Effect of Automatic Sprinkler Protection on Smoke Control Systems

horizontally throughout the fire compartment. AP" calculatedusing the average temperature on the fire side <strong>of</strong> the wall<strong>of</strong> the stairshaft in Equation I gave good agreement withthe measured AP• at that location. Actual values <strong>of</strong> AP•measured between the fire floor and the stairshaft rangedfrom 0.008 to 0.016 in. H 2 0 (2 .to 4 Pa).To conclude this discussion on buoyancy pressures, thetests indicated that fire-induced buoyancy pressures decreasedas spray density increased and that a reduction <strong>of</strong>50% <strong>of</strong> the design pressure difference for zoned smokecontrol in sprinklered buildings is adequate but conservative.Also, measured pressure differences compared wellwith predicted values when the average temperature acrossthe stairshaft wall was used. Note that predicting the averagetemperature at a specific location in the fire compartment,with wide variation in the temperatures between onepart <strong>of</strong> ·the compartment and another, could be quitecomplex.Rapid Expansion <strong>of</strong> Steam There was some interestin whether the introduction <strong>of</strong> a water spray into the hotgases in the early stages <strong>of</strong> the fire would create a suddenpressure increase due to the rapid evaporation <strong>of</strong> water.One <strong>of</strong> the fires in the one-story room was allowed tobecome fully developed and the room very hot before thesprinklers were turned on. In that case, a rapid expansion<strong>of</strong> steam occurred, forcing smoke and steam out <strong>of</strong> the testroom at high velocity. Under normal conditions <strong>of</strong> sprinkleroperation, however, sprinklers are activated by the firstflow <strong>of</strong> hot gases rising from the fire. Ambient conditionsat that stage are not hot enough to cause instantaneousevaporation <strong>of</strong> a large volume <strong>of</strong> water. In the tests in theone-story room, the plots <strong>of</strong> AP versus time typicallyshowed that the rapid drop in temperature <strong>of</strong> the combustionproducts, on activation <strong>of</strong> the first sprinklers, resultedin an immediate pressure reduction that more than compensatedfor the change in pressure caused by the rapidevaporation <strong>of</strong> a relatively small amount <strong>of</strong> sprinkler spray.Pressure Required to Prevent Smoke Spread Acrossa Boundary Figure II shows the results <strong>of</strong> a series <strong>of</strong> testsconducted in the one-story test room and attached corridor(see Figure I) to determine how much pressure wasrequired to prevent smoke ·from entering the corridor atdifferent temperatures in the fire room. The spray densitywas adjusted to a certain level, and conditions in the fireroom were allowed to stabilize. A fan supplying air to thecorridor was adjusted to create a positive pressure betweenthe corridor and the fire room. The flow rate <strong>of</strong> the fan wasthen gradually reduced, and the pressure differences (atceiling level) between the two rooms at different flow rateswere recorded. When the value <strong>of</strong> AP between the twospaces reached zero, smoke could be observed leaking intothe corridor.These tests indicated that, when the fire-inducedbuoyancy pressure at the ceiling <strong>of</strong> the fire test room wasequal to or less than the prefire pressurization <strong>of</strong> thecorridor (AP d.sign), smoke would not flow into the protectedspace. These measurements confirm that the movementTemperature, oc0 100 200 300 400 soo 6000.06 .-~...,-~-,.-.-..-~-..-.~...,--,...--.--,0.0.5~.5 0.04 -~ 0.03cI0.02O.otTest points I, 2, 3, 4 indicate pressure -14difference produced by corridorpressurization to prevent smoke entry,- 12one~storey test room results.....10 c:-•0smoke entryP«ssure diffe)v~t~11!c• eil~- 4causod by fuc'\,2 . !o Smoke entry 2'•/omL-~~200L-~-... ~_. __ 600L-~-800~~~,ooo~_.~,~Figure 11Temperature. opPressure difference required to prevent smokeentry into corridor from the fire room, as afunction <strong>of</strong> fire room temperature.<strong>of</strong> smoke through leakage openings can be opposed by anequal pressure on the nonfire side <strong>of</strong> the barrier. Given thatthe maximum pressure difference between the floor andceiling (AP•) created by a sprinklered fire was about 0.05in. H 2 0 (12.5 Pa) in the one-story test room and 0.016 in.H 2 0 (4 Pa) in the Tower, the accepted practice, which is todesign for AP 1<strong>of</strong> 0.05 in. H 2 0 (12.5 Pa), appears to bereasonable, i.e., adequate, but not excessive.<strong>Effect</strong>s <strong>of</strong> <strong>Sprinkler</strong>s on Gas ConcentrationsStudies conducted by Klote (1990), Walton (1988), andWalton and Budnick (1988) to measure the ability <strong>of</strong>sprinklers to suppress wood crib fires and fires in <strong>of</strong>ficefurnishings demonstrated that concentrations <strong>of</strong> carbondioxide (COz) and carbon monoxide (CO) gases in theproducts <strong>of</strong> combustion from a sprinklered fire were low.C0 2 may have reached 2% or 3% (ambient is 0.4% ), whileCO concentrations were between 0.05% and 0.3% (50 and300 ppm) (ambient air contains no CO). The concentrations<strong>of</strong> these gases first increased as the fire grew, then decreasedafter the sprinklers operated and the fire began tobe extinguished. The cited literature suggests that theamount <strong>of</strong> CO and C0 2 produced in an unsprinklered fireis much higher than in a suppressed fire because the fire islarger, bums longer, and consumes more <strong>of</strong> the availableoxygen.In contrast, as illustrated by Figures 12a and 13a,shielded crib fires on the seventh floor (the fire floor) <strong>of</strong> theTower produced C0 2 concentrations as high as 8% and 9%and CO concentrations between 1.0% and !.5% (10,000 to15,000 ppm). These gas concentrations were measured ata distance <strong>of</strong> 1.7 m above the floor, approximately 10. ft(3.05 m) from the wood crib, at the entrance to the west'ASHRAE Transactions: Research505