What happens when one automatic door closing device is activated?

When one automatic door closing device is activated within a smoke-proof enclosure, it triggers all doors in that enclosure to close. This is a crucial safety feature designed to contain smoke and fire, preventing it from spreading to other areas of a building. By ensuring that all doors in the enclosure respond simultaneously, it enhances the effectiveness of smoke control and helps to maintain a safer environment for occupants.

The design and operation of these systems are typically governed by fire safety codes and standards, which necessitate an integrated response to fire alarms. This interconnected function is important in terms of maintaining egress routes and minimizing smoke travel, which can be critical during a fire event.

In contrast, the other choices do not align with this safety function. If only one device closed, or if there was no effect on other devices, it could lead to unsafe conditions where smoke could escape or propagate through the building. Similarly, the closing of only the main entrance would not provide the comprehensive protection needed in a smoke-proof enclosure. Therefore, the operation of all doors is essential for enhancing the overall safety strategy during emergencies.