Why UV-C Cannot Produce Ozone

Property Management | Lamps | Terminology

Why UV-C Cannot Produce Ozone

Why UV-C Cannot Produce Ozone

The 253.7nm Ultraviolet Germicidal Irradiation (UV-C) wavelength is an invaluable tool for an HVACR system. By leveraging germicidal energy to keep refrigeration coils free of microbial growth, facility managers also enjoy the benefit of reducing the spread of airborne infectious agents.

However, some facility managers may hesitate to leverage these benefits due to a concern about ozone. The Ultraviolet spectrum has four wavelengths, (see illustration below), labeled: UV-A (400 to 315 nm); UV-B (315 to 280 nm); very high energy and destructive UV-C (280 to 200 nm); and Vacuum UV (200 to 100 nm).  Only this last wavelength, Vacuum UV, is capable of producing ozone.  Therefore, lamps operating at 253.7nm–the most common germicidal wavelength–CANNOT produce ozone.

Another layer of ozone protection has to do with the construction of low-pressure mercury vapor lamps.

Most germicidal lamps, including those from UV Resources, are produced with doped quartz glass, which blocks the transmission of the 185nm ozone-producing wavelength. The doped quartz glass allows the 253.7nm radiation to pass through, but it blocks the 185nm wavelength from escaping. Therefore, germicidal lamps with doped glass CANNOT produce ozone.

Ironically, a 253.7nm germicidal UV-C lamp will actually destroy ozone!

HOW IT WORKS

UV-C’s germicidal or germ-killing effects are well proven. The 253.7 nm electromagnetic waveform is well absorbed by DNA and RNA (the genetic code for all lifeforms), changing its structure. This change alters a cell’s nucleic acids and protein structure through a process known as photodimerization which causes two consecutive DNA/RNA bases to bind together. This genetic damage inhibits the ability of the affected cells to reproduce, meaning that they cannot infect and are no longer dangerous.

The most common lamp used to produce germicidal UV-C radiation is the low-pressure mercury vapor lamp, which has its main (>90%) emission at 253.7nm, near the 265nm peak wavelength for inactivating microorganisms.[1]

While all lamps from UV Resources do not create ozone, some of our fixtures have been certified to meet UL-2998, a zero-ozone verification standard.

WHAT IS OZONE?

Ozone (O3) is a toxic gas that can cause respiratory tract irritation, asthma, and even permanent lung damage.

Ozone is present in low concentrations throughout the earth’s atmosphere. Some researchers say that this chemical is “good up high, but bad down low.” Without the ozone layer protecting our Earth’s stratosphere, for example, the Sun’s ultraviolet radiation would make life on Earth uninhabitable. At street level, however, a high concentration of ozone is toxic to plants and animals. In humans, ozone can irritate nasal passages, cause nausea and extended exposure can lead to lung inflammation.

Ozone, also called Vacuum Ultraviolet (UV-V), is a gas molecule that contains three (3) oxygen atoms – and as such, it has a destabilizing effect on oxygen in the air (leading to its irritation and danger to humans). A UV lamp “tuned” to 185nm can create ozone from oxygen (O2) by disrupting the O2 molecule and splitting it into two oxygen atoms. These two oxygen atoms attempt to attach to other oxygen molecules (O2). It is the attachment of this third oxygen atom that creates ozone (O3).

Ironically, UV light in the 240 – 315nm wavelength will break this third oxygen atom attachment explained above and convert it back to oxygen. The peak ozone destruction occurs at the 254nm wavelength. So, a UV-C lamp operating at the most common 253.7nm germicidal wavelength will actually destroy ozone!

ASHRAE has said that certain air cleaners produce ozone and thus, its position is to recommend discontinuing “devices that use the reactivity of ozone for the purpose of cleaning the air.” [2]

KEEPING PERFORMANCE SUSTAINABLE 

Keeping buildings operating at their most efficient level and sustaining that performance over the life of a building is one of today’s key challenges for specifying engineers, HVACR contractors and facility managers. Today, with germicidal technology, virtually all HVACR systems are potential candidates because of the many proven operational benefits it offers, including:

    • Destruction of surface and airborne microorganisms;
    • The restoration and preservation of heat transfer and airflow capacities to “as-built” conditions;
    • Greatly improved indoor air quality; and
    • Reduced maintenance.

Again, while UV-C technology has been proven to restore HVACR performance to its original capacity, specifying engineers, HVACR contractors and facility managers can rest assured that the germicidal wavelength is incapable of producing ozone. Moreover, the 253.7nm germicidal wavelength will destroy ozone.

So stay ozone free in the 254nm zone.

[1] ASHRAE. (2019). ASHRAE handbook—HVAC applications. Atlanta: ASHRAE. Retrieved from https://www.ashrae.org/file%20library/technical%20resources/covid-19/i-p_a19_ch62_uvairandsurfacetreatment.pdf

[2]  ASHRAE (2015). ASHRAE Filtration and Air Cleaning Position Document Committee. 2015. “ASHRAE Position Document on Filtration and Air Cleaning.” Retrieved from https://www.ashrae.org/File%20Library/About/Position%20Documents/filtration-and-air-cleaning-pd-2.2.21.pdf