To ensure safety, which area around a crane should be routinely checked for personnel during operation?

The rear swing radius is critical to check for personnel during crane operations because this area poses a significant risk of collision with the crane's counterweights or superstructure as it swings during operation. Cranes can have large and unpredictable rear swing movements, particularly when maneuvers involve rotating the boom or traveling with a load. Ensuring that this area is clear helps prevent accidents and injuries to personnel who might not be visible to the operator or might misjudge the crane's movements.

The other options, while important in their own rights, do not specifically address the unique risks presented by the rear swing. Checking all areas within 20 feet of the crane is a broader precaution but does not focus on the specific hazards associated with the rear swing. The operator's blind spots are definitely areas of concern, yet they pertain more to the visibility challenges faced by the operator rather than the direct hazards of crane movement. The area directly underneath the load is crucial to avoid dropping hazards, but it is also limited to a smaller radius where the load is suspended, and does not account for swinging movements. Therefore, maintaining awareness of the rear swing radius enhances overall safety by mitigating the risk of accidents associated with this specific area.