Appendix 19. Upper room ultraviolet germicidal irradiation (UVGI) system

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    The use of UVGI in the upper part of rooms may be effective in killing or inactivating M. tuberculosis generated by infected persons.

    19.1 Mechanism of action

    UV lamps are installed into fixtures suspended from a ceiling or mounted on a wall. Fixtures are shielded with louvers or bafflers in order to block radiation below the horizontal plane of the fixtures. UV lights create in the upper portion of the room a germicidal zone where the bacilli are killed (Figure 1). Patients in the lower portion of the room are not exposed to UVGI lights. Good air mixing is needed to transport the air (and thereby the bacilli) to the upper portion of the room. Disinfection is achieved through the rapid dilution of contaminated lower room air with clean irradiated upper room air.

     

    Figure 1

     

    TB-Appendix 19 Figure 1
    * 1 feet = 0.3048 m


     

    From the WHO, Implementing the WHO Policy on TB Infection Control in Health-Care Facilities, Congregate Settings and Households

     

    The lamps should irradiate the entire surface of the upper part of the room (Figure 2), in order to disinfect the largest possible volume of air mixed at a low speed between the upper and lower part of the room.

     

    UVGI Upper-room Irradiation

    Figure 2

     

    TB-Appendix 19 Figure 2

     

    From Guidelines for the Utilization of Ultraviolet Germicidal Irradiation technology in controlling transmission of tuberculosis in health care facilities in South Africa [1] Citation 1. I Coker, E Nardell, B Fourie, P Brickner, S Parsons, N Bhagwandin and P Onyebujoh. Guidelines for the Utilisation of Ultraviolet Germicidal Irradiation technology in controlling transmission of tuberculosis in health care facilities in South Africa. MRC.
    http://www.sahealthinfo.org/tb/guidelines.pdf

     

    Several factors influence the efficiency of UVGI systems:

    • Ventilation rate: in controlled environment, at rates up to 6 air change per hour (ACH), UVGI systems increase the effect of air cleaning to > 12 ACH [2] Citation 2. Xu P. Ultraviolet germicidal irradiation for preventing infectious disease transmission. Boulder, CO: University of Colorado, Department of Civil, Environmental, and Architectural Engineering; 2001. . But when ventilation rates are increased above 6 ACH, UVGI system effectiveness could be reduced because the time for bacteria irradiation is shorter [3] Citation 3. Collins FM. Relative susceptibility of acid-fast and non-acid-fast bacteria to ultraviolet light. Appl Microbiol 1971;21:411–3. [4] Citation 4. Kethley TW, Branch K. Ultraviolet lamps for room air disinfection. Effect of sampling location and particle size of bacterial aerosol. Arc Environ Health 1972;25:205–14. .
    • Effective mixing within the room may be provided by natural convection currents or fans, preferably, ceiling ones. Low velocity ceiling fans boosted UVGI system’s effectiveness up to 33% when ACH was below 6 [5] Citation 5. Riley RL, Permutt S. Room air disinfection by ultraviolet irradiation of upper air. Air mixing and germicidal effectiveness. Arch Environ Health 1971;22:208–19. [6] Citation 6. Riley RL, Kaufman JE. Air disinfection in corridors by upper air irradiation with ultraviolet. Arch Environ Health 1971;22:551–3. [7] Citation 7. Ko G, First MW, Burge HA. The characterization of upper-room ultraviolet germicidal irradiation in inactivating airborne microorganisms. Environmental Health Perspectives 2002;110:95–101. .
    • Relative humidity: studies [8] Citation 8. Ko G, First MW, Burge HA. Influence of relative humidity on particle size and UV sensitivity of Serratia marcescens and Mycobacterium bovis BCG aerosols. Tubercle Lung Dis 2000;80:217–28. [9] Citation 9. Peccia J, Werth HM, Miller S, Hernandez M. Effects of relative humidity on the ultraviolet induced inactivation of airborne bacteria. Aerosol Science and Technology 2001;35:728–40. [10] Citation 10. Riley RL, Kaufman JE. Effect of relative humidity on the inactivation of airborne Serratia marcescens by ultraviolet radiation. Appl Microbiol 1972;23:1113–20. have reported rapidly decreasing air cleaning effectiveness in UVGI systems when the relative humidity goes above 70%.
    • Installation: the height of the room should be minimum 2.5 m and UVGI fixtures should be installed at the minimum height of 2.1 m. As a thumb rule, a 30W lamp should be sufficient for 18 m2 of surface [11] Citation 11. First MW, Nardell EA, Chaisson W, Riley R. Guidelines for the application of upper-room ultraviolet germicidal irradiation for preventing transmission of airborne contagion—part I: basic principles. ASHRAE Trans 1999:105:869–876. [12] Citation 12. Riley RL, Nardell EA [1989]. Clearing the air: the theory and application of ultraviolet air disinfection. Am Rev Respir Dis 139(5):1286–1294. , but room shape and type of fixture should be taken into consideration when calculating the needs. For instance, wall-mounted lamps would have a smaller germicidal area than ceiling-mounted ones. Lamps should be on whenever there is a risk of TB transmission. For example, in rooms with hospitalized patients, the lamps should be turned on 24 hours a day.
    • Maintenance: see below.

    19.2 Maintenance

    Dust-covered and/or old UVGI lamps are less effective, hence the need for a careful maintenance, including regular cleaning:

    • Lamps and fixture surfaces should be wiped at least monthly (more often if necessary) with a cloth dampened with 70% alcohol. Do not use water and soap or any detergent. The cleaning should be performed when lamps and fixtures are cool.
    • Measurement of UVGI level must be done at installation and at least once a year. A UV light meter programmed to detect UV light on a wavelength of 254 nm is needed. Measurements should be performed at eye level in the occupied zone (~ 1.6 m) and in upper irradiated portion of the room, at a distance of 1.2 m from the fixture in all possible directions (imitating a circle with measurements done while moving in circumference spaced of 1 m). Ideally, all upper room measurements should be around 30 μW/cm2 to 50 μW/cm2. Persons doing these measurements should wear protective equipment (UVprotective glasses, clothing made of tightly woven fabric, soft cotton gloves) and cover exposed skin with opaque creams with solar-protection factors > 15.
    • UV lamps last between 5 000 and 10 000 hours of continue use (7 to 14 months). Check manufacturer’s information. After this period, UV lamps rapidly lose effectiveness and need to be changed.

    19.3 Disposal

    UV lamps contain mercury and quartz and are considered as hazardous waste. Disposal is extremely difficult in many countries; this should be considered before implementing them. If adequate disposal of the lamps by specialized enterprises is not possible in the country, neither their repatriation; UV lamps should be disposed of by encapsulation (sealed in a metal 200 litre drum filled with concrete and then buried away from water sources).

    Safety considerations

    Reflecting surfaces in the irradiation area of UV lamps must be avoided (i.e. oil painted ceilings, etc.).

     

    At certain wavelengths (including UV-C) UV exposure may be harmful. Skin exposure can produce sunburn (erythema). Exposure of the eyes can produce conjunctivitis (feeling of sand in the eyes, tearing) and/or keratitis (intense pain, sensitivity to light). These symptoms typically commence 6 to 12 hours after exposure.

     

    Despite the fact that these are reversible conditions, health care workers should immediately report them to the IC officer. This could mean that UV irradiation is higher than previously thought at lower room level (lamp poorly positioned? Reflecting surface?).

     

    The USA National Institute for Occupational Safety and Health (NIOSH) states that safe exposure limits are set below those found to initiate eye irritation, the body surface most susceptible to UV. Next table shows the permissible exposure times for given effective irradiances at 254 nm wavelength.

     

    Permissible exposure time (a) Citation a. The occupational exposure limit for UV-C at 254 nm is 6,000 μJ/cm2. This can be also calculated with the following formula: Dose (in μJ/cm2) = Time (in seconds) * Irradiance (in μW/cm). Effective irradiance
    (μW/cm2)
    (Units given) (Seconds)

    8 h

    28,800

    0.2

    4 h

    14,400

    0.4

    2 h

    7,200

    0.8

    1 h

    3,600

    1.7

    30 min

    1,800

    3.3

    15 min

    900

    6.7

    10 min

    600

    10

    5 min

    300

    20

    1 min

    60

    100

    30 s

    30

    200

    10 s

    10

    600

    1 s

    1

    6,000

    0.5 s

    0.5

    12,000

    0.1 s

    0.1

    60,000

    Exposures exceeding this limit would require the use of personal protection equipment to protect the skin and eyes.

     

    In order to avoid overexposure of UVGI, education of health care workers should include basic information on UVGI systems and their potential harmful effects of if overexposure occurs.

     

    • (a)The occupational exposure limit for UV-C at 254 nm is 6,000 μJ/cm2. This can be also calculated with the following formula: Dose (in μJ/cm2) = Time (in seconds) * Irradiance (in μW/cm).
    References
    • 1.I Coker, E Nardell, B Fourie, P Brickner, S Parsons, N Bhagwandin and P Onyebujoh. Guidelines for the Utilisation of Ultraviolet Germicidal Irradiation technology in controlling transmission of tuberculosis in health care facilities in South Africa. MRC.
      http://www.sahealthinfo.org/tb/guidelines.pdf
    • 2.Xu P. Ultraviolet germicidal irradiation for preventing infectious disease transmission. Boulder, CO: University of Colorado, Department of Civil, Environmental, and Architectural Engineering; 2001.
    • 3.Collins FM. Relative susceptibility of acid-fast and non-acid-fast bacteria to ultraviolet light. Appl Microbiol 1971;21:411–3.
    • 4.Kethley TW, Branch K. Ultraviolet lamps for room air disinfection. Effect of sampling location and particle size of bacterial aerosol. Arc Environ Health 1972;25:205–14.
    • 5.Riley RL, Permutt S. Room air disinfection by ultraviolet irradiation of upper air. Air mixing and germicidal effectiveness. Arch Environ Health 1971;22:208–19.
    • 6.Riley RL, Kaufman JE. Air disinfection in corridors by upper air irradiation with ultraviolet. Arch Environ Health 1971;22:551–3.
    • 7.Ko G, First MW, Burge HA. The characterization of upper-room ultraviolet germicidal irradiation in inactivating airborne microorganisms. Environmental Health Perspectives 2002;110:95–101.
    • 8.Ko G, First MW, Burge HA. Influence of relative humidity on particle size and UV sensitivity of Serratia marcescens and Mycobacterium bovis BCG aerosols. Tubercle Lung Dis 2000;80:217–28.
    • 9.Peccia J, Werth HM, Miller S, Hernandez M. Effects of relative humidity on the ultraviolet induced inactivation of airborne bacteria. Aerosol Science and Technology 2001;35:728–40.
    • 10.Riley RL, Kaufman JE. Effect of relative humidity on the inactivation of airborne Serratia marcescens by ultraviolet radiation. Appl Microbiol 1972;23:1113–20.
    • 11.First MW, Nardell EA, Chaisson W, Riley R. Guidelines for the application of upper-room ultraviolet germicidal irradiation for preventing transmission of airborne contagion—part I: basic principles. ASHRAE Trans 1999:105:869–876.
    • 12.Riley RL, Nardell EA [1989]. Clearing the air: the theory and application of ultraviolet air disinfection. Am Rev Respir Dis 139(5):1286–1294.