# Bazant: An alternate covid calculator

Most of what I see people use [Microcovid.org](http://microcovid.org) for now is estimating risk for large gatherings, which it was not designed for and thus doesn’t handle very well. I spent a few hours going through every covid calculator I could find and [this calculator from the Bazant lab at MIT](https://indoor-covid-safety.herokuapp.com/apps/advanced), while less user-friendly than Microcovid and having some flaws of its own, is tailored made for calculating risks for groups indoors, and I think it is worth a shot. 

![](https://lh6.googleusercontent.com/aQ878SuHNklyIohvC2femKWmrmT909as3vaMNQX_5tw_mg0VuPgqUH0n77HO5lPuavJB-xim3A7dQOVp0j3gIK96G1stO412gGmUWP9yCVVPb8fXAkUG2ijfcwO7nk6VqtQdbAiH)

\[Note: I’ll be discussing the advanced version of the calculator here; I found the basic version too limited\]

The Bazant calculator comes out of physics lab with a very detailed model of how covid particles hang and decay in the air, and how this is affected by ventilation and filtration. I haven’t checked their model, but I never checked Microcovid’s model either. The Bazant calculator lets you very finely adjust the parameters of a room: dimensions, mechanical ventilation, air filtration, etc. It combines those with more familiar parameters like vaccination and mask usage and feeds them into the model in [this paper](https://www.medrxiv.org/content/10.1101/2020.08.26.20182824v4) to produce an estimate of how long N people can be in a room before they accumulate a per-person level of risk between 0 and 1 (1 = person is definitely getting covid = 1,000,000 microcovids per person; .1 = 10% chance someone gets sick = 100,000 microcovids per person). It also produces an estimate of how much CO2 should accumulate over that time, letting you use a CO2 monitor to check its work and notice if risk is accumulating more rapidly than expected.

Reasons/scenarios to use the Bazant calculator over Microcovid:

*   You have a large group and want to set % immunized or effective mask usage for the group as a whole, instead of configuring everyone’s vaccinations and masks individually.
*   You want to incorporate the mechanics of the room and ventilation in really excruciating detail. 
*   You want to set your own estimate for prevalence based on beliefs about your subpopulation.
*   You want a live check on your work, in the form of the CO2 estimates.

Reasons to use Microcovid instead:

*   Your scenario is outside – Bazant calculator doesn’t handle this at all.
*   You don’t want to have an opinion on infection prevalence, immunization, or mask usage.
*   Your masks are better than surgical masks (Bazant doesn’t handle N95 or similar. Also, it rates surgical masks as 90% effective, which seems very high to me).
*   Your per-person risk tolerance is < 10,000 microcovids (Bazant calculator can’t bet set at a lower risk tolerance, although you can do math on their results to approximate this).
*   You’re still using a bubble model, or tracking accumulated risk rather than planning for an event.

Scenarios neither handle well

*   Correlated risk. You might be fine with 10% of your attendees getting sick, but not a 10% chance of all of the attendees getting sick at once.
*   Differences in risk from low-dose vs. high-dose exposures.

I’m not currently planning any big events, but if someone else is, please give this a try and let us know if it is useful.