The Simulation of Fires in Underground Parking Floors by Fire Dynamic Simulator

Abstract

Traffic flow in cities is increasing rapidly as cities modernize. The problem of parking is getting worse and worse due to insufficient parking lots in large cities, and people are paying more attention to safety issues in buildings due to the development of underground parking floors. There are new problems for fire safety because a building's functions and materials, structural type, size, and supporting facilities are very different between the traditional buildings and buildings with underground parking floors. When a fire occurs in an enclosed underground parking floor, it is hard for people to evacuate due to incomplete combustion producing heavy smoke. In this work, we use the Fire Dynamic Simulator (FDS) to study the effect of a mechanical smoke ventilation system to retard the development of a smoke layer. The simulated results indicate that, although the installation of a mechanical smoke ventilation system would retard the deposition of a smoke layer, fresh air also drawn in increases the heat release rate of a car fire. Most importantly, a mechanical smoke ventilation system can extend the escape time for people during the initial stages of a fire.

Full text

429
Sensors and Materials, Vol. 29, No. 4 (2017) 429–443
MYU Tokyo
S & M 1336
*Corresponding author: e-mail: hmw6789@yahoo.com.tw
**Corresponding author: e-mail: wtm@cc.kyu.edu.tw
http://dx.doi.org/10.18494/SAM.2017.1525
ISSN 0914-4935 © MYU K.K.
The Simulation of Fires in Underground Parking Floors
by Fire Dynamic Simulator
Ming-Wen Hsu,* Shin-Ku Lee,1 Lin-Lin Huang,2 Yaw-Kuang Chen, and Chun-Mu Wu3**
Department of Architecture, National Cheng-Kung University, Tainan, 701, Taiwan, R.O.C.
1Research Center for Energy Technology and Strategy, National Cheng-Kung University, Tainan, 701, Taiwan, R.O.C.
2Department of Architecture and Interior Design, Cheng Shiu University, Kaohsiung 833, Taiwan, R.O.C.
3Department of Mechanical Engineering and Automation Engineering, Kao Yuan University,
Kaohsiung 821, Taiwan, R.O.C.
(Received August 30, 2016; accepted January 12, 2017)
Keywords: undergroundparkingoor,FDS,smokeventilationsystem
 Trac ow in cities is increasing rapidly as cities modernize.  The problem of parking is
gettingworseandworseduetoinsucientparkinglotsinlargecities,andpeoplearepayingmore
attentiontosafetyissuesinbuildingsduetothedevelopmentofundergroundparkingoors.There
arenewproblemsforre safetybecauseabuilding’sfunctionsandmaterials,structural type,size,
and supporting facilities are very dierent between the traditional buildings and buildings with
underground parking oors.  When a re occurs in an enclosed underground parking oor, it is
hard for people to evacuate due to incomplete combustion producing heavy smoke. In this work,
we use the Fire Dynamic Simulator (FDS) to study the eect of a mechanical smoke ventilation
system to retard the development of a smoke layer. The simulated results indicate that, although the
installation of a mechanical smoke ventilation system would retard the deposition of a smoke layer,
freshair alsodrawninincreases theheatreleaserateof acarre.Most importantly,amechanical
smokeventilationsystemcanextendtheescapetimeforpeopleduringtheinitialstagesofare.
1. Introduction
 Withacceleratingurbanmodernizationanddevelopmentoftheautomobileindustry,thequantity
and volume of trac due to automobiles and motorcycles in cities increases continuously. The
parkingdicultiesresultingfrominsucientparking facilities has become increasingly severe in
thelargecitiesofTaiwan.Theunsustainablegrowthofparkingdemandandrelativelyinsucient
supplyofparkingfacilitieshavebroughtaseriesofproblemstourbandevelopment,suchastrac
jams resulting from vehicle parking, trac volume resulting from looking for a parking space,
environmental pollution resulting from slow running while looking for parking. This parking issue
has become a bottleneck that obstructs the further development of the national economy. Therefore,
some large cities have actively developed public underground parking buildings and aerial parking
forbusy areas withinsucient land resources. As these undergroundparking buildings are very
dierent from traditional architecture, building materials, structural style, size, and supporting
facilities,theycausemanynewproblemsforresafety.

430 Sensors and Materials, Vol. 29, No. 4 (2017)
 The annual re accident rate in parking lots increases with their annual usage.  For this
research, 5 re accidents occurring in underground parking oors have been collected from the
literature. The descriptions are as follows: On February 12, 2007, the underground parking in a
23-storyamalgamated buildinginTaichungCitysueredare atabout6p.m.,in whichoneman
died and two persons had slight smoke inhalation.  The eld remen connected smoke exhaust
fans to the smoke extraction pipes to extract the dense smoke from the basement. On March 27,
2014,thebasementofabuildinginTaipeiCitysueredare,andaconagrationbrokeoutatthe
scene while the re department was rescuing people.  Five remen were injured and sent to the
hospital, and the 36 year old team leader of Huashan Station lost his life while being transported
to the National Taiwan University Hospital. On June 27, 2014, the underground parking in an
amalgamatedbuildinginNewTaipeiCityraisedarealarmat9:45p.m.,andthelocalrebureau
sent out rescue personnel; according to the report, a reman went downstairs to search for the
originof the reandanypersonsin trouble andexperiencedseriouschokingwhen he inhaledtoo
muchhightemperaturedensesmoke.Althoughhewassenttothehospital,thereghterdied.At
about 7:45 a.m. on November 20, 2014, in the underground parking area of the legislator research
buildingoftheLegislativeYuan,awhiteBMWcarbegantosmokeandcaughtre,andalthough6
or7reextinguisherswereemptied,therewasnotextinguishedandthedensesmokeobstructed
escape.OnMarch22,2015,arebrokeoutintheundergroundparkinglotofa7-storyapartment
buildinginTainanCity,andonewomandied.Inrecentyears,undergroundreshavecausedmany
casualtiesamong remen.Whether byaccidentorarson,most automobileresarecausedby re
inthe engine bay. Toextinguishsuchare,theenginehoodmustbeopened, and other oils may
ignite,causingtheretospread.Whenuntrainedpeopletrytoextinguisharebythemselves,they
maymisstheopportunitytoescape,especiallyfromwithintheconnesofanundergroundparking
facility, as the parked vehicles make the re and smoke dicult to control; such dense smoke
mayresult in poor visibility within a few minutes, andif the re extinguisher fails to eectively
extinguishthere,themediumfromthereextinguisherswillacceleratetheeectofthere;when
extinguishing fails and they attempt to escape, the diused extinguishing medium may obstruct
theirescape.  In addition, dense smoke mayobstruct the remen’sabilityto search for survivors
andthe origin of re.An eectivelayout of mechanical smoke vents is veryhelpful for people’s
escapeandremen’sabilitytorescue,andwhencombinedwithautomaticresprinklersorreor
smokecompartments,theymayaugmenttheeciencyofreprotectionfortheentireunderground
parking space.
The most combustible items in underground parking areas are automobiles, which consist of
complexpartscomposedofinammableoils(e.g.,gasolineandengineoil),foam,rubber,batteries,
andplastics;thus,whenareoccurs,itspreadsquicklyandproducesagreatdealofdensesmoke.
Therearenumerouscausesforvehicleres,andthecommonconditionsaredescribedasfollows:(1)
(1) Fuel system leak
 The ash point of 95 unleaded gasoline is −43–−38 °C (−45–−36 °F), and the self-ignition
temperatureis280–456°C(536–853°F);theashpointofdieseloilis>52 °C(>125.6°F),andthe
self-ignition temperature is about 177 °C (351 °F).Thedatashowthataashremayoccuriffuel
vaporcontacts a spark;forexample,thehightemperature ofanexhaustpipeissucient for even
dieseloilfueltoinitiateamassreinsuchcases.
(2) Wire sparking or electrical faults
 Like residential res, many underground parking res are caused by a sparking wire instead
of a gas leak. The electric wiring in vehicles is aged by long-term over-heating, even though

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the material is more resistant to heat than general household wire. The storage battery is another
problem; if the charge/discharge condition is poor or a poor storage battery is used, the storage
battery may explode.
(3) Lubricating oil leak in an engine bay
A part of the leaking vehicle phenomena results from long-term aging, and part results from
faults.Whileenginesleakingoilandtransmissionuidaremostfrequentlyseen,theoilforpower
steering,brakeuid,andgasoline/dieseloilmayalsoleak.Basically,suchoilproductsusuallyleak
fromthe spaceroroilseal;however,leaksmostfrequently occurintheenginebay. Manypeople
maynot know that cooling uid leaks may cause re as well, because the cooling uid contains
a large amount of ethylene glycol, which is inammable.  In addition, some of these oils are
comburent,especiallytherequisitegasoline/dieseloilforenginecombustion,whichistheoptimum
combustible,and ifitleaks,serious hazardsarise.Thesehazards includethedesignofthe system,
as the gasoline/diesel oil pipes in many vehicles go through the front and rear ends of a vehicle at
the bottom.
(4) Engine overheating
The automobile engine is a large metal block which does not burn. There is only one cause for
an engine to overheat: poor heat radiation. There are many causes for poor heat radiation, such as
cooling tank faults, cooling fan faults, and coolant loss; however, the cooling system is usually the
cause. Incomplete combustion is also a cause, where unburnt gas continues to burn in the exhaust
manifold, resulting in high temperatures. When the engine is overheated, and as the catalytic
converter is overheated, the peripheral comburents reach the combustion temperature and burn. In
addition, there are more peripheral components than the catalytic converter, such as the many wires,
joints, plastic containers, plastic pipes, oils, and fuel pipes around an engine, which all age with
high temperature and may melt due to excessive temperature. Some components are combustible
aftertheyaremolten,whilesomeliquidsarecomburentaftertheyleak(e.g.,engineoil).
(5) Catalytic converter overheating
 Forthecurrentinternalcombustionengine-basedvehicles,theexhaustsystemisequippedwith
acatalyticconverter,whichhasthebasicfunctionofoxidizingtheHC,CO,andNOx in the exhaust
system into water and CO2, and reducing part of the NOx to nitrogen. As the catalytic converter
must convert HC, CO, and NOx simultaneously, it is also known as a three-way catalytic converter.
In a general manner, the operation of a catalytic converter requires a xed temperature range,
and it will become overheated if forced to work in a high temperature range for a long time, thus
constitutingtheheatsourceforare.Iftheconverterexistsinanoverheatedoperatingrangefora
longtime,thereisprobablyaproblemwiththecombustioneciencyoftheengine.
(6) Arson
Cases of arson, which may be arise from emotion or money, are often seen on the news. Arson
is unlike the indirect or direct factors of vehicles seen in the previous cases; its burn is the fastest,
the least preventable, and it usually results in property loss and casualties.
 Are in an underground parking space behavesasfollows:“the environmental space opening
is limited and conned; lighting is insucient; the smoke is dicult to exhaust, control, or
extinguish”;“theoutsideairsupplyislimited;incompletecombustionmayproduceagreatdealof
dense smoke, especially when burning cables and wires produce toxic gas, obstructing those inside
from escaping and remen from rescuing”; “as the space is conned, heat radiation and smoke
extractionaredicult,hightemperatureislikelytocausetherescenetemperaturetoriserapidly,
thus obstructing the initial rescue and escape, which may cause heavy casualties and evolve into a
severe disaster”.(2)

432 Sensors and Materials, Vol. 29, No. 4 (2017)
 Chen indicated that “underground buildings” include basements, underground streets, and
underpasses and that the structures of underground buildings are very similar to conned high-
rise buildings.  Therefore, an underground building re has similar features to a high-rise re.(2)
Undergroundparkingisatypeofbasement,anditscharacteristicsareclassiedasfollows:
1. Theresceneisreachedthroughstairsoraliftduringrerescue.
2. Whenanundergroundbuildingisonre,itislledwithdensesmokeandtoxicgases,because
therearefeweropeningsontheundergroundoor,theairisinsucient,andreismorelikely
to produce a great deal of dense smoke.
3. The heat cannot dissipate; the storage of heat certainly leads to high temperatures. As the
undergroundareaofabuildingis completelyconned,theretemperatureisoftenhigherthan
1000 °C.
4. Therespreadsupwardrapidlyinanundergroundbuilding,andonce an undergroundooris
onre,theoorsunderthegroundoorareinimmediatedanger.
5. Itisdiculttoescapefromanundergroundbuilding,theundergroundoorisdark,andwiththe
obstructionofcompartments,passages,doors,orotherspace,itisverydiculttoescape,andin
the dense smoke and high heat, life is endangered in a short time.
6. It is very dicult to carry out a rescue from underground buildings when an underground
oorhasa high temperature.  Becausetherescuers must carry respirators,theycannot remain
undergroundforlong.Inaddition,itisdark,diculttojudgetheextentofthecombustion,and
eectiveprotectioncannotbeadopted.
 In addition to the features similar to a high-rise re, underground parking has the following
special characteristics:
1. Theundergroundbuildingrescenechangesfromtimetotime.
2. The rescue work is dangerous.
3. Itisdiculttondtheoriginofthere.
4. Itisdiculttounderstandthere’sdevelopment;
Chung and Chiu(3) described the characteristics of underground building spaces (including
underground parking spaces):
1. As the opening into the space is limited and conned, it is dicult to perceive the internal
condition of the underground building space from aboveground; it is dicult to know the
ground conditions in an underground building.
2. Undergroundbuildingshavecomplexstructures,andtherescenechangesquickly,presenting
a very unstable state.
3. It is dicult to nd the re’s origin and control its behavior in an underground building,
remen’srescue islikely to belimited by the distance between the gateway andthe origin of
there,andthepath andspaceleadingtotherecannotcontaintoomany rescuepersonnelor
equipment,orreinforcementwillberestricted.
4. As underground building spaces are without windows or are conned spaces without open
oors,theoutsideairsupplyisrestricted.Thus,duetotheinsucientairforare,combustion
will remain in the smoldering state, rendering the problem of dense smoke more severe,
especiallyinareofsmoke-producingmaterials,suchascablesandelectricalequipment.
5. If the underground space is connected to other facilities, wherever a re breaks out, it may
spread to the other side.
6. The water jetted by an automatic re-extinguishing system or a remen’s hose is likely to
accumulate, thus obstructing rescue and escape, and resulting in heavy water damage and loss.

Sensors and Materials, Vol. 29, No. 4 (2017) 433
Zhang et al.(4) simulated re spread and fume ow in a simulated underground parking lot,
and the re spread rate and ow of smoke were observed under dierent ventilation conditions
by setting the same automobile re heat release rate.  The plume in the parking space was very
disorderlyat15min,andtherebehaviorwasexpanded,makingrescueandescapedicult.Merci
and Shipp(5)discussedtheeectofsmokeandtemperatureonan undergroundparkinglot,smoke
extraction by mechanical ventilation, and the dynamics of smoke and heat. The condition of spray
sprinklers was input into the probable result, and the probabilities were studied. Deckers et al.(6)
testedfumecontrolinalarge-scalemotorparkusingcomputationaluiddynamics(CFD)software
tosimulatetheeectofmechanicalsmokeextractiononthefumeandfoundthat,ifthesmokewas
stuckintherecirculationzone,evenifthesmokeextractionratewasincreased,itwasimpossibleto
eliminate the smoke layer.
In this study, we use the Fire Dynamic Simulator (FDS) to observe the generation time and
rangeof dense smokein an undergroundparking re anddiscuss a mechanicalsmoke extraction
system to study how to postpone the smoke layer generation time and prevent a disaster from
developing further.
2. Methodology
2.1 Basic theory and governing equation of FDS
This study uses FDS 6.0 to build the experimental model and discusses smoke movement, the
reheatreleaserate,andsmokeheight inanundergroundparkingoorre.Thecharacteristicsof
FDS 6.0 are described as follows:(7,8)
 FDS is a eld-based re simulation software developed by the Building and Fire Research
Laboratory, National Institute of Standards and Technology (NIST). It is a CFD model, which
takestheuidmotioninareasthe mainmodelobject.Theresultsofcalculationsareprocessed
by post-processing software (Smokeview), with which the plume, gas temperature distribution,
and ow eld distribution in the re scene are displayed in animation, the re scenario can be
establishedrapidly,andtheresceneinformationcanbeknownintime.Theprocessstructureand
leformatofFDSandSmokeviewareshowninFig.1.
 FDS is a special computational uid dynamics software using 3D numerical calculation to
simulate the air ow driven by re buoyancy. The core of the software is the Navier–Stokes
equationset.Theequationsaredescribed,asfollows:
1. Massconservationequation
∂ρ
∂t
+∇ρu=
0
· (1)
ρ:uiddensity(kg/m3)
u:uidairvelocity(m/s)
2. Momentumconservationequation
ρ
∂u
∂t
+(u·)u+∇p=ρg+f+∇τ
∇
[
[
· (2)

434 Sensors and Materials, Vol. 29, No. 4 (2017)
p: pressure (Pa)
f: external force term, including friction (N), resulting from water droplets sprayed from the
sprinkler head
g: gravity + air velocity (m/s2)
τ: viscous stress tensor
3. Energyconservationequation
∂
∂t(ρh)+∇·ρhu =
Dp
Dt −∇·q+∇·k∇T
r+
l
∇·hlρDl∇Yl (3)
h: entropy (J/kg)
k: thermal conductivity (W/m·K)
T: temperature (K)
Dl:diusioncoecient(m2/s)
Yl: mass fraction of species l
4. Speciesconservationequation
∂
∂t
ρYl+∇·ρYlu = ∇·(ρD)l∇Yl+˙m′′′
l
(
(
(4)
ml′′′:massproductionrateperunitvolumeofspeciesl
5. Idealgasequation
p = ρRT (5)
Fig.1. OrganizationalstructureandsimulationcomputingprocessofFDSandSmokeview.

Sensors and Materials, Vol. 29, No. 4 (2017) 435
 TheFDS classiesthetemperature,density,andpressureintospatiallyaveragedquantitiesand
perturbationsaccordingtotheBoussinesqapproximationequation,whichisexpressedasfollows:
T=T0(t)1 + ˜
T
( )
(6)
ρ=ρ0(t) (1 + ˜ρ)
(7)
p(r,t)=p0(t)−0(t)gz +˜
p(r,t)ρ
(8)
 The spatially averaged quantity can be expressed by Eqs. (1), (2), and (5), and the adiabatic
process is as follows:
p0
∂Ω
u·dS+
V
γ
dp
0
dt
=
γ−1
γΩ
qdV +
∂Ω
k∇T·dS (9)
p0 = ρ0RT0 (10)
ρ0
ρ
∞
=p0
p
∞
1
γ (11)
The perturbation of velocity, temperature, and pressure can be expressed as:
∂˜
T
∂t
+u·∇˜
T= 1 + ˜
T∇·u+
dp
0
dt
(12)
∂u
∂t
−u×ω+∇H=
1
ρ
(ρ−ρ∞)g+f+∇·τ
[
[
(13)
∇
2H=−
∂∇·u
∂t
−∇
F
()
(14)
where H is the total pressure,
H
=
˜p
ρ0
+
|u|2
2
(15)
F
=−u×ω−
1
ρ
(ρ−ρ∞)g+f+∇·τ
[
]
(16)
 Tosumup,FDSusestheenergyequation,Eq.(13),themomentumequation,Eq.(14),thetotal
pressureequation, Eq. (15), and the spatial average temperature, density,and pressure equations,
Eqs. (9)–(11), to compute the velocity, temperature, density, and pressure of the computational
domain.In terms of the numerical method of the governing equation, FDS uses the second-order
central dierence method for the derivative term of space coordinates and uses the dominant
second-order Runge–Kutta method to discretize the derivative term of time. The total pressure
dierentialequationinthePoissonequationformiscomputeddirectlyusingfastFouriertransform.

436 Sensors and Materials, Vol. 29, No. 4 (2017)
2.2 Undergroundparkingremodelsetting
The subject selected for simulation in this study is a one-story underground parking lot, which
is36mwide,36m long, and 3 m high. Atwo-way entrance–exit islocatedonboththeleft and
right, and the lane is at the bottom left corner. There are 21 cars parked in the parking lot. Each
caris 4.6mlong,1.9m wide,and1.4mhigh. Theinammable materialsaresetasgasoline and
afoamingsubstance,andthere arethreereoriginsinthisstudy.Therstreoriginisset asthe
rstcaron the upper left; the second re originissetastherstcarontheleftofthe lower row;
thethird re origin is set as therst car on the right of the lower row(labeled in red in Fig. 2).
There are six smoke height monitoring points shown in Fig. 3. The smoke height is estimated from
a continuous vertical prole of temperature.  The method(9,10) is described as follows: Consider a
continuous function T(z)deningtemperatureTasafunctionofheightabovetheoorz, where z =
0istheoorandz = Histheceiling.DeneTu as the upper layer temperature, Tl as the lower layer
temperature, and zintastheinterfaceheight.Computethequantities:
Tu + zintTl =
H
0
T (z) dz = I
l
H−zint (17)
H−zint
1
Tu
+zint
1
Tl
=
H
0
1
T(z)
dz =I
2
(18)
Solve for zint:
Fig.2. (Coloronline)Thereignitionlocationsdenedinthisstudy.
Fig. 3. (Color online) Location of smoke height monitoring systems.
(a) (b) (c)
(a) (b)

Sensors and Materials, Vol. 29, No. 4 (2017) 437
zint =
l
I1I2−H
2
I1+I2T
2
l−2TlH
T (19)
Let Tl be the temperature in the lowest mesh cell and, using Simpson’s Rule, perform the
numerical integration of I1 and I2. Tuisdenedastheaverageupperlayertemperaturevia
H − zint T
u
=
H
zint
T(z)d
z
(
) (20)
 In addition, this paper discusses the eect on the smoke height and re heat release rate of
mounting one and two mechanical smoke vents. The smoke vent is 0.5 m long and 0.5 m wide, and
its location is shown in Fig. 4. The computing grids used in this study are the maximum grid at 0.36
m and the minimum grid at 0.2 m; thus, the total number of computing grid points is 150000 (100 ×
100 × 15).
3. Results and discussion
Case1:Undergroundparkingreinactualstate(withoutmechanicalsmokeventilation)
To obtain a basis for comparison, the condition of an underground parking lot without a smoke
extractor is simulated rst.  The simulated result in Fig. 5 shows that, when the rst car on the
upperleftoftheparkinglotisthere’sorigin,thesmokelayerattheS1monitoringpointdescends
Fig. 4. (Color online) Location of smoke vents. (a) Case 2 and (b) Case 3.
(a) (b)
Fig. 5. (Color online) Analysis of smoke height without smoke vent (Case 1-1).
(a) (b)

438 Sensors and Materials, Vol. 29, No. 4 (2017)
to a height of about 2.3 m at 20 s, and visibility is sucient for escape, as most of the smoke
layeraccumulatesnearthe re’sorigin, andtherehas not yet spread. At 50 s, the smokelayer
beginstodepositnearExit2,andthesmokeheightisabout1.5m.At80sofre,theheightofthe
neutral plane of the smoke layer at the S1 monitoring point is about 2 m, the smoke layer at the S2
monitoringpointdescendstotheheightof about1.6m, therebeginstospread,andvisibilityfor
escapeis severely inuenced. At 100 s, the smoke layer does not descend continuously,and the
smokeheight is1.6–2m. However,asthe rehasspread,the areaofthesmokelayer expandsto
the lane, thus severely obstructing escape.
 Figure6 shows thesmokedepositwithoutasmoke vent when therstcaronthelower left of
theparkinglotison re.Thesmoke layer begins to deposit attheS2monitoringpoint under the
eectofthesmoke plume; however,as the smoke layercontinuesto diuse horizontally,itstops
depositing downward, and the smoke height is maintained above 2 m. The smoke deposits at the
S4 monitoring point at 40 s, rapidly descends to 0.7 m, and most of the dense smoke is discharged
through Exit 2; thus the smoke height at S4 returns to 1.7 m. However, the dense smoke begins to
aecthumansightifpeoplelookfortheexit.ThesmokelayerdiusestoS1at60s,andthenal
smoke height is lower than 1.5 m.  Dense smoke diuses to the monitoring points (S3, S5, and
S6) near Exit 1 and the lane; however, because the lane is wide enough, the smoke height does not
inuencevisibility.
 Figure7 showsthesmokedepositwhenthe rst caronthelowerright of theparkinglotison
re.AsmokejetpassestheS2monitoringpointbefore20s,this resultisidenticaltotheprevious
Fig. 6. (Color online) Analysis of smoke height without smoke vent (Case 1-2).
Fig. 7. (Color online) Analysis of smoke height without smoke vent (Case 1-3).
(a) (b)
(a) (b)

Sensors and Materials, Vol. 29, No. 4 (2017) 439
Fig. 8. (Color online) Fire HRR simulation results.
(a) (b)
(c) (d)
(e)
case.AstheS4monitoringpointisclosetothereorigin,thesmokelayerbeginstodepositat20
s. The smoke begins to deposit at S1 at 40 s, and because there is no mechanical smoke extraction,
thenalsmokelayerislowerthan1.59m.Asthere’soriginisontherightsideoftheparkinglot,
mostofthedensesmokeaccumulatesontherightandspreadstotheabovegroundoorsviaExit2.
Thestairsmaycauseastackingeectduetothedensesmoke,leadingtoheaviercasualties.There
islittledense smoke deposit at the left measuring point; thus the smoke height does not inuence
sight.
 While the re’s origins are dierent in the re simulation, as there is no enough fresh air
imported,the car on re isnotburntcompletely,andthemaximumheatrelease rate of Case 1-1–
Case 1-3 shown in Fig. 8(a) is 1 MW.

440 Sensors and Materials, Vol. 29, No. 4 (2017)
Case 2: With one smoke vent
In this simulation, a mechanical smoke vent is mounted at the center of the underground parking
lot.  Figures 9–11 show the simulated results of the upper left, lower left, and lower right cars
beingonre. When the re occursintheupperleftcar,the smoke layer deposition rate attheS1
monitoringpointintherst80sisalmostthesameascase1,meaningthesmokelayerdescendsto2m.
At 100 s, the smoke layer at the S1 monitoring point descends to 1.55 m, which is lower than the
smokelayer without smoke extraction,meaning that smoke extractioncan accelerate theair ow
in the underground space, the heat release rate is increased, and the dense smoke layer descends
fasterthaninthecasewithoutsmokeextraction.Figure8(b)indicatesthatthereheatreleaserate
Fig. 9. (Color online) Analysis of smoke height with one mechanical smoke vent (Case 2-1).
Fig. 10. (Color online) Analysis of smoke height with one mechanical smoke vent (Case 2-2).
Fig. 11. (Color online) Analysis of smoke height with one mechanical smoke vent (Case 2-3).
(a) (b)
(a) (b)
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Sensors and Materials, Vol. 29, No. 4 (2017) 441
ofCase2-1isclosetoCase1at theinitialstageofthere,butthereheatreleaserateatthelate
stage of Case 2-1 exceeds 1.0 MW, which is higher than the value of Case 1, meaning fresh outside
air is imported by the smoke exhaust system, which supports combustion. In addition, the smoke
layer begins to deposit at the S2 monitoring point after 80 s.  The smoke layer is quite obvious
and dense at the S4 monitoring point near Exit 2, and the smoke layer descends to 1.43 m. When
asmoke vent ismounted in thecenter,the dense smoke ow is more disorderly than inthe case
without smoke extraction, and the smoke layer descent is not retarded in some areas. At S5, the
airow resultingfromthesmoke ventattractsthedensesmoke todiusetotheleft. Thestarting
time of deposit at S5 is almost the same as S1, which is much earlier than the case without smoke
extraction.
 Whenthe re breaks out in the rst car on the lower left of the parking lot, theblack smoke
generatedbythere isattractedbythemechanicalsmokevent,andthesmokediuses fasterthan
the case without smoke extraction (Case 1). Furthermore, the fresh air imported by mechanical
smokeextraction acceleratesthere,and thegenerationofdense smokeisgreaterthanin Case1;
therefore, the dense smoke cannot be completely discharged from the smoke vent, and the dense
smoke accumulates at Exits 1 and 2. Figure 9 is the smoke height analysis. The smoke layer at Exit
2 (S4 monitoring point) is lower than 1.5 m, and the smoke height changes greatly, meaning the
poorsmoke extraction eectresultsinaturbulentstream.  Ontheotherhand,asthe dense smoke
isattractedbythemechanicalsmokevent,itisdeectedtowardstherightside(Exit2).Therefore,
the starting time of the smoke layer deposit at Exit 1 (S5 monitoring point) in this case is later than
thecasewheretherebreaksoutattheupperleftcar.Whentherebreaksoutintherstcaron
the lower right of the parking lot, the dense smoke soon reaches Exit 2 (S4 monitoring point); thus
itdeposits after 20 s,and the smokeheight is 1.5–2.0 m.The smoke beginsto deposit at Exit1
(S5 monitoring point) after 70 s; however, the smoke volume is increased as the heat release rate is
increased by mechanical smoke extraction, and the smoke layer at S2 descends to 1.43 m, which is
lower than the smoke layer in the case without smoke extraction.
 Inthe caseofonesmokevent, there’soriginhasasignicanteect onthere’sheatrelease
rate.Whenthere’soriginisontheupperleft,lowerleft,orlowerright,themaximumheatrelease
rate[Figs.8(b)–8(d)]is2.1,2.5,and1.0MW,respectively.Whenthe rebreaksoutonthelower
left,asthemechanicalsmokeventisclosetothere’sorigin,thefreshoutsideairdrawninbythe
mechanicalsmokeextractionincreasesthere’sheatreleaserate.However,when the re breaks
out on the lower right, the fresh outside air cannot be imported into the re scene, and the heat
release rate is close to the case without smoke extraction; thus there is smoldering or extinguishing
after 70 s.
Case 3: With two smoke vents (symmetrically allocated)
 Thiscasediscussestheeect on the smoke layer accumulation and heat release rate of having
two mounted mechanical smoke vents in the underground parking re. The mechanical smoke
vents are located at the S1 and S2 monitoring points, and the total exhaust smoke level of the two
smokeventsisthesameasthepreviouscase.Figures12–14showthesimulationresultsofsmoke
layeraccumulationwhentherebreaksoutintheupperleft,lowerleft,orlowerrightcars.When
therebreaksoutintherstcarontheupperleft,partofthedensesmokeisexhaustedfromsmoke
vent 1, thus reducing the descent speed of the smoke layer. The smoke height at the S1 monitoring
pointisstabilizedat2.1minthesimulation,andthesmokelayerattheS2monitoringpointbegins
to deposit 70 s before that, as the mechanical smoke extraction accelerates dense smoke ow.

442 Sensors and Materials, Vol. 29, No. 4 (2017)
However, the smoke height is maintained at 1.7 m, which is a little higher than the smoke height
inCase1.ThesmokelayersatS4andS5(Exit2andExit1)aremaintainedabove1.8–1.9m;this
result shows that the smoke layer in the case with two smoke vents is higher than the case without
a smoke vent, which is very helpful for escape. However, according to the simulation results of
Cases 1–3, the location and number of smoke vents can inuence the volume of imported fresh
outsideair;thusthereheatreleaserateischanged.Mechanicalsmokeextractioncanincreasethe
heatreleaserate,andthere heat release rate is 2.0 MWin thecasewithtwomechanical smoke
vents[Fig.8(e)].
Fig. 12. (Color online) Analysis of smoke height with two mechanical smoke vents (Case 3-1).
Fig. 13. (Color online) Analysis of smoke height with two mechanical smoke vents (Case 3-2).
Fig. 14. (Color online) Analysis of smoke height with two mechanical smoke vents (average) (Case 3-3).
(a) (b)
(a) (b)
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Sensors and Materials, Vol. 29, No. 4 (2017) 443
 Whenarebreaks out in therstcar on the lowerleftof the parking lot, thedensesmoke at
there’soriginisconnedtothere’sorigin;the smokelayeratS2descends rapidlytoabout1.5
m. However, because the smoke vents continuously discharge the smoke, the smoke layer at S2 is
maintainedat1.5m.ThoughS1isfarfromthe re’soriginandthere isasmokeventnearby,the
smokedoesnotdeposit until 72 s, andtheheight is stabilized at about1.8m.Thesmoke height
atS4ismaintainedat1.7–1.8m. Asthereoriginisclosetothelane,thestartingtimeofsmoke
deposit at S5 is earlier than in Case 3-1, and there is little smoke deposit at S6.
 Whentherebreaksoutintherstcaronthelowerrightoftheparkinglot,asthereoriginis
fairlyfarawayfromthetwosmokevents,thedensesmokediusesuniformly,andthedensesmoke
begins to deposit at S2 and S4 at almost the same time. As the smoke is attracted by smoke vent 1,
the starting time of smoke deposit at S1 (47 s) is earlier than that at S5 (70 s).
4. Conclusions
 Oncearebreaksoutinanundergroundparkinglot,whichisaoorwithoutanopening,the
building structure is damaged.  It is necessary to enhance the re safety of underground parking
lotssothatpeoplecanbesafelyevacuatedandreextinguishingworkcanbesmoothlyperformed.
Inthispaper,weuseFDSsoftwarefortheanalysisofsimulatedres inundergroundparkinglots.
According to the results of this study,the eective layout of smoke vents can create the critical
time required for escape and initial rescue.  The smoke vent location is signicantly correlated
withsmoke deposit.Ifthesmokevent islocatednearthere, the importedoutsideairmakesthe
reandsmokespreadquickly.Foranundergroundparking lot smaller than 1000 m2, the present
re code does not require mounted smoke exhaust fans.  However, the simulations show that an
ecient layout of smoke vents (compared with one smoke vent for 500 m2 specied for smoke
compartments) can eectively prolong escape time.  The ndings of this study can provide a
reference for underground parking lots to install the smoke detection sensors for detecting smoke at
earlyregrowingstagesinthefuture.
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