What is the required design strength for hangers supporting pipes?

The correct design strength for hangers supporting pipes, according to NFPA 13, must account for both the weight of the water-filled pipe and additional safety factors to ensure structural integrity and reliability during a fire event. The requirement of five times the weight of the water-filled pipe plus a minimum of 250 pounds recognizes the variable loads that systems can experience, including potential impact loads, thermal expansion, and other dynamic forces.

This safety factor is critical in achieving a dependable installation that can withstand operational and emergency conditions, which aligns with the overarching goal of NFPA standards to enhance safety and performance in fire protection systems. By ensuring that the hangers can support this increased load, the installation is better equipped to handle unexpected stresses that may occur in a fire scenario or due to the normal dynamics of the system.

Other options do not provide adequate safety margins, which could lead to structural failures, compromising the effectiveness of the sprinkler system. Therefore, the requirement outlined in the correct answer aligns with best practices in ensuring robust and safe installations.