Energy Curing Users Resource Group

UV curing systems emit a combination of ultraviolet wavelengths classified as Vacuum UV (100 – 200 nm), UVC (200 – 280 nm), UVB (280 – 315 nm), UVA (315 – 400 nm), and UVV (400 – 450 nm).

Vacuum UV and UVC wavelengths shorter than 240 nm are capable of breaking the bonds of an oxygen molecule (O2) to produce two oxygen atoms (O and O). These oxygen atoms (O and O) combine with other oxygen molecules (O2) in the atmosphere to form ozone molecules (O3). As soon as this ozone (O3) is created, the molecular bonds immediately begin breaking apart to form an oxygen molecule (O2) and an oxygen atom (O). These single oxygen atoms (O) quickly combine with each other to form oxygen (O2). The entire cycle happens relatively quickly.

The molecular bonds formed when the output from UV curing lamps interacts with oxygen in the atmosphere to form ozone are not very strong. As the newly created ozone molecules are exhausted away from the curing system through closed ducting, they easily revert to oxygen. Because this happens quickly and with certainty, there is no accumulation of ozone over time. As a result, ozone generated by UV curing systems poses no issue to the surrounding environment. It is best practice for UV curing systems to be ducted away from the press or machine and outside the roof of the production facility. By the time the exhaust is emitted from the roof, it is basically warm air with negligible ozone. Exhausting to the roof provides a safe worker environment with no impact on the surrounding environment.

Government agencies regulate emissions that contain pollutants such as nitrogen oxides (NOx) and volatile organic compounds (VOCs). These pollutants react with oxygen in the presence of sunlight and high temperatures to form ground-level ozone otherwise known as smog. High-temperature combustion processes generate these pollutants and are an indirect contributor to ground-level ozone formation, especially during hot, sunny weather. UV curing systems are all- electric processes and do not emit combustion contaminants such as NOx or VOCs. Therefore, they are not a direct cause of the ozone regulated by government agencies. Any direct ozone potentially generated by UV curing systems is unstable and has a very short life. The ozone generated by UV curing systems does not contribute to smog.

It is difficult to calculate or predict the amount of ozone generated by UV curing systems. It depends on system design, lamp power, lamp length, wavelength emission, and airflow. Every installation is different. To know exactly, users can measure ozone concentrations at the press or machine, at the exhaust duct on the roof, and at ground level outside the plant. Measured ozone concentrations will be negligible and well within safe exposure limits for properly designed UV curing systems installed with sufficiently sized extraction fans and ducting.

On or about 2023, the South Coast Air Quality Management District conducted testing to measure ozone emissions from UV lamps used in air purifiers. Not only did the agency find that no ozone was generated but one of the units actually removed ozone from the SCAQMD lab. According to the district, at all positions and fan speeds, the measured ozone concentration was 16-53% lower than the background laboratory ozone concentration. “This means the unit does not produce ozone and actually removes some ozone from the air”—read the report from the SCAQMD staff. The testing concluded that any ozone generation from the UV devices was well below the ozone limits mandated by the California Air Resources Board. Ultimately, the district included UV units in their air filtration program which provides $13.7 million in grants for air filtration systems for public schools in Southern California’s most polluted areas.

Despite ozone from properly exhausted UV curing systems being a non-issue, users should still consult local regulations prior to installation. Some communities require emissions permits anytime an exhaust hole is put in a roof. This requirement is often unavoidable despite the exhaust emissions having an inconsequential impact on the environment and surrounding community.

The chemical bonds in ozone that are generated by UV curing lamps are not very strong. As the ozone molecules drift through 30 to 50 feet of atmosphere, they revert to oxygen. There is no accumulation of ozone over time that would cause issues to the surrounding environment. Ozone generated by UV lamps has a short life and is not a concern like the ozone emissions created by internal combustion engines and other processes that the EPA regulates.

UVC output below 240 nm breaks the bonds in oxygen molecules (O2) and produces two oxygen atoms. An oxygen atom combines with an oxygen molecule to form O3. As soon as the ozone (O3) is produced, the molecules immediately begin breaking apart to form (O2 and O). The single oxygen atoms then combine with each other to form O2.

It is not easy to calculate or predict the amount of ozone generated. It depends on lamp power, wavelength emissions, and airflow. Every installation is different. To know exactly, end users need to measure ozone concentration at the lamp heat exhaust, at the exhaust duct on the roof, and at ground level. In doing so, you will find the greatest concentration of ozone is at the lamp(s).

What is emitted from the roof should just be warm and, depending on the length of duct, minimal ozone. It should be zero at vertical and horizontal distances from the roof or ground level of the plant.

Ozone emitted by mercury vapor lamps is a respiratory irritant and has an odor that is bothersome to operators and plant personnel. This is why UV curing lamps should be ducted outside the roof of the building. Exhausting to the roof provides a safe worker environment with no impact on the surrounding environment.

RadTech thanks Jennifer Heathcote, VP Business Development,
GEW (EC) Limited for preparing this response and assisting a UV user on behalf of RadTech