Smoke spread experiment in a multi-storey building and computer modelling

FireSafetyJournal28 (1997) 139-164 (~ 1997ElsevierScienceLimited All rights reserved.Printedin NorthernIreland 0379-7112/97/$17.00 ELSEVIER

PII:

S0379-7112~96)00081-1

Smoke Spread Experiment in a Multi-storey Building and Computer Modelling Yaping He & Vaughan Beck Centre for Environmental Safety and Risk Engineering, Victoria University of Technology, PO Box 14428, MCMC, Melbourne, Victoria 8001, Australia (Received 28 November 1995: revised version received 22 October 1996: accepted 24 October 1996)

ABSTRACT The C E S A R E - S M O K E model is a network model which can be used to estimate smoke spread in a multi-storey building when subjected to fire. The model calculates time-dependent temperature and species concentrations at locations remote from the room o f fire origin. Spatial variation o f physical parameters in a single enclosure with large aspect ratio can also be estimated. This paper describes a series o f full-scale fire experiments that were designed to investigate the validity o f the model. The experiments, involving steady state burning rates and a number o f ventilation conditions, were conducted in a four-storey building. Temperature, pressure, flow velocity, smoke density and species concentrations were measured in various parts o f the building. The chimney effect and its influence on temperature distribution in a stair shaft were observed. Comparisons are made between the experimental results" and the model predictions. The experimental results are also compared with the predictions o f the C F A S T two-zone model. Suggestions are made for further improvements to the network model. ~) 1997 Elsevier Science Ltd.

1 INTRODUCTION The importance of modelling smoke m o v e m e n t in multi-storey and m u l t i - c o m p a r t m e n t buildings has long been recognised. Yet it is not a simple task to model the m o v e m e n t of smoke and the concentrations of toxic species in various enclosures with acceptable accuracy and efficiency so as to estimate the times of critical events, such as the detection of the fire and d e v e l o p m e n t of untenable conditions. The concept of the zone model was introduced 1 to reduce c o m p u t a t i o n a l complexity without u n d u l y sacrificing accuracy. Sophisticated models have been developed 139

140

K He, V. Beck

for fire growth and smoke m o v e m e n t predictions. 2 For large c o m p a r t m e n t building fire, network and graphic approaches have been used :L4 in which each enclosure is treated as one element. Programs exist for smoke control analysis ~ and steady-state airflow throughout a building." Recently, researchers at the National Research Council of Canada ( N R C C ) have developed a smoke spread model that treated a large c o m p a r t m e n t , such as an a p a r t m e n t unit, corridor or stair shaft, as a single well-stirred cell, except for the corridor on the floor of the fire origin where the two-zone m e t h o d was used. 7 The N R C C models are very efficient in predicting fire growth and smoke m o v e m e n t in large multi-storey buildings. Despite their merits, zone models do have limitations due to the simplifications and assumptions made. The reliable prediction of the conditions in enclosures with large aspect ratio has proven to be a difficult task for zone models, since the assumption of uniform condition breaks down in such enclosures. Empirical correlations have to be employed to address the variations in various quantities along the longitudinal direction of the enclosures, 7~ although the correlations are only valid for steady state conditions. The assumption of the uniform condition in a zone infers the instantaneous mixing of the incoming smoke with the fluid that is already in the zone. As a result, zone models fail to recognise the finiteness of the velocity at which smoke propagates along the enclosures with large aspect ratio. Experimental investigation by H o k u g o e t a l . " showed that when smoke e n t e r e d a stair shaft, there was a t e m p e r a t u r e drop from thc level of the fire floor to the upper levels due to mixing and probably heat loss through the walls of the stair shaft. The spatial variation of physical parameters in a single enclosure will affect the p e r f o r m a n c e of smoke detectors and h u m a n behaviour in the case of fire. Hence, it may b e c o m e crucial for a smoke m o v e m e n t model to be able to predict such spatial variations without the r e q u i r e m e n t of intensive c o m p u t e r power that is associated with field models. '''-~ It was against this background that a c o m p u t e r program, C E S A R E - S M O K E , ~-" which uses zone model and network approach for the modelling of smoke spread in large residential buildings, was developed at the Centre for E n v i r o n m e n t Safety and Risk Engineering ( C E S A R E ) , Victoria University of Technology. In this program enclosures with large aspect ratio, such as stair shafts and corridors~ are divided into a n u m b e r of finite volumes. T e m p e r a t u r e s and species concentrations are evaluated for each individual volume. The program is capable of predicting both horizontal and vertical smoke spread at the locations r e m o t e from the floor of fire origin. The predictions obtained from the model for the smoke spread in a smoke tower agreed quite well with the experimental results by H o k u g o e t al. '~

Smoke spread in multi-storey building

141

Although ample experimental data exist in the literature for smoke movement in tunnels, is multi-enclosure and multi-storey builings, H~5 experiments involving both horizontal and vertical smoke spread in residential buildings and producing data suitable for comparison with the network model are scarce. The experiment reported herein was designed to obtain such data and to validate the newly developed computer model. The experiments involved controlled fire types which were conducted under steady state burning conditions. The fire source had a constant heat release rate throughout a particular experimental period. The heat release rate was changed only for different experiments. While the controlled fire source may not closely resemble a realistic fire scenario, the experiments, nevertheless, generated valuable data for the purpose of model validation. The experimental data are compared in this paper against the predictions of a well-known zone model, CFAST, L~ and the C E S A R E - S M O K E network model.

2 E X P E R I M E N T A L FACILITY The experiments were conducted at the C E S A R E ' s Experimental Building-Fire Facility (EBFF) which consists of a four-storey full-scale building. The facility contains a large versatile building based on a steel frame and composite concrete floor-slab structure, a service core containing stair, lift and air handling shafts, together with associated services including sprinklers. Part of the facility has been fitted-out to represent a portion of a multi-storey apartment building. Each level of this building, except for level 4, comprises four rooms and a corridor connecting the rooms. Level 4 is simply a corridor. The layout of the first level is illustrated in Fig. 1. Room 102 on the first level of the building was designated as the burn room which had a dimension of 2.4 × 3.6 × 2.4 m. All the doors in the building had the standard dimension of 0.8 × 2.0 m. The corridor on level 1 was partitioned in the middle to prevent smoke engulfing the eastern part of the corridor during the experiments. The height of each level is given ,n Fig. 2. The stair shaft was 2.4 m wide and 4.8 m deep. The lift shaft was closed to the rest of the building but its top was open to the surrounding atmosphere. Except for the stair shaft and lift shaft, all the walls in the building were constructed of plasterboard. The walls of the stair shaft and lift shaft were constructed of light weight concrete blocks. There were, however, gaps between the blocks. The total leakage area constituted by the gaps to the stair shaft was 0.18 m 2. The aspect ratios

142

Y. lie, V. Beck

Corridor (l.4x9.2m) TC3, 1.5m apart.

0.75 J 4------~

L

TC2

TC4

TC1

4.8x2.4m)

DI01

Lift shaft

~10~

Room 101 (4.8x2.4m)

±

,

Fig. 1.

Instrumentation room

Room 102

Landing Key

M

Room 103

| Itl Thermocouple Species sample point Pressure transducer Smoke densitometer Mcaffreycup

Fuel

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Air

Instrumentation layout on level 1. Arrows indicate smoke path.

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Smoke spread in multi~storey building

143

(length/width) of the first floor corridor, the stair shaft and the fourth floor corridor were 6.6, 4.3 and 11.4, respectively. F o r the present study, instruments were installed on the first and fourth floor, and in the stair shaft. The layout and the instrumentation setup are given in Figs 1 and 2. A 0.3 x 0.3 m sand-filled p r o p a n e burner was placed in the centre of the burn r o o m floor as a fire source. Air was supplied to the burn r o o m through an air supply fan. The volumetric air supply rate was controlled via an auto-transformer. The air supply unit was located at the same height as the p r o p a n e burner (100 m m above the floor level) and 600 m m from the eastern wall of the burn room. T e m p e r a t u r e s were m e a s u r e d with t h e r m o c o u p l e arrays TC1, TC3 and T C 6 at doors D101, D1 and D4, respectively. The t h e r m o c o u p l e arrays were m o u n t e d vertically along the centre line of the doors. Each of these arrays consisted of 10 t h e r m o c o u p l e s with 0 . 2 m spacing. The lowest t h e r m o c o u p l e was 0.1 m a b o v e the floor. A n array of ten t h e r m o c o u p l e s (TC2) was placed in the centre of the first floor corridor with 0.25 m spacing and 0.15 m minimum height a b o v e the floor. The vertical array of t h e r m o c o u p l e (TCT) in the centre of the fourth floor corridor had a spacing of 0 . 2 7 m and a minimum height of 0 . 1 2 m above the floor. Vertical t e m p e r a t u r e distributions along the stair shaft were m e a s u r e d at 1.4 m a b o v e each floor level (array TC5). T h e r m o c o u p l e arrays TC3 and TC8 were also placed horizontally along the corridors on levels 1 and 4, respectively, at a height of 1.4 m from the floors. All t h e r m o c o u p l e s had a diameter of 0.5 mm and were C h r o m e l - A l u m e l K type. S m o k e obscuration meters were positioned in the areas r e m o t e from the fire source to avoid hot s m o k e causing damage to the instrument. Three meters were placed in the stair shaft and another three were placed in the corridor of the fourth floor. Chemical compositions were m e a s u r e d using a custombuilt gas analysing unit. A sampling p r o b e of the unit was positioned at the a p a r t m e n t d o o r D101 along the vertical centre line at the height 1.4 m. The gas sample streams were cooled, dried and filtered before passing the gas analyser. The carbon m o n o x i d e and carbon dioxide transducers used an infra-red optical bench with a m a x i m u m range of 0 - 1 0 % by volume. The oxygen sensors were galvanic cell type with a range of 0 - 2 5 % by volume. Pressure differences from the stair shaft to the lift shaft which was open to the surrounding a t m o s p h e r e were m e a s u r e d with differential pressure gauges at the elevations of levels 2, 3 and 4. The pressure transducers were m o u n t e d on the lift shaft side of the wall. A piece of plastic tube c o n n e c t e d one terminal of the transducers to the a t m o s p h e r e in the stair shaft through a hole in the wall. Bi-directional velocimeters were used to m e a s u r e s m o k e m o v e m e n t velocities. T w o velocimeter

144

Y. He, V. Beck TABLE 1 Experimental Conditions

Test no.

Heat release rate ( k W )

Air sat)ply to the h u m room

Air/fitel ratio

Erternal wind (kin~h)

Ambient T (°C)

52 38 38 38

6W 6W 5 SW 6 SE

12 14 14 13

(re'Is) 1 2 3 4

100 300 300 300

0.064 0-136 0.136 0.136

p r o b e s were placed at the a p a r t m e n t door D101 at the heights of 0 . 7 m and 1.4 m, respectively.

3 EXPERIMENTAL

CONDITIONS

Four experiments, which are d e n o t e d as Test 1, Test 2, Test 3 and Test 4, were conducted. The experimental conditions of these tests are listed in Table 1. The first experiment was a preliminary one. It was c o n d u c t e d to test the working conditions of the instrumentation. Fire strength was then increased to 3 0 0 k W in Test 2. Test 3 is a repeat of Test 2. Ventilation conditions for these three experiments were the same. Test 4 was designed to investigate the s m o k e distributions to various corridors. In this experiment, all the doors from the stair shaft to various corridors were open fully. Tests 1 and 2 were c o n d u c t e d in the same day. Tests 3 and 4 were c o n d u c t e d on separate days and the initial interior t e m p e r a t u r e s in these experiments were the same as the ambient temperature. The air to fuel ratios for all the experiments were greater than stoichiometric air to fuel ratio so that sufficient oxygen was supplied to facilitate complete combustion. The ventilation conditions for the experiments are given in Table 2.

4 EXPERIMENTAL

RESULTS

A large quantity of data was obtained from the series of four experiments. There were many similarities b e t w e e n the results of Tests 1, 2 and 3. This paper reports mainly the results of Test 3. Results of the former two

Smoke spread in multi-storey building

145

TABLE 2 Ventilation Conditions

Test

D101

D102

D103

D1

D2

D3

D4

D42

O O O O

C C C C

O O O O

C C C O

C C C O

O O O O

O O O O

no.

1 2 3 4

O* O O O

* O = open: C = closed. All other doors in the building were closed during the experiments.

experiments are briefly referenced. Results of Test 4 will be d o c u m e n t e d in another publication. Figure 3 displays the temperature distribution at the door D101 in Test 3. The coordinate y is the distance from the floor. From these temperature traces it is plausible to divide the experimental period into two stages: the growth period and the quasi-steady period. The growth period includes the first 5 min when the temperature near the upper edge of the door increased significantly from 16°C to 210°C. Based on the temperature profile it can be deduced that during the growth period the smoke layer quickly descended to about 1 m above the floor. A layering effect can be T( c 250220-

190. 160 130 100 70

4C 1(

0.3

Fig. 3.

0"10

Measured temperature distribution along the centre line of door D101. The y-axis is the elevation from the floor.

146

Y. lie, V. Beck

discerned from the t e m p e r a t u r e changes along the vertical direction at given times. The average rate of t e m p e r a t u r e change in the upper layer was much higher than that in the following quasi-steady period in which the hot layer t e m p e r a t u r e only increased by about 20 degrees over a time span of 25 min. H o w e v e r , the t e m p e r a t u r e distribution does not indicate a distinct b o u n d a r y b e t w e e n the hot upper layer and the relatively cool lower layer. There was a region in the lower part of the d o o r where t e m p e r a t u r e remained uniform. On the other hand, the t e m p e r a t u r e in the upper region continuously increased with height y up to the top edge of the d o o r frame, indicating that the t e m p e r a t u r e in the hot layer was not uniform. The height of the lower uniform t e m p e r a t u r e region decreased with time until the steady state was reached. Constant t e m p e r a t u r e contour lines revealed a quick descending trend with respect to height in the transition period and was then maintained at almost constant heights in the quasi-steady period. The t e m p e r a t u r e vertical distributions in the middle of the first floor corridor and at door D1 on level 1 showed a similar trend (Figs 4 and 5) to that at d o o r D101. H o w e v e r , the layering effect a p p e a r e d to be s o m e w h a t m o r e p r o n o u n c e d at door D1. There was a substantial j u m p in temperature b e t w e e n y = 1.1 m and y -- 1.3 m. T e m p e r a t u r e variations within the region y < 1.1 m were relatively small. T e m p e r a t u r e distribution along the first floor corridor at the height of 1.4 m exhibited a dip b e t w e e n x -- 2.25 m to x = 5.25 m as shown in Fig. 6.

""

"

0.15

Fig. 4. Temperature vertical distribution measure with TC2 in the middle of the corridor on level 1. The y-axis is the elevation from the floor.

Smoke spread in multi-storey building

147

0.1

Fig. 5.

T

Temperature distribution measured along the centre line of door D1. The y-axis is the elevation from the floor.

1130-160

(oc)

]100-130

160-

170-100 ~40-70

130

110-40 IO0 7C

~0

4( 11

v.l,~

8.25

Fig. 6. Measured temperature horizontal distribution along the corridor on the first floor at the height of 1.4 m. The x-axis is the distance from the partition end of the corridor (refer to Fig. 1).

148

Y. He, V. Beck

This was possibly due to the counter flow mixing in the region between the two doors D101 and D1 located at x = 1.2 m and x = 7.2 m, respectively. In the stair shaft, the walls were constructed of light weight concrete blocks, and the stair flights were constructed of concrete slabs and steel frames. Accordingly, some amount of heat conveyed by the smoke may have been absorbed by the building construction. Although building construction temperatures were not measured during the experiment, moisture condensation was observed on the surfaces of concrete walls and steel frames immediately after the termination of the experiment, indicating significant heat loss to the building construction in the stair shaft during the experiment. In addition, smoke leakage through the concrete block walls of the stair shaft was observed during the experiment. Thus, thermal energy would have been lost with the smoke which leaked to the outside. Consequently, the measured gas temperature rises in the stair shaft (shown in Fig. 7) were much smaller than those measured in the corridor on the floor of fire origin during the experiment. So were the temperatures measured at the door to the fourth floor corridor (Fig. 8). The staircase assisted with the mixing of fluid in the shaft. The layering effect was inhibited by this mixing process. Temperatures measured at door D4 showed essentially little variation with vertical distance y (Fig. 8). In the other two experiments (Tests 1 and 2) the temperature vertical distribution along the centre line of door D4 was close to uniform. The temperatures in the middle of the corridor on the fourth floor demonstrated a more or less uniform vertical distribution as shown in Fig. 9.

(°C) 110 9O

,0

i, ,0.9O i

[=50-70[ le30-50 I ~3o

j

I0

0 ~r.... 0 9.2

Fig. 7.

6.6 ~

(m)

Measured temperature vertical distribution in the stair shaft. The y-axis is the elevation from floor of the first level (refer to Fig. 2).

Smoke spread in multi-storey building

149

T(' 50

40

30 2C

0.3 0.10

Fig. 8.

Temperature distribution measured along the centre line of door D4. The y-axis is the elevation from the floor.

m ~

T (°C

B40-501

50

[] 30-401 4o • 20-301 30

• 10-201

lq

o

Fig. 9.

O

Temperature vertical distribution measured with TC7 in the middle of corridor on the fourth floor. The y-axis is the elevation from the floor.

150

Y. He, V. Beck

T (°( 5o

40

30 20 1o

,..:

~

o

Fig. 10. Measured temperature horizontal distribution along the fourth floor corridor. The x-axis is the distance from the western end of the corridor (refer to Fig. 2).

T e m p e r a t u r e horizontal distribution along the fourth floor corridor decreased from the entrance end to the exit as shown in Fig. 10. The distance x in this figure is m e a s u r e d from the western wall of the corridor towards the east (see Fig. 1). Figure 11 displays smoke optical densities measured in the stair shaft and the corridor on level 4 of the building. The measured results showed an increase in smoke density with time and a decrease with the distance 1.5 ..a'--,

~.

o~

OB2

~

0.5 OB6 ......

~

OB3 OB5

°°0

/~...lIF~'~

,

5

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~0

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,

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2o

|

25

1

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3o

t (ram) Fig. 11.

Smoke optical densities measured in the stair shaft and the fourth floor corridor.

Smoke spread in multi-storey building

151

1.2

~ 0.8 0.6 "~ 0.4

~ 0.2 ~

0.0 -0.2 41

43. 0

m ,

I

5

i

i

l0

,

I

15

i

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20

i

i

25

i

l

30

t (n-fin) Fig. 12.

Measured flow velocities across door DI01.

away from the fire origin. At any given time, smoke density in the stair shaft was reduced dramatically from the second level to the third. This p h e n o m e n o n coincided with the temperature drop in the shaft (Fig. 7), suggesting that smoke infiltrating into the shaft was diluted by the fresh air leaked through the gaps in the walls. In addition, the deposition of smoke particles onto surfaces of the building structure might also be responsible for the reduction in smoke density. Given in Fig. 12 are flow velocities of the flow across door D101. The strong fluctuations in the measured velocities were attributed to the influence of external wind, since both the velocities in the upper and lower layer displayed a similar pattern of fluctuation. The positive value of velocity at y = 1.4 m indicates that smoke was flowing out of R o o m 101, and the negative value represents the in-flow velocity.

5 ZONE MODEL RESULTS AND COMPARISON C F A S T is a two-zone model developed by researchers at the Building and Fire Research Laboratory, National Institute of Standards and T e c h n o l o g y . " The C F A S T model has been widely used to predict fire growth and smoke spread in multi-enclosure buildings. The model calculates the time evolving distribution of temperature and concentration of species throughout a building during a user-specified fire. In this model, each enclosure is divided into two z o n e s - - a n upper hot zone and a lower cool zone. Physical quantities of interest are assumed to be uniformly

152

Y. He, V. Beck

distributed within each zone. Governing equations are solved for each zone to obtain temperature, species concentrations, gas flow rate across vent and other quantities. To simulate smoke m o v e m e n t for the experiment conducted in the present study, a total n u m b e r of five c o m p a r t m e n t s was prescribed in the input data file, which included the burn room ( R o o m 102), R o o m 101, the first floor corridor, the stair shaft and the fourth floor corridor (see Figs 1 and 2). The heat release rate was set to 300 kW. The air supply fan f o r m e d a forced ventilation to the burn room. The effect of external wind was neglected in this computation run. The content of the input data file used to run C F A S T model is listed in the Appendix. The computation results are c o m p a r e d with experimentally m e a s u r e d data hereinafter. Since the vent flow to the stair shaft was not m e a s u r e d in the experiment, the estimated vent flow from (?FAST together with the measured flow t e m p e r a t u r e were used as input data for the network model to predict conditions in the stair shaft and the corridors on the floors other than that of fire origin. The results of the network model will be discussed in the next section. It has been shown earlier that the m e a s u r e d t e m p e r a t u r e s in various enclosures did not show a definite interface between upper and lower layers. In order to obtain average zone t e m p e r a t u r e s from measured data and c o m p a r e with the model predictions, an N-percentage rule H was applied to the measured vertical t e m p e r a t u r e profile to estimate the interface height. The t e m p e r a t u r e profile was then divided with the interface into two regions and averaged over each region to obtain zone temperatures. The predicted interface height and zone t e m p e r a t u r e s in the first floor corridor are presented and c o m p a r e d with the measured results in Fig. 13. According to the C F A S T model, the interface height in the first floor corridor descended quickly from the ceiling height to 0.75 m above the floor within 4min. It then receded back to a steady level of about 1.1 m. The interface height estimated from the measured t e m p e r a t u r e profile, however, displayed an almost m o n o t o n o u s decreasing trend to the end of the experimental period. A quasi-steady period may be identified from 7 to 30rain during which the m e a s u r e d interface height was maintained a r o u n d 1.0 m [see Fig. 13(a)]. For this particular experiment with a heat release rate of 3 0 0 k W , the model over-estimated the upper layer t e m p e r a t u r e by about 25 %. The model's prediction of the temperature rise in the lower layer agreed with the experiment reasonably well. Both the experimental result and model prediction show that the t e m p e r a t u r e rise in the lower layer was insignificant during 30 min of the experimental period. It should be noted that the C F A S T predictions represent the average zone values, whereas, the measured data in Fig. 13(b) were taken in the middle of the first floor corridor. These measured

153

Smoke spread in multi-storey building 3.0-

'160-

1402.5-

"

120-

Upper layer

~2.0 100.

1.5-

o

80-

60-

1.0\

/

Lower layer

40-

0.5 20-

0.0

i

0

I

5

i

I

10

l

i

l

15

20

I l l

25

0

30

0

i

I

5

10

t (min)

Fig. 13.

i

i

i

20

25

30

t (min)

(a) Interface height; - -

i

15

(b) Layer temperatures. measured; . . . .

CFAST predicted.

Interface height and layer temperatures in the first floor corridor.

data only approximately represented the average conditions in the corresponding enclosures, notwithstanding the uniformity assumption of zone models. A n o t h e r source of discrepancy is related to the radiation error, though relatively small, in the measured temperature data. According to the analysis by Janssens and Tran, 17 a thermocouple having a diameter of 0.9 m m may produce a temperature reading that is 8% lower than the actual temperature for a temperature level of 300°C in the surrounding gas. This error will be reduced significantly if the gas temperature is reduced and the diameter of the thermocouple is smaller. For the present investigation, the gas temperature in the first floor corridor was less than 180°C (see Fig. 4) and the thermocouple diameter was 0.5 mm. Therefore, the error in the average temperature reading due to radiation would be much smaller than 8%. In Fig. 14, the measured and predicted concentrations of oxygen and carbon dioxide in the upper layer of R o o m 101 are compared. The model over-estimated both the oxygen depletion and CO2 concentration in comparison with the measured results. A quasi-steady period is discernible from the measured results. However, the model predicted a continuous decrease in oxygen concentration and a continuous increase in carbon dioxide concentration (see Fig. 14). Figure 15 presents the C F A S T calculated and the measured conditions at the first floor stair door D1. The difference between the upper region

22L

154

Y. He, V. Beck 6-

20

4

18

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16-

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i 30

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t (min)

i 25

i 30

t (mm)

(a) Concentration of oxygen; - Fig. 14.

I 20

(b) Concentration

measured; . . . .

of carbon

dioxide.

CFA ST p redicted

Comparison of the measured and predicted species concentrations in the upper layer of R o o m 101.

120 -

0.6

1O0

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J .........................

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t (min)

(a) Calculated vent flow rates across door D 1. --from the corridor to the stair shaft; ...... from the stair shaft to the corridor. Fig. 15.

0

(b) Measured average temperature of the exhaust stream.

Conditions at the first floor stair door D1.

155

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.

.

f

,

10

30

t (rain) (b) Conditions in the fourth floor corridor. ......

lower layer temperature; ........

interface height.

CFAST predictions of interface heights and zone temperatures in the stair shaft and the fourth floor corridor.

out-flow rate to the stair and the lower region in-flow rate to the corridor was due to the air and fuel supplies (see Table 1 and Fig. 1) to the burn r o o m and the thermal expansion of air in the burn room, R o o m 101 and the first floor corridor. The C F A S T prediction of interface height and layer t e m p e r a t u r e s for the stair shaft and the fourth floor corridor are shown in Fig. 16. Since the t e m p e r a t u r e distribution in the stair shaft was opposite to the two-zone m o d e l assumption, the N - p e r c e n t a g e rule can not be applied to process the m e a s u r e d t e m p e r a t u r e data (Fig. 7) for comparison with the model predictions. Neither can it be applied to the m e a s u r e d data in the fourth floor corridor w h e r e t e m p e r a t u r e vertical distribution was almost uniform (Fig. 9). The differences b e t w e e n the m e a s u r e d and two-zone model predictions for these two enclosures are not only quantitative but also qualitative.

6 NETWORK

MODEL RESULTS AND COMPARISON

As discussed earlier, there m a y be difficulties with two-zone models, such as C F A S T , w h e n predicting conditions in enclosures with large aspect ratio, such as the stair shaft involved in this study. E x p e r i m e n t a l results have d e m o n s t r a t e d that w h e n smoke e n t e r e d the stair shaft, there was a t e m p e r a t u r e drop from the level at the fire floor to the upper levels due

156

Y. He, V. Beck

to mixing and heat loss through the walls of the stair shaft. The same p h e n o m e n o n was o b s e r v e d along the long corridor on the fourth floor. F o r the p u r p o s e of predicting the conditions in these enclosures, the n e t w o r k model C E S A R E - S M O K E was used. In the C E S A R E - S M O K E model, enclosures with large aspect ratio are divided into a series of finite volumes. O n e - z o n e technique is applied to these volumes, i.e. conditions in each volume are assumed to be uniform. Each volume is treated as a node in a network, and all nodes are c o n n e c t e d by links which may represent vent openings or imaginary boundaries. Conservation equations of mass and energy are considered in deriving the set of differential equations which are solved to obtain t e m p e r a t u r e and species concentrations at each node. H e a t losses to the surroundings are considered in the model. H e a t transfer to the wall includes radiation and natural convection. H e a t conduction in the walls is treated as a one-dimensional transient problem. Hydrostatic pressure variation along the stair shaft due to the stack effect is c o m p u t e d from the t e m p e r a t u r e distribution. ~ The pressure in a corridor is assumed to be uniform. The concept of effective flow area ~' was used in calculating s m o k e spread on floors a b o v e the floor of fire origin. Conservation of m o m e n t u m is coupled with pressure equation. If a link b e t w e e n two nodes in the n e t w o r k represents an opening, the mass flow rate from one node to the other is related to the pressure difference across the opening by the orifice equation. If a link b e t w e e n two nodes represents an imaginary b o u n d a r y , there will be no pressure difference b e t w e e n the two nodes and the mass flow rate is calculated from conservation of mass. A detailed account of the model and the description of c o m p u t a t i o n algorithm can be found in the early publications. '~~ Figure 17 is a simplified sketch of the E B F F and the network representation for the modelling. The floor levels are d e n o t e d as F1, F2, F3, F4. Each corridor was divided into 10 finite volumes which are d e n o t e d as C1, C2 .... C10. The vent flow rate obtained from the C F A S T corridor C1 C2 C3 C4 C5 C6 C7 C8 C9 CI0

I I

F3

I

F2

' Fig. 17.

1

outout were used as inout

Simplified sketch of the EBFF (left) and a network representation for modelling (right).

Smoke spread in multi-storey building

157

;) 0

0 9.2

u.u

y (m)

Fig. 18. Predicted temperature distribution in the stair shaft. The y-axis is the elevation from the floor of the first level (refer to Fig. 2).

prediction and the temperature measured at the vent door (Fig. 15) were used as the input to the network model. Given in Figs 18 and 19 are C E S A R E - S M O K E predictions of temperatures in the stair shaft and the corridor on the fourth floor, respectively, under the condition of Test 3. In comparison with the measured temperatures presented in Figs 7 and 10, the general trends of temperature variations in the structures involved were well predicted by the model. As mentioned earlier, a leakage area existed in the stair shaft wall and smoke leakage from the shaft to the outside was observed during the experiments. It was also expected that fresh air might leak into the shaft from the bottom part of the structure where the inside pressure was lower than the outside. Figure 20 displays measured and predicted pressure differences at various levels in the stair shaft. Pressure in the shaft is seen to be lower than the atmospheric pressure at the lower level and greater at the higher level. The ventilation condition involved in the experiment would allow air to be drawn into the stair shaft below a neutral plane where the pressure difference was zero between inside and outside, and smoke to be expelled out of the shaft above this plane. This p h e n o m e n o n is called the chimney effect. The chimney effect, together with mixing and heat transfer processes, would prevent the formation of stratified hot upper layer and lower cool layer. As a result, the process of temperature rise in the stair shaft was hindered. The phenomenon of distributed leakage was, however, not considered in the network model, and the

158

Y. lie, V. Beck

T (o( 50-

40

30

20 1C

,,6

x(m)

Fig. 19.

'~ "----~_:> ~6 ~'o~ ~'~ m I"..m

,-

~

t(min)

0

Predicted temperature distribution in the fourth floor corridor. The x-axis is the distance from the western end of the corridor (refer to Fig. 2).

lO

M e a s u r e d : .............. F2; . . . . . . . . . F3;

F4.

Predicted:

F4.

F2;

F3;

5 ...._..,.

."',

0

:

..

'.~

:

" :

': i

..'..," .-- .'

"~':"

-5

% -1o }

-15 -20

i i'

".,...'

\...~

"-.:~"-.. ~

'; .,.~,,-~...,./,.

" i'

0

,%

,'5

:'4

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t (min) Fig. 20.

Pressure difference between the stair shaft and outside.

d0

Smoke spread in multi-storey building

159

predicted temperatures in both the stair shaft and the fourth floor corridor were therefore higher than measured values. The discrepancies between the measured (Fig. 7) and the modelled (Fig. 18) temperatures in the stair shaft may also be attributed to the inaccuracies in (a) the use of the measured data and the CFAST output and (b) the finite volume approximation. Due to limited resources the vent flow to the stair shaft, which was required by the network model as input, was not measured. Instead, the CFAST model prediction of the vent flow rate at the stair door [Fig. 15 (a)] was used to generate such input data which may deviate from the actual condition in the experiment. The present model employs the finite volume approach to calculate the conditions for each node in the network. Hence, the predicted quantities at a node represent the averaged values over the finite volume. On the other hand, the experimental readings were taken at a single point in the volume, hence errors due to non-uniformity could be expected. The network model did not take into account the effect of external wind on pressure distribution inside the building. The calculated variations in pressure difference between the stair shaft and outside due to the stack effect are both smoother and smaller than the measured results (Fig. 20). The calculated pressure drop on the second floor was almost 50% smaller than the measured value. Apart from the stack effect, the external wind also made significant contributions to the measured pressure differences between the stair shaft and outside. Although the weather condition was relatively calm on the day when the experiment was conducted (the average wind speed was about 5 km/h), occasional wind gusts of 15 k m / h were recorded and the pressure transducers registered relatively strong fluctuations. The fluctuation components were sometimes even greater than the mean values, and all the three pressure transducers gave similar patterns of fluctuation. In addition, the pressure level on the third floor was only slightly less than that on the fourth floor. A possible reason is that the plastic tube which connected the pressure transducer to the stair shaft was excessively long and the tube opening was facing downwards, registering a dynamic rather than static pressure. It should also be noted that the initial pressure differences registered on levels 3 and 4 were not zero, indicating that pressure was already established prior to the start of the experiment due to external wind. Predictions of oxygen concentration distributions in various enclosures are given in Figs 21 and 22. U n d e r the assumption of no leakage, the network model predicted more or less uniformly distributed oxygen concentrations during the quasi-steady period of the experiment. For the growth period, the modelled results indicated increases in oxygen level with elevation y in the stair shaft, and with distance x from the entrance

160

Y. He, V. Beck

i%)

I

L ~ililll]

I0

21

-'4 ~"

9.2

27 1.4

Fig. 21.

4 y (m)

Simulated oxygen concentration in the stair shaft. The y-axis is the elevation from floor of the first level (refer to Fig. 2).

• 19-21 I I~ 17-19l

'm15-17

~_~ ~

x(m)

t~ ~ % ~ i 5

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6 Fig. 22.

Simulated oxygen concentration in the fourth floor corridor. The x-axis is the distance from the western end of the corridor (refer to Fig. 2).

Smoke spread in multi-storey building

161

in the fourth floor corridor at any given time. Due to limited resources, species concentrations in remote areas other than at door D101 were not measured. No experimental data were, therefore, available for comparison.

7 CONCLUSIONS A N D R E C O M M E N D A T I O N A series of experiments was conducted in the C E S A R E ' s EBFF to obtain results on smoke movement in a multi-storey building. The results were compared with the predictions by the smoke spread models CFAST and C E S A R E - S M O K E . The experimental results indicated that the chimney effect would be present in a large vertical enclosure with multiple openings and distributed leakage. The chimney effect, together with the mixing and heat transfer processes, would prevent the formation of a stratified upper hot layer and a cool lower layer. The measured temperature data on the fourth floor of the experimental facility indicated that for fires of moderate strength the layering effect was not dominant in areas remote from the room of fire origin. These results provided a verification for the one-zone treatment of the nodes in the network model. The comparison of the CFAST model predictions with the experimental results in the present study showed qualitative agreement for the upper layer in the corridor of the floor of fire origin and qualitative disagreement for the stair shaft and corridor remote from the floor of fire origin. The CFAST model tended to over-estimate average temperature and species concentrations in the upper layer of the first floor enclosures, though reasonable agreement was reached for the lower layer temperature in the first floor corridor. The representations of the average zone parameters with evaluated parameters based on the measurements taken at a single point or with a single array of thermocouples have limited accuracy, especially for the enclosures with large aspect ratio. Heat transfer to the walls of the building was not measured. It was difficult to estimate how much the heat loss had contributed to the lower-than-expected temperature rise in the experiment. The agreement between the measured results and the predictions of the C E S A R E - S M O K E model was qualitative. The observed discrepancies between the measured and predicted results may be attributed, in part, to the leakage in the building construction, which was not accounted for in the model. The C E S A R E - S M O K E network model relied on the CFAST model to provide smoke flow rate as input data. The result of the former would have inherited some of the uncertainties in the result of the latter.

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Y. He, V. Beck

Nevertheless, the results demonstrated the general validity of the model for predicting horizontal and vertical smoke movement in remote and long enclosures of multi-storey buildings subjected to fire. Temperature variations along the longitudinal direction of the enclosures of large aspect ratio were revealed by both the experimental results and computer predictions. Concentrations of toxic gases in smoke are important parameters for the assessment of risk faced by building occupants. More experimental data are needed for evaluating the performance of the network model in predicting conditions at various parts of the building. Heat transfer to the building construction represents significant energy loss from the heated air, resulting in a low temperature rise in areas remote from the fire origin. It will be appropriate to investigate the temperature distribution in the wall to determine the heat transfer rate. Experiments involving transient state and realistic fire scenarios are planned. Extensive flow velocity and chemical composition measurements, as well as temperature and pressure measurements, will be carried out. The C E S A R E - S M O K E model is a smoke movement model which requires measured data or data from other fire growth models as input. Further research work will be conducted to combine this network model with other fire growth models to predict both fire growth and smoke spread in multi-storey buildings.

ACKNOWLEDGEMENT This research work was supported by an Australian Research Council Collaborative Research Grant which is conducted in association with BHP and the National Association of Forest Industries, Australia. The authors are indebted to Mr Scott Stewart, the laboratory manager, and Dr Mingchun Luo of the Centre for Environmental Safety and Risk Engineering for their support and assistance in the experiments.

REFERENCES 1. Kawagoe, K., Fire behaviour in rooms. Building Fire Research Institute, Ministry of Construction (Japan), Report No. 27, Tokyo, 1958. 2. Friedman, R., An international survey of computer models for fire and smoke. J. Fire Prot. Engng, 4(3) (1992) 81-92. 3. Yoshida, H., Shaw, C. Y. & Tamura, G. T., A FORTRAN IV program to

Smoke spread in multi-storey building

4. 5. 6. 7. 8. 9.

10. 11. 12.

13. 14. 15. 16.

17. 18. 19.

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calculate smoke concentrations in a multi-storey building. D B R Computer Program No. 45, National Research Council of Canada, June 1979. Matsushita, T., Fukai, H. & Terai, T., Calculation of smoke movement in building in case of fire. Proceedings of the First International Symposium on Fire Safety Science, 7-11 October 1985, pp. 1123-1132. Klote, J. H., A computer program for analysis of smoke control systems. NBSIR 82-2512, National Bureau of Standards, Gaithersburg, MD, USA, June 1982. Sander, D. M., F O R T R A N IV program to calculate air infiltration in buildings. D B R Computer Program No.37, National Research Council of Canada, May 1974. Hadjisophocleous, G. V. & Yung, D., A model for calculating the probabilities of smoke hazard from fires in multi-storey buildings. J. Fire Prot. Engng, 4(2) (1992) 67-80. Evers, E. & Waterhouse, A., A computer model for analysing smoke movement in buildings. BRE CP 69/78, Building Research Establishment, Watford, UK, 1978. Hokugo, A., Yung, D. & Hadjisophocleous, G. V., Experiments to validate the NRCC smoke movement model for fire risk-cost assessment. Proceedings of the Fourth International Symposium of Fire Safety Engineering, Canada, 1994, pp. 805-816. Cox, G., Chitty, R. & Kumar, S., Field modelling and the King's Cross fire investigation. Fire Safety J., 15 (1989) 103. Luo, M. & Beck, V., The fire environment in a multi-room building-comparison of predicted and experimental results. Fire Safety J., 23 (1994) 413-438. He, Y. & Beck, V., A computer model for smoke spread in multi-storey buildings. In Proceedings of the Eighth International Symposium on Transport Phenomena in Combustion, ed. S. H. Chan. Taylor and Francis, San Francisco, 17-20 July 1995, pp. 713-723. Charters, D. & McIntosh, A., Tunnel fire safety assessment. Proceedings of ASIAFLAM'95, International Conference on Fire Science and Engineering, Hong Kong, March 1995, pp. 87-97. Cooper, L. Y., Harkleroad, M., Quintiere, J. & Rinkinen, W., An experimental study of upper hot layer stratification in full-scale multi-room fire scenarios. J. Heat Transfer, 104 (1982) 741-749. Peacock, R. D., Jones, W. W. & Bukowski, R. W., Verification of a model of fire and smoke transport. Fire Safety J., 21 (1993) 89-129. Peacock, R. D., Forney, G. P., Reneke, P., Portier, R. & Jones, W. W., CFAST, the consolidated model of fire growth and smoke transport. NIST Technical Note 1299, Building and Fire Research Laboratory, National Institute of Standards and Technology, Gaithersburg, MD, USA, 1993. Janssens, M. L. & Tran, H. C., Data reduction of room tests for zone model validation. J. Fire Sci., 10 (1992) 528-555. He, Y. & Beck, V., Estimation of neutral plane position in high rise buildings. J. Fire Sci., 14 (1996) 235-248. Klote, J. H., Smoke control. In The SFPE Handbook of Fire Protection Engineering, ed. P. J. DiNenno. Society of Fire Protection Engineers, 1988, pp. 3.14-3.157.

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APPENDIX VERSN 2 EXPERIMENT 3 TIMES 1800 I00 20 0 TAMB 288. 101300. 0. EAMB 288. 101300. 0. 7.60 HI/F 0.00 0.00 0.00 0.00 WIDTH 2.40 2.40 1.40 2.40 1.40 15.60 DEPTH 3.60 4.80 9.20 4.80 2.70 HEIGH 2.40 2.50 2.57 10.60 0.000 HVENT 1 2 1 0.800 1.960 0.000 HVENT 2 3 1 0.800 1.960 HVENT 3 4 1 0.800 2.000 0.000 7.600 HVENT 4 5 1 0.800 9.600 HVENT 5 6 1 0.800 2.050 0.000 0.000 1.00 1.00 1.00 CVENT 1 2 1 1.00 1.00 1.00 CVENT 2 3 1 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 CVENT 3 4 1 1.00 1.00 1.00 1.00 1.00 CVENT 4 5 1 1.00 1.00 1.00 1.00 1.00 1.00 CVENT 5 6 1 1.00 1.00 1.00 MVOPN 1 1 V 0.15 0.07 MVOPN 6 2 V 0.15 0.07 MVFAN 2 1 0.00 i00.00 0.135E+00 0.100E-04 INELV I 0.15 2 0.15 CEILI GYPSUM GYPSUM GYPSUM GYPSUM GYPSUM BRICK GYPSUM WALLS GYPSUM GYPSUM BRICK CONCRETE CONCRETE FLOOR GYPSUM CONCRETE CONCRETE CHEMI O. 30. 5.0 46000000. 293. 393. 0 . 0 0 0 LFBO 1 LFBT 2 FPOS 1.20 1.20 0.00 FTIME 200. i000. 2000. 2800. 3300. 6185. FMASS 0.0065 0.0065 0.0065 0.0065 0.0065 0.0065 0.0065 FHIGH 0.30 0.30 0.30 0.30 0.30 0.30 0.30 FAREA 0.i0 0.i0 0.I0 0.i0 0.i0 0.I0 0.i0 3.00E+05 3.00E+05 3.00E+05 3.00E+05 FQDOT 3.00E+05 3.00E+05 3.00E+05 CJET OFF HCR 0.200 0.200 0.200 0.200 0.200 0.200 0.200 CO 0.050 0.050 0.050 0.050 0.050 0.050 0.050 STPMAX 5.00 DUMPR EXP3.HI DEVICE 1 WINDOW 0 0. 0. 1 2 7 9 . 1 0 2 3 . 4 0 9 5 .

1.00 1.00 1.00 1.00 1.00