COVİD-19& HVAC SYSTEMS

The name of the COVID-19 is the combination of the initials of COrona VIrus Disease and the year 2019 that the disease appeared. COVID-19 is a disease caused by Coronavirus whose full name is Severe Acute Respiratory Syndrome Coronavirus and is called SARS-CoV-2 shortly. The meaning of the Corona is crown in English. However, it is mostly used to mean a circle of light that can be seen around the stars. The virus was discovered under the microscope with similar to these figures and named with it.

HOW is COVID-19 transmitted?

There are 3 transmission routes supported by epidemic models and case studies for COVID-19:

1. Transmission through surfaces (Fomite Transmission): Fomite Transmission means that to be infected through contact with contaminated surfaces or objects. For example, if a person cough through the object or touch to the surface with hands after sneezing, surface might be contaminated. People who touch the fomite and then touch their eyes, nose, or mouth without washing their hands may be exposed to the virus. Life span of the virus depend on the surface type and environmental conditions. Covid-19 virus can be detected on surfaces with different characteristics at certain times. But, the amount of infectious virus decreases in time. The transmission rate of the virus with the fomite can be minimized by frequent cleaning and disinfection of touched objects, using non-contact alternatives (exp. Automated doors, contactless payment) and frequent hand washing.

2. Transmission by droplets (in close range): Aerosol can be generally defined as suspension of fine solid particles or liquid droplets in the air. Scientists describe the particles that spread out and fall on the ground after few meters as “droplets” (>5 microns in diameter) and much smaller ones (<5 microns in diameter as “aerosols”. Close range contact transmission through the droplets means, the virus is transmitted in a short distance by sneezing or coughing directly into the face of the infected person. Social distance and face masks can minimize the risk of the transmission risk. 

3. Transmission by aerosols (in long range): Could the COVID-19 virus be transmitted by airborne transmission? This question has been the source of COVID-19 uncertainty for a long time. A paper about Airborne Transmission of COVID-19 accepted by the World Health Organization on the 6 of July, which signed by 239 scientists around the world became the turning point. Since then, Scientists stated that, they suspected of the aerosols which could hang in the air for a minute, could cause infection and perhaps, it could be spread large area through aerosols. This claim is seen as a major change since the early days of the outbreak when the large droplets contaminating surfaces by infected person coughing or sneezing were thought to be the main cause of the spread of COVID-19. Furthermore, coughing or sneezing to others faces directly is the only way of the transmission of the virus beside contaminated surfaces, if the aerosols removed from the reasons. Outbreaks are the major of epidemiologists and infectious disease specialists. On the other hand, aerosols are depending on physics, chemistry and engineering. When the deep and well-known nature of the Aerosols combined with the insufficient evidence of COVID-19 transmission through the droplets, requires to think twice how the corona virus spreads. Transmission with Aerosols refers that, spreading the virus with transmission of the aerosol that occurred when the infected person talks, cough or sneeze inhaled by another person. (According to scientist, a cough can create almost 3000 droplets, but sneezing can create approximately 40.000 droplets and most of them could be small droplets (1-10 micron). The size of the 80-90% droplets exposed to transmission with the aerosols due to the normal speaking and breathing are <1 micron. Speaking can create more aerosols compared to singing, yelling or breathing. Aerosols with different diameters that are 0.12 microns (about one-sixth of a human hair) wide are suspected of carrying SARS-CoV-2 viruses. The virus transmitted by aerosols can also infect the people who do not interact closely with the infectious person but being in the same room for a certain period of time by hanging in the air. The important point is people who do not know they are infected yet can also transmit the virus by talking or breathing into the place.

Accepting the fact that COVID-19 can be transmitted through the air cause another question: If these invisible particles floating in the air are a source of serious infection, how can we slow the spreading rate of the disease? Although washing hands, social distance, and wearing masks are very important precautions, rising of the aerosols as a transmitting method forced the community to find new methods against to the virus. All the strategical purpose of fighting with virus is making the place more secure with taking necessary measurements and reducing the risk.

Methods of fighting against COVID-19:

• Each building’s characteristic, therefore its air conditioning and ventilation systems are different. These buildings should be inspected by expert engineering firms, precautions to be applied and fortifications throughout the pandemic period should be executed uniquely to each building.

• Limiting the occupants who remain on interiors should be limited (2-meter social distancing greatly reduces aerosol transmission.)

• Processes executed within interior sections of the building, should migrate to exterior parts if possible.  

• Places where aerosols are building up without proper ventilation or where aerosols can travel frequently between close people should be avoided, if occupying the area is a must, time intervals should be kept short. Particles carrying virus can remain airborne where ventilation is insufficient. Time period of virus loaded particles’ remaining airborne is based on properties of the area. Higher times spent in these areas, increase the exposure risk.

• Increasing fresh air ratios of HVAC systems and air circulation periods (5-6 cycles per hour)

• Filters that have MERV-13+ rating are recommended (If it is possible to apply on existing AC central, or portable air cleaners are suitable as well). MERV13 can filter up to 99,97% of particles greater than 0,3 micron. Virus loaded particles dispersed from respiratory systems can travel particles bigger than 1 micron. Smaller particles can gather up easier due to particle physics.

• UV-C application, is a viable solution to an already existing AC central. It should be reminded that applications without proper training and certification can be harmful to human health.

• HVAC systems installed in buildings should be maintained by expert teams on consistent periods.

On the other hand, getting infected by being exposed to COVID-19 loaded aerosols depends on time of exposure and aerosol concentration. Lowering the aerosol concentration in the environment, lowers the exposure risk, therefore the risk of getting infected. Although exposure is a function of density, frequency and time; risk is determined by many additional factors. Most important, personal risk, depends on personal susceptibility. This is determined by age, gender, preexisting conditions or genetics. Hence, two people with the same exposure may have vastly different risks. Debates on risk is codependent with personal risk tolerance. Finally, risk is also a function of capacity of health facilities, efficiency of current treatments and underlying contagion degree; which are non-personal factors.