How many rungs past the roof line should aerial ladders be extended?

Aerial ladders should be extended 5 rungs past the roof line to provide adequate safety and stability for personnel. This extension allows firefighters to securely position themselves above the roof's edge, ensuring a safe access point for entry or rescue operations. It also helps in creating a more stable platform while performing tasks such as ventilation, as it reduces the likelihood of slipping or losing footing at the roof's edge. Additionally, extending the ladder beyond the roof line allows for better clearance from the building’s parapet or overhang, which is crucial when supporting firefighting operations or evacuating individuals.

The other options suggest an extension that may not offer the same level of safety and functionality. For example, extending fewer rungs might not provide enough height for secure access, leading to potential hazards during operations on the roof.