What CAN'T a Respirator Do?
No respirator will protect against many toxic chemicals that exist in building fire-smoke. That requires Self Contained Breathing Apparatus or SCBA similar to SCUBA equipment.
But, a respirator can help you survive when you need to get out of a fire-smoke enviroment. You may literally have minutes to get out of such environments. The right respirator and goggles help increase your chances of surving those minutes.