Going beyond 95%

We breathe about 2000 gallons of air a day. That's a lot. And if we are working in person or mixing with strangers, there is risk of breathing in infected air.

The CDC and others have asked people to wear masks. But the quality varies a lot. If you have a mask that is 50% effective, that might be better than average. 90% effective and you're probably in the top tier of people. But is 90% enough? You don't win an award for being better than average. The virus is just looking to be in one of those 2000 gallons that you breathe each day.


Rather than uses percentages, it helps to think in terms of particles that are stopped by a filter vs particles that pass through.



Getting to 95% protection is very hard to do with other techniques like ventilation or reducing time. It's just math.

50% filtration means 5000 out of 10000 particles pass through. (5000 are filtered out)

90% filtration means 1000 out of 10000 particles pass through. (9000 are filtered out)
That's a 80% reduction going from 5000 to 1000. To get there via ventilation means a 5x increase in ventilation.

95% filtration means 500 out of 10000 particles pass through. (9500 are filtered out)
That's a 90% reduction going from 5000 to 500. To get there via ventilation means a 10x increase in ventilation.

99% filtration means 100 out of 10000 particles pass through. (9900 are filtered out)
That's a 98% reduction going from 5000 to 100. To get there via ventilation means a 50x increase in ventilation.

99.99% filtration means 1 out of 10000 particles pass through. (9999 are filtered out)
That's a 99.98% reduction going from 5000 to 1. To get there via ventilation means a 5000x increase in ventilation!


When the risk is high, like for essential workers whose bosses control their environment, sometimes going beyond 90% is what is needed.

We tend to think that 95% and 99% and 99.99% are very similar. This is because they are all "A" grades.

But in the world in infectious control, they are big differences. 500 virus particles allowed through compared to just 1.


Good luck and stay safe.

Go back to the main page.