Effect of Automatic Sprinkler Protection on Smoke Control Systems

hI'J]48'i'12.8'Air Serv. Eev. Eev. Floor Area • Watersupp y!5 2"0 Shaft ShaftSupplyVestibule·suShaftI Air mJ"sm~~(~ .,;,-Exh. /Sh~ L~_jShaft:l*.!:.11-.1~ ~.-Crib, 4' X 4' X 3'Viewing1-->r,-: \ LArea00West COII:idor 1 5'"'Notes:* = pendent sprinklerFigure 2including data-processing areas, are listed. as "light hazard"in NFPA Standard 13. That is, "quantities and/or combustibility<strong>of</strong> contents are low and fires with relatively low rates<strong>of</strong> heat release are expected" (NFPA 1991). No values arestated in .NFPA Standard 13 to quantify what constitutes a"relatively low" heat release rate (HRR), ·which is notsurprising, given that it depends on the specific occupancyarld compartment conditions. Various authors have treatedwood cribs as representative <strong>of</strong> light hazard fuel packages(Walton 1988; Madrzykowski and .Vettori 1992). A woodcrib canilot completely simulate "real" burning conditions,however, in that the fuel is concentrated in a limited· arearather than· distributed over a large space. All <strong>of</strong> the fuelwithin the crib can bum at once, whereas fuel distributedQver a larger area will bum sequentially as fire spreadsfrom one object to another .. For test purposes, it waspractical to use wood cribs that produced an HRR representative<strong>of</strong> a typical <strong>of</strong>fice workstation in which a certain mass<strong>of</strong> fuel is concentrated within a relatively small area.Madrzykowski and Vettori (1992) tested typical <strong>of</strong>ficeworkstation fuel packages consisting <strong>of</strong> a desk, table,padded chairs, boxes <strong>of</strong> paper partially shielded under thedesk, etc., weighing a total <strong>of</strong> 639 Jb (290.5 kg). Averageheat release rates during unsuppressed burning <strong>of</strong> this fuelpackage were reported to be approximately 570 Btu/s (600kW), with several peaks as high as 1,235 Btu/s (1,300 kW)as various components <strong>of</strong> the package ignited sequentially.Madrzykowski and Vettori's workstation HRR results canbe used as a benchmark for comparison with the wood cribfires used in these tests.Wood cribs <strong>of</strong> two sizes were used in these experiments.·In the 10-story tower, cribs weighed approximately600 Jb (272 kg). The unsprinklered heat release rate fromPlan <strong>of</strong> the J().story tower, seventh floor.these cribs was measured at 1,150 Btu/s (1,200 kW). Theywere 66 lb (30 kg) heavier than the workstations describedin Madrzykowski and Vettori (1992); however, the exteriorrows <strong>of</strong> wood in the cribs, which were wetted by sprinklerspray, did not bum. The actual weight <strong>of</strong> fuel consumed byfire was typically 350 Jb (160 kg), or about 50% <strong>of</strong> theinitial crib weight (Mawhinney et al. 1992). These woodcribs compare reasonably well to the light hazard fuelloadings representative <strong>of</strong> an <strong>of</strong>fice occupancy described inMadrzykowski and Vettori (1992).In the tests in the one-story room, larger wood cribswere used, typically weighing 1,200 Jb (545 kg). Again, notall <strong>of</strong> the fuel could bum because <strong>of</strong> wetting <strong>of</strong> the wood onthe outer edges <strong>of</strong> the crib. Unsuppressed, and with themaximum ventilation that could be provided in the one-storyroom, a peak heat release rate <strong>of</strong> 2,850 Btu/s (3,000 kW)was measured for these cribs. Most <strong>of</strong> the tests wereconducted at Jess than full ventilation conditions, however,which limited the heat release rate <strong>of</strong> an unsuppressed fireto 1,900 Btu/s (2,000 kW). These cribs did not represent alight hazard fuel loading, but, as stated earlier; the P.rimaryobjective <strong>of</strong> the testS in the one-story room was to evaluatethe nature <strong>of</strong> the interaction between sprinklers and the fire.This co.uld be dqne by creating a fire that could be sus·tained at relatively steady-state conditions for a long time,while ventilation and sprinkler density were varied.Wood. cribs were constructed using 3.5-in. by 3.5-in.(90-mm by 90-mm) dry white pine sticks, spaced 3.5 in.(90 mm) apart and piled 10 rows (36 in. [0.91 m]) high. Inthe one-story room, sticks were 70 in. (1.78 m) .long; in thetower, 48 in. (1.22 m) long. The total mass <strong>of</strong> wood in thecribs in the one-story room was typically 1,200 lb (545 kg);those in the Tower were on·~verage 700 Ib (320 kg).ASH RAE Transactions: Research497