True/False: When doing trench rescue operations, vibrations can cause secondary cave-ins, so all bystanders, nonessential personnel, apparatus, and heavy equipment must be kept back from the trench lip.

• A. False
• B. Not specified
• C. Unknown
• D. True

Answer: (D)

In trench rescue, the trench’s walls can be very unstable and sensitive to disturbance. Vibrations from machinery, vehicles, or even activity near the trench can travel through the soil and trigger a secondary cave-in along the trench face. Because of that risk, an exclusion zone is established around the trench lip, and bystanders, nonessential personnel, apparatus, and heavy equipment are kept well back from the edge. This buffer protects people and equipment from triggering another collapse and gives rescuers space to stabilize and work safely. So the statement is true.