Technical
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• UV-C exposure hazards
• Electrical safety
• Lock-out / tag-out ( for in-duct units ) Health hazards of mercury
• Rotating machinery ( for in-duct units )
• Slippery condensate pans ( for in-duct units )
• Sharp unfinished edges ( for in-duct units )
• Confined-space entry ( if applicable ) ( for in-duct units )
• Emergency procedures
The Centre for Disease Control and Prevention ( CDC ) and National Institute for Occupational Safety and Health ( NIOSH ) published a recommended exposure limit ( REL ) for occupational exposure to UV radiation xxiii .
The REL is intended to protect workers from the acute effects of UV exposure , although photosensitive persons and those exposed concomitantly to photoactive chemicals might not be protected by the recommended standard . Exposures exceeding CDC / NIOSH REL levels require that workers use personal protective equipment ( PPE ) consisting of eyewear and clothing known to be non-transparent to UV-C penetration , and which covers exposed eyes and skin . UV inspection , maintenance , and repair workers typically do not remain in one location during their workday , and therefore are not exposed to UV irradiance levels for 8 hours .
Threshold Limit Value ® ( TLV ®) consideration should be based on real-time occupancy of spaces treated by UV-C xxiv . This recommendation is supported by UV monitoring data from First et al . ( 2005 ), which showed that peak meter readings poorly predict actual exposure of room occupants .
Individuals working on UV-C must be protected to prevent UV hazards to the eyes and skin . UV-C should not be used to disinfect the hands since mild erythema ( sunburn ) occurs when skin is exposed to UV-C . UV-C is almost entirely absorbed by the outer dead layer ( stratum orneum ) and outer skin ( outer epidermis ), with very limited penetration to the deeper cellular layers of skin where new cells are constantly created . which is why UV-C fixtures are typically installed overhead ( or called upper-room ), preventing UV light exposure to humans .
The human eye is the organ most susceptible to UV-C because it has no outer dead protective layer . When the UV-C source is overhead , the eyes receive very little exposure during normal activities , just like sunlight when the sun is overhead . It appears there are no known long-term consequences from an accidental UV-C overexposure xxv .
The CDC has provided guidelines for the use of UVGI lamps in upper rooms and AHUs as a supplemental control measure for air disinfection xxvi , xxvii , xxviii
To ensure the safe use of UVGI lamps for air disinfection , follow these guidelines xxix :
• All lamps - Workers should place warning signs near upperroom UVGI lamps and on AHU access panels where internal UVGI lamps are installed . Activation switches should be
RACA Journal I January 2022 clearly labelled and protected with switch guards to prevent accidental activation by unauthorised personnel . If exposure cannot be avoided , workers should wear plastic or glass face shields to protect the eyes and face , nitrile gloves or work gloves to protect the hands , and full-coverage clothing with tightly woven fabrics to protect all other exposed skin . Many fixtures incorporate a safety switch that breaks the circuit when fixtures are opened for servicing and should contain baffles or louvers appropriately positioned to direct UV irradiation to the upper air space . Baffles and louvers must never be bent or deformed .
• Upper-room UVGI lamps - Proper installation is critical to ensure the safe use of these lamps . It is important that ceiling reflectance at the UV-C wavelength be studied before installing in a new location , since downwelling UV-C could be increased . Regular work activity should not resume in rooms with upper-room UVGI lamps unless qualified measurements have confirmed that the potential radiant exposures in the lower room are within the 8-hour exposure limit . Except in very large rooms , the emitting lamps should not be visible to occupants in the lower room .
• AHUs with internal UVGI lamps- Access panels for AHUs with internal UVGI lamps should be interlocked with automatic shutoff switches to prevent accidental exposure to UV radiation . An inspection window that blocks germicidal UV energy ( e . g ., plastic or glass ) should be installed to allow workers to see whether the UVGI lamp inside the AHU is operating .
• During commissioning and before operation of the UV-C installation , hand-held radiometers with sensors tuned to read the specific 254 nm wavelength should be used to measure stray UV-C energy and should be used in upper-room systems . xxx
• UV irradiation should never replace sterilisation of surgical instruments .
CONCLUSION UV-C is now used as an engineering control to reduce transmission of pathogenic organisms .
Primary applications include
• Using upper room UVGI systems
Secondary applications include
• In-AHU UVGI ( coil , filter and drain irradiation )
• In-duct and in-AHU UVGI ( airstream disinfection )
• Mobile air cleaning UVGI units
• Mobile whole room ( bare light ) UVGI units
Where feasible , a whole-building approach to UV should be considered .
Various articles suggest that the SARS-CoV-2 virus can be inactivated by UV-C at 254 nm if directly illuminated by
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