What hazard is associated with trenches deeper than 4 feet?

Trenches deeper than 4 feet pose significant risks, primarily due to the potential for cave-ins. When excavating a trench, the walls can become unstable, particularly if they are not properly supported or if the soil is loose or saturated with water. A cave-in occurs when the sides of the trench collapse, which can lead to serious injuries or fatalities for workers inside the trench.

Understanding the mechanics of trench collapse is vital for safety in excavation work. The deeper the trench, the greater the risk because of the increased weight of the soil above and the potential for gravitational forces to compromise the trench walls. To mitigate these risks, safety measures such as shoring, sloping, or benching are often necessary to prevent cave-ins.

While options like water accumulation and vibration from nearby traffic can present hazards in excavation work, they are not as immediate and dangerous as the risk of a cave-in in deeper trenches. Electrical interference is also a concern, but it relates more to the presence of utility lines rather than a specific risk directly associated with trench depth. Hence, cave-ins remain the most critical hazard associated with trenches deeper than 4 feet.