Facts on How to Design and Apply Ultraviolet Germicidal Lamps for Air Disinfection in Public Places

The germicidal “killing” effect of 253.7nm radiation on bacteria has been well documented over the past 75 years.  Most bacteria and virus cells being small in size are capable of airborne transmission from host to host. One of the inherent dangers with this airborne transfer is that the original host can release the bacteria or virus molecules through respiration, sneezing, coughing etc. and the pathogen remains in the room long after the original host departs. This can lead to the infection of many people by a single individual host if the air in a commonly used room or area is contaminated with airborne bacteria or viruses.  Common areas of concern include: physician and hospital waiting rooms, examining rooms, public/private schools and universities, prisons, holding areas (in the case of detention and processing centers), treatment rooms, dog kennels, and anywhere else where people or animals congregate.

Since Germicidal UVC works as a line of sight process, direct exposure/contact of the pathogen to the UVC has to be achieved.  This is much less difficult to accomplish in a room than one may think. Fixtures that project the UVC up toward the ceiling or at a vertical angle can be mounted to the wall. The proper mounting would be to aim upward, irradiating the ceiling area. Fixtures have to be mounted above eye level (7½ feet or more) to avoid exposure of the eyes to the harmful UVC rays. The natural air movement by convection will bring contaminated air from below the fixtures, upward towards the ceiling where the air is irradiated by the UVC and disinfected.   This air then continues the cycle, mixing with the untreated air, reducing the concentration of pathogens. The “mixed” air continues the cycle, becoming further UVC exposed and thus reducing the amount of pathogen contamination. In rooms that have better ventilation and/or frequent air exchanges (4+ times per hour) the germicidal “killing” effect is accelerated by the increased air turbulence.

Room air disinfection by this upper air convection process is a very efficient and effective method of disinfecting the air in common spaces. The fixtures required are relatively simple and low cost. The lamps used have an effective life of more that one year (1 year plus).  Once the UVC destroys the pathogen there is no harmful residue left behind as opposed to filtration. In the case of filtration, the filter medium becomes a holding and breeding ground for bacteria. Filters must be frequently replaced and disposed of thus putting the worker at risk of infection.

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