COVID-19 simulation: Walking, running or cycling close to another risks exposure
Social distance of 1-1.5 metres when standing still is recommended to prevent COVID-19
Dubai: UAE, along with most countries in the world, have imposed restrictions on movement on the public to combat the spread of the novel coronavirus - SARS-CoV-2. So technically you are not supposed to be running, jogging or cycling for non-essential purposes, i.e. anything other than grocery runs or medical requirements. Dubai has announced a fine of Dh3,000 for violations along with an online permit facility for anyone who wishes to step out to make an essential purchase or medical visit.
What is the recommended social distance?
It is important to know that it is possible to increase exposure to the virus if proper distance is not maintained when you're out and about. The World Health Organisation (WHO) recommends a minimum distance of 3 feet or 1 metre between two people as a safe distance to avoid spread of the virus. The Centre for Disease Control and Prevention (CDC) in the US recommends 2 metres for effective social distancing.
This distance, however, applies to a situation where both people or all people are standing still, like waiting in line.
Going out for a run, walk or bike ride
In some countries, stepping out for exercise is still being allowed. As long as areas don't get crowded, many people step out for fresh air while maintaining the recommended one to two metre distance.
But, does it work when you are moving at a certain speed?
A Belgian-Dutch aerodynamic report by engineers claims this distance may not protect you or another person in your vicinity from possible COVID-19 infection while running, walking or cycling - dependant on certain parameters. The study uses Computational Fluid Dynamics (CFD) simulations to understand the way droplets move given distance, speed and other criteria.
"External wind is considered absent and different person configurations are analysed, side by side, inline and staggered, and the exposure of the second person to the droplets emitted by the first person is assessed," the pre-print of the study claims.
Findings
An important term the researchers used is 'slipstream' or 'wake'. This is the region behind a moving object, in this case a human, which leaves behind a trail or wake of particles, in this case droplets. The simulations analysed low speed and fast movement with two subjects in various positions relative to each other to predict risk of exposure.
The report claims that even with a distance of 1.5 metres between two moving people, if one person runs, walks or cycles directly behind the other, risk of exposure to particles from sneezing or coughing remains high. This is because the second person is in the slipstream of the first person moving - even after a 1.5 metre gap.
The researchers found: "For walking at 4 km/hour, a distance of about 5 metres leads to no droplets reaching the upper torso of the trailing runner. For running at 14.4 km/hour, this distance is about 10 metres." The researchers add that a distance of 20 metres is appropriate when cycling fast at an average speed of 30km/hour. These distances are applicable if and when the second person is directly behind or in the 'wake' of the first person.
The report puts forward tentative recommendations of moving out of the slipstream, in staggered formation to reduce risk of exposure to droplets, along with the distances mentioned earlier.
Limitations
- The simulation does not take into account wind effect
The researchers address the limitation of not taking the effect of wind in spread of droplets. They said in the report, "Cross-wind will cause the slipstream to be not straight but obliquely positioned behind the runners, and while it is expected that also in this case the droplets will mainly remain entrained in the slipstream, this should be confirmed by future simulations. External wind will also increase the turbulence intensity and might cause stronger mixing of the droplets in the slipstream, and potentially also allow a small fraction droplets to escape the slipstream."
- The report is yet to be vetted by health experts
The research involves physics and aerodynamics, is not a virology paper and hasn't been vetted by health experts yet. In a follow-up Q&A to the initial findings, authors Bert Blocken and Thierry Marchal said, "This study does not draw any conclusions on the infection risk associated with particular social distances or droplet exposure. We are sharing these results with healthcare authorities and remain at their disposal for further information."
- Controversial backlash
After a post about the research in Medium and other media outlets, the authors faced backlash. Critics questioned the credibility of the research which has not been peer-reviewed yet. Blocken, one of the authors of the report reacted, "Not yet. Crisis is urgent, so exceptionally we turned order upside down: (1) media, (2) today I submitted the proposal for funding (3) peer review article later. Public cannot wait months for peer review. I have a short text, I will post it on Linked In within the next hour."
A pre-print of the research was later published, along with a follow-up Q&A article.