UV Definitions

As the UV air, surface and water sterilization technology becomes widely popular, the need of uniform terminology becomes more and more apparent. The following UV abbreviations and definitions represent the most common UV terminology used in association with UV and germicidal UV technology systems. The germicidal UV definitions and terminology were developed by the IUVA and published in the UV Standards and Guidelines. A member of IUVA, American Air & Water intends to contribute for further development and establishment of uniformed UV terminology and definitions.

BPF: Building Protection Factor

Building Protection Factor (BPF): A rating systems that defines the effectiveness of the building in purging itself of airborne microbiological contaminants.

Design Basis Attack Scenario: A bioweapon or biocontaminant release scenario which produces 99% casualties (infections or fatalities) in a building that has 15% outside air and no filtration or other air treatment. Used as the basis for evaluating the effectiveness of air treatment systems.

Fluence Rate: The UV fluence across a surface, typically in units of µJ/cm². This is the technically correct term that describes UV irradiance on non-flat surfaces.

ID50: Infectious Dose 50% - the dose of a pathogen that produces infections in 50% of the population.

ID99: Infectious Dose 99% - the dose of a pathogen that produces infections in 99% of the population.

Kill Rate: The percent of a population removed of disinfected by an air treatment system. The complement of survival in percent.

LD50: Lethal Dose 50% - the dose of a pathogen that produces fatalities in 50% of the population.

LD99: Lethal Dose 99% - the dose of a pathogen that produces fatalities in 99% of the population.

MERV: Minimum Efficiency Reporting Value. An ASHRAE test method for rating filters.

Overload Attack Scenario: The use of a quantity of a bioweapon in excess of that need to cause 100% casualties.

Rate Constant: The rate constant k in the decay equation lnS=-kD where S=survival and D=dose. Defines the slope in a log plot of survival.

Scenario A: Gradual release of a bioweapon agent inside the air handling unit. Used as one basis for evaluating the Building Protection Factor.

Scenario B: Gradual release of a bioweapon agent in the general area or first floor of a building. Used as one basis for evaluating the Building Protection Factor.

Scenario C: Sudden release of a bioweapon agent in the outside air intakes. Used as one basis for evaluating the Building Protection Factor.

Ultraviolet: Electromagnetic radiation with wavelengths shorter than the wavelengths of visible light and longer than those of X rays; situated beyond the visible spectrum at its violet end.

URV: UVGI Rating Value. A scale for rating UVGI air treatment systems based on the UV fluence or UV dose produced.

UV: Ultraviolet. Ultraviolet light is part of the spectrum of electromagnetic energy. The UV part of the spectrum is located between the visible light and x-rays. UV has wavelength shorter than visible light and longer than the x-rays. UV wavelength is between 400nm and 1nm. Since UV is not visible, it is technically not "light", but use of the term "ultraviolet light" is so widespread that it will be used here. Most sources of light generate some UV.

UVA: Ultraviolet light in the range 315-400 nm. Has a minor disinfecting effect.

UVB: Ultraviolet light in the range 280-315 nm. Has a minor disinfecting effect.

UVC: Ultraviolet light in the range 200-280 nm. Has a major disinfecting effect.

UVGI: Ultraviolet Germicidal Irradiation.

UV Dose: The amount of UV irradiation absorbed by an exposed population of microbes, typically in units of mJ/cm² (mJ/cm² = 1,000 µW/cm² per second). Often assumed to implicitly represent total absorbed dose.

UV Fluence: The total radiant energy incident on an infinitesimal sphere. Technically, this term is more accurate than the more commonly used term “UV dose.”

UV Intensity: An indefinite term often used to describe the irradiance field of a UVGI system. Virtually synonymous with the preferred term UV irradiance. Measured in µW/cm² at 1m. The UV intensity greatly depends on the distance from the UV emitter and the transmittance of the medium.

UV Irradiance: The total radiant energy incident on some surface from all directions.  Measured in µW/cm² at 1m. The UV irradiance greatly depends on the distance from the UV emitter and the transmittance of the medium.

Z: The Z value, which is sometimes used in place of the rate constant for UV applications. Sometimes written Zeff and defined as Zeff = k.