Maintain safe distance while jogging as respiratory droplets with coronavirus may travel over 6 feet: Study
What is a safe distance when running, biking and walking during the coronavirus pandemic? It should be more than the recommended social distancing of 1.5 to 2 meters or 6 feet, say researchers.
According to a group of researchers from the Netherlands and Belgium, the 1.5-meter rule is based on people standing still. But when people are moving, they found the droplets can travel much further and potentially infect anyone following behind.
The researchers explain that when someone breathes out, sneezes or coughs during a run, those particles stay behind in the air. The person running behind in the so-called "slip-stream" goes through this cloud of droplets.
Researchers came to this conclusion by simulating the occurrence of saliva particles of persons during movement (walking and running) from different positions — next to each other, diagonally behind each other and directly behind each other.
The results indicate that the largest exposure of the trailing person to droplets for walking and running is obtained when this person is in line and with the leading person and positioned in the slipstream of this person.
Exposure increases as the distance between the leading and trailing person decreases. Their computer modeling shows droplets released from breathing or a sneeze can travel up to 5 meters behind a person walking at 4km/hour, and up to 10 meters behind a person jogging at 14.4km/hour.
The team says that people are better off walking or running side-by-side, keeping the recommended 1.5-meter distance apart, or when in one line allowing at least 5 meters apart for walking fast (4 km/h), 10 meters for running fast (14.4 km/hour) and at least 20m for cycling fast (30 km/hour).
These recommendations are in the absence of headwind, tailwind and cross-wind.
The researchers emphasize that when there is substantial cross‐wind, the suggestion is to stay out of the slipstream. This means that it is advised to not walk/run/cycle directly behind others but offset to the upwind side.
"This leads to the tentative advice to walkers and cyclists that if they wish to run behind and/or overtake other walkers and runners with regard for social distance, they can do so by moving outside the slipstream into staggered formation when having reached this distance of about 5 meters and 10 meters for walking fast and running, respectively," say the researchers in their findings. They have also released animations to illustrate the findings.
"When overtaking a person, be kind to this person and only when you have reached a certain distance from this person (the recommended distances), move back on the same straight line as this person," says the team from Eindhoven University of Technology, Netherlands, and KU Leuven, Belgium, among others.
The team clarifies that while there is an infinite number of combinations of runner body geometry, wind speed, wind direction, turbulence, droplet size, relative humidity, they chose to start from the most basic choices: two identical runners, no external wind, typical droplet size from literature, etc. as this situation is not only the most common but could also be a worst-case scenario. They recommend further work considering different values for these parameters.
The study has been released as a pre-print, which implies that the findings are yet to be peer-reviewed. "We will have our study peer-reviewed because we wish to publish it in a journal. But that did not seem most urgent to us now, certainly because the study confirms common sense and adhering to the guidelines of the study cannot have harmful consequences," says the team.
"The value of this study is to indicate where exhaled droplets go (that is, in the slipstream) and which specific social distances should be used in walking/running/cycling to be equivalent to 1.5 m standing still," they add.
Since the study is not peer-reviewed, researchers attempted to answer several questions separately. Why this study? According to researchers, the starting point was the 1.5 meter (or in some countries 2.0 meters or 6 feet) social distance that is recommended to be kept between two people standing still to avoid respiratory droplets of person A reaching person B.
"When a person sneezes, coughs or even exhales, he or she is emitting small droplets – often too small to see with the naked eye – that can carry the virus. The receiving persons can be infected by inhaling these droplets, or by getting these droplets on their hands and then touching their face."
"That is why during the COVID-19 crisis, countries worldwide have declared – sometimes by law – a 'social distance' of about 1.5 m to be kept between individuals. This is considered important and effective because it is expected that most of the droplets indeed fall down and reach the floor and/or evaporate before having traveled a distance of 1.5 meters," says the research team.
They further say, "However, this social distance has been defined for persons that are standing still. It does not take into account the potential aerodynamic effects introduced by person movement, such as walking fast, running and cycling. This aerodynamics study investigates whether a first-person moving nearby a second person at a 1.5-meter distance or beyond could cause droplet transfer to this second person."
Researchers emphasize that this is an aerodynamics study, not a virology study. "The only two facts we adopt from virology are two basic and well‐established facts: respiratory droplets are an effective way of transferring this type of viruses (well‐established in scientific literature); It is better to not be exposed to other people’s saliva droplets than to be exposed to them (common sense)," they say in their analysis.
What is meant by "aerodynamically equivalent social distance" for walking, running, cycling? "The aerodynamically equivalent social distance is the social distance that two persons need to maintain when walking/running/cycling to have the same level of (non‐)droplet exposure risk as in the case of 1.5 meters, 2 meters or 6 feet for two persons standing still and facing each other," they explain.
Should people stop exercising outside? No, say researchers, adding that the crisis is very large and mental and physical health is important. The study is intended to indicate how social distancing should be done in those situations, says the team.
The team further says that this is not a study related to treatment and there is no risk in following their guidelines. They explain that 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. This is not a situation that can be compared to advising people to take certain medications that have been insufficiently tested and that can have adverse health effects."
"There are no adverse effects for you to walk, run or cycle in staggered arrangement instead of inline, except increased air resistance. We believe that in this exceptional situation, increased air resistance should be preferred over potential health risks," says the team.