Experimental study on influence of stack effect on fire in the compartment adjacent to stairwell of high rise building.
Shi, Wen Xi ; Ji, Jie ; Sun, Jin Hua 等
Introduction
Many high rise buildings have been constructed in the world. The
fire safety of these buildings has drawn public attention due to the
occurrence of many catastrophic fires (Chow 2005; Guo et al. 2009,
2010). A notable example is the MGM Grand Hotel fire in 1980 (Best,
Demers 1982), 85 people died in this fire, with 68 victims located on
the upper floors far away from the ground floor where the fire occurred,
one significant reason of this phenomenon is that the hot smoke movement
from the lower to the upper floors was induced by the stack effect of
stairwell in the building (Klote, Fothergill 1983; Council ... 1992).
Stack effect is the phenomenon observed in cold weather when a tall
building acts like a chimney, with air entering through openings in
lower floors, flowing upward in the building, and leaving through
openings in upper floors (Tamura 1994; Klote 1994; Evans, Klote 2003).
Stack effect results from the difference in density between warm inside
air and cold outside air (Barrett, Locklin 1969). It's a common
construction that the door face stair hall or lift lobby in high-rise
residential building (Chow, Hung 2003; Chow, C., Chow, W. 2009). For
this kind of building structure, in case a fire occurs in the room
adjacent to stair hall or lift bobby, the fire-induced smoke will not
only spread horizontally along the room and corridor ceilings, but also
move vertically under the influence of stack effect. The air flow
pattern in the compartment where fire starts has significant influence
on the fire behaviours and smoke movement. Chow (2003, 2010, 2011)
reported that the duration of a fire depends on the fire load and
available ventilation. If there is sufficient fuel in the compartment, a
small fire, once ignited, will grow. Adding to that, a plenty of fresh
air is sucked into the fire room by stack effect. Big fires might occur
due to providing fresh air contributing to burning large amount of
combustibles and causing severe damage. So it is worthy to research the
influence of stack effect on fire in the compartment adjacent to
stairwell to improve the safety level of high-rise residential buildings
structure.
A number of authors have studied stack effect of stairwell or shaft
in building spaces in the last decades (Zukoski 1995; Cooper 1998; Zhang
et al. 2006; Mowrer 2009; Ji et al. 2012a, b, 2013; Li 2013); however,
little attention has been focused on the influence of stack effect on
fire in the compartment adjacent to stairwell. Sun (2009) investigated
the smoke movement in a full-scale six-storey stairwell induced by a
fire in an adjacent compartment and discovered that the flame was tilted
to the stairwell due to stack effect, but he did not further explore the
flame shape of fire and the temperature of hot smoke in the room. The
air flow induced by stack effect is natural convection. Another kind of
natural air convection, external wind, effect on compartment fire has
been discussed by several researchers. The effect of wind speed on the
movement of hot smoke in four different buildings has been studied by
Porch and Trebukov (2000). Huang et al. (2009) explored the fire growth
process in a reduced-scale compartment under different external wind
conditions. It was found that external wind had two opposing effects.
One was to promote combustion within the compartment and thus raised the
temperature, the other was to blow away and dilute the combustible gases
in the compartment and decrease the temperature, or hasten its
extinction. Chen et al. (2008) also reported that the ambient wind had
two contradictory effects on the compartment fire, and then inferred a
critical wind velocity to prevent hot smoke to outflow from the upstream
vent, which was regarded to influence enclosure fire behaviour greatly.
Roh et al. (2007a, b) investigated the effect of longitudinal
ventilation velocity on the burning rate in tunnel fires and discovered
that the increase in ventilation velocity reduced the burning rate of
the methanol fuel. In fact, external wind is different from stack effect
action on compartment fire. For the former, external wind is existent
before fire occurred and the velocity of air flow is almost constant.
For the latter, stack effect is almost nonexistent before fire occurs,
and then the velocity of air flow acted on the fire plume is
instantaneous, which is related to the heat release rate, ventilation
state and building geometry. Therefore, the fire behaviour is more
complex in the compartment adjacent to the stairwell. The flame shape
and the heat transfer mechanism are significantly changed and then the
fire spread process is influenced by the stack effect action.
In this paper, a set of experiments were conducted to study the
influence of stack effect on fire in the compartment adjacent to
stairwell in a 1/3 scaled 12-layer-stairwell configuration (Sun 2009).
The temperatures and fire properties in the compartment were
investigated.
1. Experiments
The experimental facility consists of stair, atria and room, as
shown in Figure 1. The dimensions of the 1/3 scale building model with
12 levels is 12.2 m high, 2.6 m long, and 1.5 m wide. The ground floor
is 1.2 m high and the other floors are 1.0 m high. The cross-sections of
stair, atria and room are 1.5 x 1.0 m, 0.8 x 0.8 m, 0.8 x 0.8 m,
respectively. Each floor has three doors with the size of 0.6 m (height)
x 0.4 m (width). The left and front sidewalls of model are a
fire-resistant glass (12 mm thickness) for observation, and the other
parts are constructed of steel plate with thickness of 2 mm.
The temperatures of hot gases of room, atria and stairwell were
measured by 47 K-type fine wire thermocouples, including 25
thermocouples in the room and 12 thermocouples in the stairwell. The
detailed location of the thermocouples is shown in Figure 2. Four
velocity probes of hot-wire anemometers (Kanomax, KA12) at a 10 cm
vertical interval were installed 5 cm away from the right side of the
first floor door 3 to measure the airflow speed. All the pools were
placed on an electronic balance to measure the transient mass of the
burning pool fire with sampling intervals of 1 s. The weight resolution
of the balance is 0.1 g. A Digital Vidicon and a Digital Camera were
used to record the flame development of the pool fire in the room.
[FIGURE 1 OMITTED]
There were 12 cases in the experiments. Methanol was used as fuel
and ambient temperature was about 5-7[degrees]C. Fire source was located
in the centre of the room on the ground floor. Only three doors on the
ground floor were open, the other doors were close. The top vent with
size 0.9 m (height) x 0.7 m (width) was located in left side of
12-layer. The detailed experimental cases are shown in Table 1.
2. Results and discussions
2.1. Compartment fire behaviours
The development of flames of different pool fires was observed in
those experiments. From the video recording, it can be found that the
flame inclined towards the direction of stairwell under the influence of
stack effect after ignition for a while, which was also reported by Sun
(2009), but he did not conduct further discussion. The flame inclination
may ignite distant combustibles and enhance the possibility of fire
spread in the horizontal direction. Knowledge of flame behaviour has
been playing an important role in the fire safety design. The typical
flame shapes of Case B3 are shown in Figure 3. At the beginning of the
fire, the methanol burned quietly and the flame did not tilt towards any
directions in the compartment, as shown in Figure 3(a). The hot smoke
symmetrically flowed out from the doors at two sides of compartment, and
then the temperatures in stairwell rose. At about 90 s, the flame began
to incline towards the direction of the stairwell due to the occurring
stack effect. As time passed, the stack effect was more significant with
an increase of temperature in the stairwell from 90 s to 350 s. After
350 s, the flame almost attached to the ground, as shown in Figure 3(d).
Figure 4 shows the velocity of fresh air flowing into fire room from
door 3 in Case B3. It can be seen that the velocity of air flow
increases continually from 0 s to 350 s and then remains almost
unchanged.
[FIGURE 2 OMITTED]
[FIGURE 3 OMITTED]
To quantitatively compare flame shapes in different cases, a flame
tilt angle [theta] (shown in Fig. 5) is often defined as the angle
between the centreline of flame region and vertical direction. The
typical instantaneous images of flame were captured from the
experimental videos in a relatively steady state when the velocity of
air flow into fire room got the maximum value and remained unchanged for
a period of time, then the flame tilt angle 8 in all cases could be
determined.
The calculated flame tilt angle [theta] and the mean air flow speed
V through Door 3 in a steady state of different cases are shown in
Figure 6. As shown in Figure 6, the flame in the cases with top vent
closed (Case C1-C4) also inclined to the direction of stairwell. It may
be caused by different state of air entrainment at two sides of the fire
plume. For a fire room adjacent to the stairwell with top vent closed
(Case C1-C4), fuel consumes continually surrounding air (oxygen) after
ignition. At the beginning, the quantity of air entrained from any
direction is almost equal, and then the fire plume stands vertically. As
time passed, the side of fire plume pointing to the stairwell could not
obtain enough fresh air and only the side pointing to the Door 3 could.
Therefore the flame inclined to the direction of stairwell, resulting
from the pressure difference between both sides of fire source. Sun
(2009) and Chow, C. and Chow, W. (2009) also observed that the flame was
tilted to the stair-well in their experiments conducted in a full-scale
six-storey stairwell without top opening. This is different with the
case that the fire plume in single compartment with symmetrical opening
does not incline to any directions in a quiescent condition described in
reference (Chen et al. 2008).
[FIGURE 4 OMITTED]
[FIGURE 5 OMITTED]
It is shown from the Figure 6 that the flame tilt angle [theta] is
remarkably enlarged in the cases with top vent open (Case A1-A4 and Case
B1-B4), compared with the cases with top vent closed (Case C1-C4). When
top vent is open, the hot smoke flowing into stairwell could easily
induce the occurrence of the stack effect, resulting in larger velocity
of air flowing into the fire compartment. Contrarily, in the cases with
closed top vent (Case C1-C4), the stack effect could not be formed and
only the buoyancy drove the hot smoke to spread vertically. Therefore,
the velocities of air flowing into compartment from the door 3 in the
cases with top vent open are much larger, resulting in larger flame tilt
angle [theta].
The flame tilt angle [theta] of case A1-A4 and case B1-B4 are
compared in Figure 6. It is shown that the flame tilt angle [theta] of
cases with the same pool size is very close. In addition it can be found
that an increase in pool size leads to an increase in air speed V flow
into fire room. The velocity V in the cases with pool size of 25 cm
(Case A4 and Case B4) is the maximum. However, it is shown that the
flame tilt angle [theta] first increases and then decreases with an
increase in pool size for the same ventilation state. The flame tilt
angle [theta] of 20 cm pool size (Case A3 and Case B3) reached a
maximum. To interpret this phenomenon and analysis air flow effect on
flame shape of pool fire, a non-dimensional number (Richardson number)
is introduced as follow.
[FIGURE 6 OMITTED]
The flame tilt angle is determined by the relative magnitude of the
buoyancy of fire plume in vertical direction and the inertia force of
air flow in horizontal direction. The relative magnitude can be
expressed as a Richardson number (Ri) (Woods et al. 2006). The physical
interpretation of the non-dimensional number (Ri) is the ratio of the
total buoyant force associated with hot combustion products to the total
transverse air momentum interacting with the combustion products. When
the assumption of complete combustion has been applied to the mass flow
rate of fuel leaving the pool, the Richardson number is calculated by
the following equation (Woods et al. 2006):
Ri= [DELTA][rho]/[[rho].sub.a] [gL/[V.sup.2]], (1)
where: [DELTA][rho] is the density difference between the air and
the products of combustion; g is the gravitational constant; L is the
stream-wise dimension of the pool; pa is the density of the air upstream
of the pool; and V is the transverse air speed. Assuming ideal gas
behaviour and that the ratio of molecular weights of air and the
products of combustion is near unity allows a more easily calculated,
characteristic Richardson number to be rewritten as:
Ri = (1 - [T.sub.0]/[T.sub.f]) gL/[V.sup.2], (2)
where [T.sub.0] and [T.sub.f] are the absolute upstream air
temperature and adiabatic flame temperature, respectively. In our
experiments, [T.sub.0] is 278 K and [T.sub.f] is 973 K, respectively.
To avoid the singularity in the quiescent case, the inverses of the
Richardson number ([Ri.sup.-1]) are calculated based on the experimental
data, and the results are listed in Table 1. The relationship between
flame tilt angle [theta] and [Ri.sup.-1] is shown in Figure 7. It can be
found that a linear relationship between flame tilt angle [theta] and
[Ri.sup.-1] As shown in Figure 7 the flame tilt angle 9 increases with
an increase in the value of Ri and their relationship can be well
approached by a linear fitting with related coefficient of 0.87. As can
be seen from the Table 1, the value RF1 of 20 cm pool size (Case A3 and
Case B3) is the maximum for the same ventilation state, the flame tilt
angle [theta] of 20 cm pool size (Case A3 and Case B3) is the largest
accordingly.
[FIGURE 7 OMITTED]
2.2. Compartment temperature
Twenty-five K-type fine wire thermocouples were arranged in the
compartment room. The detailed locations of those thermocouples are
shown in Figure 2. The thermocouple T3 was located 5 cm away from the
left side of door 3 and was the same height level of the top of door 3.
The direction of airflow through door 3 is identified by the
thermocouple T3. If the temperature of T3 is much higher than outside
temperature, which indicates that the air outflows from fire room
through the door 3. In contrast, if the temperature of T3 is the same as
the outside temperature, which indicates that the air inflows from
outside. The temperatures of T3 in cases with top vent open and cases
with top vent closed are shown in Figure 8. When the top vent of
stairwell is closed, the air flows out of fire room through door 3. This
is the same as the normal compartment fires. However, when the top vent
of stairwell is open in the case B1-B4, the temperature of T3 increases
rapidly at the beginning, and then decreased to the outside temperature,
which indicates that the air firstly flows out of fire room and then
flows into fire room from the outside. It is because a large quantity of
air is sucked into fire room due to the stack effect. It also can be
distinctly seen from Figure 8 that the time when temperature T3 began to
decrease becomes earlier with increased pool size. The reason is that
the stack effect occurs earlier for the bigger pool size.
[FIGURE 8 OMITTED]
The thermocouples T1, T6, T11, T16 and T21 (shown in Fig. 2) were
located at 0.9 m height and measured the temperature of the upper hot
gases in the compartment. The mean temperatures of the thermocouples T1,
T6, T11, T16 and T21 in a relatively steady state in different cases are
shown in Figure 9. It is shown that the mean temperatures of upper hot
gases in cases with top vent opened are much lower than those in cases
with top vent closed. A possible explanation for this phenomenon is that
the velocity of airflow into fire room is much larger under the action
of stack effect. On one hand, a large amount of fresh air mixes with hot
gases and cools down the temperature. On the other hand, most of smoke
is sucked into the stairwell before it rises to the compartment ceiling.
So the temperatures of upper hot gases are much lower in cases with top
vent opened. It also can be distinctly seen from Figure 9 that the
temperature in cases with top vent closed increases significantly with
an increase in pool size, compared in cases with top vent open. It is
possible that the hot smoke produced by fire source gathers more easily
due to smaller air flow speed in cases with top vent closed.
[FIGURE 9 OMITTED]
The hot smoke produced from fire source in fire room spread to
atria and stairwell successively after ignition. The temperatures of
stairwell increase and lead to the occurring stack effect which
significantly influence the fire behaviours in fire room. The strength
of stack effect is closely related to the temperature of stairwell, so
we record the temperatures of hot smoke to analysis the air flow pattern
and the influence of stack effect on fire in the compartment. Taking
Case B4 (pool size: 25 cm, top vent: open, door 3 size: 0.24 [m.sup.2])
for example, the fire room temperature, stairwell temperature and
airflow speed V are shown in Figure 10. As can be seen from Figure 10,
the temperature in the fire room (T3 and T11) firstly increases after
ignition, and then the hot smoke induced by buoyancy spreads to the
atria and stairwell. At about 25 s, the hot smoke from fire room flows
in the stairwell and the temperature in the first floor of stairwell
(T36) begins to rise. Then the hot smoke start to spread upward and the
temperatures increase gradually in the stairwell. When the temperature
of T3 (inside the door 3) decreases firstly at about 70 s, which
indicates that the hot smoke is no longer outflow the fire room and the
fresh air is sucked into the fire room by the stack effect action. It
can be concluded that at about 70 s, the stack effect begins to occur.
After more cooling fresh air flowing into the fire room, at about 80 s,
the temperature above fire source (T11) also begins to decrease. As time
passed, at about 140 s, it can be found that the temperature of T47
(located in 12 floor of stairwell) begins to increase, which indicates
that the hot smoke spread to the twelfth floor of stairwell and flow out
from the top vent. Meanwhile, the temperature of T3 decreases to the out
door temperature after a long time of air cooling effect. It also can be
seen that the velocity of air flow through door 3 enters the slow growth
stage after a dramatic increases from 0-140 s. From these changes in
temperature and velocity in Figure 10, it can be concluded that the
stack effect begins to occur at about 70 s and almost completely forms
when the hot smokes spread to the twelfth of stairwell at 140 s, and
then all the parameters have little change, but the temperature of T11
fluctuates significantly after 350 s, a possible explanation for this is
that the heat release rate of fire source show a great fluctuation under
the influence of the transverse air flow, which will be proved in the
following section about mass loss rate.
[FIGURE 10 OMITTED]
2.3. Mass loss rate
The electronic balance recorded the instantaneous mass loss of
methanol fuel in different cases in this experiment. Taking 25 cm pool
size for example, the curves of mass vs. time and the mass loss rate in
different cases are shown in Figure 11. It is shown from Figure 11 that
before the occurrence of stack effect in the stairwell (about 70 s), the
mass loss rates of 25 cm pool size in four cases are almost same, and
then the mass loss rates decrease with the strength increasing of stack
effect. In the case C4 with top vent closed, from about 70 s to 200 s,
the mass loss rate is slightly smaller than the value in case in open
space. After 200 s, the velocity of air flow from the outside induced by
natural air supply is relatively small, and so the mass loss rates in
two cases are almost the same. It can be concluded that for the cases
with top vent closed, after the smoke reaches the twelfth floor of the
stairwell, the combustion of the pool fire achieves the relatively
stable state and the heat release rate is slightly influenced by the air
flow from the outside. However, in cases B4 and A4 with top vent opened,
after the occurrence of stack effect, the velocity of air flow from the
outside induced by the stack effect is relatively large. The mass loss
rates fluctuate significantly and the averages are smaller than that in
open space, indicating a smaller heat release rate. Therefore, as seen
from Figure 11, the whole burning times in open space and cases C4 are
less than that of Case A4 and Case B4.
[FIGURE 11 OMITTED]
The fresh air sucked into fire room due to stack effect influences
the burning rate of pool fire. Generically, in a single compartment, the
fresh air flow has two opposing effects (Huang et al. 2009; Chen et al.
2008; Woods et al. 2006; Kumar, Naveen 2007). One is to promote
combustion within the compartment and thus raise the temperature, the
other is to blow away and dilute the combustible gases in the
compartment and decrease the temperature, or hasten its extinction.
Which effect predominates mainly depends on the airflow velocity. The
average mass loss rates in steady state in all cases are plotted in
Figure 12. It is obvious that the average mass loss rate increases as
pool size increases. For 10 cm and 15 cm pool size, the mass loss rates
in all the cases are almost the same as those in open space. However for
20 cm and 25 cm pool size, the mass loss rates in cases with top vent
closed (case C3-C4) and open space are larger than those in cases with
top vent opened (case A3-A4 and case B3-B4), which indicates that the
second effect predominates and leads to reduce the burning rate of the
methanol pool fire. This result can be supported by those data from
Figure 9. It is clearly seen from Figure 9 that the temperatures of
upper hot gases in fire room in case A3-A4 and case B3-B4 are very low,
about 40[degrees]C, after the strong stack effect forms.
Roh et al. (2007a, b) discovered that the burning rate of methanol
pool fire with different pool length decreased with the transverse air
flow velocity ranged only from 0 to 1.68 m/s. This is different with the
results obtained by our experiments. From the data in Figure 6, the
maximum of the velocity of air flow is 0.62 m/s in case C1-C4, but the
burning rate is the same as that in open space and do not decrease
obviously. One possible reason is that the fire is located in a small
compartment and the temperature in the room is higher when the top vent
of stairwell is closed (as shown in Fig. 9). The fire-induced smoke and
walls in the compartment with high temperature result in high heat
feedback to fire source. This is different with the situation described
in Roh's research (2007a, b). The temperature around the fire
source decreased rapidly after flame tilt under the transverse air flow
action in tunnel, and then the radiant heat feedback from the hot smokes
and tunnel walls reduced significantly leading to decreased burning
rate. The cases where the top vent of stairwell is open (case A3-A4 and
case B3-B4) are similar with the situation in the tunnel. The stronger
air flow occurs in the compartment with two opposite doors at the two
sidewalls. So the temperature around the fire source decreases obviously
by the action of air speed from 0.88-1.03 m/s (as shown in Fig. 9) and
the burning rate of methanol fuel decreases in case A3-A4 and case B3-B4
(as shown in Fig. 12).
[FIGURE 12 OMITTED]
The strength of stack effect influenced directly by the heat
release rate determines the size of the air flow speed. Therefore, the
air flow speed through door 3 and heat release rate may have a certain
relationship. Tanaka et al. (2000) discovered the relationship between
the plume velocity at the shaft and heat release rate of fire source
located at the centre of shaft bottom as follows:
w [varies] [square root of
(g)][([??]/[c.sub.p][[rho].sub.z][T.sub.0][square root of (g)]).sup.1/3]
[(Z/A).sup.1/3], (3)
where: w is the plume velocity at the shaft; Z is the height above
the source; [??] is the heat release rate of the fire source; [c.sub.p]
is specific heat of air at constant pressure; [[rho].sub.Z] is
characteristic density of smoke at Z; g is the acceleration due to
gravity; [T.sub.0] is ambient temperature; A is the horizontal section
area of the plume at the shaft.
It is obviously seen from the Eqn (3) that the velocity of plume at
the shaft is proportional to 1/3 to the heat release rate. However, in
this study, the fire source located at the centre of room and the shaft
was replaced by stairwell. The fresh air was sucked into fire room only
through door 3. When the top vent of stairwell is open, all the hot
smoke from the fire room spread to the atria and stairwell in steady
state after ignition. In addition, the methanol is clean fuel, and the
smoke produced during combustion is very little. So based on ideal plum
theory, the mass flow rate of plum fire is approximately equal to the
mass flow rate of air flow through Door 3. According to conservation of
mass, the mass rate of air flow into fire room is equal to that of the
plume through the horizontal section area at the shaft, as follows:
[[rho].sub.z]Aw = [[rho].sub.0]SV, (4)
where: [[rho].sub.0] is ambient air density; S is the size of Door
3; V is the velocity air flow into the fire room through door 3.
Based on the state equation of ideal gas, the following relation
can be obtained:
[T.sub.0][[rho].sub.0] = [T.sub.z][[rho].sub.z]. (5)
Substituting Eqns (4) and (5) into Eqn (3) yields the relationship
as follows:
V [varies] [square root of
(g)][([??][T.sub.z]/[c.sub.p][[rho].sub.0][T.sup.2.sub.0] [square root
of (g)]).sup.1/3] [(Z/A).sup.1/3] A/S [T.sub.0]/[T.sub.z], (6)
where [??] can be calculated according to the follow equation:
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (7)
where: [lambda] is combustion efficient and can be approximately
equal to 1 for the methanol; [??] is mass loss rate; [DELTA]H is heat of
combustion, this [DELTA]H = 20 KJ/g.
It is obviously found from the Eqn (6) that the velocity of air
flow into fire room is proportional to 1/3 power of the heat release
rate of fire source located at the centre of fire room in the building
model. The experimental data in cases with top vent opened (case A1-A4
and case B1-B4) is shown in Figure 13. Those data indicate that the
liner relationship between air speed V and heat release rate
[[??].sup.1/3] claimed by Tanaka et al. (2000) is reliable and accurate
in the stairwell. The present results can provide data and be used as a
reference for the researchers and engineers of high rise building fire
protection.
[FIGURE 13 OMITTED]
Conclusions
In this paper, to study the influence of stack effect on fire in
the compartment adjacent to the stairwell, a total of 12 experiments
were conducted by varying the pool size (10, 15, 20, 25 cm), top vent
state (open or close) and size of door 3 on the ground floor (0.12 or
0.24 [m.sup.2]) in a 1/3 scaled 12-layer-stairwell configuration. The
temperatures and fire properties in the compartment were investigated.
The results are summarized as follows:
--The methanol flame inclines towards the direction of stairwell
under the influence of stack effect after ignition. The flame tilt angle
[theta] is influenced by the air flow and remarkably enlarged by the
stack effect action. The results show that the flame tilt angle [theta]
increases with an increase in [Ri.sup.-1].
--The mean temperatures in the fire room in cases with top vent
opened decrease due to the cooling effect of fresh air sucked into fire
room induced by stack effect, and the time of temperature of hot smoke
began to decrease is earlier with an increase in pool size. It is
because that the stack effect occurs earlier and is stronger for the
bigger pool size. When the hot smoke rises to the top floor, the stack
effect almost completely forms and is extremely obvious. The
temperatures in the fire room almost decreases to minimum and the air
speed through door 3 almost increases to maximum, and then all the
values do not change significantly.
--The fresh air sucked into fire room due to stack effect plays a
significant role in the burning rates of pool fire. The burning rates of
the methanol pool fire decrease in cases with top vent opened. The
reason for this phenomenon is that the fresh air induced by the stack
effect blows away and dilutes the combustible gases in the compartment.
In addition, the air flow speed and heat release rate have a certain
relationship. The results indicate that the velocity of air flow into
fire room is proportional to 1/3 power of the heat release rate in the
stairwell.
Nomenclature
Ri--Richardson number;
g--gravity acceleration (m/[s.sup.2]);
Z--height above the source (m);
L--pool length (m);
[DELTA]T--pressure difference caused by the stack effect (Pa);
[??]--heat release rate (kW);
[c.sub.p]--specific heat of air at constant pressure (J/kg x K);
[DELTA]H--heat of combustion (kJ/kg);
[T.sub.0]--air temperature (K);
[T.sub.f]--flame temperature (K);
V--air speed through door 3 (m/s);
w--plume vertical velocity at the shaft (m/s);
A--horizontal section area of the plume at the shaft ([m.sup.2]);
S--size of door 3 ([m.sup.2]).
Greek symbols
[DELTA][rho]--the density difference between the air and the
products of combustion (kg/[m.sup.3]);
[rho]--density (kg/[m.sup.3]);
[[rho].sub.a]--density of the air upstream of the pool;
[[rho].sub.Z]--characteristic density of smoke at Z;
[theta]--flame tilt angle ([degrees]);
[lambda]--combustion efficient.
Subscript
0--outside air; f--flame; z--height above the source.
doi:10.3846/13923730.2013.802729
Acknowledgement
This research was supported by the National Basic Research Program
of China (973 Program) under Grant No. 2012CB719700, National Natural
Science Foundation of China under Grant No. 91024027 and the Fundamental
Research Funds for the Central Universities under Grant No.
WK2320000014.
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Wen Xi SHI (a, b, c), Jie JI (a), Jin Hua SUN3 (a, c), S. M. Lob
(b, c), Lin Jie LI (a), Xiang Yong YUAN (a)
(a) State Key Laboratory of Fire Science, University of Science and
Technology of China, Hefei 230026, China
(b) Department of Civil and Architectural Engineering, City
University of Hong Kong, Hong Kong, China
(c) USTC-CityU Joint Advanced Research Centre, Suzhou, China
Received 26 May 2012; accepted 28 Jun 2012
Corresponding author: Jie Ji
E-mail: jijie232@ustc.edu.cn
Wen Xi SHI. A doctoral student of University of Science and
Technology of China from September 2011 to present, and he has
participated in joint training project of the University of Science and
Technology of China and City University of Hong Kong in 2010. His
research interest includes smoke spread and control method in high rise
buildings.
Jie JI. An Associate Professor of State Key Laboratory of Fire
Science, University of Science and Technology of China, and is also a
life member of International Association of Fire Safety Science. He
received his PhD degree in Fire Safety Engineering from University of
Science and Technology of China in 2008. His main research interests
include smoke movement and ventilation control method in building fires
and characteristics of flame spread over surface of solid combustibles.
Jin Hua SUN. A Professor and Vice Director of State Key Laboratory
of Fire Science, University of Science and Technology of China. He is
also a Vice Chairman of Asia-Oceania Association for Fire Science and
Technology and Director of the International Association for Fire Safety
Science. He received his PhD from the University of Tokyo in 1999. To
date he has authored over 200 research papers of which 100 were indexed
by SCI and EI, including over 20 published in h-factor top journals and
six books. His main research interests include fire dynamics and basic
fire prevention technologies, large-scale evacuation and rescue in
emergencies, hazardous chemical disaster prediction and prevention
methods.
S. M. LO. A Professor of the Department of Civil and Architectural
Engineering, City University of Hong Kong. He received his PhD in
Architecture from the University of Hong Kong and is an Authorized
Person registered under the Hong Kong Buildings Ordinance. His main
research interests include building design, spatial planning for
pedestrian flow and evacuation, decision support system and fire safety
engineering.
Lin Jie LI. A doctoral student of University of Science and
Technology of China from September 2011 to present. His research
interest includes smoke spread and control method in high rise
buildings.
Xiang Yong YUAN. A postgraduate of University of Science and
Technology of China. His research interest includes smoke spread and
control method in high rise buildings.
Table 1. Experimental details
Case Pool Size 1F-Door 3 Size Top Vent V (m/s)
(height x width)
A1 10 cm x 10 cm Open 0.6
A2 15 cm x 15 cm 0.3 m x 0.4 m 0.78
A3 20 cm x 20 cm 0.98
A4 25 cm x 25 cm 1.03
B1 10 cm x 10 cm Open 0.53
B2 15 cm x 15 cm 0.6 m x 0.4 m 0.67
B3 20 cm x 20 cm 0.88
B4 25 cm x 25 cm 0.95
C1 10 cm x 10 cm Close 0.24
C2 15 cm x 15 cm 0.6 m x 0.4 m 0.39
C3 20 cm x 20 cm 0.46
C4 25 cm x 25 cm 0.62
Case Flame tilt [[Ri.sup.-1]
angle [theta]
A1 62[degrees] 0.51
A2 71[degrees] 0.58
A3 73[degrees] 0.69
A4 60[degrees] 0.6
B1 59[degrees] 0.4
B2 67[degrees] 0.43
B3 72[degrees] 0.55
B4 61[degrees] 0.52
C1 34[degrees] 0.08
C2 31[degrees] 0.14
C3 41[degrees] 0.15
C4 47[degrees] 0.22
