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Building and Environment 49 (2012) 1e8

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Building and Environment

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Comparative study on carbon monoxide stratification and thermal stratification ina horizontal channel fire

D. Yanga,*, R. Huob, X.L. Zhangb, S. Zhub, X.Y. Zhaob

a Faculty of Urban Construction and Environmental Engineering, Chongqing University, Chongqing 400045, Chinab State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei, Anhui 230026, China

a r t i c l e i n f o

Article history:Received 9 February 2011Received in revised form4 September 2011Accepted 7 September 2011

Keywords:Channel fireCarbon monoxide stratificationThermal stratificationLongitudinal ventilationHeat loss

* Corresponding author. Tel.: þ86 23 65120750; faxE-mail addresses: yangd8210@gmail.com, yangdon

0360-1323/$ e see front matter � 2011 Elsevier Ltd.doi:10.1016/j.buildenv.2011.09.009

a b s t r a c t

Carbon monoxide (CO) stratification and its relationship with thermal stratification are quite importantfor dealing with issues related to building fire safety. This experimental study compares the CO strati-fication and thermal stratification in channel fires. The results show that the relationship between COstratification and thermal stratification depends on heat loss intensity from smoke flow to walls. In theconditions with considerable amount of heat loss, the vertical gradients of CO volume concentration aresmaller than those of temperature rise beneath the ceiling. However, in the conditions with negligibleheat loss, the vertical profile of dimensionless CO volume concentration becomes similar with dimen-sionless temperature rise. The longitudinal ventilation, as a prevailing smoke control or ventilationmethod, has a strong effect on the relationship between CO stratification and thermal stratification. Alarger longitudinal air flow velocity leads to smaller heat loss intensity from smoke flow to walls and thusa higher similarity between CO stratification and thermal stratification.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

Channel-like configuration, such as tunnel and corridor, isa common architectural style. Channel fires often cause seriousdisasters. Such accidents include [1e4], e.g., a subway tunnel fire inDaegu of Korea in February, 2003, killed 198 people, a fire in MontBlanc tunnel inMarch,1999, killed 39 people, a fire in Tauern tunnelin May, 1999, killed 12 people and a corridor fire at the HillhavenNursing Home of Norfolk, Virginia in October, 1991, killed 10people. For the reason, the fire safety of a channel-like configura-tion has become one of the most critical issues in fire safety field inthe past decades [3,5].

In a fire situation, both toxic smoke and heat will be continu-ously released by the fire source (see Fig. 1) and become the twomost fatal factors [6e8]. Carbon monoxide (CO) is known to be themost dangerous fire-induced toxicant [7,8], which is responsible forover 75% of the fatalities in fire accidents [7e9]. Distributions of COand temperature rise are therefore of primary concern for channelfire studies. Such studies include, for example, the ones conductedby Yang et al. [10], Hu et al. [11], Lee et al. [12], Ingason et al. [13]and the one conducted by Lattimer et al. [14]. It is noted that theabove studies investigated the distributions of CO and temperature

: þ86 23 65121660.g@cqu.edu.cn (D. Yang).

All rights reserved.

rise separately. However, the transport of heat may be differentfrom CO in a channel fire environment, due to their differentcontrolling mechanisms. The information about the relationshipbetween the distribution of CO and temperature is very importantfor dealing with issues related to channel fire safety, e.g., (1)localization of fire detection systems and selection of heat sensorsor gas sensors; (2) fire hazard evaluation, concerning that peopleescaping through the lower parts of the channel in a fire emer-gency. A recent numerical study has shown that there could beremarkable differences between the longitudinal distribution of COconcentration and temperature rise in a channel fire [15]. However,limited studies have been reported on comparing carbonmonoxidestratification and thermal stratification in a channel fire, except anearly study of Newman [16]. Newman’s experimental study wasperformed in a longitudinally ventilated horizontal mine passage(61 m-long � 2.4 m wide � 2.4 m high) [16,17], and the resultssuggested that the vertical profile of CO concentration followstemperature rise at the locations downstream of the fire source[16,17], i.e., YCO;t=YCO;aver ¼ DTt=DTaver, with YCO;aver ¼ _G= _m andDTaver ¼ _Qf =Cp _m, respectively. However, the Newman’s study didnot account for the effects of heat loss intensity from smoke flow toboundary walls. The heat loss to boundary walls is a primarydifference between the transport of heat and CO, because normallythere is no mass loss of CO through the boundaries. It is still unclearhow the heat loss intensity affects the relationship between COstratification and thermal stratification. Further, the longitudinal

Nomenclature

B longitudinal decay rate of temperature (m�1)C ratio of the convective heat loss to the total heat flux of

smoke flowCp specific heat capacity (kJ/(kg�C))g gravity acceleration (m/s2)_G generation rate of CO species (kg/s)Gr Grashof numberh height from floor (m)hc lumped heat transfer coefficient (kW/m2 K)H height of the channel (m)_m mass flow rate (kg/s)P perimeter of smoke flow in the cross section (m)Pr Prandtl numberq00 convective heat flux from smoke flow towalls (kW/m2)_Qf convective heat release rate of fire (kW)Sc Schmidt numbert0 duration time of steady state (s)DT local temperature rise (�C)DTaver average temperature rise (�C)

DTt temperature rise at the top measurement point (�C)T* dimensionless temperature riseT0 ambient temperature (�C)u longitudinal flow velocity (m/s)u0 characteristic velocity (m/s)U0 velocity of longitudinal ventilation (m/s)v vertical flow velocity (m/s)X measured parameterX average measured parameter during quasi steady

periodYCO, aver average CO volume concentration (ppm)Yco local CO volume concentration (ppm)Yco,t CO volume concentration at the top measurement

point (ppm)

Greek symbolsa thermal diffusivity (m2/s)n kinematic viscosity (m2 s�1)r Density (kg/m3)ε relative deviation

D. Yang et al. / Building and Environment 49 (2012) 1e82

ventilation, as the most prevailing smoke control method ina tunnel [18], could significantly change the thermal environmentdownstream of the fire source [11e13,19]. This implies that thelongitudinal ventilation would also be the factor for changing theheat loss intensity and their relationship as well. Therefore, it issuggested that further studies should be carried out for the rela-tionship between thermal stratification and CO stratification, withconsidering the effects of heat loss intensity.

In this work, experiments have been systematically performedto investigate the relationship between thermal stratification andCO stratification. The main difference between this work and thework of Newman is that it takes into account the effects of longi-tudinal air flow velocity and the resulting change in heat lossintensity. The results of this work would provide references forboth fire safety designers and the fire science researchers.

2. Experimental procedure

Experiments are conducted in a quasi 1/6 reduced-scale hori-zontal tunnel with internal dimensions of 66.0 m-long � 1.5 mwide � 1.3 m high. The scaling approach used in this work is theFroude scaling [13,20]. The most important parameters related tothis study, e.g., heat release rate, fan flow rate, velocity arepreserved according to the scaling correlations shown in Table 1. Aschematic view of the experimental tunnel is shown in Fig. 2. Thetunnel ceiling and the side walls are made of fire-resistant glasswith thickness of 12 mm. The tunnel floor is made of steel platewith thickness of 3 mm.

The fire source was simulated by a propane gas burner withdimensions of 0.86 m � 2.16 m, which was positioned at 9 m awayfrom the entrance connected to the longitudinal ventilation system

Fig. 1. Schematic of fire smoke transport in a horiz

(see Fig. 2). The fuel supply rate was controlled by a gas flow-meter.The heat release rates in the conditions without longitudinalventilationwere demarcated by calorimeter measurements in priorto formal tests. Different HRR design values are recommended byguidelines for tunnel fires [3,21]. In this work, the heat release rateis kept to be 156 kW for the conditions without longitudinalventilation. The corresponding full-scale HRR is about 13.7 MW,which is estimated to be near the maximum HRR released by a vanfire [3,21].

Longitudinal air flow was supplied by an electrical centrifugalfan attached to one entrance of the tunnel. A 4 m-long rectangularbox with screens was installed between the fan and the tunnelentrance to create a uniform and steady air flow for the experi-mental section. The air volumetric flow rates can be controlled byusing an electrical frequency converter, with the maximumvalue of8.3 m3/s. The critical ventilation velocity required to suppress back-layering was determined with the assistance of laser sheet visual-ization technology. For the test conditions of this work, the criticalvelocity is measured to be approximately 1.0 m/s. Sub-criticalventilation velocities were also used by this work for consider-ation of different ventilation intensities [22]. The ventilationvelocities adopted in this work were 0.0, 0.4, 0.8 and 1.2 m/s,respectively. The other entrance of the tunnel was completely open.

The measurement layout is also shown in Fig. 2. K-type shieldedthermocouples of diameter 1 mm were used to measure temper-ature. Vertical profiles of temperature and CO volume concentra-tion were measured at the distances of 11, 17, 29 and 41 mdownstream of the fire source, respectively. In order to obtain thelongitudinal temperature profiles and their corresponding longi-tudinal decay rates, B, the temperature measurements were alsocarried out at 5, 23, 35 and 47 m, respectively. The vertical interval

ontal channel without longitudinal ventilation.

Table 1Summary of scaling correlations for reduced-scale tests.

Variable Scaling

Heat Release rate (kW) QM=QF ¼ ðLM=LF Þ5=2Velocity (m/s) VM=VF ¼ ðLM=LF Þ1=2Fan flow rate (kg/s) _mM= _mF ¼ ðLM=LF Þ5=2Temperature (K) TM=TF ¼ ðLM=LF Þ0

L is the length scale, M denotes model scale and F denotes full-scale.

D. Yang et al. / Building and Environment 49 (2012) 1e8 3

between thermocouple is 0.1 m. The total uncertainty of temper-ature measurement was mainly attributed to three sources, theerror related to measurement instruments, the error due to radia-tion exchange between thermocouple and ambient environment,and the error related to measurement repeatability. The measure-ment error of thermocouple is less than 1 �C for the temperaturerange of this work [23]. The radiation correction is difficult toperform precisely, because determination of effective surroundingtemperature is difficult in a spatially varying environment.However, the maximum radiation error can still be estimated fromthe results of previous theoretical works [24]. The radiation error isless than 6% for the typical smoke temperature of this work (e.g.,less than 120 �C). The repeatability of the measured temperaturewas determined to be approximately 5% through comparison ofthree tests running under the same conditions. The total errorcombining all the sources can be calculated from the fundamentalmethods, such as the one introduced by the example Ref. [25]. Thetotal error for temperature measurement is 8%.

The CO volume concentrations were measured by a 6-channelgas analysis system (Testo, Co. Ltd., Model 350XL). The sampledgases were drawn through a 1.2 m-long stainless steel pipe (shownin Fig. 2 (b)) and a 2.2 m-long flexible hose by a pump with volumeflow rate of 1.0 L/min, then passed through filters to removemoisture and soot particles, and were finally directed into the gasconcentration analyzers. The smoke volume flow rate was about33,600 L/min in the condition without longitudinal ventilation andbecame larger in the conditions with longitudinal ventilation,which were much greater than the volume flow rate exhausted bythe pump. The inspiration velocity at the sample inlet was less than0.1 m/s, which was much smaller than the average smoke flowvelocity, e.g., 0.7 m/s in the condition without longitudinal venti-lation. The effects of inspiration pump on the velocity filed wereaccordingly considered to be negligible. The smoke gases were

Fig. 2. Sketch and details of the experimental arrangement. a) Layout o

sampled at the heights of 1.18, 0.88, 0.58 and 0.28 m, respectively.The measurement error of dry CO volume concentration was notedby the manufactures as being 5 ppm for measured ones rangingfrom 0 to 99 ppm and being 5% for the ones higher than 100 ppm[26]. The error associated with the wet CO volume concentration isestimated to be less than 8% by using the method proposed byLattimer et al. [25]. The repeatability of the measured CO concen-tration was determined to be approximately 10% throughcomparison of three tests running under the same conditions. Thetotal error for CO measurement is then estimated to be 13% bycombing the above two error sources.

A multichannel-anemometer (KANOMAX Model 1560) wasused to monitor the velocities of longitudinal air flow and smokeflow. The measurement accuracy was �0.1 m/s for the range of0.25e4.99 m/s [27]. Table 2 presents the information about thedetails of the sixteen test series. As shown in Table 2, these testswere carried out under different longitudinal ventilation velocities.The datawere all collected during the quasi steady state period. Thequasi steady period corresponds to the duration time when thesmoke has flown out the tunnel outlets and the measured flowparameters vary little with time. The temporal profiles of temper-atures and CO volume concentrations for Test 9 (29 m downstreamof the fire source) during the quasi stead-state period are presentedin Fig. 3.

Measurement duration time was approximately 450 s. Datapresented in this paper were all taken as the time-averaged valuesduring the quasi steady periods:

X ¼Z

t0

Xdt (1)

where t0 is the duration time of quasi steady state.

3. Results and discussion

3.1. Results of thermal stratification vs. CO stratification

The vertical profiles of CO volume concentration and tempera-ture rise, DT ¼ T � T0, for Test 1 (without longitudinal ventilation)are shown in Fig. 4. It is shown that the temperature rise decreaseswith decreasing in height, while the CO volume concentration ata lower height (e.g., 0.58 m) remains as high as the one beneath the

f measurement system (Test 1eTest 4), b) sketch of test scenario.

Table 2Summary of test conditions.

Test No. Measurementlocation (m)

Fuel supplyrate (m3/h)

Longitudinalventilationvelocity (m/s)

Mass flow rateacross the tunnel(kg/s)

Longitudinal decayrate of temperature(m�1)

Test 1 11 m 8.0 0 0.62 0.050Test 2 11 m 8.0 0.4 0.90 0.032Test 3 11 m 8.0 0.8 1.87 0.022Test 4 11 m 8.0 1.2 2.81 0.010Test 5 17 m 8.0 0 0.62 0.056Test 6 17 m 8.0 0.4 0.92 0.038Test 7 17 m 8.0 0.8 1.80 0.020Test 8 17 m 8.0 1.2 2.88 0.018Test 9 29 m 8.0 0 0.65 0.055Test 10 29 m 8.0 0.4 0.87 0.043Test 11 29 m 8.0 0.8 1.86 0.020Test 12 29 m 8.0 1.2 3.00 0.015Test 13 41 m 8.0 0 0.58 0.060Test 14 41 m 8.0 0.4 0.83 0.042Test 15 41 m 8.0 0.8 1.78 0.024Test 16 41 m 8.0 1.2 2.81 0.017

D. Yang et al. / Building and Environment 49 (2012) 1e84

ceiling. The CO volume concentration starts to decrease at theheights lower than 0.58 m, because the lowest measurement pointwas located outside the smoke layer. To compare the verticalprofiles of CO volume concentration and temperature rise, the localtemperature rise and CO volume concentration are normalized by:

T� ¼ DT=DTt (2)

Y�co ¼ Yco=Yco;t (3)

where the subscript t denotes the parameters measured at theheight of 1.18 m.

Fig. 5 correlatesY�co, and T� with the normalized height, h=H, at

different distances downstream of the fire source for the conditionswithout longitudinal ventilation. As shown in Fig. 5, differences invertical variation trend between the vertical profile of T� and Y�

cocan be observed in the conditions without longitudinal ventilation.

Longitudinal ventilation has strong effects on both the transportof heat and CO. Figs. 6 and 7show the vertical profiles of T� and Y�

counder different longitudinal ventilation velocities, at 11m and 29mdownstream of the fire source, respectively. It is shown that thereare also appreciable differences between the vertical profile of Y�

coand T� at small ventilation velocities (e.g., Test 2 and Test 10).However, the vertical profiles of Y�

co become similar with T� atrelatively larger longitudinal ventilation velocities (e.g., Test 3, Test4, Test 11 and Test 12).

300 350 400 450 500 550 600 650 7000

20

40

60

80

100

120

140

160

180

200

Te

mp

era

tu

re

ris

e (

)

CO

v

olu

me

c

on

ce

ntra

tio

n (p

pm

)

Time from ignition (s)

1.18m CO

0.88m CO

0.58m CO

0.28m CO

0

10

20

30

40

50

60

70 1.18 Temperature rise

0.88 Temperature rise

0.58 Temperature rise

0.28 Temperature rise

Fig. 3. Temporal profiles of CO volume concentration and temperature rise at 29 mdownstream of the fire source (Test 9) during quasi steady period.

In Newman’s study, another two dimensionless parame-ters,YCO;t=YCO;aver and DTt=DTaver, were used to characterize the COstratification and thermal stratification. The dimensionlessparameters proposed by Newman were also used here forcomparison. The average values, YCO;aver, and DTaver, are obtainedby directly averaging the measured vertical profiles in this work.

The difference between YCO;t=YCO;aver and DTt=DTaver is quanti-fied by a fundamental formula, i.e., relative deviation [28]:

ε ¼��YCO;t=YCO;aver � DTt=DTaver

��DTt=DTaver

(4)

Fig. 8 plots ε against mass flow rate including all the test series ofthis work. On the whole, a larger mass flow rate corresponds toa smaller ε. The reason for this will be explained in the subsequentsection.

3.2. Discussion on effects of heat loss

The transport of channel smoke flowcan be studied by boundarylayer type theories [29]. At temperatures lower than 800K, oxi-dization reaction of CO is frozen [30], and thus the dimensionlessequations of temperature and CO are represented as [31]:

Fig. 4. Vertical profiles of temperature rise and CO volume concentration for Test 1.

0.0

0.2

0.4

0.6

0.8

1.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2

T * & Y *CO

Non

dim

ensi

onal

hei

ght

Test1 T*

Test1 Y*CO

0.0

0.2

0.4

0.6

0.8

1.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2

T* & Y *CO

Non

dim

ensi

onal

hei

ght

Test5 T*

Test5 Y*CO

0.0

0.2

0.4

0.6

0.8

1.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2

T* & Y *CO

Non

dim

ensi

onal

hei

ght

Test9 T*

Test9 Y*CO

0.0

0.2

0.4

0.6

0.8

1.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2

T* & Y *CO

Non

dim

ensi

onal

hei

ght

Test13 T*

Test13 Y*CO

Fig. 5. Vertical profiles of normalized CO volume concentration and normalized temperature rise at different distances in the conditions without longitudinal ventilation.

D. Yang et al. / Building and Environment 49 (2012) 1e8 5

u�vT�

vx�þ v�

vT�

vy�¼ 1

Gr1=2$Pr

v2T�

vy�2(5)

u�vY�

covx�

þ v�vY�

covy�

¼ 1

Gr1=2$Sc

v2Y�co

vy�2(6)

where x� ¼ x=H, y� ¼ y=H, u� ¼ u=u0, v� ¼ v=u0, u0 is the char-acteristic velocity and u20 ¼ gHDTt=T0. Gr is the Grashof numberðGr ¼ H3gDTt=T0n2Þ, Pr is the Prandtl number and Sc is the Schmidtnumber.

The value of Pr is quite close to that of Sc at the temperatureslower than 800 K [31,32]. This indicates there is an analogybetween the transport equation of heat and CO. However, theboundary condition of heat transport could differ with that of COtransport. The primary difference is that the heat loss from smokeflow to ceiling is significant [33] and results in the reduction intemperature along the longitudinal direction [12,13], but there is nomass loss of CO through the ceiling. The heat loss intensity can beestimated from one-dimensional analysis. For a control volumeshown in Fig. 1, the energy equation is written as:

q00Pdx ¼ �Cp _mdðDTaverÞ (7)

where P is the perimeter of smoke flow at the cross section, q00 is theheat flux to walls, Cp is the specific heat capacity, and _m is the massflow rate downstream the fire source. DTaver is the averagetemperature rise at the control surface, as calculated by:

DTaver ¼ 1H

Z

H

DTdz (8)

It is deduced from Eq. (8) that the heat flux q00 correlates withthe longitudinal profile of average temperature rise:

q00 ¼ �Cp _mP

dðDTaverÞdx

(9)

The intensity of heat loss is represented by the ratio of heat lossto the total heat flow rate:

C ¼ q00

Cp _mDTaver¼ �dðDTaverÞ

dx=PDTaver (10)

The heat flux q00 to the boundary walls can also be representedas:

q00 ¼ hcDTaver (11)

where hc is the lumped heat transfer coefficient.Combining Eq. (11) with Eq. (7), gives:

DTaverðxÞ ¼ DTaver;ceð�BxÞ (12)

with

B ¼ hcP_mCp

(13)

where DTaver;c is the smoke average temperature at a referencepoint.

Therefore, it is indicated from Eq. (12) that the averagetemperature rise follows an exponential decay in the longitudinaldirection, as also reported by the previous references [13,19,34].

0.0

0.2

0.4

0.6

0.8

1.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2

T* & Y*CO

Non

dim

ensi

onal

hei

ght Test1 T*

Test1 Y*CO

0.0

0.2

0.4

0.6

0.8

1.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2

T* & Y*CO

Non

dim

ensi

onal

hei

ght

Test2 T*

Test2 Y*CO

0.0

0.2

0.4

0.6

0.8

1.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2

T* & Y*CO

Non

dim

ensi

onal

hei

ght

Test3 T*

Test3 Y*CO

0.0

0.2

0.4

0.6

0.8

1.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2

T* & Y*CO

Non

dim

ensi

onal

hei

ght

Test 4 T*

Test 4 Y*CO

Fig. 6. Vertical profiles of normalized CO volume concentration and normalized temperature rise at 11 m downstream of fire source at different longitudinal ventilation velocities.

D. Yang et al. / Building and Environment 49 (2012) 1e86

Inserting Eq. (12) into Eq. (10), it leads to:

CfB ¼ hcP_mCp

(14)

Thus, the intensity of heat loss is characterized by the longitu-dinal decay rate of temperature, B. It is deduced from Eq. (14) that Bis inversely proportional to the mass flow rate. In the conditionswithout longitudinal ventilation, the smoke mass flow rate on eachside of the fire source is nearly one half of plume mass flow rate. Inthe conditions with sub-critical ventilation velocity, the mass flowrate downstream of the fire source increases due to enhanced airentrainment into the fire plume [35]. In the conditions with criticalventilation velocity, the mass flow rate downstream of the firesource could be equal to the summation of mass flow rate suppliedby longitudinal ventilation and that of combustion products.Although there could be no explicit relation between the mass flowrate and ventilation velocity, the mass flow rate downstream of thefire source could increasewith the longitudinal ventilation velocity.In this work, the mass flow rates downstream of the fire source aredetermined by the measured vertical profiles of temperature andhorizontal velocity. As shown in Table 2, a larger ventilation velocityresults in a larger mass flow rate downstream of the fire source.

To determine the value of B for a certain point, the measuredlongitudinal temperature curves across the correspondingmeasurement point were fit with the exponential relation shown inEq. (12). The local longitudinal temperature curve consisted of thecorresponding point, and its neighboring four points which wererespectively located on both sides of it. The values of B for all thetests are presented in Table 2. It is shown that B decreases as theventilation velocity increases for a certain measurement location.This is consistent with the results shown in the previous tunnel fire

experiments [13,19]. A larger ventilation velocity results in a largermass flow rate, and thus smaller heat loss intensity, B. Themagnitude of B determines the degree of difference in boundaryconditions between CO transport and heat transport. This must bethe reason for that the similarity between thermal stratificationand CO stratification becomes higher when the ventilation velocityincreases.

3.3. Considerations on extension to actual tunnel/corridor fires

Both the material and wall thickness of an actual tunnel orcorridor might be different from what are used in this work. Thus,the question might be raised whether the condition necessary forthe creation of difference between thermal stratification and COstratification occurs in a realistic tunnel or corridor fire. For actualtunnel or corridor fires, there could be some cases where the heatloss is quite small. For example, the road tunnel fire tests of Hu et al.[19] have shown that, the values of B are in the range of0.0025e0.0068 for 1.6e3.0 MW full-scale road tunnel fires, whichare much smaller than this work. It is noted that the temperaturerise in tests of Hu et al. are lower than 100 �C. However, in an actualtunnel fire, the heat release rate would exceed 100 MW and thusleads to a maximum temperature near 1000 �C [36]. Both theRunehamar tunnel tests [13,37,38] and the Memorial tunnel firetests [13,39] show that the temperature rise experiences sharpdecay along the longitudinal direction. The corresponding values ofB for the Runehamar tunnel tests and the Memorial tunnel tests,i.e., from 0.24 to 0.27 [13], are much larger than this work (e.g., theones shown in Table 2), which implies amuchmore significant heatloss intensity in these two full-scale fire tests compared to the testscenarios of this work. Therefore, there is a possibility for the

0.0

0.2

0.4

0.6

0.8

1.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2

T* & Y*CO

Non

dim

ensi

onal

hei

ght

Test9 T*

Test9 Y*CO

0.0

0.2

0.4

0.6

0.8

1.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2

T* & Y*CO

Non

dim

ensi

onal

hei

ght

Test 10 T*

Test 10 Y*CO

0.0

0.2

0.4

0.6

0.8

1.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2

T* & Y*CO

Non

dim

ensi

onal

hei

ght

Test 11 T*

Test 11 Y*CO

0.2

0.4

0.6

0.8

1.0

-0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2

T* & Y*CO

Non

dim

ensi

onal

hei

ght

Test 12 T*

Test 12 Y*CO

Fig. 7. Vertical profiles of normalized CO volume concentration and normalized temperature rise at 29 m downstream of fire source at different longitudinal ventilation velocities.

Fig. 8. Relative difference between vertical profile of CO volume concentration andthat of temperature rise versus mass flow rate.

D. Yang et al. / Building and Environment 49 (2012) 1e8 7

occurrence of significant difference between the thermal stratifi-cation and CO stratification in an actual tunnel or corridor fire.

4. Conclusions

The heat loss plays an important role in the relationshipbetween thermal stratification and CO stratification for a channelfire. In this work, the heat loss intensity (i.e., the ratio of heat lossrate to total heat flow rate) is characterized by the longitudinal

temperature decay rate, B. The results show that B is stronglydependent on longitudinal ventilation velocity. In the conditionswithout longitudinal ventilation or with small ventilation velocity,B is relatively large and thus leads to a great difference betweenthermal stratification and CO stratification. In such conditions, thevertical gradients of CO volume concentration are much smallerthan those of temperature rise at the upper part of the tunnel. Inthe conditions with relatively large ventilation velocity, B getssmaller and this results in a higher similarity between thermalstratification and CO stratification. It is also proposed by this workthat the condition necessary for creation of difference betweenthermal stratification and CO stratification could exist in a realistictunnel or corridor fire environment. Futurework will be carried outon the effects of channel geometry, such as height to width aspectratio, on the relationship between thermal stratification and COstratification.

Acknowledgments

The corresponding author gratefully acknowledges the supportfrom National Natural Science Foundation of China (NSFC) underGrant No. 51106189, and Project No. CDJRC10210007 supported bythe Fundamental Research Funds for the Central Universities.

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