A team of plumbers is excavating a trench 2.5 metres deep for a new drain line. The soil is a mix of sand and gravel, known for being unstable. What primary method should be employed to ensure worker safety from a trench collapse?

Question: A team of plumbers is excavating a trench 2.5 metres deep for a new drain line. The soil is a mix of sand and gravel, known for being unstable. What primary method should be employed to ensure worker safety from a trench collapse?

Answer options:

• Regularly inspect the trench walls for cracks ✅ Slope the trench walls back to a safe angle, or install an engineered trench support system
• Implement a buddy system for continuous watch
• Conduct daily atmospheric monitoring within the trench

Correct answer: Slope the trench walls back to a safe angle, or install an engineered trench support system

Explanation: For deep trenches (over 1.2 m, and especially in unstable soil), the primary protection against collapse is either to slope the walls back to a safe angle (determined by soil type) or to install an engineered trench support system, such as shoring or shielding. Simply inspecting or monitoring the atmosphere does not prevent structural collapse.