Giving Far UVC all-areas access
Along with cost, safety concerns have stood in the way of the widespread deployment of UVGI lights throughout the spaces in which we work, live and play. Although fears about the supposed harms posed by use of UVC germicidal light in occupied spaces are often overblown and unsupported by evidence, in order for this vital technology to become mainstream it is necessary to address concerns about potential negatives while educating the public about the overwhelming benefits. Here at Candelo, we are passionate about activating our unique technology to democratise access to affordable, safe and effective Far UVC lighting. Our patented filterless 207 nm tube overcomes the dilemma of price and safety issues (both real and perceived), and can facilitate the expansion of germicidal UV devices into a range of buildings and usages previously thought impossible at a scale hitherto unaffordable.
Prior to the commercialisation of Far UVC, most UVGI solutions for inactivating airborne viruses and other pathogens in enclosed spaces have utilised wall-mounted just below ceiling height. Such upper-room UVGI devices work on the premise that as warm exhaled air rises up it can be sterilised by the UVC light beam without exposing people to excessive levels of 254 nm UVC emissions. Solutions utilising 254nm and LED UV light sources are safe and effective when confined to the overhead space, with proper design and commissioning to ensure ongoing adherence to TLV guidelines. Despite this, they can be difficult to safely deploy in many spaces, such as modern buildings with ceiling heights of less than 3 metres, where human head height is necessarily close to the light source. Furthermore, reflective surfaces such as glass or polished steel can result in reflections of the UVC beam that create unintended irradiation vectors that need to be managed through lighting design.
Far UVC, in particular the 207nm wavelength, overcomes these challenges by virtue of the fact that it is vastly better tolerated by human skin and eye tissue when compared to the higher wavelengths. This allows for the deployment of Far UVC bulbs in nearly any indoor environment, with the possibility of retrofitting our revolutionary 207 nm tubes into existing light fixtures like regular lightbulbs. As a result of being able to place the UVGI beam closer to people without the design constraints posed by higher wavelengths like 254nm, the germ-killing efficacy is also greatly boosted due to its closer proximity to the site of viral transmission (primarily the mouth and nose).
The ability to place Far UVC closer to the vectors of spread, combined with the lower wavelengths’ enhanced viral inactivation capabilities, provides a UV lighting solution that kills viruses like SARS-CoV-2 in ‘mid-flight’, in real-time, as they float throughout enclosed spaces as invisible aerosols.
Far UVC germicidal lighting – an essential tool in the fight against airborne diseases
It is now widely accepted that airborne transmission of SARS-CoV-2 is the primary vector of spread between people. Tiny particles (<5 μm) generated when an infected person coughs, sneezes, talks loudly, or even via normal breathing, can become airborne and travel several metres, with the contained viral particles able to remain viable for hours. The current tools at our disposal – physical distancing, face masks and indoor air quality enhancements (HVAC upgrades and HEPA filters) – go some way to controlling aerosol spread, but they each have their own drawbacks and limitations.
- Physical distancing: The notion of encouraging people to maintain personal exclusion zones of around 2 metres / 6 feet was based on the idea that large droplets (fomites), such as those visible ones expelled when a person sneezes, will fall to the ground within this range. Not only has this idea been questioned by recent research, but it remains true that smaller aerosols contained in plumes emitted during coughing or sneezing can travel far beyond 2 metres (up to 8 metres according to some studies);
- Face masks: A properly fitted mask of at least N95 certification (filters 95% of particles >0.3μm) does provide some protection against aerosol and fomite spread, whereas the widely used surgical mask or homemade cloth variety will only provide limited protection from fomites. The other major problem with relying on face masks is that it is contingent on individual ‘buy in’ to be effective;
- Indoor air quality: Improving air circulation in indoor environments and preventing the recirculation of virus by capturing them in HEPA filters likely carries some benefits in mitigating the airborne spread of disease. However, increased air movement will not necessarily stop an infected person transmitting a payload of viral droplets via aerosols to another person and infecting them. Moreover, re-engineering HVAC systems and adding HEPA filtration carries high costs and has therefore had low uptake by businesses and organisations facing budgetary pressures.
Progression to the next stage of ‘living with Covid’ requires a multi-pronged mitigation strategy aimed at limiting aerosol spread. Far UVC germicidal lighting is poised to become the missing piece in the puzzle.
Inactivation of SARS-CoV-2 in X seconds within X hours of safe exposure
The latest scientific research into Far UVC (Ma et al), read in conjunction with the updated 2022 threshold limit values (TLVs) for UVC irradiation published by the ACGIH, suggests that it is possible to apply a 1:1 ratio of the time required in seconds to inactivate the SARS-CoV-2 virus to the time in hours that people can be safely exposed to the 207nm light source.
Inactivation of SARS-CoV-2 in X seconds within X hours of safe exposure
The latest scientific research into Far UVC, read in conjunction with the updated 2022 threshold limit values (TLVs) for UVC irradiation published by the ACGIH, suggests that it is possible to apply a 1:1 ratio of the time required in seconds to inactivate the SARS-CoV-2 virus to the time in hours that people can be safely exposed to the 207nm light source. By way of example, consider a typical office environment where workers are inside for 8 hours each working day.
The TLV guidelines say human skin can receive ~4J/cm2 (Dosage) over this 8 hour period at 207nm.
There are 28800 seconds in 8 hours (8*60*60)
Power/cm2 (Intensity) = Dosage / Time = 4 (J/cm2) / 28800 (seconds) = 139 μW/cm2
Although the new TLVs for eyes are significantly lower than those for skin, eyes are well protected from ceiling-mounted lighting and the dosage received is a fraction of that absorbed by the skin, due to the lack of direct exposure (people don’t stare at lights, so only reflected light will be absorbed for the majority of the exposure time). Research indicates eyes receives around a third of the dosage that the skin will in a typical setting, well within the new eye TLV.
So we need to carry out lighting design so that at head height the office workers are receiving of no more than 139 μW/cm2. The results of Ma et al.’s study published in 2021 by the American Society for Microbiology show a linear relationship between lowered UVC wavelength and increased germicidal efficacy, such that the inactivation dosage for SARS-CoV-2 at 207 nm is likely just over 1 mJ/cm2. At about 139 μW/cm2 the required dosage of 1 mJ/cm2 will be reached within 8 seconds.
Therefore, the inactivation dosage in the office can be achieved in 8 seconds in an environment where the occupants are able to be safely exposed for 8 hours per day.
With their high density of passengers and often poor ventilation, public trains and buses present a real risk for airborne spread of diseases like Covid-19.
If we take the example of a metro train, where a commuter who catches the subway to and from work might spend a maximum of 2 hours in a carriage per day, we can determine the appropriate design of the 207 nm UVC lighting for optimum germicidal efficacy within safe levels of exposure.
There are 7200 seconds in 2 hours (2*60*60)
Intensity = Dosage/Time = 4/7200 = 555 μW/cm2
Therefore, the inactivation dose in the train carriage can be achieved in 2 seconds in an environment where the occupants are exposed for 2 hours per day.
Passenger lifts and elevators, being highly confined with varying HVAC standards, pose a high risk of airborne transmission.
Let’s assume even the most active user wouldn’t spend more than 30 minutes inside an elevator on any given day.
There are 1800 seconds in 30 minutes (0.5*60*60)
Intensity = Dosage/Time = 4/1800 = 2222 μW/cm2
Therefore, the inactivation dose in the elevator can be achieved in half a second in an environment where the occupants are exposed for half an hour per day.
The pandemic has shown that older people are especially vulnerable to negative health outcomes and death from diseases like Covid-19. Rightly, there have been special efforts made to protect the frail and elderly in settings like nursing homes and aged care facilities.
Let’s take the example of a shared space like a dining hall, where a resident might spend a maximum of 4 hours over three meal sittings per day.
There are 14400 seconds in 4 hours (4*60*60)
Intensity = Dosage/Time = 4/14400 = 278 μW/cm2
Therefore, the inactivation dose in the aged care facility can be achieved in 4 seconds in an environment where the occupants are exposed for 4 hours per day.