Technical
Figure 9 : Intensity of different UV Lamps vi
It is important to take the application condition of the lamp into account , as the surface temperature and airflow speed in contact with the lamp tube affects the lamp output .
Figure 10 : Effect of lamp surface temperature on UV output .
The ballast selection affects the lamp output and serviceable life , and may also create audible noise ( electromagnetic ), EMI / RFI and affect power quality .
EFFECTIVENESS OF UV-C TO INACTIVATE SARS-COV-2 Various articles vii suggest that the SARS-CoV-2 virus ( responsible for Covid-19 ) can be inactivated by UV-C at 254 nm if directly illuminated by UV-C at the effective dose level . UV light exposure is a direct antimicrobial approach viii , ix and its effectiveness against different strains of airborne viruses has long been established x , xi .
The National Emerging Infectious Diseases Laboratories ( NEIDL ) xii at Boston University in the US have conducted research in conjunction with the lighting company Signify to validate the effectiveness of UV-C light sources on the inactivation of Covid-19 . Their research applied a dose of 5mJ / cm ², resulting in a reduction of the Covid-19 virus of 99 % in 6 seconds xiii . Based on the data , it was determined that a dose of 22mJ / cm ² will result in a reduction of 99.9999 % in 25 seconds .
It is worth mentioning that the performance of far UV-C light ( 207-222 nm ) was compared xiv with UV-C light ( 254 nm ) and found these results :
• Very low doses of far-UV-C light can inactivate the airborne human coronavirus . Tests have shown that a dose as low as 1.2 to 1.7 mJ / cm ² of 222-nm light has inactivated 99.9 % of the airborne human coronavirus .
• Safety studies have shown that far-UV-C light cannot penetrate either the human stratum corneum ( the outer dead-cell skin layer ), nor the ocular tear layer , nor even the cytoplasm of individual human cells xv , xvi , xvii , xviii , xix , xx , xxi . Thus , far-UV-C light ( 222 nm ) cannot reach or damage living cells in the human skin or the human eye . Together with these safety studies mentioned and studies with aerosolised influenza-A ( H1N1 ) xxii , these results suggest the utility of continuous low-dose-rate far-UV-C light ( 222 nm ) in occupied indoor public locations such as hospitals , transportation vehicles , restaurants , airports , and schools , potentially representing a safe and inexpensive tool to reduce the spread of airbornemediated viruses .
Therefore , low-dose-rate far-UV-C exposure can potentially safely provide a major reduction in the ambient level of airborne coronaviruses including SARS-CoV-2 , while staying within the current regulatory dose limits .
UV-C SAFETY UVGI lamps pose a health hazard to the eyes and skin . Only trained maintenance staff with UV specific training should be allowed to work on UV-C systems or work in any area where UV-C is present . All UV-C systems require periodic inspection , maintenance , and lamp replacement to ensure proper system performance . Whenever maintenance is performed on UV-C systems , the appropriate safety guidelines , listed below , should be carefully followed . Training topics should include at least the following :
www . hvacronline . co . za RACA Journal I January 2022 55