Which factor is crucial for determining excavation safety in trenches?

Soil type plays a fundamental role in determining excavation safety in trenches because different soil types have varying properties that affect their stability and the likelihood of cave-ins. For example, cohesive soils like clay can hold their shape better than granular soils like sand, which can be more prone to sloughing. Understanding the soil type allows workers to implement appropriate safety measures, such as the right type of shoring or trench protection, to prevent soil collapse during excavation. Additionally, knowledge of the soil structure helps in planning the trench's width and depth effectively, reinforcing the safety protocols needed for the operation.