The right type of ultraviolet technology is key for your facility.
Ultraviolet light, specifically UVC has proven capabilities to irradiate pathogens such as viruses.
The Science Precedes COVID-19
(Read before purchasing any equipment)
1. Scientific Highlights: The Sun generates Ultraviolet (UV) light across the wavelength range in nanometers from 100-400 nm. UV is divided into three bands: UVA (315-400 nm), UVB (280-315 nm), and UVC (100-280 nm). The ozone layer in the stratosphere absorbs UVC. Life on Earth has evolved without exposure to UVC, which makes a broad range of life forms vulnerable if exposed to it. The UVC photons are energetic enough to damage the DNA and RNA of microorganisms, destroying their ability to replicate. Different microorganisms respond differently to UVC. Viruses are very susceptible to it, bacteria are less susceptible, and fungal spores are the least susceptible. This means that applying the right dose of UVC is the key to killing the pathogens.
2. Technology Highlights: Unless otherwise noted, the lamps used in the devices described on this website are similar to typical fluorescent tubes in offices around the world, but they do not have the phosphorescent coating which delivers the soft white light. Many commercial UVC lamps are low pressure mercury lamps that emit UV energy at 253.7 nm, which is an ideal wavelength for disrupting the DNA of microorganisms such as viruses. The wavelength of the devices described online here are 253.7 nm. The Center for Disease Control and Prevention (CDC) and The National Institute for Occupational Safety and Health NIOSH have recommended permissible exposure limits for different UV wavelengths. For UVC, at 253.7 nm wavelength, the recommended exposure limit (REL) is 6,000 joules per centimeter squared (6 mJ/cm2) for a daily 8 hour work shift. UVC devices are being used at increasing levels all over the world in various form factors and applications to disinfect water, air and surfaces.
3. Safety and Disinfection Dosage: For In Room wall mounted devices: When people enter the room, they see a blue glow coming from the wall mounted UVC device. Time, intensity, and distance = dose. At the device intensity, an occupant would have to stand on a chair and stare straight into the light for a while to achieve the harmful levels of dose. At 10 ft away from this device, the intensity factor is .115. The intensity at 1 meter is 120 uW/cm2 (Micro-Watts per square centimeter) and at 10 feet away the intensity is 13.8 uW/cm2. This is key, because effective germicidal impact is over 10 uW/cm2. (chart below). In joules per second, this equates to 0.0138. The wall mounted devices have been engineered and installed over many years at many facilities to provide the key combination of both safety and disinfection. See: Reducing Infectious disease transmission with ultraviolet germicidal irradiation (UVGI) – ASHRAE Report 2020-2017
4. Pros and Cons of Direct Dosage vs Fan Based Systems: Irradiating pathogens does not happen instantly. Disrupting the DNA of microorganisms such as viruses can take up to 100 seconds, subject to germicidal UVC dosage levels. Fan based devices come in many shapes, sizes, and price points. Some of them are designed to be placed on the floor or a counter, while others are designed for ceiling installation. Regardless of the form factor and location, fan based devices typically draw air into the equipment, partially treat it, and exhaust it without fully irradiating the pathogens. The cycle then continues. With these types of devices, the air speed passing the UV or UVC luminaire is a key factor in addition to the wattage of the luminaire relative to the number of pass-by air intervals needed to fully kill the pathogens. For a 10’ x 12’ room with a 9’ ceiling (approx 1,000 cubic feet), it may take 15 minutes or more to clean the air in the room. Plus, the sides and corners of the room farthest from the fan device are treated less acutely than the air near the device. By contrast, direct dosage devices, such as the upper air wall mounted technology described on this page, can irradiate all of the air in the same size room within 5 to 7.5 minutes. This is due to the fact that code compliant HVAC systems in rooms, such as dental operatories, have 8 to 12 Air Changes per Hour (ACH). The air moves slowly around the room and across the ceiling giving the UV time to kill the pathogens rather than rushing it by the UV elements inside of a fan based device. The result is faster and more thorough air disinfection with direct dosage. There is a place for fan based devices or in-duct devices for properties such as office buildings that do not need acute disinfection. Dental operatories and other healthcare facilities warrant the most aggressive form of pathogen irradiation, as do certain quick serve restaurants and other facilities with high traffic of different people moving though the space.
5. UVC and UV: Not all ultraviolet wavelengths are created equal when it comes to irradiating pathogens. Ultraviolet-C (UV-C) is between 100 and 280 nanometers (nm). UVC has been proven to have an incredibly high capacity to kill pathogens, including viruses. UV is a broader range 100-400nm, and 405nm is just outside of UV and is used by some manufacturers. The 405nm wavelength has demonstrated capacity to reduce the mitigation of some viruses, but it is not as potent as UVC. Remember that time, intensity, and distance = dose. While the number 405 is higher than 100-280, the intensity is inverted. The devices described on this website use 253.7nm, which is the peak performance for germicidal effectiveness. (See chart below and ASHRAE Report 2020-2017). When considering a UV or UVC device, ask your potential service or technology provider about the nanometers used in the equipment. Facilities with acute needs such as dental operatories and other healthcare facilities warrant germicidal UVC light, as do certain quick serve restaurants and other facilities with high traffic of different people moving though the space.
- ASHRAE Handbook (2020). Position Document on Airborne Infectious Diseases – Reaffirmed by Technology Council February 5, 2020.
- ASHRAE Handbook (2016). HVAC Systems and Equipment, Ultraviolet Lamp Systems. Ch. 17 Section 5 Safety – Exposure Limits. Recommended exposure limit (REL) 8 hour work shift for UVC.
- ACGIH (2015). Theoretical Limit Values and Biological Exposure Indices, Cincinnati Ohio.
- Kauffman R (2011). Study the degradation of typical HVAC materials, filters and components irradiated by UVC energy. ASHRAE Research Report RP-1509.
- IESNA (2000). Lighting Handbook: Reference & Application IESNA HB-9-2000, New York.
- Harm W (1980). Biological Effects of Ultraviolet Radiation, New York. Cambridge University Press.
- NIOSH (1972). Criteria for a recommended standard: Occupational exposure to ultraviolet radiation. Publication 73-11009, Washington D.C.
RELEVANT ARTICLE for Germicidal Ultraviolet Irradiation (UVGI) for HVAC integration:
Effect of ultraviolet germicidal lights installed in office ventilation systems on workers’ health and well-being: Double-blind, multiple crossover trial.
“The use of UVGI lights was associated with significant (99%) reduction of microbial and endotoxin concentrations on irradiated cooling coils and drip pans in the HVAC system.” Source: The Center for Health Design
For more see: UVC OFFICE SOLUTIONS