What is the minimum inside diameter of a manhole?

What is the minimum inside diameter of a manhole?

• A. 24 inches
• B. 42 inches
• C. 36 inches
• D. 48 inches

Answer: (B)

Access space inside a manhole has to be enough for a person to enter, work, and maneuver tools and equipment safely. A 42-inch inside diameter provides roughly 9.6 square feet of usable floor area, which lets a worker stand or crouch and still have room to move around the sewer invert, use a ladder or access tools, and carry lighting or small devices. If the opening were much smaller, moves would be cramped, increasing the risk of injury and making cleaning, inspection, and maintenance much harder. On the other hand, making manholes larger than necessary adds cost and structural footprint without providing proportional benefits. So, 42 inches strikes a practical balance, giving sufficient working space while keeping construction and maintenance reasonable. Smaller options like 24 or 36 inches would be impractical for typical maintenance tasks, and larger ones like 48 inches are common but not required by the minimum standard.