Sanding hazard question ?

I was hand sanding a leather fire helmet (removing paint and primer from helmet) and I was wearing a p100 mask that is slightly big. I felt a seal around my face and no air blowing out anywhere. Can I have inhaled any dust and if so is there any damage that can be done to my body? I never really sanded anything before so I don’t know if one exposure matters or not.
Thanks! 

2017-04-11T00:37:33.809Z