According to regulations, when must fire curtains be closed?

Fire curtains are critical safety devices designed to contain fires and prevent the spread of smoke in theatrical venues. According to regulations, fire curtains must be closed during all dark times to ensure safety when the audience is not present, which includes the period when the theater is not operational, such as during set changes, maintenance, or when the venue is empty. Keeping the fire curtain closed during these times helps to mitigate potential fire hazards, ensuring that if a fire were to occur, it would be contained and not interfere with emergency egress routes or affect adjacent spaces.

While there are various operational scenarios presented in the other options, none appropriately account for the continuous function of fire safety standards as effectively as closing the curtains during all dark times. This proactive approach is essential for maintaining a safe environment for performers, crew, and patrons alike.