Virus Transmission Pathways
The virus spreads by three possible ways: by respiratory droplets, aerosols, and through contaminated surfaces – as explained in greater detail by the CDC.
Respiratory droplets, including small bits of saliva and respiratory fluids, are propelled through the air – mostly when an infected individual coughs or sneezes. They fall to the ground after traveling 3-6 feet (hence the recommendation for a social distance). Published research, which has been replicated, shows that when it comes to talking in close proximity, droplets are less important than aerosols.
Aerosol transmission is similar to droplet transmission with one key exception – the bits of respiratory fluids are much smaller and can linger in the air for much longer, from minutes to hours. Therefore, being in a small indoor space together with many other people and without good ventilation presents a higher risk of contracting the virus. Aerosol transmission is the main component in spreading measles and chickenpox, and at least a strong contributor to the transmission of tuberculosis and influenza. Many scientists believe that the same can be stated about Covid-19.
Face masks provide various degrees of protection against droplets and aerosols in the contaminated air. As they muffle speech, a person naturally tries to speak louder, whereby exacerbating the problem of a forceful exhalation.
While N95 respirators are best when fitted properly, it is difficult to breathe while wearing this mask, especially for a long period of time. Because of this, they are not used frequently. Surgical masks and cloth masks are used by most people for everyday activities when around other people. While these products can limit the droplets, aerosols can pass through easily, both for inhaled as well as exhaled air. Basically, with masks: Easy breathing = Easy passing of aerosols
The ActivAir provides full protection against both forms of airborne transmission, via droplets as well as aerosols. It features a first-ever wearable active disinfection chamber designed to destroy the virus in the passing air stream. Once disinfected, the air stream is directed towards the face of the user providing a personal source of continuously supplied virus-free breathing air. The user can breathe easily without exerting an effort to move the air through a mask filter.
Covid-19 is transmitted through aerosols. We have enough evidence, now it is time to act. Jose-Luis Jimenez. Time magazine, August 25, 2020. Link
Particle sizes of infectious aerosols: implications for infection control. KP Fennely. The Lancet. Respiratory Medicine, 2020. Link
Identifying airborne transmission as the dominant route for the spread of COVID-19. Renyi Zhang, Yixin Li, Annie L. Zhang, Yuan Wang, Mario J. Molina. Proceedings of the National Academy of Sciences Jun 2020, 117 (26) 14857- 14863; DOI: 10.1073/pnas.2009637117 Link
How face masks can help prevent the spread of Covid-19. Diana Kwon. The Scientist. July 8, 2020. Link
Visualizing the effectiveness of face masks in obstructing respiratory jets. Siddhartha Verma. Manhar Dhanak, John Frankenfield. Physics of Fluids. 32, 061708 (2020) Link
Ultraviolet Light is a Known Disinfectant
Using UV light to destroy bacteria and viruses is not new. As far back as in the 1930s, William F. Wells, an instructor in sanitary science at the Harvard School of Public Health, introduced the idea of an aerosolized infection and postulated that a room could be rid of these airborne germs by an ultraviolet lamp and proper air circulation. This led to the installation of UV ventilation systems in schools and other public buildings aimed to limit the spread of tuberculosis and measles.
Modern-day hospitals use UV light to disinfect operating rooms and ventilation systems.
Since early March 2020, research has confirmed the vulnerability of the SARS-CoV-2 virus against UV light, provided it has the right wavelength and the right intensity. To be effective in destroying the virus, the ultraviolet irradiation has to be within a UVC range of wavelengths, preferably from 250 nm to 270 nm. This wavelength has to be delivered with suitable intensity and over a certain minimum time to achieve an effective irradiation dosage.
Large UVC sterilization robots have been developed by Amazon for their food stores and by Honeywell for disinfecting airplane cabins.
Recent advances in UVC LED technology make it now possible to miniaturize UVC devices while preserving their disinfection power.
It takes a good blend of innovation, engineering, and science to develop an effective wearable air disinfection device. The device has to provide enough UVC irradiation to destroy the virus, while at the same time minimize energy consumption and dissipate the heat generated by the UVC LEDs. This is what was accomplished for the first time with the ActivAir – a well-balanced design to satisfy a myriad of conflicting requirements.
UV-C irradiation is highly effective in inactivating and inhibiting SARS-CoV-2 replication. Andrea Bianco, Mara Biasin, Giovanni Pareschi, et. al. medRxiv 2020.06.05.20123463. Link
Back to normal: an old physics route to reduce SARS-CoV-2 transmission in indoor spaces. F. Javier Garcia de Abajo, Rufino Javier Hernandez, Ido Kaminer, Andreas Meyerhans, Joan Rossell-Llompart, Tilman Sanchez-Elsner. ACS Nano 2020, 14, 7, 7704-7713. Link
Effect of ultraviolet germicidal irradiation on viral aerosols. Christopher M Walker, Gwangpyo Ko. Environ. Sci. Technol. 2007, 41, 5460-5465. Link
Computer modeling of airflow was used to optimize the speed of the air blower to maximize the residence time of air inside the disinfection chamber and assure a sufficient dosage of UVC irradiation.