2KNO3 + heat ==> 2KNO2 + O2
So if KNO3 is in excess and it's just popped out of the inflated bag and nothing else happens, then I don't think the KNO3 would have a damaging effect. However, as we all know, in accidents, many things can happen. IF the temperature goes up(for example, a fire starts (not all that unusual), then the KNO3 could produce oxygen and we certainly don't want any excess oxygen around with a fire.