Which of the following is the correct factor used to estimate collapse zones?

• A. 2
• B. 1-1/2
• C. 1
• D. 1/2

Answer: (B)

The principle here is using a multiplier of the building’s height to estimate a collapse zone, giving crews a safe distance to stay clear of falling debris. The best choice is 1.5 times the height. This 1.5 factor provides a practical safety buffer to account for unpredictable collapse directions, swinging or leaning debris, and progressive failure, which can extend debris beyond the base height alone. It’s the commonly taught rule of thumb for sizing collapse zones in firefighting safety.

For example, a 40-foot-tall structure would have an estimated collapse zone of about 60 feet.

Using a factor of 2 would be more conservative than needed in many cases and could unnecessarily impede operations. A factor of 1 or 0.5 would place personnel inside or far too close to where debris could travel, increasing risk.