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  • Writer's pictureMitchell Wilkie

Air & Surface Sanitation in Grow-ops & Greenhouses – Ozone Generators or UVGI?

Updated: Mar 25, 2019

With indoor growing operations (pharma medical, vertical farming, greenhouses) a major objective is to assist in the management of mold, mildew and other potentially dangerous pathogens in the air, on surfaces, tools, seedlings, flowers and plants and to reduce unpleasant odours. In addition to cannabis, there are dozens of plants that can produce offensive or undesirable odours when mass produced indoors.

Active and passive methods for air and surface sanitation with indoor growing may consist of organic pesticides, heat, hydrogen peroxide, hypochlorite, carbon and HEPA particle filters, biofilters, photocatalytic oxidation, chemical scrubbers, ultraviolet light, and ozone, among others. Two very common proactive approaches are using Commercial Grade Ozone Generators or Ultraviolet Germicidal Irradiation (UVGI). I’ll give you an overview of these two systems and a recommendation.

Viruses, Bacteria, & Mold


Ozone or trioxygen, is an inorganic molecule that forms a colourless or pale blue gas with a fresh smell odour suggestive of chlorine. Ozone Generators produce very high concentrations up to 3 grams (g) per hour of ozone by a variety of methods that include thermal to non‐thermal plasma and plasma catalyst. Ozone generators also often feature pre-filters and HEPA filters to remove particulates from the air with forced circulation.

Ozone is one of the most powerful oxidizing agents in the world, and a potent disinfectant 3,000 times more effective than chlorine bleach in broad spectrum antimicrobial activity. Ozone expended into a room atmosphere can destroy large amounts of spores, bacteria, viruses, mold, fungus, mildew, odours and other contaminants. Because ozone has a spare, unstable oxygen molecule, as soon as it touches a pathogen, the spare atom breaks off and attacks the cell walls of the pathogen, rupturing them and killing it instantly.

It is very important to correctly size ozone generation to a grow space. This can range from an ozone output of 200 to 400 milligrams (mg) per hour for a small space to upwards of 1 gram (g) of output per hour in large commercial operations. An important question is when does a facility operator run an ozone generator? Because ozone is very dangerous, people should never be present in a room when an ozone generator is operating. This impacts production.

Dangers of Ozone

Exposure to ozone can bring on headaches, burning eyes, coughing, shortness of breath, chest pains, irritation of the throat and asthma symptoms. Even very low concentrations of ozone in air are very destructive to organic materials such as latex, rubber, plastics and lung tissue. When in high enough concentrations to eliminate bad smells, it will react with your skin, eyes, lungs, and other exposed areas and cause long-term damage (i.e. lung scarring, asthma, bronchitis) and induce heat attacks and other cardiopulmonary problems. Ozone will cause similar types of long-term bodily damage as volatile chemicals like gasoline; however, it does smell better if that’s any consolation.

There are serious dangers with ozone when you're trying to kill viruses, mold and bacteria

The Canadian Centre for Occupation Safety and Health reports that: "Even very low concentrations of ozone can be harmful to the upper respiratory tract and the lungs. The severity of injury depends on both by the concentration of ozone and the duration of exposure. Severe and permanent lung injury or death could result from even a very short-term exposure to relatively low concentrations."

Recommended Limits for Ozone vary around the world. Acceptable concentrations can range from 60-120 parts per billion (ppb) or 0.06-0.12 parts per million (ppm) over a 1-hour to 8-hour period. The U.S. Occupational Safety and Health Administration established a permissible exposure limit (PEL) of 0.1 μmol/mol, calculated as an 8-hour time-weighted average. Higher concentrations are especially hazardous, and the National Institute for Occupational Safety and Health (NIOSH) established an Immediately Dangerous to Life and Health Limit (IDLH) of 5.0 μmol/mol.

From the plant perspective, it has been documented since the late 1960's that ozone damages crops. The effect of ambient ozone at ground level on fruit corps in the 1970’s was the foundation of our current emissions regulations. The industry and building codes we operate by today are designed to protect our immediate and global environment.

There is a lot of misleading information from manufacturers and distributors in Canada and the USA that is available to the public regarding ozone generators and air purifiers. This includes ambiguities in the product’s sales literature and biased opinions-of-use approval qualifications that are in fact not from authorities having jurisdiction. To assess whether ozone is harmful or good, as well as to inform the public about health effects of ozone and ozone generators, the U.S. Environmental Protection Agency (EPA) has conducted research. The EPA has declared that there is "evidence to show that at concentrations that do not exceed public health standards, ozone is not effective at removing many odor-causing chemicals" or "viruses, bacteria, mold, or other biological pollutants". Furthermore, its report states that "results of some controlled studies show that concentrations of ozone considerably higher than these [human safety] standards are possible even when a user follows the manufacturer’s operating instructions".


UVGI is a disinfection method that uses short-wavelength ultraviolet (UV-C) light to kill or inactivate microorganisms by destroying nucleic acids and disrupting their DNA, leaving them unable to perform vital cellular functions. There are four types of UV radiation that are classified according to their wavelength. They differ in their biological activity and, in terms of human safety, the degree to which they can penetrate our skin.

UV-C – has a short wavelength (200-280 nm) and is the most harmful UV radiation from the sun, but it is less able to penetrate skin. Outdoors, it is completely filtered by the atmosphere and does not reach the earth's surface. This UV-C is the UV light generated by lamps in UVGI devices and they do not produce ozone. However, I must note that some UVGI systems intended primarily for odour control (i.e. unoccupied garbage rooms) may also have separate lamps that generate visible UV-V light with the shortest wavelength (100-200 nm) that are an effective oxidizing reactor for producing ozone to deodorize. Since UV-V lamps produce dangerous ozone, they tend to be controlled by an ozone detector set to a maximum ozone output concentration level of 0.025 ppm (25 ppb). Currently, this is an acceptable weighted average exposure limit over a 24-hour period set by Environment Canada.

UV-B – is a medium-wavelength (280-315 nm) and is very biologically active but cannot penetrate beyond the superficial skin layers. It will age and burn skin and can lead to the development of skin cancer. Most solar UV-B is filtered outdoors by the atmosphere. It is not used in UVGI systems.

UV-A – is a long-wavelength (315-400 nm) and accounts for approximately 95% of the UV radiation reaching the Earth's surface. It can penetrate to the deepest layers of the skin and contributes to skin ageing and wrinkling. Recent studies strongly suggest that it may also enhance the development of skin cancers. It is not used in UVGI systems.

UVGI appliances using UV-C light essentially sterilize air that passes UV lamps via forced air to 99.9999% effective. Air purification UVGI systems in grow facilities are installed in forced air handling units so that the circulation for the premises moves micro-organisms past the UV-C lamps. Placement of the UV lamps is important along with a good filtration system to remove the dead micro-organisms. UVGI systems don't cause sticky biofilm contamination on surfaces like ozone generators. Forced air systems by design impede line-of-sight, thus creating areas of the environment that will be shaded from the UV light. However, a UV lamp placed at the coils and drain pan of a cooling system will keep micro-organisms from forming in these naturally damp places. Another very effective method for treating the air in addition to placement at the coils is with in-line duct systems. These systems are placed in the center or, with an engineered aluminum reflector, to one side of the duct and parallel to the air flow, rather than perpendicular to air flow. This increases the time (exposure) and intensity (strength of UV source) for a greater kill rate of the contaminant. When UVGI units are placed at the side of the duct and parallel with the air flow, the entire duct surfaces light up and reflect the light in the duct. The controls for the UV lamp mount and are accessible on the other side of the duct. A UVGI system can be monitored and controlled together with the grow room control systems and considerations of occupancy and HVAC system operation.

There are many types of UV lamps that include: hot-cathode, cold-cathode, regular intensity, high intensity, amalgam, soft glass, and quartz glass among others. Although there are different types of UV lamps, one thing is certain, all UV energy can benefit from a few helpful features which can dramatically increase the effectiveness of the UV light produced such as an excellent quality and well-shaped lamp, a long dwell time for the kill rate and superb reflection to get the light where its needed and protect the lamp from air flow buffeting. Clean lamps are important to maintain proper light transmittance and there are self-cleaning UVGI systems available, so it doesn’t need to be added work.


It should be obvious that ozone generators have a serious health concern if not used properly. While safe measures can be taken, you certainly can’t have people present when they are operating and for a period of time afterward. This could be detrimental to facility productivity as their operation needs to be scheduled for specific times and they won’t be on 24/7. They also result in bio-film residue clinging on surfaces, which is often fouling to lighting, work tables and other equipment or machinery.

I recommend UVGI systems installed in parallel within air handling units, which are very effective and safe. Workers are never exposed to UV light, it doesn’t leave bio-film residue within a room and the system can operate 24/7 to always mitigate any contamination risks that are forever present when people, plants or equipment enter and leave a grow room. Do not use UVGI systems that also have UV-V lamps in indoor-grow operations. Our company, TRAK International Green Energy Resources always specifies Sanuvox UVGI products in our HVAC/R designs and we have had excellent results with our clients.

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