Theatres have always been a fire risk, which is why even today, the safety curtain or ‘iron’ must be lowered in the sight if the audience, to prove that they will be safe from an on-stage fire.
Theatre lighting was the main source of fires for many years, but a minor revolution is taking place in theatres. Traditional lanterns are being replaced with LED-based, low energy equivalents that run cooler, so curtains and scenery hung near them do not get so hot. Also, the increased effectiveness of fire-retardant sprays ensures that the fire risk is now lower.
However, the combination of hot lights, dust, cloth, wood, onstage pyrotechnics and stage machinery requires CO2 and water fire extinguishers plus fire blankets, at the least. After all, Shakespeare’s original Globe Theatre burnt to the ground due to a prop cannon setting the roof on fire!