What is the required standpipe riser size for Class II standpipes in buildings under 50 feet?

What is the required standpipe riser size for Class II standpipes in buildings under 50 feet?

• A. 1 inch
• B. 2 inches
• C. 3 inches
• D. 4 inches

Answer: (B)

Two inches. For Class II standpipes, which use a 1.5-inch occupant hose, the vertical riser must be sized to deliver the needed flow with manageable pressure loss. In buildings under 50 feet tall, a 2-inch riser provides sufficient capacity (about the 100 gpm design flow) to reach all outlets without excessive friction loss, allowing the occupant to effectively fight a fire with the hose. A smaller pipe would drop pressure too much and limit flow, while larger sizes (3 or 4 inches) aren’t necessary for this height and would add unnecessary cost and complexity.

Two inches. For Class II standpipes, which use a 1.5-inch occupant hose, the vertical riser must be sized to deliver the needed flow with manageable pressure loss. In buildings under 50 feet tall, a 2-inch riser provides sufficient capacity (about the 100 gpm design flow) to reach all outlets without excessive friction loss, allowing the occupant to effectively fight a fire with the hose. A smaller pipe would drop pressure too much and limit flow, while larger sizes (3 or 4 inches) aren’t necessary for this height and would add unnecessary cost and complexity.