A trench 90 ft long and 6 ft deep requires egress so no worker travels more than 25 ft laterally to a ladder. A ladder placed mid-run protects 25 ft in each direction, or 50 ft total. What is the minimum number of ladders required?

Giải thích

Each ladder covers 50 ft of trench (25 ft of lateral travel on each side), so 90 ft / 50 ft = 1.8, which rounds up to 2 ladders. The 25 ft maximum travel ensures rapid exit if a wall fails or the atmosphere changes. Egress is required in any trench 4 ft or deeper and must extend above the top edge.