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I haven't seen that particular exemption. What I have seen are broad "health and safety" exemptions.
There's a couple of changes in our understanding of coronavirus that led to a change on facemasks:
- The original understanding was that facemasks wouldn't protect the person wearing the mask from inhaling virus. That is true since the virus is small enough to penetrate the filters in most masks. What changed is our understanding that it's not a matter of virus floating free in the air. Most coronavirus is being transmitted via water droplets. Cloth masks are able to filter droplets to a certain extent. If you stop the droplets from being inhaled, you'll reduce the chance that the virus will be transmitted.
- The masks stop exhaled droplets, sneezed droplets and coughed droplets from a person who has an infection. The more layers in a cloth mask and the higher filtration level in a paper mask, the less likely an exhaled droplet will be circulating in the air around the person wearing the mask. So, if an infected person is wearing a mask, the people around them are less likely to encounter droplets from the infected person. If both the infected person and uninfected person are wearing masks, then the level of protection is increased exponentially.
There's some interesting case studies coming out about masks. In one case, a salon had hairdressers who tested positive for coronavirus. Both hairdressers wore masks when servicing their clients. None of their 140 clients and 6 coworkers tested positive. The belief is that the masks and the social distancing prevented the virus from being transmitted from the infected hairdressers.
Hairstylists with COVID-19 didn't infect any of their 140 clients. Face masks may be why [Live Science]
One thing to keep in mind about masks:
- Masks are needed most when you cannot maintain social distancing (e.g. when in grocery stores or in a workplace).
- Masks are most effective when contact is short-term since the length of time of the exposure also increases the risk. If you're indoors in a large gathering (like a Trump Rally) for a long period of time, the masks may not provide enough protection to prevent infection. For this reason, avoid prolonged encounters indoors (e.g. gyms) and always avoid exposure to crowds (e.g. sporting events).
- Masks are most effective when everyone is wearing one. If there's an infected person walking around without a mask, they're putting everyone around them at increased risk.
Here's a video demonstrating how a mask stops droplets from being dispersed into the air:

