A study by the Indian Institute of Technology (IIT) Bombay states that surgical and N-95 masks can reduce the volume of a Covid-19-laden cough-cloud by 7 and 23 times, respectively. The study was published by the American Institute of Physics in the journal Physics of Fluids on October 20, 2020, estimated the volume of air contaminated by the cough of a Covid-19 patient. The results were based on the volume, temperature, and relative humidity of the cloud produced by coughing to understand their dispersion in the surrounding air.
The researchers used a mathematical model to analyse the fluid dynamics and thermodynamics of the cough cloud. They found that the cough cloud lasted between 5 and 14 seconds after which it would dissipate. The findings showed that the first 5 to 8 seconds after coughing are crucial for suspending infectious droplets in the air and, thereby, spreading the disease. It was found that after that time period, the cough cloud (the cloud of aerosols formed after a cough) starts dissipating.
The presence of a mask significantly cuts down the risk of infection to the other people present in the room. Similarly, actions such as coughing into the elbow and the use of a handkerchief can reduce the volume of a cough cloud and, therefore, the chances of dispersion of the virus.
When a person with Covid-19 infection coughs, sneezes or sings, infectious droplets are released into the surrounding air, thereby contaminating a large volume of surrounding air due to the jet-like flow created by the cough. Small virus-containing droplets have the ability to convert into aerosols, which can remain in the surrounding for much longer. Aerosols can also travel several metres (up to 8 metres), thus increasing the risk of infecting people at a larger distance.
The scientists found that an average-sized saliva droplet of diameter 10 micrometres takes around 15 minutes to fall to the ground. This increases the risk of infection transmission even when the social distancing rules are followed. This risk of transmission increases when the relative humidity is high or if the area is poorly ventilated.
With this study, scientists concluded that wearing a mask may not provide complete protection but can greatly reduce the risk of transmitting the infection to other persons present in the vicinity. The N95 mask or ‘respirator’ is designed to achieve a close fit as compared to other face coverings and has the ability to block even the smallest particles.
The World Health Organization (WHO) has stated that masks are key in helping to suppress transmission of the virus. A well-fitted mask is more important than a vaccine. An infected person can contaminate the air even with normal breathing and talking. By not wearing face masks, those carrying the virus can rapidly contaminate the air, especially in closed spaces.
It is, thus, advisable to wear masks in crowded indoor locations and in public transport, that is, in places of high population density. In enclosed settings, where there is poor ventilation, it is also very important to increase the rate of air change, reduce recirculation of air, and increase the use of outdoor air.
Courtesy: Hindustan Times, Zenger, Firstpost, Republic World