Well, yes... Because then firefighters have to seperate themselves from the fire to deal with triage and medical duties (at least in the places where firefighters and medical personel are one in the same)...
The police should in theory be at every fire to not only be crowd control, but trafic management, and the occasional flight to a store to buy a large amount of water bottles...
That, and people should know better... As kara said somewhere, "don't throw **** at an armed man, and don't stand next to a person who throws **** at an armed man" or something similar...