SANTA MARIA, Brazil — There was no alarm, no working fire extinguisher, no sprinkler and almost no escape from the nightclub that became a death trap for more than 200 Brazilian college students.

As investigators began poking through the rubble and families mourned their dead, the university city in southern Brazil tried to understand how the Sunday morning blaze that killed 231 people could have been sparked in the first place, then rage rapidly out of control.

Why was there only one door available for exit and entry? What was the flammable material in the ceiling that allowed the conflagration to move so quickly? And, more pointedly, why was a band playing at the club allowed to use pyrotechnics inside the building?