A hydroxyl generator provides an alternative to air ozone generators because hydroxyls can oxidize contaminants,
remove odors and disinfect bacteria and viruses from indoor air without using high concentrations of ozone. Hydroxyl
generators create reactive hydroxyl molecules and super-oxide ions that effectively oxidize, or burn away, contaminants
into harmless carbon dioxide and water without harming occupants. Hydroxyls also perform a more gentle cleaning
and don't require wait times to re-enter a building that has been treated.
But how does a hydroxyl generator work and are they always safe to use around people and pets? Can a hydroxyl generator work better than an ozone generator? Are all hydroxyl generators basically the same or do some use different technology? What is the best hydroxyl generator to buy? These are the questions that consumers face when they consider buying a hydroxyl generator for the first time. This article will explain the pros and cons of various types of hydroxyl generators to consider before buying a hydroxyl generator.
Hydroxyl Generator Topics
BoiE is an EPA-registered, American company that builds high-power hydroxyl generators using the latest hydroxyl
generation technologies and high-quality, energy-efficient components that last. We design hydroxyl generators
for both home and commercial use. BoiE high output hydroxyl generators remove strong odors without damaging sensitive
materials or necessarily having to vacate a property. Our portable hydroxyl machines are powerful and durable units,
generating hydroxyls using multiple methods.
When you have serious odor problems and challenging conditions you'll want to buy a BoiE hydroxyl generator to do the job right. Simply put, BoiE manufactures serious commercial-grade hydroxyl generators for consumers who want high-performing products directly from an American manufacturer at the best price point. Plus, BoiE stands behind every machine we build with a money-back guarantee and lifetime customer support. BoiE hydroxyl generators will never become obsolete and with minimal maintenance, can last a lifetime.
The hydroxyl radical (ĽOH), is a single oxygen and a single hydrogen atom. The word "radical"
means that it is neutral with no net charge. A hydroxyl radical has an unpaired electron and searches for other
electrons. A hydroxyl radical abstracts (takes away) an atom from pollutants, which is how hydroxyls break down
contamination one molecule at a time.
In the atmosphere, hydroxyl radicals are formed by the reaction of ultraviolet (UV) light from the sun disassembling water vapor (H2O) into hydroxyl radicals (ĽOH). Atmospheric hydroxyl radicals react with and neutralize concentrated pollutants in outdoor air. The atmospheric cleaning effects of hydroxyls are massive, breaking down the smoke from forest fires and many other atmospheric pollutants.
However, with an average life of less than a second, naturally-formed hydroxyls are limited to the outdoors and have little to no effect on indoor air. Most naturally-produced hydroxyls never pass through an exterior doorway. Hydroxyls are not harmful to people, pets or plants, as we are directly exposed to hydroxyl radicals every time we are outdoors.
A hydroxyl generator duplicates the natural process to create hydroxyl radicals and super-oxide ions. The hydroxyl
generator circulates indoor air through a chamber where hydroxyl radicals are continuously formed. As a hydroxyl
generator runs, the air in the room moves through its chamber where pollutants are gradually broken down (oxidized)
into carbon dioxide and water. By continuously running the hydroxyl generator, the overall level of air contamination
In addition to creating hydroxyl radicals, a hydroxyl generator produces peroxides and superoxides. All of these are called reactive oxygen species (ROS) because they contain oxygen and break down airborne contamination, safely eliminating airborne fungal spores, viruses (including corona-type viruses¹), bacteria and dangerous biological agents in milliseconds. In fact, following the Amerithrax attacks in 2001, the federal government invested billions on biodefenses.² One countermeasure developed was a system that generated ROS to safely neutralize weaponized anthrax.³
Hydroxyl generators are widely used by water and fire damage restoration companies along with mold remediation professionals because the hydroxyl radicals generated are non-toxic to humans. Also, hydroxyl generators work exceptionally well in hot, humid environments without causing damage to sensitive materials or requiring wait time to reoccupy a treated area.
Hydroxyl generators are used in the restoration industry in environments where concentrated ozone is undesirable
either because it could damage materials or because workers or occupants are present. Hydroxyl generators are often
used after floods or fires have been extinguished and the building is full of smoke odor because hydroxyl generators
easily break down smoke odor.
Hydroxyl generators can be left running at the job site in the days before work begins on a restoration project to help purify the air and prevent mold from spreading . Hydroxyl radicals react with over 5,000 compounds and will break apart odors from fire and smoke, floods, chemical fumes, fuel oil, VOCs and trauma without damaging sensitive contents.
There are two basic methods to generate hydroxyls for indoor air purification: Photocatalytic Oxidation (PCO)
or an Advanced Oxidation Process (AOP). PCO uses an Ultraviolet (UV) light-activated catalyst to generate hydroxyls
that oxidize contaminants in the airflow. The catalyst surface creates hydroxyls by abstracting hydrogen atoms
from passing molecules in the air. The chief advantage of PCO is that the process is the safest method to produce
hydroxyls without generating unsafe byproducts. Photocatalytic Oxidation is FDA-approved for use in Class II medical
devices. Examples of Class II medical devices include air purifiers, powered wheelchairs and infusion pumps.
PCO technology, originally developed in 1994 by NASA to purify air onboard a spacecraft,4 is the only hydroxyl generation method that is always safe to use around people. UV-C germicidal light shines on a nano-catalyst where massive numbers of hydroxyls form. Contaminants that come in contact with the light-activated catalyst are instantly oxidized. The germicidal wavelength has the added effect of sterilizing airborne germs, viruses and bacteria that pass close to the light source. PCO is the only method of hydroxyl generation that can be left running unmonitored in occupied spaces without requiring fresh air ventilation.
An AOP refers to any process that generates hydroxyls from chemical reactions without requiring a catalyst. Also called direct hydroxyl production, an AOP may combine ozone or hydrogen peroxide to directly generate hydroxyls and super-oxide ions that oxidize contaminants in air or water. An AOP generates more hydroxyls because the reaction area is not limited to a catalyst surface. The disadvantage is that byproducts including ozone and hydrogen peroxide off-gassing may reach unsafe levels for workers, so monitoring is needed for occupied areas.*
BoiE manufactures PCO and combination PCO/AOP hydroxyl generators. The BoiE Hydra Bliss,
Waterfall, Cloud-9, Induct
, Pro-2, and Pro-3 are pure PCO hydroxyl generators.
These PCO models use UV light that cannot produce ozone, making them safe to use in all occupied environments.
The BoiE Hydra Pro 4 and Pro XL are PCO hydroxyl generators with optional AOP technology. The units can operate solely in PCO mode for safe operation in occupied spaces, or in AOP mode when more cleaning is needed. The AOP technology breaks down low-concentration UV ozone or hydrogen peroxide vapor (HPV) to increase hydroxyl production. Contaminants are oxidized both in the air stream and on the catalyst surface, which increases the overall coverage area.
The BoiE Hydra Stedi-Mist Pro operates solely in AOP mode for use in unoccupied spaces or with appropriate PPE. The Stedi-Mist Pro uses BoiE's Hydroxyl Carrier System (HCS) that produces a continuously-generated fine mist of ozonated water, with or without a hydrogen peroxide accelerant present, distributed by a fan that fills a space with a vaporous cloud of recurring hydroxyl reactions that oxidize contaminants in the air and on surfaces that come in contact with the cloud.
AOP mode requires an unoccupied area or close monitoring and worker protection to ensure that ozone or hydrogen peroxide do not build up to unsafe levels* during the treatment cycle before they naturally revert to harmless oxygen and water, respectively. Both PCO and AOP hydroxyl generation technologies are much safer than air ozone generators and provide a gentle cleaning. AOP hydroxyl generators are highly-effective after a flood or a fire.
A hydroxyl generator that moves air, can kill airborne mold spores and removes mold odors, but has a limited
effect on surface mold. This is because hydroxyl generators that move air do not penetrate materials or kill mold
that has already become established on surfaces due to hydroxyls not lasting long enough. It is important to understand
that a hydroxyl generator is not a magic bullet. A hydroxyl generator that is safe to use in occupied areas acts
primarily on the air inside the machine and the air nearby. The further away the contamination, the less chance
that hydroxyls can reach it.
While there are anecdotal stories of hydroxyl generators decontaminating distant surfaces through cascading reactions of contaminants, there is no third-party study proving that hydroxyl generators safe to use in an occupied area, can kill mold on surfaces or disinfect porous materials across a room while maintaining EPA-safe air quality for occupants. For a typical building environment most reactions that involve hydroxyls disinfecting mold will occur either within or very close to the hydroxyl generator.
The exception is the BoiE Hydra Stedi-Mist Pro that can kill mold on surfaces by using a fogging system that carries reactants that form hydroxyls all the way to surfaces, however, the EPA requires fogging units to operate in unoccupied areas and for workers present to wear appropriate personal protective equipment (PPE).
A Photocatalytic Oxidation (PCO) hydroxyl generator is most beneficial when the hydroxyl machine can be run
for long periods of time with occupants or workers present. A PCO hydroxyl generator is recommended for 24x7 home
use or commercial use. A PCO hydroxyl generator can be left behind after a project is complete to eliminate contaminants
that later become airborne. PCO hydroxyl generation will not harm the young, the old or those with allergies, asthma
or compromised immune systems.
PCO was originally developed by NASA with a specific intent not to harm occupants in a closed environment onboard a space station. PCO uses a UV-C germicidal light wavelength that activates a permanent catalyst to form hydroxyls. The UV-C wavelength has the added effect of sterilizing airborne germs, viruses and bacteria that pass close to the light source, but requires the optics to be shielded from view.
PCO technology is enhanced by water vapor in the air that helps fuel reactions, so humidity is beneficial for good results. When conditions are very dry, a PCO hydroxyl generator will still function, but less effectively. In dry conditions, humidity can be added to the air near the hydroxyl generator to increase the moisture level of the air that is drawn into the machine. BoiE manufactures an Ultrasonic Hydroxyl Accelerator for this purpose. All BoiE hydroxyl generators have a PCO mode option for occupied areas where a humidifying system is useful.
An Advanced Oxidation Process (AOP) hydroxyl generator is most beneficial when the hydroxyl machine can be run
for long periods of time without occupants or unprotected workers present. An AOP hydroxyl generator is recommended
for commercial work including fire and water damage restoration projects or mold remediation work areas because
AOP is a more powerful method. An AOP hydroxyl generator uses ozone-producing UV-C light, hydrogen peroxide vapor
(HPV) and other combinations to generate hydroxyls. Contaminants are oxidized in the air around the reactants,
which increases the coverage area.
AOP technology can also be enhanced by adding water vapor (H2O) or hydrogen peroxide vapor (H2O2) to fuel reactions, but less humidity is required compared to PCO. An AOP hydroxyl generator can also be used with a humidifying system such as BoiE's Ultrasonic Hydroxyl Accelerator to increase the moisture level of the air that is drawn into the machine, resulting in greater hydroxyl generation.
AOP mode requires an unoccupied area or close monitoring and worker protection to ensure that HPV and/or ozone off-gassing do not build up to unsafe levels* during the treatment cycle before they naturally revert to harmless water and oxygen, respectively. Despite the off-gassing hazards, an AOP hydroxyl generator provides a much more gentle cleaning process than concentrated gaseous ozone and will not harm plants or sensitive materials.
Hydroxyl generators react much faster than ozone, remove thousands more contaminants, do not damage natural
rubber and certain adhesives that concentrated ozone can, and require no wait time to reoccupy a treated area.
However, since contaminated air has to move through a chamber, hydroxyl cleaning takes a longer period of time
and has a limited effect on surface contamination.
Ozone can spread quickly throughout a room, saturate porous materials and attack surface contamination over a shorter period of time. However, concentrated ozone can damage sensitive materials such as natural rubber, nylon and adhesives. An ozone treatment also requires an unoccupied area with all living things removed and a wait time for ozone to revert back into normal oxygen before re-entering an area after a treatment.
If the question is which odor removal technology is better -- ozone or hydroxyls, the answer is neither because
both methods remove odors from the air very well. If the question is which technology is safer, then a hydroxyl
generator clearly wins. And if the question is which technology saturates and disinfects surfaces the best, then
the answer is an ozone generator. The truth is that neither technology can claim superiority over the other and
results will vary based on the type of use and the environmental conditions.
BoiE manufactures both ozone generators and hydroxyl generators and we know from our customer experiences that the product needed depends on how the customer intends to use it, and that can quickly change with each new project. A professional service company should consider investing in both ozone and hydroxyl technologies for that reason. A service business should consider buying the Hydra Pro-4 or Hydra Pro XL and the Hydra Stedi-Mist Pro because you get the advantage of having PCO and AOP with a surface disinfection option and can decide which one to use.
A small business owner should consider buying the Hydra Pro-2 or Hydra Pro-3 to get a powerful, but safe hydroxyl generator that can run continuously in an occupied problem area or the Hydra INDUCT to deal with HVAC problems. Hydroxyl generators, despite being available for over a decade, are still a relatively new technology to many, and a potential buyer should invest time in learning about the science behind the technology and its pros and cons before purchasing.
1. Foster, Howard & Ditta, Iram & Varghese, Sajnu & Steele, Alex. (2011). Photocatalytic disinfection using titanium dioxide: Spectrum and mechanism of antimicrobial activity. Table 7. Viruses shown to be killed by photocatalytic disinfection: SARS coronavirus. Applied Microbiology and Biotechnology. 90. 1847-68. 10.1007/s00253-011-3213-7.
2. Hylton, Wil S. "How Ready Are We for Bioterrorism?" New York Times, Oct. 30, 2011: A4. Print.
3. Titan Systems Corporation, Defense Advanced Research Projects Agency (DARPA). Project Name: Immune Building (ROS technology for the neutralization of anthrax spores), DARPA Contract No. MDA97203C0092 Special Projects Office (2003).
4. Graf, John C. "Using Spacecraft Trace Contaminant Control Systems To Cure Sick Building Syndrome" NASA, Washington, Technology 2003: The Fourth National Technology Transfer Conference and Exposition, Volume 1; p. p 258-265 (1994)
* The U.S. Occupational Safety and Health Administration (OSHA) Permissible Exposure Limit (PEL), averaged over an eight-hour work shift, for ozone is 0.10 ppm and 1 ppm for HPV. When used in AOP modes in confined spaces, the HYDRA Pro XL may exceed PEL and require appropriate personal protective equipment (PPE). Monitoring is required if workers are present.
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