How often do you change Respirators or P100 cartridges???

Hi Everyone,
I have not found a guide that states when you should change respirators or your P100 cartridges, I assume once a year!!! Is this too often, or not often enough? Anytime I go into a crawlspace or attic I always wear my respirator, I was curious what you guys do…

For under $40.00 buying a new one every year, is not a bad idea…I guess…

Justin
www.americandreamhomeinspection.net