Effect of Automatic Sprinkler Protection on Smoke Control Systems

smoke from the building. Studies such as these contributeto a quantitative understanding <strong>of</strong> the interaction betweensprinklers and the buoyant layer. They are theoretical,however, and most have not yet been validated by full-scaletesting.In the absence <strong>of</strong> full-scale test data on the maximumfire size to be expected in a sprinklered <strong>of</strong>fice building,Morgan and Hansell (1985) conducted a review <strong>of</strong> Britishfire loss statisticsc Their objective was to identify' a "designfire" size for use in designing smoke ventilation systems foratria in sprinklered and unsprinklered buildings. Theirreview indicated that the maximum heat release rates andareas <strong>of</strong> fire involvement in sprinklered buildings weremuch lower than in unsprinklered buildings. Fires insprinklered buildings were estimated to have attained heatrelease rates between 285 and 2,850 Btu/s (300 and 3,000kW) before being extinguished by the sprinklers, with theprobability <strong>of</strong> occurrence <strong>of</strong> smaller fires much higher thanfor larger fires. This study supported the British designpractice for smoke contrpl systems <strong>of</strong> assuming a 5-MWdesign fire under sprinklered conditions, with an area <strong>of</strong> 10n:Jl. Morgan and Hansell's information is a useful startingpoint for examining the question regarding the likelihood <strong>of</strong>occurrence and size <strong>of</strong> shielded fires in sprinklered buildings.Gustafsson (1989), Heskestad (1974), Hinkley (1989),and Battrick (1986) report on the long-standing controversybetween sprinkler and ventilation experts about whether ornot ventilation <strong>of</strong> hot gases from a sprinklered buildingthrough ro<strong>of</strong> Vel)tS during a fire is beneficial to the control<strong>of</strong> the fire. <strong>Sprinkler</strong> experts argue that automatic smokevents detract from proper performance <strong>of</strong> the sprinklersystem. Smoke ventilation specialists, in tum, argue thatreduced smoke logging <strong>of</strong> the building improves interiorfirefighting and reduces smoke damage. Although somefull-scale studies have been done (Gustafsson 1989), theyare usually based on either a one-story warehouse buildn1gor a shopping mall, with ro<strong>of</strong> vents, and are therefore notimmediately useful for analyzing the impact <strong>of</strong> sprinklers onan operating zoned smoke control system in a high-risebuilding.Two notable exceptions to the shortage <strong>of</strong> full-scaleexperimental work involving sprinklers and smoke controlmeasures are studies conducted by the Seattle Fire Depart- .ment in an <strong>of</strong>fice building (Seattle FD 1984) and by Kloteat a hotel in Washington, DC (Klote 1990). The Seattlework looked at fire pressures generated by sprinklered andunsprinklered fires; carbon monoxide generated by sprinklered,shielded fires; and the performance <strong>of</strong> three smokecontrol approaches: stairwell· pressurization, elevator shaftpressurization, and zoned smoke control. The Seattle studyconcluded that sprinklers were indeed effective in reducingfire pressures and thereby improved the likelihood thatsmoke control systems designed to current standards (forassumed nonsprinklered conditions) would prevent smokespread. There was no suggestion that design standards couldbe reduced for sprinklered fire conditions. Problems <strong>of</strong> lossASH RAE Transactions: Research<strong>of</strong> stair pressurization on opening <strong>of</strong> doors, with subsequentcontamination <strong>of</strong> the stairshafts, were noted. The resultsprovide a useful starting point for further validating studies.Klote (1990) studied nonsprinklered fires with smokecontrol and sprinklered · filllS without smoke control in aseries <strong>of</strong> full-scale tests in a h9tel in Washington, DC,which was destined to be demolished. He noted that firepressures were very low in the sprinklered fires and wouldnot likely pose a challenge for a smoke control systemdesigned to meet current standards (Klote and Milke 1992;NFPA 1988). Klote (1990) noted that more tests would berequired, however, to determine how operation <strong>of</strong> thesmoke control system in the sprinklered fires would havechanged smoke spread beyond the fire floor. He also notedthat, for sprinklered fires that are not rapidly extinguished,smoke production could be significant and smoke controlcould be useful.The ability <strong>of</strong> sprinkler systems to control and extitiguishunshielded fires is well established (Richardson 1983;Walton 1988; Madrzykowski and Vettori 1992). In responseto Klote's concerns about shielded fires, however, it wasdecided to pay particular attention to fires that could not beextinguished immediately by· the sprinklers and that wouldresult in sustained smoke production under cool conditions.On the basis <strong>of</strong> Klote' s suggestions for further research, theTechnical Committee (TC 5.6) on Fire and Smoke Control<strong>of</strong> the American Society <strong>of</strong> Heating; Refrigerating and Air­Conditioning Engineers, Inc. (ASHRAE), agreed to providefunds for research to investigate the effects <strong>of</strong> sprinklers onthe performance <strong>of</strong> a zoned smoke control system. TheNational Fire Laboratory <strong>of</strong> the Institute for Research inConstruction at the National ReSearch Council <strong>of</strong> Canadaalso fu~ded the project.EXPERIMENT DESCRIPTIONA series <strong>of</strong> experiments involving shielded, sprinkleredfires was conducted at. the National Fire Laboratory's fullscalefire test facility located near Ottawa, Canada. Thefacility consists <strong>of</strong> a very large Bum Hall, in which a onestoryfire test room· was constructed, and a 10-storyexperimental tower (referred to as the Tower). Both theTower and the one-story test room were used to carry outthe testing for this project.One-Story Test RoomA one-story fire test room (Figure 1) was constructedinside the Bum Hall, equipped with sprinklers and instrumentedwit!t pressure, temperature, and gas analysis equipment.A products-<strong>of</strong>-combustion collector attached to thetest room allowed oxygen calorimetry to be used to measurethe heat release rates <strong>of</strong> sprinklered fires. The roommeasured 20ft by 20 ft by 12ft (6.1 m by 6.1 m by 3.6 m)with an a!tached corridor that was 20 ft long by 8 ft wideby 12ft high (6.1 m by 2.4 m by 3.6 m) on one side. Thecorridor could be pressurized independently <strong>of</strong> the test room495

<strong>Sprinkler</strong>s20'Exhaustopening.,""""""\Jo·_lNorth~----30'

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

In ord

1An uncertainty analysis, applied to the measurements andequations used to calculate the heat release rate from oxygenconsumption measurements, indicated that there is an uncertainty<strong>of</strong> 12% in the computed heat release rates. The presence' <strong>of</strong>significant amounts <strong>of</strong> water in the products <strong>of</strong> combustionincreased the uncertainty in the oxygen consumption calculations.The mass loss rate <strong>of</strong> the burning cribs was measured with anaccuracy <strong>of</strong> ±2%, although the combined effects <strong>of</strong> mass loss dueto burning and evaporation and mass gain due to the constantspray <strong>of</strong> sprinkler water onto the crib complicated interpretation<strong>of</strong> the mass loss measurements. The overall uncertainty in the heatrelease rates was estimated to approach 1 S%.ASHRAE Transactions: Research]"'~0:<strong>Sprinkler</strong> spray density, Lprnlm 20 2 3 4 5 6 7 8' ..'22002000 ~ UnsprinkleredOne-storey Test Room Results 20001800' 1200 lb (545 kg) wood cribs' - 18001600 f-' ' ,,#"Envelope- 16001400'50 % ltductionI ' ' 'Unshielded -400I ·=- {""\""'L 400200 f- # 'Figure 3""1400600,.2000 ' • ' 00.00 0.05 0.10 0.15 0.20<strong>Sprinkler</strong> spray densily, USgpmtft'• Nore: HRR at a given density depends on staa:e <strong>of</strong> fire developmentprior to application <strong>of</strong> water spray, See discussion in tcxL01200'1100 f-',1000tests between the computed heat release rate based onoxygen calorimetry and that determined using the measurements<strong>of</strong> mass loss, the same factor was used to determinethe heat release rate <strong>of</strong> the wood cribs in the Tower tests. 1Tests were conducted with no sprinklers, with sprinklersand shielding, and with sprinklers and no shielding. Inthe oO:e test without sprinklers, which was conducted in theone-story room, the fire in the I ,200-lb (545-kg) cribattained an HRR <strong>of</strong> more than 1,900 Btu/s (2,000 kW)under limited ventilation conditions <strong>of</strong> I ,000 cfm (0.42m 3 /s). By increasing the ventilation rate to 1,500 cfm (0.63m3/s), the HRR increased to 3,000 kW. No unsprinkleredcase was tested in the Tower, but it is estimated fromburning rates observed during periods when the sp_rinklerspray was turned <strong>of</strong>f during the course <strong>of</strong> the test that the700-lb (318-kg) cribs would have had an HRR <strong>of</strong> 1,150Btu/s (1,213 kW) under unsprinklered conditions.Several tests were conducted using fast-responsesprinklers (listed for <strong>of</strong>fice occupancies), which operated 30to 50 seconds faster than standard sprinklers. Normally,faster response would he a significant advantage for firesuppression because the HRR <strong>of</strong> the fire is smaller earlierin the fire growth, hence the fire is easier to extinguish.The advantage was soon dissipated, however, for shieldedfires. After an initial slowing <strong>of</strong> the burning rate, withinseveral minutes the fire within the shielded area regrew tothe same size it achieved with standard sprinklers.Ten tests were conducted with shielded

ecause each data point represents an early stage in thefires, such that the preceding histories <strong>of</strong> the crib fires weremore comparable than in the tests in the one-story room.Again, the dashed diagonal line linking the unsprinklered tothe sprinklered-shielded points shows a strong relationshipbetween the spray density and the HRR <strong>of</strong>a fire,From the dashed line in Figure 3, it can be conservativelyestimated that the HRR <strong>of</strong> the fires would be reducedto less than SO% <strong>of</strong> the nonsprinklered rate at an approximatedensity <strong>of</strong> 0.11 gprn!ft2 (4.5 Llmin·m 2 ). That HRR(for the 1,200-lb crib) was about 97S Btu/s (1,02S kW).For ihe 700-lb (318-kg) wood cribs in the Tower tests(Figure 4), the same SO% reduction in HRR (to S70 Btu/s[600 kW]) occurred at a density <strong>of</strong> 0.13 gprn!ft 2 (S.3Llmin·m 2 ). It is noteworthy that the reduced, sustained heatrelease rates at comparable densities were in proportion tothe mass <strong>of</strong> fuel within the shielded area.Two tests, one in the one-story room and the other inthe Tower, were conducted with the shielding removed sothat the sprinkler spray could extinguish the fires. In bothcases, the fires were extinguished in less than 12 minutes.The HRR values shown in Figures 3 and 4 for the unshieldedfires were peak values, measured just beforesprinklers activated, which then reduced to zero as the firewas extinguished.This leads to the question <strong>of</strong> what level <strong>of</strong> fire controlis expected from a typical sprinkler system designed to meetNFPA Standard 13 (NFPA 1991). That standard distinguishesbetween "fire control" and "fire suppression" andrecognizes that the sprinkler system is deemed to haveachieved .fire control if it limits the size <strong>of</strong> the fire, decreasesthe HRR, and controls ceiling temperatures. The limitson the size <strong>of</strong> the fire (area) are not stated but clearly willbe some fraction <strong>of</strong> the "design area," which is the areaprotected by the maximum number <strong>of</strong> sprinklers permitted(by the NFPA Standard 13 design criteria) to open. Thecontrol over ceiling temperatures also relates to the designarea: combustion gases must be cooled within its boundaryso as not to activate sprinklers outside the design area. Theintended degree <strong>of</strong> control over the heat release rate canthen be inferred: the HRR must be small enough that gastemperatures higher than the sprinkler temperature rating donot spread outside the design area.These experiments demonstrated that sprinklers substantiallyreduced the heat release rates <strong>of</strong> the wood crib fires,even though they were operating at lower spray densitiesthan would be normal for such fuel loads. They alsodemonstrated that the magnitude <strong>of</strong> the heat release ratedepends on the amount <strong>of</strong> fuel present within the shieldedarea and that the fuel within that area will continue burninguntil it is mostly consumed. Knowledge <strong>of</strong> the maximumarea <strong>of</strong> shielding possible in a sprinklered building (excludinga gross error in the system design) and the weight andtype <strong>of</strong> fuel likely to be held within the shielded area couldbe used to estimate the maximum beat release in a sprinklered,shielded fire.It was mentioned earlier that the statistical review done500by Morgan and Hansell (198S) concluded that fires in asprinklered <strong>of</strong>fice building were likely to be between 28Sand 2,8SO Btu/s (300 and 3,000 kW), with a higher probability<strong>of</strong> occurrence <strong>of</strong> fires in the low end <strong>of</strong> the range.The results <strong>of</strong> this series <strong>of</strong> full-scale tests indicate thatshielded fires with heat release rates as high as 97S Btu/s(1,02S kW) are possible, depending on the amount <strong>of</strong> fueland the sprinkler density. The wood cribs in these tests,however, particularly in the one-story room, represented asubstantial fuel mass arranged in an ideal burning formation.Yet, only two sprinklers, operating at minimumdensities appropriate for their listing, kept the HRR below9SO Btu/s (1,000 kW). These measurements suggest thatshielded fires in sprinklered <strong>of</strong>fice buildings are likely tohave heat release rates below 9SO Btu/s (1,000 kW). Theresults also imply that for an occupancy in which shieldedfires are a possibility, design densities higher than theminimum recommended values for unshielded conditionswould be beneficial.<strong>Effect</strong>s <strong>of</strong> <strong>Sprinkler</strong>s on Heat Fluxto SurroundingsFigure S shows the intensity <strong>of</strong> radiant heat energy inthe one-story test room, approximately 6.5 ft (2 m) fromthe wood crib, at mid-height <strong>of</strong> the room, measured atdifferent spray densities. In addition to removing convectiveheat energy from the hot gases given <strong>of</strong>f by the fire,sprinklers reduce fire severity by absorbing radiant beatenergy in the fire compartment. In an unsprinklered fire,heat radiates from the visible flames and from the hot gaslayer that develops in the upper portion <strong>of</strong> the room. Thisradiant heat reflects from surrounding surfaces back to the'¢:~1.41.21.0 -l! o.s -"' ,;=li: 0.6'a!u:I:0.40.20...,.,0.0 '0.00Figure 5<strong>Sprinkler</strong> spray density Lpm/ml2 3 4 s 6 7 8' ' ' ' '1614- 12.,~..,.1 Me10~8 ,;=li:6 'a!:!I ...y·' ' '4y ' y,Yy' ' '2''• 0o.os 0.10 O.lS 0.20<strong>Sprinkler</strong> spray density USgpmlft'Heat flux at mid-height on the south wall <strong>of</strong>the one-story test room versus sprinkler spraydensity.ASH RAE Transactions: Research... ~

fire source and contributes to increasing the burning rate(Alpert attd Ward 1983), If the heat flux is high enough,combustible materials will ignite, or vulnerable surfaces,such as windows, could be broken. Alpert and Ward (1983)report that a.radiant flux <strong>of</strong> about 1.8 Btu/s·ft 2 (20 kW/ru 2 )will cause most combustible materials to ignite from anysmall pilot flame within a few minutes. Certain plastics willignite at lower flux levels. Furthermore, tempered glass islikely to break at a heat flux greater than 1.8 Btu/s·ft 2 (20kW/m2) (Kim and Lougheed 1990). It is advantageous,therefore, to reduce the intensity <strong>of</strong> radiant heat energy inthe fire compartment.Figure 5 demonstrates that the radiant heat at thelocation <strong>of</strong> the heat flux meter was measured at about 1.1Btuift 2 (12.5 kW im 2 ) for the unsprinklered fire. Althoughnot high enough in itself to have readily ignited mostmaterials, it is the magnitude <strong>of</strong> the reduction in heat fluxcaused by the sprinklers that is <strong>of</strong> interest. Even in acontrolled situation, sprinklers were effective in reducingradiant heat energy on the walls <strong>of</strong> the test .room by morethan 65% to less than 0.4 Btu/s·ft2 (4.8 kW/m2). The plotalso reveals that, with some variability in test results, therewas an abrupt improvement in the heat flux reduction at athreshold spray density. The major benefit in heat fluxreduction occurred at spray densities greater than 0.09gpmift 2 (3.7 L/min·m 2 ).<strong>Effect</strong>s <strong>of</strong> <strong>Sprinkler</strong>s on Room TemperaturesFigures 6 and 7 show a series <strong>of</strong> temperature pr<strong>of</strong>ilesin the one-story test room at different rates <strong>of</strong> sprinklerspray application and room ventilation. Each pr<strong>of</strong>ile isplotted for a time during which burning conditions andtemperatures in the room had stabilized after any changesin spray density or ventilation rate: Figure 6 shows thetemperature pr<strong>of</strong>iles at different spray densities at a ventilationrate <strong>of</strong> 1,000 cfm (0.42 rri'is). Figure 7 shows similartemperature pr<strong>of</strong>iles for a ventilation rate <strong>of</strong> 1,500 cfm(0.63 m 3 /s). It is evident in Figure 7 that increasing theventilation rate for the unsprinklered fire greatly increasedthe heat output and room temperature. With sprinklersoperating, however, the increased ventilation caused onlyslight temperature increases.With the sprinklers shut <strong>of</strong>f, temperatures in the upperpart <strong>of</strong> the room reached approximately 1500•F (820°C) ata ventilation rate <strong>of</strong> 1,000 cfm (0.42 m 3 /s) and 1700°F(926°C) for a ventilation rate <strong>of</strong> 1,500 cfm (0.63 m 3 /s).These high temperatures existed throughout most <strong>of</strong> theheight <strong>of</strong> the room, and temperatures near the floor were·still more than 1200•F (650°C), Such temperatures represent"flashover" conditions, which implies that everycombustible in a compartment would have become involvedin the fire. Fires that reach flashover have a high probability<strong>of</strong> spreading beyond the compartment <strong>of</strong> origin andtherefore represent an augmented risk to the rest <strong>of</strong> thebuilding, according to a statistical review <strong>of</strong> fires in <strong>of</strong>ficeand residential high-rise buildings (Mailvaganam et a!.1992; Takeda and Yung 1991). It follows that there willalso be a high probability that smoke will spread beyond thecompartment <strong>of</strong> origin if flashover conditions are reached.What is striking about the temperature pr<strong>of</strong>iles inFigures 6 and 7 is the extent to which temperatures wereTemperature, •c0 100 200 300 400 500 600 700 800 900 1000123.5II2<strong>Sprinkler</strong> Density10I . 0.000 gpm/ft 2 3.0.::::92. 0.067 " E.: 8 2.5 .:3. 0.084 0 " 0..: 7c4. 0.105> "2.06 " >"0.. s . 0.109 " 5.81.5...0.E 6 . 0.110 ".2!' 4-..c7. ·;:;:I: " 3 1.0 :I:2 Room Ventilation Rate- 1000 cfm0.5I0.200 "..0 0.0200 400 600 800 1000 1200 1400 1600 1800Temperature, •FFigure 6Temperature pr<strong>of</strong>iles at north thermocouple tree in the one-story test room for different spray application rates,for ventilation rate <strong>of</strong> 1,000 cfm (0.42 m 3 Is).ASHRAE Transactions: Research 501

i.·t~', ~··~-:t··.a:Temperature, oc0 100 200 300 400 500 600 700 800 900 1000123.5II 3<strong>Sprinkler</strong> Density10I. 0.000 gpmift 2 3.0.::: 92 . 0.084 "E.: 8 2.50 3. 0.105 "~0 0

stages <strong>of</strong> a ftre, some pressure difference is created by theexpansion <strong>of</strong> the air on the fire floor as it is heated. Forsustained, shielded fires, such as those used in theseexperiments, .however, the net temperature differencebetween the fire floor and the other 'zones was the primarysource <strong>of</strong> fire-induced pressure. The effect <strong>of</strong> the sprinklerspray was to greatly reduce the temperature on the firefloor, with a corresponding reduction in the buoyancypressure differences between the fire floor Md adjacentspaces.Pressures were measured at four elevations in both theone-story test room and the seventh floor <strong>of</strong> the Tower,ranging from close to the floor to close to the ceiling. Allpressure. measurements were referenced to the adjacentnonfire space, such as the stairshaft in the Tower tests orthe Bum Hall for the tests in the one-story room. Thereference pressure is shown as a vertical line at AP = 0 inFigures 8 and 10 and as a horizontal line in Figure 9; Whenthe fire ·compartment was not purposely depressurized bybeing mechanically exhausted, the initial pressure in the firecompartment was equal to the pressure in the adjacentnonfire spaces, so that the t.P was zero. As the fire beganto grow, hot gases accumulated near the ceiling, creating atemperature difference between the floor and ceiling. Thehot, buoyant ceiling layer generated a positive AP near theceiling, while at the same time, the pressure near the floorbecame increasingly negative relative to the adjacent spaceas the fire drew air toward itself. Curve A in Figure 8shows a typical pressure pr<strong>of</strong>ile for a nonsprinklered fireunder this condition, with a positive and a negative pressurecomponent above and below the neutral plane, respectively.Curve B in the same figure shows the pressure pr<strong>of</strong>ile forthe (typical) case <strong>of</strong> a sprinklered fire: both the positive andnegative values <strong>of</strong> AP were at least SO% less than thepressures measured in a nonsprinklered fire due to cooling<strong>of</strong> the gases on the fire floor.The effects <strong>of</strong> sprinklers on the pressure conditions inthe one-story test room, with no mechanical exhaust inoperation, are shown in Figure 9. It is clear that as spraydensity increased, the maximum positive AP and negativeAP diminished significantly. At a spray density <strong>of</strong> about0.11 gpm/ft2 ( 4.S Llminm2), the peak pressure differenceswere reduced by at least SO% from the nonsprinklered case.fligher spray densities resulted in even greater reductions in'buoyancy pressure. Note that it has been standard practicein smoke control system design to allow a SO% reduction inthe design pressure difference for a sprinklered building(Klote and Fothergill 1983; NFPA 1988). This practiceappears to be appropriate for the conservative case <strong>of</strong>assumed minimal sprinkler density. For reasons describedearlier, in most real ·fire scenarios, the initial sprinklerdischarge will exceed the minimum, and the averagetemperature on the fire floor will be less than the activationtemperature <strong>of</strong> the sprinklers: It should be expected, therefore,that buoyancy pressures will be much less than SO%<strong>of</strong> the unsprinklered values.ASH RAE Transactions: ResearchComparison <strong>of</strong> Measured and Predicted PressuresAn equation is provided in Klote and Milke (1992) toestimate the magnitude <strong>of</strong> the buoyancy pressure generatedby a fire:whereAP =K, =T. ===~t.P = K, • (I/T 0-liT!) • H (1)pressure differential across a barrier,· in. H 2 0(Pa);coefficient,7.64 (3460);ambient or reference air temperature, •R {K);absolute temperature <strong>of</strong> the fire, 0 R (K); andheight above ( +) or below (-) the neutral plane,ft (m).AP is the pressure difference across a boundary, withtemperature T 0on the nonfire side and temperature 1j onthe fire side. H is the distance above or below the neutralplane, and K, is a coefficient that incorporates gas densityand unit conversions. Equation I calculates the maximumpressure difference (t.P) at distance H above or below theneutral plane, based on the difference in temperatures onthe fire floor (Tj! and on the nonfire side <strong>of</strong> a barrier (T 0).To perform the calculation, it is necessary to estimate theelevation <strong>of</strong> the neutral plane (hence H) and to assume a"fire temperature" representative <strong>of</strong> the average conditionin the fire compartment. Uncertainties about the height <strong>of</strong>the neutral plane and in the calculation <strong>of</strong> the fire temperature,both vertically and horizontally in the fire compartment,however, lead to difficulties in predicting fire-inducedbuoyancy pressure· differences. Klote (1990) found thatpredicted pressure differences across a barrier using theaverage measured temperature at the barrier were in goodagreement with measured pressure differences.For the r-ase <strong>of</strong> no mechanical exhaust <strong>of</strong> the fire floor,this positive AP ceiling shown in Figure 8 was measureddirectly by the instrumentation. When the fire compartmentis mechanically exhausted, however, and adjacent spacesare purposely pressurized in order to create a zoned smokecontrol condition, the elevation <strong>of</strong> the neutral plane on thefire floor becomes uncertain. In that case, the pressurepr<strong>of</strong>ile for the fire floor is drawn into the negative region,relative to the stairshaft, which is equivalent to raising theneutral plane above the ceiling <strong>of</strong> the fire floor, as shownin Figure 10. For the purposes <strong>of</strong> analyzing the experimentalmeasurements <strong>of</strong> the effects <strong>of</strong> sprinklers on buoyancypressures under conditions <strong>of</strong> mechanical exhaust <strong>of</strong> the firefloor, it was useful to work with the net pressure differenceacross the wall <strong>of</strong> the stairshaft between the floor and theceiling <strong>of</strong> the fire floor, or I!..P•, as illustrated in Figure 10,instead <strong>of</strong> AP calculated from Equation 1. From Figure 10it can be seen that AP• will equal AP when the value <strong>of</strong> Hin Equation I equals the floor-to-ceiling height <strong>of</strong> the firefloor. Because the instrumentation measured the AP at thefloor and ceiling levels relative to the adjacent nonfire503

I______'I·····------,+ ..,..y_;~---41'* -0.07 in. H20 (typ)MJceil-0.03 'A~_J_b==~~~~==~~~==~==~...0.~4 ...0.02 0 0.02 0.044Pf1oor - ..0.04Presswe, in. H2000.04<strong>Sprinkler</strong> spray density, Lpm/m 22 3 4 5 6 7I0,03 - Press~m:~ ner ceiling -0.02o .. 0.01"'...!:l: 0.00..:

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

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tions <strong>of</strong> 10,000 ppm were recorded, representing lifethreateninglevels on the fire floor. A rule <strong>of</strong> thumbsuggested by Kaplan and Hartzell (1984) indicates that at anexposure to 10,000 ppm <strong>of</strong> CO for more than 3.5 minutes,most people will be at least incapacitated. Peacock et al.(1989) indicated that a concentration <strong>of</strong> 15,000 ppm COwould present a severe life-safety hazard to anyone trappedon the fire floor.Figures 12b and 13b show the concentrations <strong>of</strong> C0 2and CO on the ninth floor <strong>of</strong> the Tower. In Figure 12b, nozoned smoke control was in effect, whereas in Figure 13b,the zoned smoke control system was set up for a t:J' design<strong>of</strong> 0.05 in. H 2 0 (12.5 Pa). In the former case, with nozoned smoke control in effect, for most <strong>of</strong> the fire durationsmoke was confmed to the fire floor. When the seventhfloordoor to the stairshaft was opened, however, smoke..,;c0::: 2.0• ~~03.05 10 15 20 25 30 35t.la:nillon Open 72.5c 9th Aoor: No Zone Smoke Control• uFast Rcspcmsc <strong>Sprinkler</strong>s· Shielded F"trec0 • ea:ivatc94• a&rignitiOI'l(t.,• 16 min)u 1.50u.,•• 1.0N0u40 45 50 55 60 65 70 75 80Opea edt.Test 1150.5t.coo.o0 5 10 15 20 25 30. 35 40 45 50 55 60 65 70 75 80nme, minFigure 13a C0 2 and CO concentrations on the ninth floor <strong>of</strong> the 10-story tower for a shielded fire with no zoned smokecontrol in effect.0.22Test 120.20 co,0.1891hfloor. Zone Smol:o Coaaol AP-O.ll5lo.1120..0.16 Slmdani Spriddcrs -Shlddod F ..,; • - 1221 aflerlgoilioa (It" 7 IIIia)c0::: 0.14!I•li 0.12u• 0u00.10u.,•o.oe•N 0.0680.040.02 it.£DlUonOpeaZSC DD 7'ftme. miDFigure 13b C0 2 and CO concentrations on the ninth floor <strong>of</strong> the 10-story tower for a shielded fire with smoke control ineffect.ASHRAE Transactions: Research507

escaped from the fire floor, rose in the stairshaft, andleaked into the ninth floor. The C0 2 concentration on theninth floor reached 2.65% and the CO concentrationreached 0.4%, or 4,000 ppm, over the next half-hour. Itwas observed that visual smoke contamination <strong>of</strong> thestairshaft was severe, and it is inferred that the CO concentrationsin the stairshaft were necessarily higher than thosemeasured on the ninth floor. This plot illustrates the danger<strong>of</strong> smoke spread in a sprinklered building that has noadditional smoke control features.With the zoned smoke control system operating, asmall amount <strong>of</strong> smoke leaked into the stairshaft after theseventh-floor door was opened. Visual smoke contaminationin the stairshaft was light, and the ninth-floormeasurements<strong>of</strong> C0 2 and CO showed that very little smoke was leakinginto that floor. When the eighth-floor (a pressurized zone)door to the stairshaft was opened, however, the lightlycontaminated shaft became pressurized and smoke wasforced into the ninth floor. The C0 2 concentration rose toabout 0.2%, and the CO concentration reached approxi~mately 0.01 %, or 100 ppm. Although some smoke didspread into the stairs under a zoned smoke control configuration,the concentrations <strong>of</strong> dangerous contaminants wereminimal compared to the case with no zoned smoke control.On the fire floor in ·the Tower, the sprinklered,shielded fires consistently produced concentrations <strong>of</strong>carbon monoxide greater than 5,000 ppm, which, usingKaplan's rule, would lead to incapacitation <strong>of</strong> most peoplein less than eight minutes. These dangerous concentrations<strong>of</strong> C0 2 and CO appear to be .the result <strong>of</strong> inefficientcombustion caused by burning under moist, cool, ventilation-limitedconditions. Volatized gases unable to bumcompletely inside the crib because <strong>of</strong> limited oxygennormally would have burned to completion in the roomafter escaping the crib. Because the sprinkler sprayquenched this external combustion, however, the combustionprocess was never completed. It is also possible that achemical reaction between carbon (in the wood) and watervapor (steam) occurred, producing CO and H 2 (Wiseman1983).A sustained, low-heat-output fire in a sprinklered <strong>of</strong>ficebuilding is considered to be statistically plausible (Morganand Hansell 1985). Such fires occur when the fuel isshielded from the direct effects <strong>of</strong> the sprinkler spray sothat complete extinguislunent does not occur. Given that COconcentrations can at least in some cases be dangerous! yhigh, the smoke from a shielded, sustained fire representsa life-safety hazard in a building. Measures to preventsmoke from spreading from the fire floor into the rest <strong>of</strong>the building can be justified on this basis.<strong>Effect</strong>s <strong>of</strong> <strong>Sprinkler</strong>s on Smoke SpreadThe 10-story tower was set up to represent a buildingwith features <strong>of</strong> a zoned smoke control system in conformancewith design procedures described in Klote and Milke(1992). The zones consisted <strong>of</strong> the fire floor (floor F7), the508floors above and below the fire floor (floors F8 and F6,respectively), and the stairshaft, for four zones in total. Theobjective <strong>of</strong> providing zoned smoke control was to ensurethat fire products (smoke) did not enter the stairshaft oreither <strong>of</strong> the floors above or below the fire. Three levels <strong>of</strong>initial pressurization were tested: tJ' "'"'" = 0.1 in. H 2 0 (25Pa), tJ' ""'"' = 0.05· in. H20 (12.5 Pa), and tJ' ""'"' = 0(i.e., no smoke control). The first condition represents thetJ' ""'"'recommended in NFPA 92A (1988) for a nonspriftkleredbuilding with an 8-ft (2.4-m) ceiling height; thesecond is the recommended design point for a sprinkleredbuilding; and the last condition corresponds to the case inwhich a sprinkler system is present, with no additionalfeatures to prevent smoke spread.'Floors F8 and F6 were pressurized by the injection <strong>of</strong>air directly into each floor space. The combined air inflowrate to the two floors was either 5.1 or 4.8 air changes perhour (ACH), depending on whether the tJ' ""'"'was 0.1 in.H 2 0 or 0.05 in. H 2 0 (25 Pa or 12.5 Pa), respectively.Other floors in the 10-story tower were not pressurized.The fire floor was mechanically exhausted through anexhaust shaft at a rate <strong>of</strong> either 5.6 or 4.4 ACH, so that itwas at a negative pressure relative to all other floors in thebuilding. The stairshaft, however, was not directly pressurized.The tJ' across the stairshaft door on F7 was determinedby the exhaust rate for that floor plus any air leakageinto the stairshaft from other floors or by opening theexterior door at the bottom <strong>of</strong> the stairshaft. This method <strong>of</strong>achieving the "pressure sandwich" or zoned smoke controlsystem conformed with the intent <strong>of</strong> both Klote and Milke(1992) and NFPA 92A (1988).As already stated, three values for tJ' desi n• measuredacross the wall <strong>of</strong> the stairshaft on the seven!~ floor, weretested. For the tJ'desi n = 0 condition, two tests weredone, one with an unst'lelded crib and the second with ashielded crib. For each <strong>of</strong> the other conditions <strong>of</strong> tJ'design•two shielded fires were studied, one hotter than the other.The results <strong>of</strong> each condition are reported in full in Part 2<strong>of</strong> the experiment report (Mawhinney et al. 1992). Highlights<strong>of</strong> the test results are summarized in the followingparagraphs.For the two cases <strong>of</strong> llPdesign = 0.1 or 0.05 in. H20(25 or 12.5 Pa), smoke from the shielded fire was confinedto the fire floor as long as the door to the stairshaft waskept closed. Even at the lowest sprinkler spray rates, thebuoyancy pressures created by the fire were not highenough to overcome the initial tJ'design' However, inalmost all cases, as soon as the door to the seventh floor(F7) was fully opened, smoke escaped into the stairshaft.The only time that smoke did not enter the stairshaft afteropening the door to the fire floor was when the stairshafthad been pressurized by opening one <strong>of</strong> the doors to a2 Tiiis latter condition is accepted in some building code jurisdictions,notably the National Building Code <strong>of</strong> Canada, as providingan acceptable level <strong>of</strong> protection against smoke hazards in highbuildings.ASH RAE Transactions: ResearchI

Ipressurized zone before opening door F7. This failure toprevent smoke spread into the stairshaft indicates that thestrategy <strong>of</strong> not actively pressurizing the stairshaft in thesame way as other zones to be protected, but relying on themechanical exhaust <strong>of</strong> the fire floor to hold the smoke onthe fire floor, does not reliably protect the stairshaft againstsmoke entry. Given that smoke spread occurred underconditions <strong>of</strong> sprinklered fires, in spite <strong>of</strong> low tempemturesand low buoyancy pressures and full pressurization toAPdesign = 0.1 in. H20 (25 Pa), it is certain that smokefrom a nonsprinklered fire would also spread into thestairshaft under open-door conditions.Two tests were conducted with no zoned smoke controlfeatures in effect, i.e., with AP desl 8n = 0. The first <strong>of</strong> thesetests involved an unshielded wood crib, in which the firewas extinguished in less than 12 minutes at a sprinklerdensity <strong>of</strong> 0.13 gpm!ft2 (5.3 L/minrn 2 ). A small amount<strong>of</strong> smoke did spread through interzonal leakage openingsinto the floor above the fire floor and into the stairshaftwhen the door was opened. The total amount <strong>of</strong> smokeproduced by the short-dumtion fire was low, and temperaturesand gas concentrations outside the fire floor did notreach dangerous levels. For the case <strong>of</strong> an unshielded fire,then, with no other smoke control features in effect, thesprinkler system performed as a successful smoke controlmeasure. This test supports the established expectation that,for unshielded fires, sprinklers provide a sufficient level <strong>of</strong>safety against smoke hazards in high buildings.The second test with a shielded wood crib, with nozoned smoke control features in effect, did not performnearly as well. Because <strong>of</strong> the prolonged burning <strong>of</strong> thefire,. a large volume <strong>of</strong> smoke was produced. The smokewas high in CO content ( > 4,000 ppm) and thereforedangerous. Smoke spread to floors above the fire floorthrough leakage openings before the stair door was openedand into the stairshaft when the door was opened. Thestairshaft became smokelogged within minutes <strong>of</strong> openingthe door, with complete loss <strong>of</strong> visibility and tempemtures<strong>of</strong> more than 150°F (65°C), These conditions were considereduntenable. This test clearly demonstmted that smokeproduced by a shielded. fire represents a serious threat tolife safety. Unless measures are taken to confine the smoketo the fire floor, smoke will spread through the building.<strong>Effect</strong> <strong>of</strong> <strong>Sprinkler</strong>s on Smoke ProductionIt is sometimes argued that sprinklers increase theamount <strong>of</strong> smoke produced in a fire. The shielded, sustainedfires in this series <strong>of</strong> tests produced large volumes <strong>of</strong>smoke. It is a moot point, however, as to how much moresmoke would have been produced if the fires had not beenrestmined. For an unshielded fire, the sprinklers are usuallysuccessful in extinguishing the fire, which then stops smokeproduction. For a shielded fire, the fuel bums in wetconditions at a reduced burning mte. It is impossible to sayfrom data collected in these tests whether the actual massproduction mte <strong>of</strong> soot and other products <strong>of</strong> combustionASH RAE Transactions: Researchwas greater when the sprinklers were operating. There isevidence, however, from at least one <strong>of</strong> the Tower tests,that smoke density in the exhaust shaft increased when thesprinklers were shut <strong>of</strong>f. It is believed that this increase wasdue to increased smoke production as the fire regrew,became hotter, and involved more fuel.Based on the observations in the tests in the one-storyroom and the Tower, it is noted that the fire itself is theactual source <strong>of</strong> smoke. Reducing the burning rate <strong>of</strong> a fireby application <strong>of</strong> sprinkler spray reduces the total production<strong>of</strong> smoke. However, the injection <strong>of</strong> sprinkler spmy. into the hot gases coming from a fire creates steam, whichdisrupts the flow <strong>of</strong> the gases in the hot layer. The turbulencecreated by the mpid cooling <strong>of</strong> the hot gases and theexpansion <strong>of</strong> steam deepens the smoke layer, even dmwingceiling gases down to floor level. The optical properties <strong>of</strong>the smoke and steam mixture are such that visibility ismpidly reduced at lower levels in the room. These rapidchanges in smoke-layer depth and visibility brought aboutby sprinkler opemtion do not necessarily mean that the mte<strong>of</strong> production <strong>of</strong> smoke has increased, however.A mpid reduction in visibility in the immediate vicinity<strong>of</strong> the fire when sprinklers activate may have negativeimplications for persons exiting the fire floor. However, ifa fire is allowed to continue to grow, visibility and temperatureconditions will sbon become unacceptable within aneven larger area on the fire floor and beyond. Therefore,the negative aspect <strong>of</strong> reduced visibility in a small areashould be viewed in the context <strong>of</strong> the benefit <strong>of</strong> elimination<strong>of</strong> the fire threat to a much larger area.The one-story test room used for some <strong>of</strong> these testswas located inside the Bum Hall, which is a very largespace similar to an atrium. During severn! tests in which thecapacity <strong>of</strong> the collector hood was surpassed, it wasobserved that the smoke from the sprinklered fires did notrise to the 40 ft (13 m) high ceiling <strong>of</strong> the Bum Hall.Instead, the smoke accumulated at floor level, leaving theupper portions <strong>of</strong> the Bum Hall clear.IMPLICATIOIIIS FOR DESIGN OFZONED SMOKE CONTROL SYSTEMSThe purpose <strong>of</strong> these experiments was to investigate theeffects <strong>of</strong> automatic sprinklers on the conditions <strong>of</strong> heatrelease mte, temperature, pressure, and levels <strong>of</strong> oxygen,carbon dioxide, and carbon monoxide in a building underfire conditions and to assess the effect that changes in theseconditions might have on the performance <strong>of</strong> a zoned smokeCOI)trol system. The results <strong>of</strong> the test progmm haveimplications for the design <strong>of</strong> zoned smoke control systemsin sprinklered buildings. These implications are summarizedhere.1. <strong>Sprinkler</strong>s have a good record <strong>of</strong> reliability in controllingfires and, by limiting the amount <strong>of</strong> combustiblesinvolved in a fire, also restrict smoke production. Asit constitutes both a detection system and a fire-fighting509

measure that is automatically initiated early in a fire, asprinkler system would enhance the effectiveness <strong>of</strong>fire department operations. For these reasons, a fullysprinklered building is considered by many to be themost effective and reliable smoke control measure <strong>of</strong>all those recommended in the Supplement to the NationalBuilding Code <strong>of</strong> Canada (NRCC !990b; see alsoNRCC 1990a).One <strong>of</strong> the tests in the Tower indicated the effectiveness<strong>of</strong> a sprinkler system in extinguishing anunshielded fire. The smoke contamination <strong>of</strong> the Towerwas light, with C0 2 and CO concentrations outside thefire floor at levels that would not be life-threatening.Temperatures outside the fire floor were nonthreatening,and even on the fire floor, the potentially threateningpeak temperatures were <strong>of</strong> short duration.2. The installation <strong>of</strong> a sprinkler system in a building doesnot eliminate the possibility <strong>of</strong> a fire producing largevolumes <strong>of</strong> smoke. In its definition <strong>of</strong> fire control,NFP A Standard 13, the standard for design <strong>of</strong> sprinklersystems, recognizes that sprinkler systems do notalways completely extinguish a fire; it is accepted that"control" <strong>of</strong> the burning rate and temperatures is sufficientto prevent fire from growing and spreading. Thestandard does not specify what burning rate or temperaturedefines the limits <strong>of</strong> that control, however. Evenwhen sprinkler spray is unobstructed, the fire may burnfor some time at a restrained rate before being completelyextinguished. Smoke will be produced throughoutthat burning period.NFPA Standard 13 rules for locating sprinklers inthe vicinity <strong>of</strong> obstructions are intended to ensure thatshielded areas are kept to an absolute minimum.Conditions that would produce a shielded fire are, to alarge extent, due to the manner in which the occupantuses the building, such as "temporarily" storing materialsin areas where they were not expected, e.g., undertables. A shielded fire could occur due to a buildingmodification. As an example, compact mobile shelvingunits for storing recorda <strong>of</strong> various types are beinginstalled with increasing frequency in commercialoccupancies. When in the closed position, the materialson the shelves are shielded from sprinkler spray.Once a shielded fire bas grown to involve all <strong>of</strong> thefuel within the shielded area, it is likely to be poorlyventilated, due to close packing <strong>of</strong> fuel materials orbecause <strong>of</strong> confmement inside or under the obstacle tosprinkler spray. Under certain circumstances, carbonmonoxide concentration in the smoke may be dangerouslyhigh. To prevent the spread <strong>of</strong> this smoke beyondthe fire floor, some active smoke control measures arerecommended.3. The maximum size <strong>of</strong> a shielded fire, in terms <strong>of</strong> heatrelease rate (HRR), depends on the amount and natore<strong>of</strong> the fuel, the ventilation conditions, and the adequacy<strong>of</strong> the sprinkler system design, expressed in terms <strong>of</strong>spray density. Assuming that the sprinkler system510design density meets the minimum requirements <strong>of</strong>NFPA Standard 13, it is likely that the shielded firewill be kept to less than 50% <strong>of</strong> its potential (unsprinklered)intensity. If the operating density for the sprinklersystem is significantly greater than the minimumdensity specified by NFPA Standard 13 for the unshieldedfuel load, a greater reduction in fire intensityis likely. Full"scale fire tests may be required todetermine bow much higher than the minimum thespray density must be to reduce the HRR <strong>of</strong> a givenfuel package by a given amount, under shielded conditions.For a sprinkler system that provides a densitysuitable for the unshielded fuel load, increased ventilationdue to opening doors to the fire floor will notsignificantly increase the intensity <strong>of</strong> the fire. Thismeans that concern about increasing fire severity byincreasing airflow to the fire floor (by opening doors,for example) may be much reduced for sprinkleredfires.4. The wood crib fires used in the tests contained asubstantial weight <strong>of</strong> dry fuel, ideally arranged to burn.It may be that shielded fuel arrangements likely to befound in typical <strong>of</strong>fice occupancies would not bum atthe same intensity. Noting this, it was demonstratedthat the HRRs <strong>of</strong> the wood crib fires were reduced bymore than 50% to less than S70 Btu/s (600 kW) in theTower tests (at a density <strong>of</strong> 0.13 gpmlft2 [53Llmin·m 2 ]), and to less than 97S Btuls (l,02S kW) forthe much larger cribs in the one-story room at a density<strong>of</strong> 0.11 gpmlft 2 (4.S L/min·m2). These reductions inthe beat release rate were achieved at minim11m spraydensities. This suggests that heat release rates greaterthan 950 Btu/s (1,000 kW) are unlikely for probableshielded fire scenarios in <strong>of</strong>fice occupancies.S. <strong>Sprinkler</strong>s are effective in reducing both temperatoresand iadiant heat on the fire floor. This encourages ahigh degree <strong>of</strong> confidence that the fire will not spreadand that windows on the fire floor are not likely tobreak, which bas important implications with respect tothe adverse pressures that could be induced across thefire-floor enclosure by wind and building stack actionif the windows break.6. Tests in the one-story test room indicated that pressurizationto exactly match the fire pressure can preventsmoke flow into the protected space. <strong>Sprinkler</strong> spraysreduce temperatures, thereby reducing buoyancypressures on the fire floor to essentially negligiblelevels. Accepted practice for design <strong>of</strong> zoned smokecontrol systems for sprinklered buildings, which is todesign for fl.P <strong>of</strong>0.05 1in. H 2 0 (12.5 Pa), is more thanadequate to prevent the spread <strong>of</strong> smoke across smallopenings. Pressure differentials created by buildingstack action and wind should also be considered alongwith buoyancy pressure generated by a sprinklered fire.7. The smoke control system tested in the fire tower involvedcreating positive pressure in ·the zones adjacentASH RAE Transactions: Research

LiP design = 0.05 in. H20 (12.5 Pa) in NFPA (1988)for zoned smoke control in sprinklered buildings(ceiling height < 9 ft [2.7 m]) is more than sufficientto prevent smoke movement, provided the door to thefire floor remains closed.6. Recommended practice for design <strong>of</strong> zoned smokecontrol systems should allow for some airflow into thestairshaft to prevent the spread <strong>of</strong> smoke into thestairshaft if the door to the fire floor is opened.7. The assumption that smoke will never become a threatto life safety in a fully sprinklered building needs to hereexamined. The seriousness '<strong>of</strong> the hazard posed by ashielded fire should be assessed relative to the probability<strong>of</strong> occurrence <strong>of</strong> other impediments to sprinklerperformance, such as closed water supply valves.ACKNOWLEDGMENTSThis research was carried out as a joint research projectsupported by funding from the American Society <strong>of</strong> Heating,Refrigerating and Air-Conditioning Engineers, Inc.(ASHRAE), and the National Fire Laboratory (NFL),which is part <strong>of</strong> the Institute for Research in Construction,National Research Council Canada. Appreciation is extendedto NFL technical <strong>of</strong>ficers D. Carpenter, R.A. MacDonald,G. Crampton, and M. Kanabus-Kaminska for theirwork in conducting the full-scale fire experiments and tostudent K. McCorvie <strong>of</strong> the Technical University <strong>of</strong> NovaScotia for her work in plotting the data.REFERENCESAlpert, R.L. 1984. 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