V olume 1 #4

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“Current Comments On Healthcare IAQ Issuesä”

August 7, 2003 Volume 1 No. 5

UVGI

(Ultraviolet Germicidal Irradiation)

Ultraviolet Germicidal Irradiation, also know as UVGI, was first studied for air disinfection in the 1920’s and first used for water purification in the 1930’s. Science was not as astute then about how light was affected by environmental conditions as it is now. Some tests had very positive results whereas some were only mediocre in reducing airborne pathogens. A recent six year study by the University of Colorado for the CDC’s National Institute for Occupational Safety and Health (NIOSH) has proven that, specified correctly, UVGI is extremely effective in reducing or eliminating airborne pathogens. The study was published in Atmospheric Environment, Vol. 37, 405-419 (2003) under the title "Efficacy of Ultraviolet Germicidal Irradiation of Upper-Room Air in Inactivating Airborne Bacterial Spores and Mycobacteria in Full Scale Studies"

The ultraviolet light spectrum is divided into three categories: UV-A, UV-B and UV-C. Here is a brief explanation of the different characteristics of the three bands:

UV-A - The "near" or "longwave" (320-400 nanometers) UV band is also called "black light". It is great for making certain pigments fluoresce and looks great in some hospitality establishments. It has little effect on pathogens and has no effect on human tissue.

UV-B - The "middle" UV band (280-320 nanometers) is sometimes called the "suntan ultraviolet". It is common in tanning salons and has certain industrial uses. It does inactivate a moderate amount of pathogens, though not as effective as UV-C. Prolonged exposure can cause blistering of the skin and damage to the cornea of the eye.

UV-C - The germicidal or "shortwave" (200-300 nanometers) UV band is also known as "ultraviolet germicidal irradiation" or UVGI for short. When specified correctly, UVGI will inactivate pathogens by destroying the DNA and RNA of the microbes rendering them impotent. Prolonged exposure can cause temporary reddening of the skin and temporary eye irritation ("welder’s eye"). No known permanent damage is caused by extended exposure. The ideal wavelength for eradicating pathogens is 253.7 nanometers.

University of Colorado Study

This study replicated a standard hospital room with a heated (98.6 ^oF) mannequin named "Manny". In this case, pathogens similar to M.Tb were introduced into the room under varying condition to measure the UVGI effect of commercially available UVGI devices. The study used clinical results noting the reduction of pathogen colonies to quantify the results of their testing. A number of findings were noted, such as:

Increasing the irradiance level of the UVGI lamps increased the effectiveness of inactivating the TB-like bacteria. The relationship was linear up to a certain level. Further increasing the irradiance above this high level resulted in little increase in the inactivation of the airborne TB-like bacteria.

High relative humidity above 75 percent lowered the effectiveness of UVGI to inactivate the TB-like bacteria.

Mostly, ventilation and UVGI worked together to remove or inactivate the airborne TB-like bacteria at a greater rate than either system working alone. Low to moderate levels of ventilation in the room did not negatively affect UVGI effectiveness.

The study clearly demonstrated that the air in a room must be mixed for UVGI to effectively inactive the TB-like bacteria. When warm air entered the room via a duct close to the ceiling (which may occur in the winter when the heating system is turned on), the warm air simply "rested" on the much cooler air below and the efficacy of the UVGI system was dramatically diminished. No mixing fans were on during this experiment but moderate ventilation was present.

The findings of the NIOSH-funded study provided new data to help scientists in future research projects to evaluate a novel three-dimensional measurement approach to measuring UV radiation.

Public Health Reports Study

An article entitled "The Application of Ultraviolet Germicidal Irradiation to Control Transmission of Airborne Disease: Bioterrorism Countermeasure" in the March-April, 2003, issue of Public Health Reports examined the use of UVGI as a bioterrorism countermeasure with extremely positive results. Weaponized pathogens are just as susceptible to the effects of UVGI as are the pathogen encountered on a daily basis in healthcare facilities. They recommend a multiple UVGI attack on the pathogens. This can be achieved by installing UVGI devices in the upper room area, the ducting and the heating/cooling coils in the air handling units (AHU).

Under "ideal" conditions (good air mixing, correct airflow dynamics, no "dead spots" or "short-circuiting", etc), 63% of particles will be removed for each air change from a room using standard ventilation. This ideal condition rarely occurs in the real world. The study used the "added ACH" (Air Changes per Hour) standard to define the effectiveness of the UVGI which would assist HVAC engineers in determining the design for a room. Researchers used a 200 ft.² (18.6m) room in a residence that has "natural ventilation" (4 ACH) as a standard for the initial testing of UVGI. One 17 Watt UVGI lamp added the equivalent of 10 ACH while 2 lamps added 33 ACH. In other words there was an effective air change rate of more than one every two minutes utilizing UVGI rather than one every fifteen minutes without it.

Where UVGI Should be Installed

While UVGI is not a replacement for HEPA filters, these two methods of pathogen abatement and removal definitely complement each other. UVGI should be installed in three locations to derive the maximum effect. They are:

Upper Room UVGI - These are installed above eye level usually around 7-8 feet above the floor. If the room has a low ceiling, units with louvers can be installed lower and direct the light upward without any ill effects on staff or patients. With the air supply and exhaust (intra-room airflow dynamics), the movement of persons and the natural convection in the room to provide adequate air mixing, these units can destroy airborne pathogens extremely effectively.

In-Duct UVGI - Installing in-duct units at a point just before entry into and just after air exhaust from the room will lessen the threat of airborne pathogens from entering or leaving the room and destroy any that may be resident within the room. The HVAC ducting in any facility will not be 100% secure from leaks into and out of the ducting so installing these system is a prudent measure in preventing nosocomial (secondary) infections.

Coil UVGI - The irradiation of heating and cooling coils has also been around for a very long time. This is one area where the under-specification of the irradiation needed has been a nagging problem. Looking at a 13’ x 15’ coil, a rack system of 12 to 18 UVGI lamps would be required to provide the needed dose to kill airborne pathogens and keep the coil and fins free of mold and microbe colonies (keeping heat transfer very high). The UVGI rack would be installed at 1 to 3 feet from the coil.

This system would nominally cost between $8,000 and $12,000. The ROI (Return on Investment) from the energy savings (a nice side benefit of UVGI coil irradiation) would be, usually, 1 to 3 years. Some opt for less lamps thereby reducing the effectiveness of the UVGI which defeats the purpose of installing a system in the first place.

UVGI Dose

The dose of UVGI is measured in micro-Watt seconds per square centimeter (µWsec/cm²).A dose of 100 µWsec/cm² is considered sufficient for most applications. Higher doses to kill airborne pathogens on a first pass in ducts and coils applications may be desired depending on what pathogens are expected to be encountered and whether the risk/reward ratio indicates that the extra expense would be appropriate.

UVGI is a powerful tool in the battle to stop secondary infections in the Operating Room, Protective (positive pressure) Isolation room and Infectious (negative pressure) Isolation room. Serious consideration should be given to upgrading any room that needs this kind of added protection from airborne pathogens.