How Do Goggles Get Scratched?

How do goggles get scratched? Are you sure that is the right question? For me, the critical failure mode seems to the inexorable buildup of a translucent film of scale/scum that can't be washed off. Eventually this film interferes with vision sufficiently that the goggles are not longer safe to use.

How do goggles get scratched? Are you sure that is the right question? For me, the critical failure mode seems to the inexorable buildup of a translucent film of scale/scum that can't be washed off. Eventually this film interferes with vision sufficiently that the goggles are not longer safe to use.