Ultraviolet spectral reflectance of ceiling tiles, and implications for the safe use of upper-room ultraviolet germicidal irradiation.

Ultraviolet germicidal irradiation can be used to prevent airborne transmission of infectious diseases. A common application is to irradiate upper-room areas, by passing air from the lower room into the irradiated zone. Well-designed systems do not expose people directly; however, some UV radiation may be reflected off ceiling tiles and wall paints into the lower room. Lower room exposure should be limited to the American Conference of Governmental Industrial Hygienists threshold limit value of 6 mJ·cm(-2) of 254 nm radiation per day. To limit the lower room exposure, the reflectance of upper-room surfaces must not be high. The reflective properties of wall paints have been studied, but less is known about the UV reflectance of ceiling tiles. Using a double monochromator spectroradiometer and an integrating sphere reflectance attachment, the UV spectral reflectance of 37 ceiling tiles was measured from 200 to 400 nm. The reflectances varied from 0.020 to 0.822 in this range, and from 0.035 to 0.459 at 254 nm, the main wavelength emitted by upper room low-pressure mercury germicidal lamps. These data were then used to estimate an 8 h exposure based on several simplified workplace scenarios. The implications for workplace safety are then discussed.