I suppose that the machines are safe to be around when the doors are closed, but what if someone blowing off their parts sends a chip sailing across the room into some else's eye? Even picking chips out of a hole can send a small piece flying, because chips are like little springs. What if an airline blows apart and raises a helluva ruckus blowing chips off the top of machine enclosures, or from wherever? What if the end of your deburring tool shatters and sends a fragment into an eye? What if someone blows filing dust into their own face and eyes?
You might be okay in a room full of machines all by yourself, but when you've got a bunch of other operators doing god knows what, you need eye protection.
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)