RACA Journal November 2021 | Page 49

Technical

Figure 3a : Typical elevation view of upper room UV-C applied in a hospital patient room ^xii

Figure 4 : Typical elevation view showing upper room UVGI fixture and UV intensity level ^xiii

Upper-room UV-C fixtures are selected based on the floor-toceiling height . Ceiling heights above 9.8ft ( 3m ) may allow for more open fixtures , which may be more efficient because they may allow for a larger vertical irradiation zone . In occupied spaces with lower ceilings ( less than 9.8ft ( 3m )), various louvered upper-room UV-C devices ( wall-mount , pendant , and corner-mount ) are available for use in combinations and are mounted with at least 6.9ft ( 2.1m ) from the floor to the bottom of the fixture .

The fixture should be mounted so that its UV energy is distributed parallel to the plane of the ceiling . Device construction , adjustment , and placement protect occupants from excessive ultraviolet energy . For example , in high-risk areas such as corridors of infectious disease wards , a maximum

UV irradiation of ( 1 μJ / s )/ 0.155 in ² ( 0.4 μW / cm ²) at eye level is an acceptable level based on an engineering guide ^xiv . No longterm health effects of UV-C exposure at these levels in the lower occupied part of rooms are known .

Figure 4 shows a typical installation position and illustrates typical UV-C intensity level in a room . Many UVGI fixtures produce visible light to help indicate when the fixture is turned on . A UV-C installation that produces a maintained , uniform distribution of UV irradiance averaging between 30 and 50 μW / cm ² is effective in inactivating most airborne droplet nuclei containing mycobacteria and is presumably effective against viruses as well ^xv .

Beyond UV-C irradiance , effectiveness of upper-room UV-C is related to air mixing , relative humidity , and the specific characteristics of the pathogenic organisms being addressed ^xvi . Effectiveness can improve greatly with wellmixed air ^xvii , so ventilation systems that maximise air mixing receive the greatest benefit from upper-room UV-C .

Upper room UV-C is already proven 80 % effective against tuberculosis ( TB ) spread in two hospital-controlled studies ^xviii , ^xix .

Advantages

• Suitable for all climates and ventilation conditions

• Achieves high levels of equivalent air changes / hour ( equivalent ACH )

• A permanent built-in solution for room air disinfection

• Disinfects large volumes of room air when combined with forms of mechanical ventilation , natural ventilation , or hybrid types to mix the air ; and have a secondary benefit for surface decontamination

• Can be safely deployed and effectively used with proper installation , commissioning , operation , maintenance , and facility staff training

• Mitigates airborne spread of tuberculosis

• Available in a variety of open and louvered fixtures for different room geometries

Table 2 : Suggested UV-C Fixture Mounting Heightsi ( Note ¹ )

1 Note that this table is a guidance only and additionally , manufacturer-specific advice on product operation and placement should be followed . Appropriately designed UV fixtures are available for all locations . Only the most commonly-used have been included in the table .