NIOSH approved for environments containing certain non-oil-based particles Use on top of 3M gas and vapor cartridges with 3Mâ„¢ 501 Retainer when particles are also present Use on top of 3Mâ„¢ 603 Filter Holder and 3Mâ„¢ 501 Retainer to reduce particulate exposure Replaceable particle filter for cost savings