Improved ventilation in public spaces can slow the spread of new coronavirus

To better understand the respiratory droplet spread of the new coronavirus and to explore potential preventive measures, scientists analyzed in detail the droplets produced when people cough and talk by measuring the particle size distribution, transmission distance and speed, and air propagation time at different ventilation levels, and the study confirmed that good ventilation in public spaces can dilute and remove potentially infectious aerosols. The article was published recently in the British journal Lancet Respiratory Medicine.It is generally believed that the main route of transmission of the new coronavirus is the breathing droplets of infected people. Tiny droplets (diameters from sub-microns to nearly 10 microns) produced during speech and coughing contain virus particles that can survive in aerosols for up to 3 hours and remain infectious, and these droplets can be transmitted directly through aerosols into the gas channel or indirectly through contaminated hand contact.Scientists at the Institute of Physics at the University of Amsterdam in the Netherlands, the Dutch Heart Centre and Emma Children's Hospital at the University of Amsterdam Medical Centre first used a spray droplet measurement system to perform laser diffraction measurements to determine the particle size distribution of breathing droplets produced by a single cough and speech, and then used a laser produced by another company to track the droplets by The scattering of droplets to the laser was filmed to determine the speed and trajectory of the droplets, and a number of small droplets were dispersed into the air using nozzles designed by the third company to simulate the effect of coughing in order to analyze the number of fixed laser droplets suspended in the center of the experimental device.The researchers repeated the experiment in three rooms with different levels of ventilation: no ventilation, only mechanical ventilation, mechanical ventilation and opening an entrance door and a small window. In rooms with the best ventilation, the number of droplets halves after 30 seconds, while in non-ventilated rooms, the time to halve droplets takes about 5 minutes. This result is consistent with the air resistance calculation.The study showed that good ventilation can indeed significantly reduce the amount of time breathing droplets can hover in the air. This finding is significant because, despite physical isolation measures, there are still cases of transmission of the virus in poorly ventilated and densely populated locations such as public transport and nursing homes. In such poorly ventilated spaces, the continued presence of small breathing droplets could lead to the spread of the new coronavirus, while improving ventilation in public spaces could dilute and remove potentially infectious aerosols, the researchers said. (Science and Technology Daily)