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©2017 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 59, no. 1, January 2017

Brian Rodgers; Dean Saputa, Associate Member ASHRAE

About the Authors
Brian Rodgers is the principal engineer for Heating, Ventilating and Large-Scale Cooling at UL, a global independent safety science company. Dean Saputa is vice president of sales for UV Resources and the immediate past chair of the ASHRAE TC 2.9, Ultraviolet Air and Surface Treatment.

Since the 1990s, ultraviolet germicidal irradiation (UVGI), or light in the UV-C wavelength (specifically 253.7 nm), has been used in HVAC&R equipment to maintain or return cooling capacity to as-built conditions by maximizing heat exchange efficiency. The technology deactivates biological growth on surfaces within an air handler to save energy, boost airflow levels and protect indoor air quality. 

ASHRAE Technical Committee (TC) 2.9, Ultraviolet Air and Surface Treatment, helps oversee the safety standards that protect installers and service personnel from accidental UV-C exposure. Complementary HVAC&R equipment requirements in this area are published in the UL 1995 safety standard for heating and cooling equipment.

In May 2009, UL LLC, the testing, inspection and certification part of Underwriters Laboratories, Inc., which is the entity responsible for developing HVAC equipment safety standards, approached the TC 2.9 committee with a proposal to update the fourth edition of the UL 1995 standard.

A collaborative effort ensued and work culminated in July 2015 with the release of the fifth edition of UL 1995, which carries a Nov. 2019 compliance date. This article provides an overview of how these safety enhancements will protect installers and service personnel from accidental UV-C exposure from HVAC&R equipment.


Limiting UV-C Exposure

Ultraviolet light is separated into three main segments along the electromagnetic spectrum. The most well-known wavelengths are UV-A and UV-B, which are responsible for sunburns. UV-C is also produced by the sun, but cannot penetrate the atmosphere due to its shorter wavelength. When generated by artificial sources, however, close proximity to UV-C irradiation is powerful enough to break down the skin’s collagen proteins, causing redness and irritation. It can also damage the surface layer of the cornea in the eye, resulting in photokeratitis (the same condition welders can experience with arc flashes).

Not all HVAC&R technicians receive UV-C safety training, and some may not be aware that the UV-C light in an air-handling unit (AHU) can potentially pose a safety hazard. Unlike some dangers, exposure to ultraviolet light does not offer an avoidance response (e.g., blinking of eyes) or a physical cue that protection is necessary (e.g., heat radiating from a hot stove). Furthermore, the physiological effects of an adverse dosage of UV-C exposure are delayed and can appear up to six hours later. While damage from UV-C is reversible, the HVAC&R industry takes steps to safeguard service personnel from avoidable ultraviolet exposure and the consequences of its short-term or chronic effects.

Many HVAC&R and UV-C equipment manufacturers have voluntarily implemented safeguards against the risks of UV-C exposure. Instructions and signage advise service personnel that the UV system should be turned off before performing any work in the AHU. A maintenance worker can easily take this step before opening the AHU to service the motor, change fan belts, replace filters, check coils, or drain pans. Some manufacturers include a door safety switch or lockout/tagout feature to keep the AHU closed until the UV lamp power has been disconnected.


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