A plumber is assigned to work in a trench that is 2.5 metres deep in Type C soil. The trench width at the bottom is 0.8 metres. What is the minimum slope ratio required for safe excavation if no shoring system is used?

Question: A plumber is assigned to work in a trench that is 2.5 metres deep in Type C soil. The trench width at the bottom is 0.8 metres. What is the minimum slope ratio required for safe excavation if no shoring system is used?

Answer options:

• 1:1 (45 degrees)
• 0.75:1 (approximately 53 degrees)
• 1.5:1 (approximately 34 degrees) ✅ 2:1 (approximately 27 degrees)

Correct answer: 2:1 (approximately 27 degrees)

Explanation: For Type C soil, Canadian occupational health and safety regulations typically require a maximum slope ratio of 1 horizontal to 1 vertical (1:1) when using a ladder in a trench, but when workers are in the trench without shoring and the trench is deeper than 1.2 metres, the maximum permissible slope is 1 horizontal to 2 vertical (2:1). This provides a gentler slope for less stable soil to prevent collapse. The other options represent steeper slopes, which are unsafe for Type C soil.