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UV-C Lamps: Playing it Safe
Light in the Ultraviolet-C (UV-C) spectrum has proven effective in killing virtually all known microorganisms, making it the ideal solution for cleaning HVAC cooling coils and decontaminating the upper air in public spaces such as schools and hospitals.
The potency of UV lamps, however, means that care must be taken when servicing these systems. Unlike some hazards, exposure to ultraviolet light does not offer a natural avoidance response (e.g. squinting eyes in bright sunlight) or a physical cue that protection is necessary (e.g., heat radiating from a hot pan). Furthermore, the physiological effects of UV-C exposure are delayed and can appear up to six hours later.
While damage from UV-C is temporary, the HVAC/R industry takes steps to safeguard service personnel from avoidable ultraviolet exposure and the consequences of its short-term or chronic effects.
The Power of UV-C
It’s first important to understand the properties of UV-C and how it can pose a threat if handled improperly.
UV light, also known as ultraviolet germicidal irritation (UVGI), comprises a segment of the electromagnetic spectrum between 400 and 100 nm. The UV segment has different sections, labeled UV-A (400 to 315 nm), UV-B (315 to 280 nm) and very high energy and destructive UV-C (280 to 200 nm).
Most of us are familiar with the harmful effects of UV energy transmitted by sunlight in the UV-A and UV-B wavelengths, giving rise to UV “sunburn” inhibitors, or sun tan lotions. We are also familiar with products engineered to withstand the effects of UV radiation, such as plastics, paints, and rubbers. However, unlike the UV-A and UV-B wavelengths, the UV-C band has more than twice the electron volt energy (eV) as UV-A, and it is well absorbed (not reflected) by organic substances, adding to its destructiveness.
This power allows UV-C to break through an organism on a cellular level, effectively scrambling its DNA. UV-C’s effects on the human body vary depending on length of exposure, but can cause painful burns on the skin. It can also cause temporary damage to the cornea if observed directly. Aside from these threats, UV-C is a known carcinogen for human skin.
UV-C Safety Strategies
Therefore, it is important to follow common-sense safety strategies when dealing with UV-C lamps. 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 air handling unit (AHU). These safeguards include:
- Placing warning labels near all access panels or doors to a plenum containing UV lamps, as well as on panels or doors adjacent to AHU sections where UV radiation may penetrate or be reflected.
- Installing electrical disconnect devices on AHU lamp sections, so that the opening of any access point de-energizes the UV-C system. Some manufacturers include a door safety switch or lockout/tagout feature to keep the AHU closed until the UV lamp power has been disconnected. These safety devices should never be overridden
- Instructing service personnel to never look directly at UV-C without adequate eye protection. Installing a view port is the safest way to view the light, as it will block the UV-C bandwidth. Ensure that the viewport is constructed from UL classified, fire resistant wired glass and is sized and located to allow an operating UV system to be viewed from outside of the HVAC equipment. Include proper safety signage to form a complete viewport/signage assembly.
- Making it a policy to never enter the plenum where UV-C lamps are active. If it is absolutely necessary, wear personal protective equipment including UV safety goggles, UV face shields, long-sleeved, tightly-woven clothing that covers much of the body and gloves.
These safety precautions will help ensure service personnel are protected from accidental exposure while maintaining the effectiveness of UV-C to eradicate biological contaminants.
As an added value, UV-C’s ability to constantly clean the interior workings of the AHU can extend the equipment’s life for prolonged savings. Biofilms on coil fins hamper their ability to remove heat from the air. If mechanical cleanings are incomplete or ignored, up to 25 percent of cooling capacity can be lost in as little as five years.
When used correctly, UV lighting in HVAC systems and/or the upper air can do much to save energy, raise HVAC/R efficiency, reduce maintenance and boost indoor air quality.