Covid-19 Increases Interest in UltraViolet Light for Disinfection

EXPERTS from the Illuminating Engineering Society (IES) have weighed into the animated debate about the coronavirus and ultraviolet lighting.

Scientists from the highly-respected body have confirmed that a particular section of ultraviolet light – shortwave ultraviolet light from 200 to 280 nanometres, termed UV-C – can kill the coronavirus at the right dose.

However, it cautions against using UV-C lights to disinfect surfaces and recommends that the lighting industry concentrate its efforts on disinfecting the air instead.

While UV-C could be a secondary infection control measure for disinfecting potential germ-carrying deposits on accessible (not-shadowed) surfaces, its great value would be in disinfecting air in areas where this may be a concern.

Examples could include intensive care wards.

Upper-air germicidal ultraviolet is the safest, most effective application of UV-C. 

In special locations, where viral transmission is highly likely, whole-room UV germicidal irradiation from suspended fixtures directing UV-C downward could be applied, provided strict precautions can be followed. 

It is critical that any persons remaining in the space being disinfected from overhead and side UV-C lamps wear protective clothing and eye protection, or exposure to harmful UV will occur.  UV light will also kill healthy human cells so exposure cannot be allowed.

Whole-room germicidal ultraviolet has been safely applied in unoccupied rooms where entry is forbidden during the irradiation.

The IES says that while UV-C is an excellent surface disinfectant, it does not penetrate surfaces and cannot disinfect soiled surfaces. 

The inability of the UV radiant energy to reach shadowed recesses of surfaces or to penetrate coverings like dust and other matter may negatively affect disinfection. 

For these reasons, ultraviolet germicidal irradiation (UVGI) is typically used as a supplemental control measure for disinfection. 

It refers to a study published in 2005 which concluded that UVGI lamps could have some effect on the spread of infectious respiratory diseases, but there was inadequate evidence to support recommending its wide use.

The IES is, however, positive about what’s termed upper room use of UV.

Upper-room germicidal ultraviolet is a safe means of air disinfection that is possible in rooms with high ceilings. 

In this method, specially designed and installed UV-C fixtures that irradiate only the air above 2.1 meters (7 feet) constantly disinfect the upper air volume. 

Upper-room use of ultraviolet lighting to kill air-borne viruses and bacteria.

This is most effective when there is constantly mixed air by fans and HVAC ventilation, but even without strong ventilation or fans, air constantly mixes by movements and normal convective currents. 

It says that upper-room use of germicidal ultraviolet lighting is more effective than ultraviolet in ventilation ducts or in room air cleaners. 

Upper-room germicidal ultraviolet disinfects large volumes of room air above occupants’ heads at once, resulting in high ‘equivalent’ air changes per hour in terms of air disinfection only. Germicidal ultraviolet does not dilute odours or carbon dioxide, the main functions of building ventilation. 

The IES’s intervention also provided clarification on the use of UV-C in HVAC systems. 

The problem with UV-C light at the head of air-conditioning systems is the dose has to be huge to even go close to compensate for the air velocity and limited exposure time so they usually won’t spend the money or maintain the systems.

Even filter media within air-conditioning ducting isn’t well maintained, filling with dust blocking air flow and again harbouring germs, most of which are harmless but then some not so harmless.

The overall conclusion is that while UV-C may be helpful in disinfection applications it should be considered with a high degree of caution.

Courtesy of Lux Review, April 2020