There are two types of respirator masks: one for dust and one for gas. Both are NIOSH/MSHA Approved and meet OSHA Guidelines.
The Blue Respirators (8246) are used for dust/mist protection and where solvents and organic vapors are a bother. The Gray Respirators (8247) are used for acid gas protection (chlorine, hydrogen and sulfur dioxide). They also provide dust/mist protection.