A s e r i e s of large-scale f i r e suppression t e s t s was conducted for two d i f f e re n t commodities stored in s t e e l racks of d i f f e r e n t heights, and were analyzed using a global heat balance model. In these t e s t s , water was applied uniformly on top of the storage array a t selected f i r e s i z e s t o determine the f i r e s u p p r e s s i b i l i t y f o r a commodity a t a given storage height. A f i r e suppression parameter was used t o correlate the f i r e suppression r e s u l t s of these t e s t s . The f i r e suppression parameter is a function of fuel d e n s i t y , f u e l s p e c i f i c heat, ignition temperature, heat of combustion, burning r a t e , heat of pyrolysis, and water application r a t e . The data indicate t h a t the combustible packaging and overall storage arrangement have s i g n i f i c a n t impact on the magnitude of the c r i t i c a l water density f o r f i r e suppression. KEYWORDS: water-based f i r e suppression.
The Actual Delivered Density (ADD) for rack-storage fires has been investigated experimentally, using an ADD apparatus equipped with a fire plume simulator. The fire plume simulator was calibrated to simulate the plumes of a 6.1-m (20-ft) high rack-storage fire of the FMRC Class II Commodity. Three standard upright sprinklers (17132-in. C, 112411 F & 112-in. G) were employed for the investigation. Empirical correlations in the form of power law for the water penetration ratio, which is the ratio of the ADD to the water density measured without f i e , have been established for sprinkler-fire arrangements in which the fire was centered under one sprinkler, centered below two sprinklers on the same pipe and centered below four sprinklers. In the case of a single sprinkler operation, the water penetration ratios for a given sprinkler and fire size were found independent of the water discharge rate under the present measurement range, varying from 95 Ilmin to 212 Ilmin (25 gpm to 56 gpm).
A series of seven large-scale rack storage f i e tests was conducted, using four ESFR sprinkler models, to determine the required sprinkler spray characteristics for achieving effective protection of rack storages of the FM standard plastic commodity up to 10.8 in high in a 12.2 m high warehouse. AU four models have a nominal K factor of 0.34 ~/s/(k~a)", and the sprinkler discharge pressure was maintained at 517 kPa. The sprinkler spacing was 3.05 m x 3.05 m. The test variables include storage heightlceiling clearance, ignition location and sprmkler models. The sprays of the sprinkler models used in the fire tests were characterized by their drop size distribution, center-core thrust force, and water distribution under no-fire condition. For ESFR sprinkler protection, the effect of drop size distribution was demonstrated to be unimportant through the fire tests. For the case with ignition directly over a sprinkler, the spray center-core thrust force and the water flux under no-fue condition over the top surface of a two pallet-load by two pallet-load fuel array directly underneath the sprinkler have been shown to be critical for achieving f i e suppression. A minimum centercore thrust force of 101.3 ~/ m ' measured at 1.77 beneath the sprinkler deflector, and a minimum water flux of 0.614 l/s/m2 measured over a 2.15 m x 2.15 m area 4.42 m beneath the ceiling directly under the sprinkler have been found to be necessary for achieving fire suppression. For the case with ignition centered below two sprinklers and with 10.8 m storage height / 1.77 m ceiling clearance, only the water flux under no-fire condition over the fuel array top was shown to be critical. A measured water flux of 0.667 0/s/m2 over a 2.15 m x 2.15 m area, centered below the two sprinklers, 1.77 beneath the ceiling, was found to be sufficient for achieving fire suppression.
A series of fire tests was conducted under a smooth ceiling to investigate the ceiling gas flow as affected by ceiling slope, convective heat release rate of the fire and clearance between the fuel top surface and the ceiling.Besides a horizontal ceiling reference, three ceiling slopes were investigated: 10°, 20°and 30°. Pool fires were used as fire sources. Two pool diameters, two different fuels (heptane and methanol) and three ceiling clearances were used.In each test, measurements were made of ceiling gas temperatures, ceiling gas velocities, and fuel mass loss. Empirical correlations for the near-maximum gas velocity and excess temperature of the ceiling flow along the steepest run were established in terms of ceiling slope, radius from the point of intersection of the ceiling with the pool centerline, and characteristics of the undeflected plume at the ceiling level. The ceiling slope had a more pronounced effect on velocity variation along the steepest run than on temperature variation.In the upward direction, the rate of velocity decr-ease with radius was reduced significantly as the ceiling slope increased.In the downward direction, at a certain distance from the pool cent.e r-I ine, the flow separated from the ce il ing and turned upward. The larger the ce i I ing slope, the sooner' the turning occurred. Fur thermor-e , the rate at which gas temperature approached ambient in the downward direction increased wi th ceil ing slope, while the temperature decrease in the upward direction was not much affected by change of ceiling slope.
A series of seven rack storage fire tests was conducted, using four pendent fast-response prototype sprinklers to determine the sprinkler discharge characteristics necessary for suppressing four-tier array rack storage fires under a 9.14-m high ceiling. The sprinklers had a nominal K-factor of either 11 or 14, and the sprinkler discharge pressure was maintained at 345 kPa. The commodities used as fuel consisted of polystyrene cups packaged in compartmented cartons. The commodities were arranged in double-row steel racks, two pallet-loads wide, two palletloads deep and four tiers high. Three different ignition locations with respect to sprinklers were employed. Sprinkler water distribution under a no-fire condition and spray center-core thrust force were identified as key parameters of sprinkler discharge characteristics pertaining to sprinkler fire-suppression ability. The relationships among the fire sizq at first sprinkler actuation, plume momentum flux, Required Delivered Density, sprinkler water distribution and spray center-core thrust force, with regard to suppression of the rack storage fires, were explored.For fire tests with ignition directly under a sprinkler, it was highly desirable for the sprinkler spray to overpower the fire plume to achieve efficient delivery of sprinkler water to the fire source. In the fire tests when the spray center-core thrust force was greater than the plume momentum flux and the average water flux over the top surface of the fuel array under a no-fire condition was greater than the Required Delivered Density, fire suppression was achieved.For fire tests with ignition centered below either two or four sprinklers, the fire plume was largely confined to the center flue of the fuel array, and most of the sprinkler water projected toward the top surface of the fuel array reached the top surface without passing through the fire plume. Therefore, the measured water flux over the top surface under a no-fire condition was expected to be close to that delivered during a fire. Fire suppression in these tests resulted from contributions of both the sprinkler water reaching the top surface and the side exposed surfaces of the fuel array. When the average water flux over the top surface under a no-fire condition was greater than the Required Delivered Density, fire suppression was achieved. INTRODUCTI ONSprinkler protection against rack storage fires has been a major concern of the fire protection community for the past 20 years. Rack
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