Which condition must be met when using trench boxes?

When using trench boxes, it is crucial that the box is positioned correctly to prevent shifting. Trench boxes are used to protect workers from trench collapses, and their effectiveness largely depends on proper installation. Positioning the trench box correctly ensures that it is securely set within the trench, providing adequate support against the walls and maintaining stability. This is essential for safeguarding the workers inside the trench, as improper positioning could lead to the box shifting or tipping over, thus compromising the safety measures in place.

The aspect of correct positioning involves ensuring that the box is properly aligned with the trench walls and that it is installed to the manufacturer's specifications. This is fundamental in maintaining the integrity of the trench and ensuring that the box functions as intended, holding back the surrounding soil and providing a safe working environment.