Fabricating a grate to go over the window is probably your best bet to partially protect the glass. I've seen them made out of stainless, pipe, rebar, and mild steel, even strips of 1" plate about 3" wide and welded in sideways to a frame that bolts over the window. Have also seen some made of screening plant wire. Leave enough room between the grate and the window so you can clean the glass. Vision will be somewhat obscured from the grating.
A company I worked for years ago tried some bullet proof glass about two inches thick on a Manitowoc crane using a 16 ton ball to break clumps of slag. But the splinters and shrapnel of steel ruined the glass fast to the point the operator couldn't see out. So it was replaced with regular tempered glass and a grate of the 1" steel bars.
I know of several people that have been hurt while running a breaker, particularly on very old concrete. The concrete splinters off explosively and usually has a razor sharp edge or two. The slag outfit had people hurt all the time from stuff coming in the cab through the windshield, even with the grates. When running the shop at Bethlehem Steels Gary Works, we repaired holes in the various cranes sheet metal daily, besides removing chunks of slag and steel from inside or on top of the house weighing 50 to 150 pounds. These had razor sharp edges too.
Dozer and loader operators would not go near the slag pits while the cranes were busting up slag balls and clumps of mixed slag and steel.
Good Luck!