Officials say that a technical director of a musical on the French Revolution has died of a heart attack after pyrotechnics under the musical’s stage exploded during a rehearsal.

Agnes Thibault-Lecuivre, a spokeswoman for the Paris prosecutors office, said four other people were in critical condition following Friday’s blast at Paris’ Palais des Sports auditorium.

A police official said Friday the man died of heart attack after the blast. He said early signs indicate that a worker generated a spark that came into contact with pyrotechnics under the stage.

The show’s production company did not immediately respond to an e-mail seeking comment.