On December 30, 1903 the new Iroquois Theater, thought to be fireproof, was packed with 1,900 spectators who came to see a popular musical. Well developed theater fire precautions had been created prior to 1903. Unfortunately, Iroquois Theater management did not follow them. Stage scenery and backdrops painted with flammable paint and suspended near hot lights presented major fire hazards.

During the play, a hot light ignited a nearby velvet curtain. Firemen near the stage were only equipped with a patent powder that proved ineffective when sprinkled on the flames. The asbestos curtain became stuck before reaching the floor. Iron gates added to exit doors by management took extra skill to open, and other doors opened inward trapping theater occupants. The fire led to the death of 600 audience members.

After this tragic event, the City of Chicago rewrote its fire code to mandate outward-swinging doors for all theaters and similar establishments. A new set of safety regulations were also adopted for theaters. The event is ranked as the worst theater fire in the history of the US.