CEN and NFPA have expanded the application of water mist in open environments from light solid combustible fire hazards to several in the higher hazard categories. A previous analysis and test evaluation showed that such application expansion is feasible, provided that the water mist spray meets droplet size and application density requirements for the intended fire challenge. However, this evaluation was performed exclusively for water mist sprays discharging at 1.65 m above the burning combustibles. This led to the question of whether the water mist protection could still be effective for larger clearances of nozzle discharge above the combustibles. Therefore, a series of fire tests was conducted subsequently to determine the ceiling height limits for both deluge and automatic nozzle protections. As for the previous evaluation, the two tested fire challenges were a 2-tier (2.74 m) high rack-storage of corrugated cardboard cartons on wood pallets, and a palletized storage of cartoned expanded polystyrene up to 1.68 m high. Both fire challenges were in the CEN OH-3 category, and respectively represented fire hazards in the FM Global HC-2 and HC-3 categories, which in turn corresponded to the NFPA OH-1 and OH-2 fire hazards. Each water mist spray discharged 76 l/min at 16.5 bar, with a volume median droplet diameter of around 220 µm. The nozzles were spaced 3.05 × 3.05 m to provide a designated application density of 8.1 mm/min. Quick-response thermal sensors, with an activation temperature of 74°C and a response index of 27.6 (m s) 1/2 , were employed to initiate the nozzle discharge. The tests showed that the deluge protection is applicable to both fire challenges for ceiling heights up to 9.1 m. However, for the automatic nozzle protection, the ceiling height limit is reduced to 6.1 m, with a water supply requirement of providing 17 nozzle operations for a safety factor of about 50% over the maximum number of nozzle operations observed in the tests.

中文翻译：

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开放环境中两种固体可燃火灾隐患的细水雾防护天花板高度限制

CEN 和 NFPA 已将细水雾在开放环境中的应用从轻型固体可燃火灾危险扩展到几个较高危险类别。先前的分析和测试评估表明，这种应用扩展是可行的，前提是细水雾喷雾满足预期火灾挑战的液滴尺寸和应用密度要求。然而，该评估仅针对在燃烧的可燃物上方 1.65 m 处排放的细水雾喷雾进行。这导致了一个问题，即细水雾保护对于可燃物上方喷嘴排放的较大间隙是否仍然有效。因此，随后进行了一系列火灾测试，以确定雨淋和自动喷嘴保护的天花板高度限制。至于之前的评价，两个经过测试的火灾挑战是木托盘上的 2 层 (2.74 m) 高货架存储的瓦楞纸板箱，以及高达 1.68 m 的纸盒发泡聚苯乙烯的托盘存储。这两个火灾挑战都属于 CEN OH-3 类别，分别代表 FM Global HC-2 和 HC-3 类别中的火灾危害，而这又对应于 NFPA OH-1 和 OH-2 火灾危害。每个细水雾喷雾在 16.5 bar 下排放 76 l/min，体积中值液滴直径约为 220 µm。喷嘴的间距为 3.05 × 3.05 m，以提供 8.1 mm/min 的指定应用密度。使用具有 74°C 活化温度和 27.6 (m s) 1/2 响应指数的快速响应热传感器来启动喷嘴排放。测试表明，雨淋保护适用于天花板高度高达 9.1 m 的两种火灾挑战。然而，对于自动喷嘴保护，天花板高度限制降低到 6.1 m，供水要求提供 17 次喷嘴操作，安全系数比测试中观察到的最大喷嘴操作次数高出约 50%。