OldRed, I will assume you are talking about the 3M mask that was approved for "isos".
I know I have talked with quite a number of paint suppliers who have told me that isocyanates will go right through most cartidge masks.
I switched to remote air about 20 years ago. I work 7 days a week, and spray isocyanates, or am sanding them, about 10-15% of the time. After 40 years in this biz, the only problem so far is slight kidney function loss, which may, or may not, be from the paints. I have a few friends who didn't make it this far.