Purge Virus monitors emerging technologies and offers many devices beyond ultraviolet, within the categories highlighted below. The key to successful disinfection is to align the right technology to your facility based on proven results and cost effective returns on investment. We have provided this content to also help business owners and managers better understand the terminology used across the growing landscape of disinfection options.

Ultraviolet Energy (UV-C)

  • Ultraviolet energy inactivates viral, bacterial, and fungal organisms so they are unable to replicate and potentially cause disease.
  • The entire UV spectrum is capable of inactivating microorganisms, but UV-C energy (wavelengths of 100 – 280 nm) provides the most germicidal effect, with 265 nm being the optimum wavelength.
  • The majority of modern UVGI lamps create UV-C energy with an electrical discharge through a low-pressure gas (including mercury vapor) enclosed in a quartz tube, similar to fluorescent lamps.
  • Roughly 95% of the energy produced by these lamps is radiated at a near-optimal wavelength of 253.7 nm.
  • UV-C light-emitting diodes (LEDs) are emerging for use.
  • Types of disinfection systems using UV-C energy:
  • Requires special PPE to prevent damage to eyes and/or skin from overexposure.


  • Have been common in the UV-A spectrum (315 – 400 nm)
  • LEDs are starting to be produced in the 265 nm range
  • Efficiency is dramatically less than current low-pressure mercury vapor lamps
  • Minimal UV output compared to a low-pressure mercury vapor lamp
  • For equal output, UV-C LEDs are more expensive than current low-pressure mercury vapor lamps
  • Limited availability; not yet practical for commercial HVAC applications

UV-C In-Duct Air Disinfection

  • Banks of UV-Lamps installed inside HVAC systems or associated ductwork.
  • Requires high UV doses to inactivate microorganisms on-the-fly as they pass through the irradiated zone due to limited exposure time.
    • Systems typically designed for 500 fpm moving airstream.
    • Minimum irradiance zone of two feet
    • Minimum UV exposure time of 0.25 second.
  • Should always be coupled with mechanical filtration.
    • MERV 8 filter for dust control
    • Highest practical MERV filter recommended
    • Enhanced overall air cleaning with increased filter efficiency

UV-C Upper-Air Disinfection

  • UV fixtures mounted in occupied spaces at heights of 7 feet and above.
  • Consider when:
    • No mechanical ventilation
    • Limited mechanical ventilation
    • Congregate settings and other high-risk areas
    • Economics/other
  • Requires low UV-reflectivity of walls and ceilings
  • Ventilation should maximize air mixing
  • Use supplemental fans where ventilation is insufficient

UV-C In-Duct Surface Disinfection

  • Banks of UV-Lamps installed inside HVAC systems, generally focused on:
    • Cooling coils
    • Drain pans
    • Other wetted surfaces
  • UV irradiance can be lower than in-duct air disinfection systems due to long exposure times.
  • Goals are:
    • Even distribution of UV energy across the coil face
    • Generally, 12 to 36 inches from the coil face
    • Operated 24/7

UV-C Portable Room Decontamination

  • For surface decontamination
  • Portable, fully automated units; may use UV-C lamps or Pulsed Xenon technology
  • Settings for specific pathogens such as MRSA, C. difficile, both of which are harder to inactivate than coronaviruses.
    • >99.9% reduction of vegetative bacteria within 15 minutes
    • 99.8% for C.difficile spores within 50 minutes

Photocatalytic Oxidation (PCO)

  • Consists of a pure or doped metal oxide semiconductor material
    • Most Common Photocatalyst is Ti02 (titanium dioxide)
  • Activated by a UV light source
    • UV-A (400-315nm)
    • UV-C (280-200nm
    • UV-V (under 200nm) Ozone can be formed at UV-V wavelengths
  • Light mediated, redox reaction of gases and biological particles absorbed on the surface
  • Some units claim disinfection from gaseous hydrogen peroxide.
  • Possible by-products formed by incomplete oxidizing.
  • Some air cleaners using PCO remove harmful contaminants to levels below limits for reducing health risks set by recognized cognizant authorities.
  • Some are ineffective in reducing concentrations significantly; manufacturer data should be considered carefully.

Bipolar Ionization/Corona Discharge

  • High voltage electrodes create reactive ions in air that react with airborne contaminants, including viruses.
  • The design of the corona discharge system can be modified to create mixtures of reactive oxygen species (ROS), ozone, hydroxyl radicals and super­oxide anions.
  • Systems are reported to range from ineffective to very effective in reducing airborne particulates and acute health symptoms.
  • Convincing scientifically-rigorous, peer-reviewed studies do not currently exist on this emerging technology; manufacturer data should be carefully considered.
  • Systems may emit ozone, some at high levels. Manufacturers are likely to have ozone generation test data.


  • Ozone (O3) is a reactive gas that can disinfect air and surfaces by killing viruses, bacteria, and fungi.
  • Ozone is harmful for health and exposure to ozone creates risk for a variety of symptoms and diseases associated with the respiratory tract.
  • ASHRAE’s Environmental Health Committee issued an emerging issue brief suggesting “safe ozone levels would be lower than 10 ppb” and that “the introduction of ozone to indoor spaces should be reduced to as low as reasonably achievable (ALARA) levels.”
  • Should only be considered for disinfection on unoccupied spaces; it should never be used in occupied spaces.
    • Available scientific evidence shows that, at concentrations that do not exceed public health standards, ozone is generally ineffective in controlling indoor air pollution.
    • Reputable cleaning and restoration companies should be used for effective, safe disinfection of unoccupied spaces.

Chemical Disinfectants

  • EPA reviews and registers antimicrobial pesticides, which include disinfectants for use on pathogens like SARS-CoV-2
  • Carefully read product labels and use as directed.
  • Most products have a required contact or dwell time, which is the amount of time a surface must remain wet to kill a certain pathogen.
  • Applying a product in a way that does not align with its intended use may render the product less effective.
  • Products on EPA List N have not been tested specifically against SARS-CoV-2, however the EPA expects them to kill the virus because they:
    • Demonstrate effectiveness against a harder-to-kill virus; or
    • Demonstrate efficacy against another type of human coronavirus similar to SARS-CoV-2.
  • All surface disinfectants on List N can be used to kill viruses on surfaces such as counters and doorknobs.
  • Because SARS-CoV-2 is a new virus, this pathogen is not yet readily available for use in commercial laboratory testing of disinfectant product effectiveness at killing that specific virus.

Vaporized Hydrogen Peroxide (VHP)

  • Liquid hydrogen peroxide (H2O2) is vaporized and the vapor fills the space to disinfect all exposed surfaces.
  • Space MUST be unoccupied during VHP treatment.
  • Requires spaces to be sealed, including all doorways, plumbing/electrical penetrations and HVAC supply and return vents, to prevent vapor from escaping.
  • After prescribed exposure times, remaining H2O2 vapor is scrubbed from space and converted ack to oxygen and water before space can be safely reoccupied.
  • The effectiveness and safety of VHP when generated inside active HVAC ducts and occupied spaces.
  • VHP is hazardous at high concentrations, and lengthy exposure is often necessary to inactivate bacteria and viruses in sealed spaces.

Pulsed Xenon (Pulsed UV)

  • High-powered UV lamps (generally containing xenon gas) used in rapid pulses of intense energy.
  • Emits a broad brand of visible and ultraviolet wavelengths, with a significant fraction in the UV-C band.
    • Uses significantly higher power outputs that usual UV-C techniques.
    • Inactivates viruses, bacteria and fungi using the same mechanisms as standard UV-C systems.
  • Typically used for healthcare surface disinfection, but can be used in HVAC systems for air and surface disinfection.

405 nm Visible Light

  • Sometimes referred to a “Near UV,” although not in the UV spectrum.
  • Generally integrated into standard room lighting systems.
  • Kills bacteria and fungi via different mechanism than UV-C.
    • Targets and excites naturally-occurring porphyrin molecules inside organisms, creating reactive oxygen species.
    • Reactive oxygen species kill by a mechanism similar to bleach.
  • Effectiveness at killing viruses, including SARS-CoV-2, is not as well documented.
  • Provides continuous disinfection of air and exposed surfaces in occupied spaces.
  • In the FAQs on Germicidal Ultraviolet (GUV), the Illuminating Engineering Society (IES) Photobiology Committee notes that effectiveness is approximately 1000 times less than UV-C and the effective doses are not practical in an occupied environment.

Far Ultraviolet

  • Far UV spectrum is 205 to 230 nm.
  • Some deactivation of bacteria and viruses at the 207 nm and 222 nm range.
  • 222 nm said to effectively penetrate microorganisms 1µm in size and smaller.
  • Unable to fully penetrate larger microorganisms.
  • UV Dose required to inactivate microorganisms is significantly higher at these wavelengths than in the UV-C range.
  • While safety concerns are reduced, can still cause damage to eyes and skin.

Special Precautions

  • Exposure to UV-C energy can cause eye and skin damage.
    • Photokeratitis (inflammation of the cornea)
    • Keratoconjunctivitis (inflammation of the ocular lining of the eye)
  • Symptoms may not be evident until several hours after exposure and may include an abrupt sensation of sand in the eyes, tearing, and eye pain, possibly severe.
    • Symptoms usually appear 6 to 12 hours after UV exposure.
    • Symptoms are fully reversible and resolve within 24 to 48 hours.
  • Maintenance workers should receive special training before working on UV-C systems.
  • If exposures are likely to exceed safe levels, special personal protective equipment (PPE) is required for exposed eyes and skin.
    • Eyewear that blocks UV-C energy
    • Clothing, suits, or gowns known to be nontransparent to UV-C


  • It is likely, but not yet shown, that COVID19 could be spread through the air.
  • Air cleaning can help mitigate disease transmission.
    • Options for air cleaning include:
    • HVAC systems
    • In-Room devices
  • Technologies that can be effective include:
    • Mechanical Air Filters
    • Electronic Air Filters/Air Cleaners
    • UV-C Systems
    • Other Emerging Technologies
  • Care and professional judgement should be taken to understand choices for filtration and air disinfection, pros and cons of each and impact(s) on existing buildings systems.

Source ASHRAE American Society of Heating, Refrigerating and Air-Conditioning Engineers

For more information, see the ASHRAE Position Document on Filtration and Air Cleaning.