What step must be taken before an entrapped person can be dug out of collapsed earth or sand?

Before attempting to dig out an entrapped person from collapsed earth or sand, it is essential to stabilize the surrounding area through shoring. Shoring involves the use of supportive structures to prevent further collapse or shifting of the ground during a rescue operation. This step is critical because any further movement could endanger both the rescuers and the entrapped individual.

By securing the area with shoring, rescuers can create a safe environment to carefully excavate the trapped person. It's a proactive safety measure that ensures that the rescue efforts do not inadvertently cause additional harm or bury the individual deeper.

The other options, while important in their own contexts, do not directly relate to establishing a safe rescue environment. Cautioning the crowd may help manage the scene, calling for backup is advisable for additional support but does not address the immediate danger of collapse, and clearing debris might be part of the rescue process but is only feasible once the area is stabilized. Thus, shoring is the necessary step to ensure safety before proceeding with any digging or extraction efforts.