Updated: Aug 15, 2021
ASHRAE and CDC recommendations about UV-C energy
The entire ultraviolet (UV) spectrum can kill or inactivate microorganisms, but UV-C energy (in the wavelengths from 200 to 280 nm) provides the most germicidal effect, with 265 nm being the optimum wavelength.
The majority of modern UVGI lamps create UV-C energy at a near optimum 254 nm wavelength.
UVGI inactivates microorganisms by damaging the structure of nucleic acids and proteins with the effectiveness dependent upon the UV dose and the susceptibility of the microorganism.
The safety of UV-C is well known. It does not penetrate deeply into human tissue, but it can penetrate the very outer surfaces of the eyes and skin, with the eyes being most susceptible to damage.
Therefore, shielding is needed to prevent direct exposure to the eyes. While ASHRAE Position Document on Filtration and Air Cleaning (2018) does not make a recommendation for or against the use of UV energy in air systems for minimizing the risks from infectious aerosols, Centers for Disease Control and Prevention (CDC) has approved UVGI as an adjunct to filtration for reduction of tuberculosis risk and has published a guideline on its application (CDC 2005, 2009).7 (Evidence Level A)
The majority of modern UVGI lamps create UV-C energy at a near optimum 254 nm wavelength. UVGI inactivates microorganisms by damaging the structure of nucleic acids and proteins with the effectiveness dependent upon the UV dose and the susceptibility of the microorganism. P.11
In-duct ultraviolet germicidal irradiation (UVGI) systems can be used to disinfect pathogenic particles transported by air moving through ventilation systems. The proper design of these systems is quite important for energy consumption and disinfection performance, according to a recently published Science and Technology for the Built Environment paper.
Ultraviolet germicidal irradiation, or UVGI, is the use of ultraviolet (UV) energy to kill viral, bacterial, and fungal organisms. UVGI fixtures produce UV-C energy, which has shorter wavelengths than more penetrating UV-A and UV-B rays and pose less risk to human health. Upper-room UVGI refers to a disinfection zone of UV energy that is located above people in the rooms they occupy. This kills airborne pathogens in the room where they are released. Fixtures are installed to prevent direct UV exposures to people in the room.
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 for damaging DNA and RNA.
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 soft glass or quartz tube, similar to fluorescent lamps.
Roughly 95% of the energy produced by these lamps is emitted at a near-optimal wavelength of 253.7 nm.
UV-C light-emitting diodes (LEDs) are emerging for use.
Requires special PPE to prevent damage to eyes and/or skin from overexposure.
The Illuminating Engineering Society (IES) Photobiology Committee published a FAQs on Germicidal Ultraviolet (GUV) specific to the COVID-19 pandemic.