How to assess your COVID risk before going out – eat this, not that

Conflicting advice from public health officials has been a frustrating (albeit understandable) aspect of the COVID-19 pandemic since day one, so it’s important to understand risk assessment in everyday life. “As we are in the ‘assess your own risk’ phase of this pandemic, it would be helpful if public health officials provided a master class on risk assessment. It looks like academics and engineers will have to do this instead.” says professional engineer Joseph Fox, P.Eng., MASc. “To assess the risk of space, you first need to know how you get infected and what contributes to it.” Here’s how to assess your COVID-19 risk, according to an expert. Read on to learn more – and to protect your health and the health of others, don’t miss it Already had COVID? These symptoms may “never go away”.


“The primary way you contract COVID is by breathing in an infectious dose over a period of time,” Fox says. “The dose is defined by 4 factors: dose = virus concentration x time x respiratory rate x airway deposition rate. The dose is related to the likelihood of infection. You can also get infected with a low dose (like outdoors), it’s just a low probability. Therefore it is problematic to say that something is ‘safe’. Reducing the dose reduces the risk of infection but does not eliminate the risk.”

Women with face masks down

“Time: The longer you’re exposed to a certain concentration, the higher the risk,” says Fox. “For activities that do not require prolonged periods of time, such as visiting a store, minimizing time is an effective risk mitigation measure.”

People wearing surgical masks sit on the subway in Shanghai

“Breath Rate: For some reason, the ‘hold your breath’ method wasn’t sufficiently promoted. If your respiratory rate is 0, you don’t get infected by breathing in,” Fox jokes. “The faster you breathe, the more air you breathe in over a period of time. If you add time and breathing rate together, the risk depends on the number of breaths you took. More breaths mean higher risk.”


“Deposition rate: A lot of the virus particles that you breathe in don’t stay in you, you just breathe them out,” says Fox. “You can only infect those that are deposited inside you. However, I think that this is not relevant for the risk assessment. One possible exception is that they have innate immunity and can remove those particles that have settled rather than infecting you, so low humidity prevents this and increases the risk of buildup. Run a humidifier if it’s dry inside.”

Young sick woman lying in her bed.

“Virus Concentration: The final and most complicated factor,” explains Fox. “The higher the concentration you inhale, the fewer breaths it takes to reach an infectious dose. So how do you assess the virus concentration? Reach – As you exhale, you begin with a stream of concentrated air in front of you (think of a smoker’s breath). exhale or smell someone else’s breath). Virus concentration is highest a short distance from the source. Therefore, the risk of infection is highest with close contact. However, most of the air you breathe in at close range is not from that person’s breath. Most of the air is still from the room, so low concentrations of virus in the rest of the room make a difference – even at close range. After the short-range jet, the virus-laden aerosols in the air then diffuse into the room, many factors affecting the final virus concentration, and they are important for risk assessment.”


Follow public health principles and help end this pandemic no matter where you live – get vaccinated or boosted as soon as possible; If you live in an area with low vaccination rates, carry an N95 face masknot travelling, maintaining social distancing, avoiding large crowds, not going indoors with people you are not sheltering with (especially in bars), practicing good hand hygiene and protecting your life and the lives of others, not visiting any of these 35 places where you are most likely to contract COVID.

Ferozan Mast

Ferozan Mast is a science, health and wellness writer with a passion for bringing science and research-backed information to a wide audience. Continue reading

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