The spread of coronavirus has tested medical science in its ability to control and treat a highly infectious and dangerous virus. Coronavirus has been determined to spread via respiratory droplets from close person to person contact, or by touching infected surfaces and then touching the mouth nose or eyes. However, some research has started to suggest that the virus may maintain an airborne presence in the form of drop nuclei, which may stay active and contagious for several hours. Furthermore, given correct environmental conditions, some surfaces and areas may maintain an infectious level for several days.

Germicidal UV (GUV) light can be used in an environmental intervention role to help reduce the spread of infectious bacteria and viruses in both airborne and contact spread cases. This has been done so successfully, and more importantly safely, over the last 70 years. However, it does not come without inherent health and safety risks and its use must be applied correctly and with the appropriate knowledge. Failure to do so poses potential issues to human health and safety and risks providing sufficient disinfection of the infectious agent. Under no circumstances is the use of GUV in the home or on human skin advised, except when it has been justified or it is medically required.

What is GUV

As part of the spectrum of radiation, UV has more energy than the more visible radiation that is experienced as light by people. From this come GUV, which is simple Ultraviolet radiation used in a germicidal capacity.
Ultraviolet radiation is categorised into 3 distinct regions:

● UV-A – Radiation within the range of 315-400 nm
● UV-B – Radiation within the range of 280-315 nm
● UV-C – Radiation within the range of 100-280 nm

With a higher level of energy than the other 2 regions, UV-C is considered the most effective part of the spectrum to use for the purposes of GUV. However, the other 2 regions can be used to cause some damage to some micro-organisms and viruses.

The required radiant exposure for an effective deactivation of infectious agents by up to 90% greatly depends on the current environmental conditions and the specific agent that is being targeted. The typical range is anywhere between 20 J/m2 and 200 J/m2 if using mercury lamps. This also assumes that these lamps are emitting radiation levels at around 254nm.

How to apply GUV for Disinfection

Disinfection of water sources has been a successful use of UV-C for several years now. Also, UV-C is often used within air handling units to disinfect air through the management of biofilm build-up. Historically, UV-C Sources were used to sterilise operating theatres and other rooms overnight, in many different countries. This was until the widespread introduction of polymer materials in the medical environment as well as access to, and the availability of, appropriate antibiotics.

Over time, and especially recently, the use of whole-room exposure to UV-C devices as a means to disinfect air and surfaces has seen a resurgence of interest. Such UV-C devices can be strategically placed within the room for a predetermined period of time or moved around by automated robotic devices. Such devices can also be placed close to surfaces, in order to target infected surfaces more effectively. As it currently stands only limited use of UV-C of PPE has been explored and only in limited countries.

UV-C now has growing evidence that its use as supplementation to manual cleaning methods can be effective in practice. However, to do so safely and effectively specific guidelines and practices for the application must be developed and encouraged. Testing procedures must also be standardised and implemented as well.

UV-C sources can also be mounted above head-height in rooms where circulating air is present. Due to the successful use of UV-C sources in limiting tuberculosis transmission, the WHO recommended UV-C as a control method for the prevention of the spread of tuberculosis.

Human health and safety risks with GUV use

UV-C Exposure does not come naturally to most people. By the time UV-C from the sun reaches someone, it has already been filtered out within the atmosphere. Normally the exposure people receive is from artificial sources. The UV-C will only penetrate the uppermost levels of the skin and rarely if ever, will reach the base level of the skin. It also does not seem to penetrate the eye any further than the cornea. This does not mean that it cannot cause any damage or painful effects. Exposure of the eye can cause a painful issue called Photokeratitis, a condition that feels like rough grains of sand being rubbed into the eye. This can last up to 48 hours, from initial exposure to the subsiding of the symptoms.

Skin exposure to large amounts of UV-C radiation also comes with the potential for damage. High exposure can cause erythema. Erythema is a reddening of the skiing, similar to a sunburn. This can be misdiagnosed as such, especially if the medical professional isn’t aware of recent exposure to UV-C. While less painful than damage to the eyes, some evidence has suggested that repeated exposure may cause damage to the immune system. As of yet, this hasn’t been 100% confirmed.

While UV is often considered a carcinogenic no evidence yet has suggested that UV-C alone is a cause of cancer in humans. Some reports have identified GUV from mercury lamps as a potential cause of cancer. However, the levels of radiation are less than that of even the Sun and pose no long-term significant risks to health.

Exposure guidelines have been set out by the International Commission on Non-Ionising Radiation Protection and state clearly what levels of UV radiation workers should be exposed to. These are as follows for unprotected eyes and skin (please note that these are daily limits):

● Maximum exposure of 30 J/m2 for 270nm
● Maximum exposure of 60J/m2 for 254nm
● Maximum exposure of 240 J/m2 for 222nm

Care must be taken when using certain UV-C emitting products as many will also emit UV-A and UV-B. Some do not even emit UV-C, even though they state they do. As consistent exposure to such products comes with risk, regardless of how small, measures must be taken to protect anyone nearby. If working in an area that has been heavily UV irradiated, appropriate industrial clothing, masks, gloves, and goggles must be worn.

Measuring UV-C

UV-C is easily measured on-site with a hand-held UV-C Radiometer. The Radiometer should be calibrated by an accredited lab so that measurements can be traced to the International System of Units. The lab in question should be accredited to ISO/IEC 17025. Remember that whatever source was used in the calibration report is the only source that a unit should be used to measure in the future. Using the radiometer on any other unit can cause massive discrepancies in future testing.

The lab that performs the calibration and produces the report should ask for and be aware of the unit that the Radiometer is to be used for. This is to ensure that the report is produced using the correct source and that future tests with the radiometer produce accurate results. For specific calibration ISO numbers, further advice is given here.

Current Consumer products on the market

In the current pandemic, there are many products being marketed as hand-held UV-C devices that claim to be capable of disinfecting areas from COVID-19. As there is much that must be known about the correct usage of UV-C emitting devices and due to their complex nature, consumers must be wary of purchasing such products. The general public must be aware that unaccredited products with no official validation may not be producing UV-C at all or they may be using the product unsafely.

Conclusion

UV-C emitting products are incredibly useful in disinfecting areas known to be contaminated with specific bacteria and viruses. They can be used to safely disinfect surfaces and air, but are warned against for disinfecting bare skin. Due to the hazardous nature of UV-C proper care and attention must be used when using UV-C emitting products as well as necessary protective equipment being worn. Safety is paramount in their usage and maintenance and as such should only be used by trained personnel, and devices should be calibrated and confirmed with a local specialist lab.