A trench shield is a protective structure placed inside an excavation to provide a safer working space if the trench sides collapse. It is commonly formed from two panels connected by spreaders. A shield does not necessarily stop the ground moving; it is designed to protect people working within its approved protected zone. 

In everyday construction use, the terms are often used interchangeably. Both usually describe two protective side panels connected by spreaders and placed in a trench. Some suppliers use 'trench shield' to emphasise worker protection and 'trench box' as the common product name, so the actual design, capacity and manufacturer’s instructions matter more than the label. 

Excavation protection is required whenever there is a foreseeable risk of collapse or material falling into the excavation. The chosen method may be a trench shield, shoring, battering or another engineered system, based on depth, soil, groundwater, nearby loads and services. The decision must be made before entry through a site-specific risk assessment and temporary works process, not by relying on a universal depth rule. 

The shield should be assembled and installed in accordance with the manufacturer’s instructions and the temporary works design. Use the designated lifting points, correctly rated lifting accessories and a suitable excavator operated by competent personnel. Nobody should enter an unsupported excavation or stand beneath the shield while it is being lifted, lowered or repositioned.