We have all felt the power of UV after spending a summer day outdoors. The sun is a powerful source of UV energy; even the slightest overexposure gives us a sunburn. Continued overexposure to UV energy can be quite harmful, but the UV spectrum offers many beneficial characteristics as well. With the right control and application UV energy can be used for UV disinfection of water, purify air and surfaces, cure adhesives and coatings and sterilize tools, just to name a few.
Ultraviolet light occurs just below the color violet which is the lowest wavelength of visible light to the human eye. The electromagnetic spectrum of ultraviolet light is typically subdivided into the following ranges:
The sun emits ultraviolet radiation in the UVA, UVB and UVC bands, but because of absorption in the atmosphere, 98.7% of the ultraviolet radiation that reaches the Earth's surface is UVA. Ordinary glass is partially transparent to UVA but blocks UVB and UVC. This feature gives sunglasses and eye wear UV protection capabilities. A positive effect of human UVB exposure is that it induces the production of vitamin D in the skin.
UVC rays are the highest energy form of ultraviolet light. Since UVC rays are filtered by the Earth's atmosphere, organisms have not developed a natural defense against UVC energy. When the DNA of a microorganism absorbs UVC energy, molecular instability occurs resulting in the disruption of the DNA sequence. This renders the cell unable to grow or reproduce. Without the ability to reproduce the cell cannot infect and it rapidly dies.
The application of UVC energy to inactivate microorganisms is known as Germicidal Irradiation or UVGI. It has been used for this purpose since the early nineteen hundreds. Artificial UVC energy is produced in germicidal ultraviolet lamps which produce UV radiation by ionizing low pressure mercury vapor. These lamps are similar to typical fluorescent household lighting fixtures but do not have the phosphorescent coating which imparts the soft white light. Ionized mercury emits a predominately discreet wavelength of 254nm - in the UVC band and, as it happens, is an ideal wavelength for disrupting the DNA of microorganisms.
The amount of UVC energy needed to inactivate a given microorganism is measured by dose, which is determined by a combination of irradiation energy and exposure time. Scientists have determined the rates at which various microbial populations decline due to exposure to biocidal factors such as UVC irradiation. Based on mathematical modeling, UVDI engineers have developed proprietary and third party validated computer modeling programs to estimate deactivation rates for target microorganisms and subsequently design UVC systems that will efficiently and effectively disinfect the air, surface or water situation of interest.
UVGI's use in air disinfection dates back to to the 1940's where it was used to control the spread of tuberculosis in hospitals. Today UVGI air disinfection has evolved to include sophisticated systems that disinfect air for residences, hospitals, commercial and industrial buildings, and public facilities such as airports.
The types of UVGI air disinfection systems in use today include single room recirculation units that are mobile or wall mounted, and in duct mounted systems for heating, ventilation and air conditioning (HVAC) systems.
Single room air disinfection units, also known as stand alone room air cleaners, recirculate room air through a specially designed series of filters and UVGI lamps. As air passes by the UVGI chamber, UVC energy deactivates airborne microorganisms such as the Influenza virus and Staphylococcus Aureus. The effectiveness of the unit depends on the rate of air changes and the size of the room. A properly sized unit will treat room air up to 12 volume changes per hour and supply purified air to room occupants.
Building air disinfection UVGI systems are commonly located in the air handling unit (AHU) of a room or building. The AHU is the heart of the HVAC system and typically houses the blower, heating and/or cooling coils, inlet air plenum and outlet air plenum to the building ductwork. AHUs vary in size from small room devices called terminal units to large commercial systems called roof top units. UVGI applications to disinfect moving air streams are commonly called "kill on the fly" where microbes traveling with the air stream are deactivated. Proper design of a UVGI air disinfection system depends on many factors including air flow, temperature, type and size of HVAC equipment, UV lamp intensity, plenum reflectivity and target microbe.
UVDI's sophisticated computer modeling program called V-Smart is necessary to design an efficient yet effective system for disinfecting air streams. When implemented correctly, UVGI has a proven track record of disinfecting air and protecting building occupants from air borne infection.
UVGI technology has been used for surface or area disinfection for many years. Direct UVGI exposure can sterilize any surface given the right amount of time. Current technology is used for prevention of potential microbiological hazards as well as remediation of existing conditions. The types of surface disinfection systems in use today include microbiological growth control as well as surface and area disinfection.
Microbiological growth typically consists of bacteria, fungi, or molds. HVAC systems are the perfect breeding ground for microbiological growth due to the coils function of removing heat from the air and producing condensate in the process. The condensate forms on the coil surfaces and collects in the drain pan. Over time a "bio-slime" film develops which consists mostly of mold growth on the coils and bacterial growth in the drain pan. With the HVAC system in the run mode, a portion of the accumulated mold and bacterial contamination is introduced to the air stream and ultimately to the occupants of the building.
When a cooling coil is exposed to a properly designed UVGI system, the germicidal effect of UVC energy on the microorganisms combined with the washing effect of the condensate clean the cooling coil of organic matter and restore healthy and efficient HVAC operations.
HVAC coil irradiation is a popular but specialized application of UVGI for disinfection. In fact, there are many situations in healthcare, institutional, industrial and commercial use where surface or area disinfection is necessary. Two areas of growing awareness and use are food processing and room surface disinfection.
Food borne spread of infection from microorganisms such as Salmonella typhimurium have recently grabbed the headline news. Several states are in process of enacting legislation designed to step up prevention and reporting of potential infectious hazards associated with processing and packaging foods. UVGI technology has gained popularity as a technique to effectively disinfect food processing equipment as part of ongoing cleaning and maintenance, as well as disinfect containers such as plastic bottles prior to filling with contents.
Room disinfection is another growing area for UVGI technology. UV systems have been developed to effectively destroy microorganisms such as mold, viruses and bacteria and to do so relatively quickly. For example, a typical hospital patient room requires thorough manual cleaning before the next occupant is admitted. The turn around time needs to be minimal but cleaning must also be effective. UVGI units such as the Mobile Room Sanitizer can disinfect a typical patient room in under 5 minutes. Other uses for room disinfection equipment include classrooms, waiting rooms, locker rooms, shelters and mold remediation to name a few.
The first use of UVGI to disinfect a municipal water system was in Marseilles, France in 1909. Since then UVGI treatment of municipal water systems has grown steadily and today is used commonly all over the world. Recently New York City approved the construction of a 2 billion gallon per day ultraviolet drinking water disinfection facility. But UVGI water treatment applications range beyond municipal systems.
Rural water: Many rural residents rely on well water or water from lakes and streams for human consumption as well as water for livestock. These sources of water can become contaminated from faulty sewage, field runoff or animal waste.
Public water: Concerns over health effects related to chlorine have prompted many community homeowners to de-chlorinate their water supply. Also, some homeowners retain a backup water supply in case of service interruption.
Commercial and industrial water: Hospitals, factories and laboratories often require high purity water. Also, some industrial processes do not tolerate chlorine.