Pictures and Videos/Movies from Simulations

Covid-19/Spread of Diseases in the Built Environment

For papers, links and further reading on this subject:

Sneezing in Transportation Security Agency (TSA) Queues:

One of the obvious vectors for viral contamination and spread are security and passport examination queues in airports. Air flow is moderate, passengers are in very close proximity, and in some airports queues wind back and forth in narrow lanes. These simulations shows a sneezing person in a TSA queuing scenarios. The distribution of particles and the absolute value of the velocity in the centerplane over time can be discerned. One can see that the large (red) particles follow a ballistic path and have some influence on the flow. This `ballistic phase' ends at about 1 second. The smaller (green) particles are quickly stopped by the air, and then sink slowly towards the floor in close proximity to the individual sneezing. The even smaller (cyan, blue) particles rise with the cloud of warmer air exhaled by the sneezing individual, and disperse much further at later times.

Sneezing in a Generic Hospital Room:

This case considers a typical hospital room. Of interest here was the dispersion of particles in the first minute after coughing/sneezing, in particular the reach into neighbouring halls and the amount of `negative pressure' needed to keep all contaminants in the room. The video shows the distribution of particles over time. Note how far the smaller particles spread over time, illustrating in a very dramatic way the serious risk health providers face in such situations.

Sneezing in a Generic University Laboratory Teaching Classroom:

This case considers a typical university laboratory teaching classroom. Of interest here was the dispersion of particles in the first minute after coughing/sneezing, in particular the reach to other students in the room. Heating, ventilation and Air Conditioning (HVAC) systems have been designed so as to mix air very efficiently. This can be seen here, here, and here for the complex flowfield that is generated by the 9 entry vents and 2 exit vents located in the ceiling of the room. Sneezing in the middle or the left of the room results in different clouds of particles. Note that as before the large (red) particles follow a ballistic path land close to the person sneezing (`2m rule'). This `ballistic phase' ends at about 1 second. The smaller (green) particles are quickly stopped by the air, and then sink slowly towards the floor in close proximity to the individual sneezing. The even smaller (cyan, blue) particles follow the air stream, and disperse much further at later times. Note how far the smaller particles spread over time, illustrating in a very dramatic way the serious risk students could face in such situations.

Sneezing in a Generic Subway Car:

This case considers a typical subway wagon. Of interest here was the dispersion of particles when coughing/sneezing, in particular the extent of possible infection via aerosol particles. HVAC systems have been designed so as to mix air very efficiently. This can be seen here, here, and here for the very complex flowfield that is generated by the 4 entry slits and 2 exit vents located in the ceiling of the wagon. Sneezing in the middle of the wagon quickly leads to a wide spread of the smaller particles. Note that as before the large (red) particles follow a ballistic path land close to the person sneezing (`2m rule'). This `ballistic phase' ends at about 1 second. The smaller (green) particles are quickly stopped by the air, and then sink slowly towards the floor in close proximity to the individual sneezing. The even smaller (cyan, blue) particles follow the air stream, and disperse quickly, covering half of the wagon in less than a minute. This case illustrates in a very dramatic way the imperative use of masks in such crowded environments. These simulation were featured in an article in the New York Times on August 10, 2020, see:

https://www.nytimes.com/interactive/2020/08/10/nyregion/nyc-subway-coronavirus.html


Sneezing in a Classroom:

This case considers a classroom. Of interest here was the dispersion of particles when coughing/sneezing, in particular the influence of proper ventilation and/or the opening of doors and windows to improve airflow. Even under normal HVAC conditions sneezing in the middle of the classroom quickly leads to a wide spread of the smaller particles. Note that as before the large (red) particles follow a ballistic path land close to the person sneezing (`2m rule'). This `ballistic phase' ends at about 1 second. The smaller (green) particles are quickly stopped by the air, and then sink slowly towards the floor in close proximity to the individual sneezing. The even smaller (cyan, blue) particles follow the air stream, and disperse quickly, covering half of the wagon in less than a minute. Wearing a mask drastically reduces the amount of particle exhaled into the surrounding air, and hence the propability of infection. With the HVAC running at low speed the spread takes longer, but eventually reaches large parts of the room. As before, wearing a mask, drastically reduces the amount of particle exhaled into the surrounding air, and hence the propability of infection, an effect seen even after 5 minutes. Opening doors and windows leads to a faster renewal of the air in the room, but given the complexity of the flowfield (notice the large vortical structures in corners), even in this case some particles remain. Wearing a mask drastically reduces the amount of particle exhaled into the surrounding air, and hence the propability of infection. This case illustrates in a very dramatic way the benefits of better air circulation and improved ventilations, as well as the imperative use of masks in such crowded environments. Some of these simulations were summarized and presented in the NBC Today Show on September 30, 2020, see:

https://www.today.com/health/ventilation-covid-19-reduce-spread-proper-airflow-t192366


Sneezing in a Narrow Corridor With Moving Pedestrians:

This case considers a generic, narrow corridor with moving pedestrians. This may be typical of train or subway stations, as well as underground passages in cities with colder climates. Of interest here was the dispersion of particles when coughing/sneezing, in particular the extent of possible infection via aerosol particles. A typical HVAC systems was considered. HVAC systems are designed to deliver comfortable air speeds, i.e. speeds below 0.3m/sec. People move at 1.1-1.3m/sec, implying that they will produce wakes and `stir the air'. This can be seen here and here. Note the very complex flowfield that is generated by the moving pedestrians. Sneezing anywhere leads to a wide spread of the smaller particles. Note that as before the large (red) particles follow a ballistic path land close to the person sneezing (`2m rule'). This `ballistic phase' ends at about 1 second. The smaller (green) particles are quickly stopped by the air, and then sink slowly towards the floor in close proximity to the individual sneezing. The even smaller (cyan, blue) particles follow the air stream, and disperse quickly, covering most of the volume in less than 20 seconds. This case illustrates in a very dramatic way the imperative use of masks in such crowded environments. A similar conclusion can be drawn by considering a transport equation for the viral load in the volume, and following its distribution at chestheight over time.