Experimental Study on the Effect of Separation Distance between Open Grid Ceiling and Upright Sprinkler Head on Water Distribution

This study experimentally evaluates the effect of open-grid ceilings on the water-spraying effectiveness of upright sprinkler heads. The work procedure guidelines of the National Fire Agency uniformly stipulate a separation distance of at least 450 mm between open grid ceilings and upright sprinkler heads. However, the National Fire Protection Association (NFPA) specifies different separation distances depending on hazard classifications (light: 450 mm and ordinary: 600 mm). This difference in standards necessitated the verification of the effective spraying performance of sprinkler heads. Therefore, in this study, water distribution and spray volume were measured by varying the separation distances to 300, 450, and 600 mm through spray distribution experiments. The experimental results showed that the 600 mm separation distance met all performance criteria, whereas the 450 mm separation distance failed to meet the standard for the average water collection distribution curve. Notably, the amount of water collected in the 7th collection container decreased by approximately 45% compared to that at the 600 mm distance. These findings suggest that the current National Fire Agency guidelines, which specify a separation distance of 450 mm, may be insufficient to prevent spray obstruction and should be reconsidered.