These are precious bits of your slate roof (or cedar, asphalt, tile or metal roof). Don't remove ice this way please.
Okay people. How many roofs do we have to repair each summer because you hired this guy? (Or because you married him?)
Hire a qualified, experienced steamer jockey and all will be well.
Using hammers, picks or axes is simply NOT a good idea. These methods can remove ice quickly. No doubt. The question is, what else comes with the ice as it is pounded off your roof?