What type of dampers must be installed in shaft enclosures penetrated by ducts and air transfer openings?

The correct choice is to install both fire dampers and smoke dampers in shaft enclosures that are penetrated by ducts and air transfer openings. This is necessary because both types of dampers serve distinct but crucial roles in the safety and integrity of the building's fire protection system.

Fire dampers are designed to prevent the spread of fire through ductwork by sealing off sections of the ducts when a certain temperature is reached. They close automatically during a fire event, helping to contain the fire to a specific area and prevent it from spreading throughout the building.

Smoke dampers, on the other hand, focus on controlling smoke movement. They help to contain smoke within certain areas and prevent it from entering other parts of the building, which is vital for maintaining safe evacuation routes and protecting occupants during a fire.

When a building is designed, it must account for both fire and smoke hazards, especially in locations like shafts where various ducts and air openings can provide potential pathways for both fire and smoke to spread rapidly. Therefore, the installation of both fire dampers and smoke dampers is essential for comprehensive protection and compliance with safety codes and standards.