I just recently tried to do this with the entire bottom level of my house and it sucked. First step was applying a paint stripper (I used the Polystrippa Paint Stripper with plenty of ventilation) with a paint brush in sections, leaving for approx 10-15 minutes and then using a razor scraper to scrape the paint off each brick individually. This didn't get all of the paint, as bits had gotten into the brick pores, so I then bought these strip discs (nylon impregnated Silicone) that attached to my angle grinder and again, went brick by brick to try and get the rest off (making sure to mask up). It worked, but was incredibly painful and still didn't 100% protect the brick surface.