In a building where primary structural members are 25 ft apart and density > 0.25, what line-to-line distance between sprinklers is permitted?

In a building where primary structural members are 25 ft apart and density > 0.25, what line-to-line distance between sprinklers is permitted?

• A. 12 ft 6 in
• B. 12 ft
• C. 10 ft
• D. 15 ft

Answer: (B)

The key idea is that sprinkler spacing in foam-water systems is driven by the need to achieve the required discharge density across the protected area while accounting for obstructions from structural members. When primary structural members are 25 ft apart and the design density is higher than 0.25 gpm/ft^2, the spray patterns must overlap sufficiently to avoid gaps under the beams and between sprinklers. NFPA guidance for line-to-line spacing in this density range caps the distance between sprinklers along a line at 12 ft, ensuring there is enough overlap to maintain the intended coverage. A larger spacing, like 12 ft 6 in or 15 ft, could leave uncovered areas due to beam shadows, while a smaller spacing such as 10 ft is more conservative than required for this scenario. Therefore, the permitted line-to-line distance is 12 ft.

The key idea is that sprinkler spacing in foam-water systems is driven by the need to achieve the required discharge density across the protected area while accounting for obstructions from structural members. When primary structural members are 25 ft apart and the design density is higher than 0.25 gpm/ft^2, the spray patterns must overlap sufficiently to avoid gaps under the beams and between sprinklers. NFPA guidance for line-to-line spacing in this density range caps the distance between sprinklers along a line at 12 ft, ensuring there is enough overlap to maintain the intended coverage. A larger spacing, like 12 ft 6 in or 15 ft, could leave uncovered areas due to beam shadows, while a smaller spacing such as 10 ft is more conservative than required for this scenario. Therefore, the permitted line-to-line distance is 12 ft.