During which type of collapse is members of the fire service most likely at risk when entering a compromised structure?

A secondary collapse refers to the failure of a structure after an initial collapse has already occurred, often due to the redistribution of loads and weakened structural integrity in surrounding areas. This type of collapse poses significant risks to fire service personnel who may enter a compromised structure, as they can be caught off guard by sudden, unexpected changes in stability.

During a secondary collapse, the remaining structural components may not be able to support their own weight or the load of firefighters and equipment, leading to additional failing elements that could result in severe injury or fatalities. Firefighters may mistakenly believe that the immediate area is safe based on the collapse they have already witnessed, only to face new and unpredictable dangers.

In contrast, an initial collapse occurs when the structure first gives way, potentially giving clear indicators such as loud noises, material falling, and visible damage, allowing firefighters to identify an immediate risk. Primary and global collapses also present risks, but the secondary collapse is particularly dangerous due to its unpredictable nature and the fact that firefighters are already inside the structure when they occur. Understanding the dynamics of these types of collapse is crucial for ensuring firefighter safety during operations in compromised buildings.