There could be several possible causes of breakage.  If the glass was toughened, these include impact damage (deliberate or accidentally), edge damage (during handling), poor installation (tight glazing, missing setting blocks, proud fixings/hard surface contact with glass), poor design (insufficient clearances, structural movement) and inclusions in the glass (foreign particles/impurities).  Only examination of the glass fragments (specifically, those around the origin of fracture) and inspection of the framing system and glazing method by an appropriate person is likely to determine the cause of failure.

If the glass has fractured, you should report this to the installer.  If the installer is no longer trading, then you should consider approaching another installer to undertake the replacement work.