Work is threatening to fire me

So I work in a factory we use machines that need a fuel called Cal fluid. It can cause burns (from irritation). So when we are filling the machines with the Cal fluid we are supposed to wear a face shield and a smock. I told them I refuse to wear the face shield because they only supply 4 for a plant of 500+ people. No offense but I have seen some of the people who wear this same face shield and it's gross. They don't have any sort of sanitation procedure for this. I also on a medication that lowers my immuse system. I have watched people sneeze in the face shield and cough and some of these people don't shower. I have asked for my own set and they refuse to provide me with one. And you can't bring in your own because it has to be a specific one.

Can they force me to use this stuff. It's seriously unsanitary.

This is what the type of face shield it is