Published:  01:53 AM, 10 August 2020

UV technology to deal with Covid-19 -- I

UV technology to deal with Covid-19 -- I

Medical treatment aside, we have to look into what can be possibly done to minimize the spread of the virus and once it is spread, what steps to take to avoid further transmission.  It makes sense for the public to understand one of the basic mechanisms of the spreading of the virus.

According to The US Govt's Centre for Disease Control, as we just sit and breathe normally, we generate about 20 particles per minute (saliva or fluid from nostrils and mouth) . If we are talking, we will be generating 200 particles per minute and if we cough or sneeze, it will create 200 million particles.  If the person has a viral infection, he will be generating a lot of virus which can be transmitted.

The need for distancing arises out of this simple mechanism which we must get into our thinking. The wearing of the mask is essential to stop the stray gust pushing the particles in our direction. It makes sound sense to wear a face shield for persons facing the public for longs hours in the banks and offices.

As we go out in public places, we are protected by the mask, face shield, the gloves and the protective clothing.  Don't forget that if they had protected you they have themselves collected the virus if they were exposed to. The very items which gave us protection have themselves got infected.                          

What next?  and what can we possibly do, now that we know that something could be sticking onto our items  of Protective Clothing  .  This answer will be given in the following paragraphs. 

Steps at Institutional Levels A lot can be done at institutional levels to ensure the safety of those working there, or those seeking the services i.e. customers/clients. Places like offices, banks, hospitals, airport, markets or any public place you can think of. Various levels of sophistication and automation can be employed.

Individual organizations have to develop their own   SOPs, otherwise known as standard operating procedures. Which will be different in a hospital, airport or a Bank or other public offices What follows in the next few paragraphs centre around the UV (ultra violet) technology.

UV (Ultra Violet) Technology
A short Introduction:  What is UV:   Uultraviolet (UV) radiation is a form of electromagnetic radiation that comes from the sun and also from man-made sources like arc welding and purpose built UV bulbs/lamps.

The color of the light we see, red, blue etc depends upon the wavelength. In the electromagnetic spectrum ,the visible light  starts from  Red which has a  wavelength about 625-740 nm (nano meter),This is  in the high end, then yellow, green ,cyan, blue, and, violet being  at the low end , and this has a wavelength of 380-435 nm. Above 740nm, i.e. above the red, the range is called infra red and below the 435nm range is the ultra violet (UV). They are both invisible to the human eye. It is this UV, we are currently interested.

UV Classification and Properties

UV has been divided into three groups.  UV A has a wavelength range of 315-400nm, UV B from 280-315 nm and UV C from 200 to 280 nm. UV A and B has very little germicidal activity. 

The UV C has the maximum germicidal capacity with the peak being around 265nm this range UV C   is absorbed by the DNA and RNA of microorganisms which causes a change in DNA, RNA structure rendering it incapable of reproducing within a host, and is therefore considered essentially dead. UV C has proven very effective against broad range of micro organisms. Viruses contain RNA or DNA and are susceptible to UV irradiation, similarly bacteria and fungi both contain DNA and are therefore vulnerable.
Sunlight in the context of UV   Sunlight is the main source of UV radiation; about 95% of the UV rays from the sun that reach the earth are the UVA, with the remaining 5% UVB. UVC gets mostly blocked in the upper atmospheres.


As previously mentioned, UV  C   has  more penetrating power than UV A ,  UV B, and it is not safe to be in the room where the disinfection is in progress (the light is ON).  UV-C is classified as "reasonably anticipated to be a human carcinogen" by the National Toxicology Program. Direct exposure to the eyes particularly and the skin is to be avoided.  Fortunately UV C is blocked very easily, by glass and most clear plastics and even thick cardboard.

Some mention of UV technology which could be used in the current scenario  UV bulbs/lamps  are gas filled which emit light at the UV C range, there is  however a class of lamp which besides primarily emitting the UV C range also emits a range which generates  in the air Ozone gas,  and this gas also acts as a disinfectant .  This type can be advantageous in certain circumstances if it can be handled properly.

The UV  disinfection   occurs only  on surfaces / air on which the UV light has fallen upon,  the ozone being a gas will permeate  and travel all over the place  even those places  where UV light was shaded and could not reach,  and in this case the ozone would act as a disinfectant in those areas as well.

There is however one disadvantage to using ozone-type bulb. If it takes 25 minutes for the sterilization process, it will take another 30 min for expelling the ozone generated, and in a closed air conditioned space, this may not be possible.  Without proper purging, ozone may cause irritation of the respiratory tract, eyes, headache, nausea, difficult breathing etc. Therefore it makes sense to specify Non Ozone generating UV C lamps is all of the equipment mentioned below.

1. UV Room air Sanitizers

i. Fan Type Circulator. This is continuous air disinfection equipment, and can operate 24 hours even in the presence of people.  All UV equipment like this one is essentially simple. One or more UV C bulbs are used to disinfect or sanitize the air passing over it.  

In the Present case the room air is drawn into a metal cabinet and flows over 2, 3 or more UV lamps/ Tube. The air remains in contact with the UV light for a few secs, killing all microbes, bacteria   virus etc. Depending upon the use, the air then may be filtered and cleaned   to the required degree of cleanliness.

HEPA (High efficiency particulate Filter) is used together with pre filters and post air filters for surgery rooms, burn centres, hospital, doctors chambers, etc. Lesser degree of filtration may be used for waiting rooms and banks etc where the HEPA filter is not used.Such equipments are used to protect occupants from infection due to air borne microbes where there is risk of cross infection in crowded and poorly ventilated areas.

The equipment  are quite like room air coolers and available in  wall recessed or free standing models  and sized according to the  room size i.e., air flow required, and depending upon the crowding and infection spreading possibility, some 4-6 (6 is better) air changes per hour are often quoted.  Mobile versions on caster wheels do not require any installation and can be taken around from room to room and serve the same purpose.

ii. FREE  or Convection Circulation Type.  This is another variant of   the continuous disinfection equipment and can operate 24 hrs if necessary and in the presence of people.

There are no fans to force the air through. This equipment is even simpler. Few UV tube lights are fixed in a metal housing on the wall and placed at such an angle so that the UV light is not focussed onto occupants or people in the room. The angle is somewhat horizontal up. Proper care has to be taken so that the light is not reflected down onto the occupants: Objects like fan, light holders, shinning surfaces and anything that reflects has to be considered.                                      
The working mechanism is simple. Since the UV rays are projected into the upper room air and due to the natural air convection flow between the upper treated air and the lower untreated air there is appreciable reduction in the number of airborne organisms, thus the danger of airborne infection is considerably reduced.                     
As we can see there is no filtration of the air, as the bacteria/virus in the air gets illuminated by the UV, they are killed and rendered harmless.In places where there is crowding of patients, staff, customers etc constant cleaning and disinfecting is not easy or may not be possible. This type seems to be the answer. It is cheaper, simple to operate.

2. Surface Irradiating Equipment
Portable Air and surface Equipment

Surface irradiation means disinfection of any surface, table, wall, bed, materials of clothing, masks, gloves etc. As the UV lamp/ is shinning on the surface, it sterilises the surface and also the air it is passing through. The objective here is to sterilise the surface rather than the air.      
These devices are, vertical UV lamps fixed in a "lantern like "housing holding the lamps. Higher wattage assemblies (100W to 500W UV) are heavy and are made mobile on caster wheels, and can be moved around from room to room.
    (To be continued...)

Tanbirul Quadir Choudhury is retired Chief Engineer,
BAEC, Dhaka

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