So, that's kind of one of my questions: when do you know that it's time?
Even if there is no visible damage to the shell of the mask, can there be damage that's not visible? How will he be able to check the shell?
The foam seems to be a good order, nothing torn, ripped, missing or cracked. But perhaps it has hardened slowly over the years and I would never be the wiser about it. I'm more concerned about the shell failing, but from what you guys are saying the foam is important too. I'm just surprised to come across expiration dates on masks. Is that just a way to sell more masks? Or perhaps avoid ongoing liability? Or is it really that the structure of the shell does break down over time, and/or the foam as well?