regarded as sufficient in itself, but is sometimes used to supplement source control and ventilation. Air filters, electronic particle air cleaners and ionizers are often used to remove airborne particles, and gas adsorbing material is sometimes used to remove gaseous contaminants when source control and ventilation are inadequate.

(To put into layman's terms:  

1: Clean up the source of the odors as well as possible.

2:  Ventilate the foul smelling area.

3:  If these do not eliminate the odors, Use odor eliminating equipment or companies to remove the odors on a microscopic level using one of the methods shown here.)


In the restoration world, odor removal is something we deal with every day. Ozone and hydroxyl generators are the two main options to get the job done. There are advantages and disadvantages to both sides, and we’re going to talk about them here. 

Before we dive in, let’s remember that both hydroxyl and ozone generators will remove odors from spaces, they will just do it differently. 

Ozone Generators

Ozone generators produce a gas called “ozone” to deodorize airborne particles in a residential or commercial area. Ozone is the main element in the ozone layer and it's composed of three oxygen molecules. This third molecule can easily detach and reattach to other substances, changing its properties. In the case of restoration companies, it will deodorize the air. 

How Does It Work?

Ozone breaks apart oxygen molecules in two ways. 

  1. Corona discharge that splits normal oxygen and creates single oxygen atoms. These atoms will then form ozone, after attaching to an O2 atom. 

  2. Ultraviolet light will split O2 into individual oxygen atoms, similar to how ozone is create in the upper atmosphere. This process is not as efficient as corona discharge. 

Once the oxygen molecules are set, the generator neutralizes the odors by oxidation. It permanently alters the molecular structure of the odor molecule, which leaves it odorless instead of masking the odor.

The thing about ozone generators is that they cannot be used on all surfaces, or around people and animals. The process isn’t safe to be around, which can be frustrating if a client needs to be in the space while restoration is happening. 

Hydroxyl Generators

Hydroxyl generators use UV radiation (the same as the sun!) to naturally clean and deodorize indoor environments. Using high energy UV lights and multiple wavelengths, hydroxyl radicals are created when these elements react with the oxygen and water vapor in the air.  

Millions of hydroxyls are created per cubic centimeter during this process. Each hydroxyl generator on the market today works just a little differently than the next. 

How Do They Work?

Hydroxyl generators are different depending on the type you’re using. The main purpose of course, is to eliminate odors and break down volatile organic compounds in indoor environments. This is done by the hydroxyl radicals dismantling the structure at a molecular level of the odors in the environment. 

A chain reaction occurs, creating other radicals and hydroxyls faster than odor molecules can reproduce - which keeps the air clean and fresh. The best part of a hydroxyl generator is you simply plug it in and turn it on - no spraying, wiping, or fogging. 

Hydroxyl generators are also safe on surfaces. They can be used while people and pets are in the space being deodorized - making it safe at all times. 

Ozone vs Hydroxyl Generators

Now that we’ve seen both sides, let’s compare the two.

  1. Hydroxyl generators are safe for pets and people. Restoration work does not have to stop while the process runs, which saves time and money!

  2. Hydroxyl does not leave behind any chemical smells. 

  3. Hydroxyl can be used in wet areas to get rid of the odors. If ozone machines are used in damp areas, it can bleach materials. 

  4. Ozone generators are not safe to use on rubber or leather. 

  5. You must use ozone machines without anyone in the room, and cannot return to the space for at least an hour after the ozone machine has completed its run. 

  6. Hydroxyl generators are great on a variety of odors.

Over all, ozone and hydroxyl generators will deodorize a restoration project. However, hydroxyl generators do provide more options and less of a threat of damage to certain materials.


The Ozone vs. Hydroxyl Debate

Which do you prefer for odor removal?

Odor removal is a critical part of almost any restoration job. There are a variety of options available from masking agents to foggers to ozone and hydroxyl generators, and so on. Today, there is a rather big inner-industry debate being waged over the benefits and dangers of those latter two options. There is a clear advantage to using machines to eliminate odors from spaces and items rather than simply trying to mask them. During the RIA’s Forensics Restoration Conference in St. Louis last fall, there were people on both sides of the aisle talking about the effectiveness of both technologies – and the downsides.

This time around, odor removal experts are taking the stand to talk odor removal science to help you make an educated decision about which technology is right for your company.

Meet the Experts

David Hart (DH) – Team Ozone – A U.S. Army veteran, David has been involved in the carpet cleaning, and later – restoration industry, since finishing his service in 1991. A problem-solver at heart, David immediately picked up on some ways the duct cleaning process could be improved and in 2007, invented what is known today as the RamAir Duct Cleaning System. He has since invented the OzoGen 10kV High-Output Ozone Generator, and runs Guarantee Cleaning Services, Inc. in Bend, Ore.

Russ McCubbin (RM) – Neutral – Russ has been in the air and water purification equipment manufacturing industry for 25 years. International Ozone Technologies Group, Inc., of which Russ is president, was incorporated in June of 1999 and their first products were the Total Zone Ozone Generators, and a line of “ozonated” oil ointments. International Ozone has been private labeling ozone generators and hydroxyl generators for 12 years and has been named “Vendor of the Year” three times.

Tom McArdle (TM) – Team Hydroxyl – Heavily involved in odor removal education and training throughout the U.S., Tom is the Vice President of the Odorox Hydroxyl Group. Odorox technology was launched in 2008, and in just a few years gained credibility among restoration contractors around the U.S. Two U.S. patents were issued for the technology in 2012.

What is the basic science behind your technology?

DH: Ozone is created when oxygen molecules (O2) are ‘sliced’ in half; the single oxygen atoms (O1) bond with ambient O2 molecules, creating ozone (O3 molecules). Ozone generators also produce ozone using these two principles- UV light and Corona Discharge.

RM: Manmade ozone is produced by two separate processes. One is with UVC ultraviolet light in the 185-nanometer wavelength. The second process is called corona discharge, which produces higher concentrations of ozone than UVC, for faster deodorization. Titan produces hydroxyls by subjecting humidity in the air to UVA light in the 365 to 385 nanometer wavelengths in the presence of a catalyst, usually titanium dioxide. This photocatalyst process splits an H off of H2O leaving OH – hydroxyl and an H.

TM: The Odorox technology was patented because it is the only process able to produce hydroxyl radicals that exit the chamber of the machine to eliminate odors not just in the air, but more importantly, odors that have been adsorbed by contents and structures. This is done by using multiple high energy ultraviolet lights inside the chamber of the hydroxyl machines. It converts water naturally found in the air to hydroxyl radicals, as well as oxy and peroxy- radicals that exit the machine. The hydroxyl radicals that exit the machine are able to eliminate odors, not mask or otherwise cover them up, by disassembling all of the odor molecules including those found deep inside porous materials.

How effective is your respective technology at removing the most common odors restorers see – like smoke, mold, biohazard waste, etc?

DH: The way ozone permanently neutralizes odors is by oxidation. The third oxygen atom in the molecule is loosely bonded to the stable O2 molecule, detaching itself from the O2 when it comes into contact with a receptive odor molecule. This permanently alters the molecular structure of the odor molecule, rendering it odorless. It doesn’t simply cover/mask odors with another odor, it basically removes the odor from existence. 

RM: Ozone is faster than hydroxyl at removing odors but must only be used in un-occupied areas. Ozone is great at removing any organic gaseous compound once the source has been removed. Ozone is great for use on mold, mildew, smoke, VOCs, bacteria, virus, etc… Titan hydroxyl generators are not for use as surface microbial kill. They are for airborne microbial kills only, but are great for area and content deodorization.

TM: Hydroxyls are the second strongest oxidant in the world behind atomic fluorine. They are one million times more reactive than ozone, which means they break down a much broader range of odors and pathogens compared to ozone. We have yet to find an odor that Odorox cannot break apart. However, the most difficult project is typically pet urine. This is not because the ammonia is hard to break apart - it’s easy. It’s because the pets were probably there for years and the urine has soaked deep into the flooring which makes it difficult for contractors to fully remove the source. It’s important to remember that disaster-related projects are different and there are always variables to consider when assessing a project. Proper training always helps.

3. What do you say to potential clients concerned about safety of hydroxyl/ozone?

DH:  People (and rightly so) are leery of things they don’t understand. There are a few misconceptions out there regarding ozone and its safety.

Nobody has ever died from ozone exposure; however, thousands of people die every year from carbon monoxide poisoning. Carbon monoxide (CO) is toxic; yet we think nothing of standing around our car while it idles, walking down a busy street downtown during rush hour, etc. By simply educating our clients on the safety of ozone, their concerns dissipate.

RM: Ozone is only to be used in unoccupied areas with return to the area at least one hour after the machine has turned off. Ozone can bleach wet materials and damage natural rubber. If a homeowner cannot leave or a store cannot shut down, hydroxyl generators are the way to go.

TM: That is definitely understandable, and part of the reason why Odorox has invested significant time and expenses in safety testing. Examples of tests performed by independent parties include measuring the amount of hydroxyls produced (approx. 2,000,000 per cubic centimeter), a 13-week toxicity study performed on rats under strict FDA GLP guidelines (no adverse effects), the amount of ozone produced so contractors comply with OSHA standards, and testing performed by the FDA which now classifies Odorox as a Class II medical device for use in occupied areas.

What are some major differences you see between these two technologies?

DH: I have to chuckle whenever I think of when a friend of mine who was asked this very question (my friend is one of the world’s leaders in forensic restoration application and education). He said: “The difference, is that ozone works!” To be fair, hydroxyl machines do have their time and place… as people can work in the same room as an operating hydroxyl machine, whereas it’s recommended that the room/building be evacuated while ozone is in use. Despite this minor convenience, hydroxyl takes much longer to work, and isn’t nearly as effective. There’s nearly always an opportunity to run an ozone generator for a few hours, which will often produce considerably better results than what would take a hydroxyl machine days to accomplish.

RM: Both ozone and hydroxyl will remove odors – hydroxyl will just take longer.

TM: Hydroxyls are one million times more reactive than ozone. This means contractors can have the confidence of going to any project knowing that the Odorox will eliminate the odors regardless of what or where they may be - skunk, protein fires, VOCs, biohazard/trauma, fuel oils, curry, etc.  Second, they are safe for both people and sensitive materials. It allows odors to be eliminated from all contents without the risk of damaging them - rubber, plastic, electronics, artwork, wet items, etc.  Finally, hydroxyls don’t leave behind the residual chemical smell that is common with ozone. An advantage to ozone is that you can produce a very high concentration of ozone as compared to the amount of hydroxyls that can be produced. This means that even though hydroxyls are significantly more reactive than ozone, ozone may eliminate odors faster on certain projects because of the high concentration. For example, in a small area, if ozone takes 24 hours to eliminate the odors, hydroxyls would probably take 36.

Give one raving odor removal story where your technology was used.

DH: My company did a promotion a while back where we offered to treat one home for each local real estate company at no charge, just to show how effective it is. We called it our “Give us your stinkiest home” special. One of the responders to this promotion was a friendly agent who called in desperation, telling me they had a beautiful home that was priced right but absolutely would not sell. The home was previously owned by an older couple who had smoked cigarettes indoors for 20+ years. They cleaned the carpets, scrubbed the walls, and yet the cigarette smoke odor was still so strong it burned my throat within 30 seconds of entering the home. After a single treatment, the home was 100 percent odor free and sold a few weeks afterward.

TM: We have so many great large loss stories, it is tough to pick just one. One that pops out in my mind was a large condo in Manhattan affected by smoke from a fire outside. More than $1 billion dollars in artwork inside the condo was damaged by the smoke. A contractor brought in some hydroxyl machines, and simply running them in the condo restored all the artwork. It was 100 percent effective, and absolutely no risk of damaging the art.


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