Hydroxyl Generators: The Definitive Guide


Hydroxyl generators are among one of the most popular odor removal tools used by disaster restoration contractors.

Contractors have long relied on other equipment, like ozone generators, but safety concerns and potential damage to contents have prompted many contractors to look for other, safer odor removal solutions.

Since first introduced to the restoration industry in 2008, hydroxyl generators have since been effectively used in thousands of small and large property losses to remove a wide range of odors. Some of these odors include those caused by fire damage, smoke odors, water damage and mold situations, crime and trauma scenes, pet odors, and many other scenarios where odor removal is a critical part of the restoration and remediation process.

They are also widely used by property managers, hotels, and similar entities to remove cigarette smoke, ethnic cooking, and other odors left behind by occupants.

 What is a Hydroxyl Generator?

Professional-grade hydroxyl generators use the same broad range of UV radiation as the sun to naturally clean and deodorize indoor environments.

The primary method for producing hydroxyl radicals is by replicating nature’s process and using multiple wavelengths of high-energy UV lights to react with oxygen and water vapor in the air.

This generation process, for which HGI Industries owns the patents, creates approximately two million hydroxyls per cubic centimeter.

There are several types of hydroxyl generators on the market today for restoration contractors, and they each work a little differently.

Contractors are encouraged to be diligent to understand the various types of generators on the market, and to evaluate their efficacy before making a purchase.

Learn more about the different options available below.

Popular Hydroxyl Generator Brands

What does a Hydroxyl Generator Do?

As mentioned in the introduction, hydroxyl generators are used to eliminate odors and break down volatile organic compounds (VOCs) in indoor environments.

Hydroxyl radicals (-OH) are created naturally in the earth's atmosphere when the sun’s ultraviolet rays cause a series of reactions to break apart water vapor (H2O).

Hydroxyl radicals rapidly decompose chemicals in the air and play a crucial role in keeping the earth’s atmosphere clear of harmful organic and inorganic compounds.

Hydroxyl radicals, in essence, dismantle the molecular structure of odors and VOCs, and react so quickly that few ever make it into indoor environments.

The half-life of a hydroxyl radical is less than one second; however, they being a chain reaction where other radicals are formed, and even more hydroxyls, to continue the cleaning process. Atmospheric scientists will confirm that hydroxyl radicals are the most important reactive species for keeping our air clean.

These hydroxyl radicals are known as the second most powerful oxidant in the world, only behind fluorine.

Hydroxyls will react with as many as 5,000 different chemicals and compounds, to eliminate a very wide range of odors and VOCs.


Hydroxyl Radical Molecule Diagram

How does a Hydroxyl Generator work?

Hydroxyl generators produce hydroxyl radicals that break apart odor molecules. It is a relatively simple process compared to other popular odor removal methods as it does not require additional intervention by masking agents, chemicals, oils, and so on. There is also no fogging, spraying or wiping. Hydroxyl generators work simply by being strategically placed throughout an odor-impacted property and turned on. While it will likely take a few days for full results, most people notice the malodor being knocked down within the first few hours.

The best way to ensure an odor removal job is complete is by inspecting and smelling porous items throughout the space – where odors would be embedded and take the longest to be remediated.

How does a Hydroxyl Generator work?

Common Myths about Hydroxyl Generators

There are a number of common myths and misconceptions about hydroxyl generators, their efficacy, their safety, and their functionality. Thanks to science, these myths are pretty easily overcome. Here are five common myths:


Myth #1: There isn’t any real-world, proven research contractors can use to prove to a homeowner and/or adjuster that hydroxyl generators work and are safe.

Wrong! Testing has been performed over the years by reputable third-party companies such as Underwriters Laboratory (UL), Lovelace Respiratory Research Institute, the FDA, Comparative Biosciences, and Wonder Makers Environmental. This research shows how many hydroxyl radicals are produced, and how much ozone is produced, proving the machines’ safety. Plus, one major hydroxyl generator brand has had its technology approved by the FDA as a Class II medical device for use in occupied areas. In addition, a 13-week toxicity study on rats following FDA GLP guidelines showed no adverse effects. Wonder Makers Environmental, a firm that operates heavily as consultants for remediation contractors across the U.S., also conducted their own testing that showed a dramatic reduction in VOCs in addition to odor elimination while running a hydroxyl generator in a space affected by fire.


Myth #2: Hydroxyl generators require 60% humidity to be effective.

This is also incorrect. While humidity does play a part in the chemical reactions that create hydroxyl radicals, the patented hydroxyl generators are effective in spaces with as little as 5 percent humidity. It is not necessary to add moisture to a space for odor removal; after all, restorers are likely trying to remove moisture from the space while concurrently doing odor removal, so adding humidity would be truly counterproductive.


Myth #3: Strong fans are necessary to blow hydroxyl radicals into further away spaces quickly since their half-life is a fraction of a second.

False. Patented hydroxyl technology creates a continuous stream of new hydroxyl radicals inside and outside of the machine; this chain reaction is also called the cascade effect. Thanks to a multitude of chemical reactions, new hydroxyl radicals are created throughout the restoration space and eliminate odors in the structure and its contents.

It should be noted that additional air movers can be helpful in distributing hydroxyls into hard-to-reach areas, and there are various strategies for essentially aiming the hydroxyls into areas that need some extra treatment. Contractors should note that one air mover is already included in the Xactimate line item for hydroxyl generators that use three UV optics as they require a separate centrifugal air mover to function properly. (CLNDODHY>)


Myth #4: The lifespan of UV optics is brief.

The best practice is to replace the UV optics after 4,000 hours of usage. Yes, it’s true, they could stay lit for 8,000 hours or more, but it’s important to realize UV lights gradually lose power over time. Therefore, the longer the optics go without being replaced, the weaker they become – and the longer it takes to effectively remove odors from a space.


Myth #5: One machine will cover the same exact square footage in every job.

Every job is different. Every odor is different. While there certainly is a general rule of thumb that one machine will cover over 1,000 to 1,500 square feet, you also need to take into account ceiling height, type and severity of the odor, and so on. For example, you wouldn’t treat a minor kitchen fire with the same intensity as a major fire within a large warehouse or commercial building. Learning and understanding hydroxyl technology and how to most effectively use the machines will result in the most success from project to project.

Pros & Cons About Hydroxyl Generators

The Pros

Hydroxyls are the strongest commercially available oxidant in the world, and will eliminate more types of odors and VOCs than any other option. Unlike ozone, atmospheric hydroxyls are safe for people, animals, plants and all sensitive materials like rubber, plastic, leather, vinyl, electronics, paper and artwork.

Contents can be wet while being deodorized without the risk of bleaching.

The manufacturer's operating instructions should be followed and machines should be properly spaced to avoid high concentrations of oxidants during occupancy.

When used properly they can be run during the entire restoration process, while workers and other occupants are in the space.

Adjusters tend to like the hydroxyl route over ozone because it can eliminate or minimize business interruption claims.

The Cons

It’s true, ozone will generally get rid of odors more quickly than hydroxyls because of the high concentration of ozone that is produced. However, that also means the space has to be vacant – generally both of people and contents.

So, in the end, this process could end up taking longer because the restoration and remediation process has to come to a screeching halt any time the machines are turned on, and the space must then be aired out once the ozone generators are turned off.

Popular Hydroxyl Generator Brands

Popular Hydroxyl Generator BrandsInternational Ozone

Newaire (Consumer Use Only)

Odorox Hydroxyl Group

Renting Vs. Buying a Hydroxyl Generator

In disaster restoration, there are definitely two sides to this coin.

For 90 percent of the odor removal jobs the average restoration contractor handles, it will be most cost-effective over time to own and stock hydroxyl generators in your facility.

On the flip side, in the event of a large loss or catastrophe event, it might be most cost effective for the contractor to rent the machines and have the cost reimbursed through the property owner’s insurance.

For example, many companies that helped victims of the California wildfires chose to rent hydroxyl generators due to the sheer volume they needed for all the necessary jobs.

It is key, when choosing to rent, especially during a CAT event, to be well-connected with your supplier or sales rep and get your order in early as equipment shortages may occur and leave contractors in a bind.

How to Use and Clean a Hydroxyl Generator

Hydroxyl generators are truly simple to use – as simple as plug them in and let them run, in many cases.

Granted, it is important for technicians or project managers to understand how many generators will be needed for the spaces in which they are working, and how to strategically place them.

One key element to using hydroxyl generators is keeping them clean and well-maintained, just like any other piece of restoration equipment.

Here are seven important maintenance steps, in addition to remembering to replace the optics every 4,000 hours or so as mentioned above.


  1. Turn off the power supply and unplug the cord. Unlock both side cover plates with the provided key.
  2. Remove the side panel and louvered grill plates from each side of the machine. In some models there is an additional panel on the outtake side which is secured with one screw – it should be removed as well.
  3. Remove the UV optics inside the machines. With a firm grip on the upper ceramic end piece of the optic, use your other hand to grip the ceramic wiring harness connector. Now ‘wiggle’ and gently pull the ceramic harness connector end from the ceramic optic end. Once the UV optics are unplugged from the wiring harnesses, use both hands to remove the optics from each optic chamber retention.
  4. Clean the UV optics and wipe down each optic chamber using a solution of 1-part isopropyl alcohol and 10-parts filtered/distilled water. Use a clean, lint-free cloth and latex gloves to avoid fingerprints and smudges. Fingerprints and smudges will diminish the performance of the optics.
  5. Using the same water/alcohol solution and cloths, wipe down the inside chamber of the machine, as well as the outside of the machine to remove any dirt or other particles.
  6. Again using both hands and wearing gloves, gently clamp the optics back in the optic chamber retentions. Reassemble the connection of the ceramic wiring harness (female) to the ceramic optic end (male) with a gentle wiggle action. 
  7. Put the side panels back on the machines. For a machine that has a clear vacuum tube be sure the tube on the outtake side goes through the hole in the panel and is not pinched. Plug in the machine’s power cord and test it before deploying it on the next job. Using UV rated eye protection, ensure all of the optics are working before locking the side panels.


Parts of this article are sourced and inspired by: Oxidation and OH Radicals

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