It can be, but breaking your car window is only to be done in an emergency situation. As such, it’s a far better option than the alternative. Car windows are made of tempered glass (safety glass), and when broken they’re designed to explode outward in tiny balls rather than shards. Some injury is always possible when breaking tempered glass, but the likelihood of it being a serious laceration is greatly diminished. The most important thing to remember is to turn your head so no pieces of glass get in your eyes.