Feynman en/of Feiten trapte gisteravond af met: ‘Anderhalve meter is volstrekt onvoldoende’. Wat naar onderstaande video linkt, de bron van de Facebook Tpook/TECH foto (screenshot).
TPOOKTECH vond het eerder al vreemd dat er geen sprake is van een mondiale veilige afstand norm voor het COVID overdragende hoest&nies gevaar. De WHO hanteert 1 meter, onder andere de VS en GB houden het op six feet of twee meter, en Nederland zit er met 1,5 meter tussenin.
UPDATE: Mans fukte up. Zat zo diep in de eerdere MIT studie, dat hij de laatste MIT studie (gepubliceerd 26 maart 2020) compleet vergat mee te nemen. Terwijl daar nu juist het ‘minstens zeven meter’ in de titel vandaan komt.
Owing to the forward momentum of the cloud, pathogen-bearing droplets are propelled much farther than if they were emitted in isolation without a turbulent puff cloud trapping and carrying them forward. Given various combinations of an individual patient’s physiology and environmental conditions, such as humidity and temperature, the gas cloud and its payload of pathogen-bearing droplets of all sizes can travel 23 to 27 feet (7-8 m).3,4 Importantly, the range of all droplets, large and small, is extended through their interaction with and trapping within the turbulent gas cloud, compared with the commonly accepted dichotomized droplet model that does not account for the possibility of a hot and moist gas cloud. Moreover, throughout the trajectory, droplets of all sizes settle out or evaporate at rates that depend not only on their size, but also on the degree of turbulence and speed of the gas cloud, coupled with the properties of the ambient environment (temperature, humidity, and airflow).
https://jamanetwork.com/journals/jama/fullarticle/2763852
Een aanschouwelijke video. Met aanvullend een BBC-ScienceFocus Q&A artikel dat ook rept van maximaal 8 meter. Maar hoe zit het precies met de achterliggende wetenschap? Her en der wordt o.a. naar een MIT studie verwezen dat in 2014 werd gepubliceerd.
Violent respiratory events such as coughs and sneezes play a key role in transferring respiratory diseases between infectious and susceptible individuals. We present theresults of a combined experimental and theoretical investigation of the fluid dynamics of such violent expiratory events. Direct observation of sneezing and coughing events reveals that such flows are multiphase turbulent buoyant clouds with suspended droplets of various sizes. Our observations guide the development of an accompanying theoretical model of pathogen-bearing droplets interacting with a turbulent buoyant momentum puff. We develop in turn discrete and continuous models of droplet fallout from the cloud in order to predict the range of pathogens. According to the discrete fallout model droplets remain suspended in the cloud until their settling speed of the decelerating cloud. A continuous fallout model is developed by adapting models of sedimentation from turbulent fluids. The predictions of our theoretical models are tested against data gathered from a series of analogue experiments in which a particle-laden cloud is ejected into a relatively dense ambient. Our study highlights the importance of the multiphase nature of respiratory clouds, specifically the suspension of the smallest drops by circulation within the cloud, in extending therange of respiratory pathogens.
https://math.mit.edu/~bush/wordpress/wp-content/uploads/2014/04/Sneezing-JFM.pdf
Experimenten en theoretische modellen voor hoesten en niezen die multiphase turbulent buoyant clouds worden. De bevindingen leveren onder andere onderstaand plaatje op (screenshot van .pdf) voor de reikwijdte van druppels van diverse grootte (d= X μm)
FIG URE18. Application of our model to realistic cough clouds containing monodisperse droplets. Trajectories of the clouds containing only particles of diameter (a)d=700μmor (b)d=30μm. (c) The cloud speed is compared with the settling speed of the droplets of various sizes, thus indicating their fallout time. (d) The non-monotonic dependence of the range on drop diameter arises because larger suspended droplets fall out earlier in the life of the cloud, hence with higher exit velocities than smaller drops that fall out later.
Een van de onderzoekers van de MIT-studie is Lydia Bourouiba. In een Nature video op Youtube (2016) gaat ze onderstaand verder in op de materie.
Samenvattend concluderend: het laatste over hoest&nies fall-out afstanden is nog niet gezegd. Dat gezegd hebbend, 1,5 meter afstand lijkt nogal aan de krappe kant.
