3m 4255 maintenance free half mask respirators 3m 4279 the 3m 4279 maintenance free half mask respirator ffabek1p3 r d is a ready to use maintenance free half mask designed for effective and comfortable protection against a combination of organic and inorganic vapours acid gas ammonia and particulate hazards found throughout industry 3m 4279 maintenance free half mask respirator ffabek1p3 r d