What condition must be met for a trench to be considered safe according to regulations?

For a trench to be considered safe according to regulations, it must be sloped or shored. This requirement is critical to prevent cave-ins, which can pose significant risks to workers. Sloping involves angling the sides of the trench to reduce the risk of collapse, while shoring refers to the use of supports to hold up the earth's sides. Regulatory guidelines detail specific angles of slope based on the type of soil present as well as the depth of the trench.

By ensuring trenches are either sloped appropriately or shored with proper materials, the risk of collapses is significantly minimized, thus providing a safer working environment for those who are within or near the trench. This safety standard is foundational in construction and excavation work, as the dangers associated with trenches are well-documented and regulated under occupational safety laws.

The other conditions listed, such as backfilling, the depth of the trench, or having guardrails, do not directly address the inherent instability that can arise from open trenches. While these may contribute to overall site safety, they are not the primary safety measures for trench stability as required by regulations.