Richard,
I own a safety supply business, and this is the first question I'm qualified to answer!!
Just a quick background on respirators, n95 or n100 is the % of particulants the filter stops. n95 stops 95% of the particulants, n100 stops 100%. OV is short for organic vapors. Usually a fliter is rated for one or the other, or both particulants and organic vapors. Also, the face masks have a size to them, and to get a perfect fit, you need to be "fit tested". Any occupional medical facility should be able to do this for you for a fee, but they may only test for one brand, such as 3M or North, ect., and all brands fit just a little different. Word of caution: "I gotta big head, so I need large" is not always correct, the "size" figures in the contour of the face as fare as the best fit.
When you go to get fit tested, if you ask them (or anyone who supplies them) what you need, it gets tough, because the manufactor will want to know all kinds of details like how many microns, or other units of lawyer terms per square inch is in the atmosphere, ect...
You're smart to use a respirator, much cheeper in the long run!!
gr
