What type of building collapse necessitates a Mayday call?

A structural collapse necessitates a Mayday call because it indicates a failure in the overall integrity of the building, which can lead to significant danger for personnel operating inside. When the structure itself is compromised—such as a roof caving in or walls failing—there is an immediate risk of injury or death due to falling debris or being trapped. This type of collapse requires urgent communication and coordination, as it can occur unexpectedly and can affect a large area within the structure.

In contrast, while the failure of outer walls, ceilings, or columns can also be serious, they may not always indicate an immediate and widespread hazard to all personnel within an affected area. A Mayday call is specifically prompted by a condition that poses an immediate threat to firefighters' safety, which is best represented by a structural collapse. Promptly notifying command through a Mayday call in such instances ensures that rescue and emergency response measures are initiated quickly to safeguard the firefighters involved.