Carleton University, 82.583 (CVG****), Fire Dynamics II, Winter 2003, Lecture # 2 1 Fire Dynamics II...

Carleton University, 82.583 (CVG****), Fire Dynamics II, Winter 2003, Lecture # 2

1

Fire Dynamics IIFire Dynamics II

Lecture # 2Lecture # 2

Ceiling Jets & Ceiling FlamesCeiling Jets & Ceiling FlamesJim MehaffeyJim Mehaffey

82.583 or CVG****82.583 or CVG****


2

Ceiling Jets and Ceiling FlamesCeiling Jets and Ceiling Flames

OutlineOutline

• Review of models for unconfined fire plumesReview of models for unconfined fire plumes• Models for ceiling jets (temperature & velocity)Models for ceiling jets (temperature & velocity)• Models for response of sprinklers / heat detectorsModels for response of sprinklers / heat detectors• Model for ceiling flame (flame extension)Model for ceiling flame (flame extension)• Flames located against a wall or in a cornerFlames located against a wall or in a corner


3

Review of Models for Unconfined Fire PlumeReview of Models for Unconfined Fire Plume


4

Unconfined Fire Plume Comprises 3 RegimesUnconfined Fire Plume Comprises 3 Regimes

• Persistent flame (flame is present 100% of time)Persistent flame (flame is present 100% of time)

0.03 < z < 0.08 0.03 < z < 0.08 Eqn (2-Eqn (2-1)1)

z = height above fire source (m)z = height above fire source (m)

= heat release rate (kW)= heat release rate (kW)

Q

Q

2/5Q

2/5


5


• Intermittent flame (flame present < 100% of time)Intermittent flame (flame present < 100% of time)

0.08 < z < 0.20 0.08 < z < 0.20 Eqn (2-Eqn (2-2)2)

• Flame height = height where intermittency is 50%Flame height = height where intermittency is 50%

(Correlation - Heskestad 1983)(Correlation - Heskestad 1983)

ll = 0.235 = 0.235 - 1.02 D - 1.02 D Eqn (2-Eqn (2-3)3)

D = fuel diameter (m)D = fuel diameter (m)

Q

2/5Q

2/5

Q

2/5


6


• Buoyant (thermal) plume (no flame is ever present) Buoyant (thermal) plume (no flame is ever present)

z > 0.20 z > 0.20 Eqn (2-Eqn (2-4)4)

• Assume heat is released at a virtual point sourceAssume heat is released at a virtual point source

zzoo = 0.083 - 1.02 D = 0.083 - 1.02 D Eqn (2-Eqn (2-5)5)

zzoo = height of virtual source above burning item (m) = height of virtual source above burning item (m)

Q

2/5

Q

2/5


7

Buoyant Plume Model (2)Buoyant Plume Model (2)

• Correlations often expressed in terms ofCorrelations often expressed in terms of

= convective heat released rate (kW)= convective heat released rate (kW)

• ““Radius” of the plume, b (m)Radius” of the plume, b (m)

b(z) = 0.195 (z- zb(z) = 0.195 (z- zoo)) Eqn (2-Eqn (2-6)6)

CONVQ


8


• Upward axial velocity, uUpward axial velocity, uaxax (m s (m s-1-1))

uuaxax(z) = 1.14 (z- (z) = 1.14 (z- zzoo))-1/3-1/3 Eqn (2- Eqn (2-7)7)

• Radial dependence of upward velocity, (m sRadial dependence of upward velocity, (m s-1-1))

u(r,z) = uu(r,z) = uaxax(z) exp(-r(z) exp(-r22/b/b22)) Eqn (2- Eqn (2-8)8)

Q

1/3

CONV


9


• Axial temperature, Axial temperature, TTaxax = T = Taxax - T - T (K) (K)

TTaxax (z) = 26 (z- (z) = 26 (z- zzoo))-5/3-5/3 Eqn (2-9)Eqn (2-9)

• Radial dependence of temperature, Radial dependence of temperature, TT(r, z) (r, z) (K) (K)

T(r, T(r, z) z) = = TTaxax(z) exp[-((z) exp[-(1.21.2r)r)22/b/b22] Eqn (2-10)] Eqn (2-10)

• Average temperature, Average temperature, TTaveave

TTaveave (z) = 14 (z- (z) = 14 (z- zzoo))-5/3-5/3 Eqn (2-11) Eqn (2-11)

Q

2/3

CONV

Q

2/3

CONV


10


• Total upward mass flow, (kg sTotal upward mass flow, (kg s-1-1))

(z) = 0.071 (z- (z) = 0.071 (z- zzoo))5/35/3 Eqn (2- Eqn (2-12)12)

********************************************************************************************************************************

• This is probably the simplest model available. This is probably the simplest model available. • More complex models have been incorporated into More complex models have been incorporated into

computer models or into standards for smoke control.computer models or into standards for smoke control.

Q

1/3

CONVpm

pm


11

Consider a Fire Plume Confined by a Ceiling Consider a Fire Plume Confined by a Ceiling


12

Unconfined Ceiling JetUnconfined Ceiling Jet• Need to model ceiling jet in order to predict time to Need to model ceiling jet in order to predict time to

activation of sprinklers or heat detectorsactivation of sprinklers or heat detectors• Properties of ceiling jet depend onProperties of ceiling jet depend on

– Rate of heat releaseRate of heat release– Diameter of fire baseDiameter of fire base– Height of ceiling (above virtual source)Height of ceiling (above virtual source)

• Models are available (Models are available (Fire Dynamics IFire Dynamics I) to predict) to predict– Max. temperature as a function of radial distanceMax. temperature as a function of radial distance– Maximum velocity as a function of radial distanceMaximum velocity as a function of radial distance– Time to activation of sprinklers or heat detectors if Time to activation of sprinklers or heat detectors if

they are subjected to max. temp & velocitythey are subjected to max. temp & velocity


13

Fire Plume Confined by CeilingFire Plume Confined by CeilingExperiments - Alpert 1972Experiments - Alpert 1972• unconfined smooth ceilingunconfined smooth ceiling• buoyant plume impinges on ceilingbuoyant plume impinges on ceiling• steady fires / no hot layersteady fires / no hot layer• variety of fuel packagesvariety of fuel packages• heat release rate: 668 kW heat release rate: 668 kW 98 MW 98 MW• ceiling height 4.6 m ceiling height 4.6 m H H 15.5 m 15.5 m

FindingsFindings• max temp & velocity close to ceiling (Y ~ 0.01 H)max temp & velocity close to ceiling (Y ~ 0.01 H)• ambient temp for Y > 0.125 Hambient temp for Y > 0.125 H

Q


14

Alpert’s Correlations - Ceiling JetsAlpert’s Correlations - Ceiling JetsFor “maximum” temperature and velcoityFor “maximum” temperature and velcoity

TTmaxmax - T - T = 16.9 = 16.9 2/32/3 (H - z (H - zoo))-5/3-5/3 for r for r 0.18 H 0.18 H Eqn (2-13)Eqn (2-13)

TTmaxmax - T - T = 5.38( /r)= 5.38( /r)2/32/3 (H - z (H - zoo))-1 -1 for r > 0.18 Hfor r > 0.18 H Eqn (2-14)Eqn (2-14)

uumaxmax = 0.96 { /(H - z = 0.96 { /(H - zoo)})}1/31/3 for r for r 0.15 H 0.15 H Eqn (2-15)Eqn (2-15)

uumaxmax = 0.195 = 0.195 1/31/3 (H - z (H - zoo))1/21/2 r r - 5/6- 5/6 for r > 0.15 Hfor r > 0.15 H Eqn (2-16)Eqn (2-16)

r = radial distance under the ceiling (m)r = radial distance under the ceiling (m)

Q

Q

Q

Q


15

Comparison with Buoyant PlumeComparison with Buoyant Plume

Temperature in Ceiling JetTemperature in Ceiling Jet• Alpert: Alpert: for r for r 0.18 H { ~ area of plume impingement as 0.18 H { ~ area of plume impingement as

radius of plume is b(z) = 0.195 (z- zradius of plume is b(z) = 0.195 (z- zoo)})}

TTmaxmax - T - T = 16.9 = 16.9 2/32/3 (H - z (H - zoo))-5/3-5/3

Axial Temperature in Buoyant PlumeAxial Temperature in Buoyant Plume

TTaxax (z) = 26 (z- (z) = 26 (z- zzoo))-5/3-5/3

oror TTaxax (z) = 20.5 (z) = 20.5 2/32/3 (z- (z- zzoo))-5/3-5/3

Q

Q

2/3

CONV

Q


16

Comparison with Buoyant PlumeComparison with Buoyant Plume

Velocity in Ceiling JetVelocity in Ceiling Jet• Alpert: Alpert: for r for r 0.15 H { ~ area of plume impingement as 0.15 H { ~ area of plume impingement as

radius of plume is b(z) = 0.195 (z- zradius of plume is b(z) = 0.195 (z- zoo)})}

uumaxmax = 0.96 { /(H - z = 0.96 { /(H - zoo)})}1/31/3

Axial Velocity in Buoyant PlumeAxial Velocity in Buoyant Plume

uuaxax(z) = 1.14 { /(z- (z) = 1.14 { /(z- zzoo))}1/3}1/3

or uor uaxax(z) = 1.01 { /(z - z(z) = 1.01 { /(z - zoo)})}1/31/3

Q

CONV

Q

Q


17

Proximity of WallsProximity of Walls

• Alpert correlations apply provided fire source is at Alpert correlations apply provided fire source is at least 1.8 H from wallsleast 1.8 H from walls

• For fire against wall, air entrainment into plume is cut For fire against wall, air entrainment into plume is cut in half. Method of reflection predicts Alpert’s in half. Method of reflection predicts Alpert’s correlations can still be applied withcorrelations can still be applied with

22

• For fire in corner, air entrainment into plume is cut in For fire in corner, air entrainment into plume is cut in quarter. Method of reflection predicts Alpert’s quarter. Method of reflection predicts Alpert’s correlations can still be applied withcorrelations can still be applied with

44

Q

Q

Q

Q


18

Example of Use of Eqn (2-13)Example of Use of Eqn (2-13)• Calculate the maximum excess temperature under a

ceiling 10 m directly above a 1.0 MW heat release rate fire. Assume z0 = 0.

46.42

(100) 16.9

C36.4T 0

35

32

max 10

(1000) 16.9TT


19

Example of Use of Eqn (2-14)Example of Use of Eqn (2-14)• Calculate minimum heat release rate of a fire against

noncombustible walls in a corner 12 m below ceiling needed to raise temperature of gas below ceiling 50°C at a distance 5 m from the corner. Assume z0 = 0.

32

3532

125

12/438.550

Q

MWkWQ 472.11472

32

35

32

max

4

38.5

HrHQ

TT


20

Example of Use of Eqn (2-16)Example of Use of Eqn (2-16)• Calculate maximum velocity at this position. Assume

z0 = 0.

65

31

max

4

195.0

Hr

HQ

u

65

31

125

12) / 1472 x (4 0.195

smu 2.3max


21

Motevalli & Marks CorrelationMotevalli & Marks Correlation

=Thickness of Ceiling Jet=Thickness of Ceiling Jet

• = distance below ceiling at which = distance below ceiling at which

T - TT - T = 1/ e {T= 1/ e {Tmaxmax - T - T } with e = 2.718} with e = 2.718

Eqn (2-Eqn (2-17)17)

forfor

H* = H - zH* = H - zoo

T

T

*24.2exp1112.0

* H

r

HT

0.2*

26.0 H

r


22

Yuan & Motevalli CorrelationYuan & Motevalli CorrelationThermal Profile of Ceiling JetThermal Profile of Ceiling Jet

• y = distance below ceiling (m) y = distance below ceiling (m)

Eqn (2-Eqn (2-18)18)

forfor

T(r,y) = T(r,y) = TTmaxmax(r) when y/(r) when y/llTT ~ 0.25 ~ 0.25

substituting into Eqn (2-17)substituting into Eqn (2-17)

y / H* ~ 0.028 [1 - exp(- 2.24 r / H*)]y / H* ~ 0.028 [1 - exp(- 2.24 r / H*)]

0.2*

26.0 H

r

TT

yy

rT

yrT

57.2exp094.024.4

)(

),(755.0

max


23

Other Correlations - Ceiling JetsOther Correlations - Ceiling JetsFor “maximum” temperatureFor “maximum” temperature

TTmm = (T = (Tmaxmax - T - T) = ) = 2/32/3 (H*) (H*) - 5/3- 5/3 f(r/H*)f(r/H*)

ReplaceReplace

H H H* H*

Q


24

Other Correlations - Ceiling JetsOther Correlations - Ceiling JetsFor “maximum” temperatureFor “maximum” temperature

ReplaceReplace

H H H*H*


25

Other Correlations - Ceiling JetsOther Correlations - Ceiling JetsFor “maximum” velocityFor “maximum” velocity

• UUmaxmax = = 1/31/3 (H*) (H*) - 1/3- 1/3 f(r/H*)f(r/H*)

ReplaceReplace

H H H*H*

Q


26

Other Correlations - Ceiling JetsOther Correlations - Ceiling JetsFor “maximum” velocityFor “maximum” velocity

ReplaceReplace

H H H*H*


27

Thermal Response of Heat Detectors & SprinklersThermal Response of Heat Detectors & Sprinklers

• Simple model (convective heating)Simple model (convective heating)

= = -1-1 (T (Tgg - T - TDD)) Eqn (2-19) Eqn (2-19)

TTDD = temp of detector / sprinkler link (K) = temp of detector / sprinkler link (K)

TTgg = temp of ceiling jet (K) = temp of ceiling jet (K)

= time constant of device (s)= time constant of device (s)

= m= mDD c cDD / (h A / (h ADD)) Eqn (2-20) Eqn (2-20)

mmDD = mass of detector / sprinkler link (kg) = mass of detector / sprinkler link (kg)

ccDD = specific heat of link (kJ kg = specific heat of link (kJ kg -1-1 K K-1-1))

AADD = surface area of link (m = surface area of link (m22))

h = convective heat transfer coefficient (kW mh = convective heat transfer coefficient (kW m -2-2 K K-1-1))

dt

dTD


28

Thermal Response of Heat Detectors & SprinklersThermal Response of Heat Detectors & Sprinklers

• If TIf Tgg is independent of time is independent of time

Eqn (2-Eqn (2-21)21)

ttrr = time of activation (s) = time of activation (s)

TTDrDr = manufacturer’s listed operation temperature (K) = manufacturer’s listed operation temperature (K)

TT = initial temperature (K) = initial temperature (K)

can be characterized by device’s RTIcan be characterized by device’s RTI

= RTI u= RTI u-1/2-1/2 Eqn (2- Eqn (2-22)22)

RTI = response time index (mRTI = response time index (m1/21/2 s s1/21/2))

TT

TT1n lt

g

Dr

r


29

Thermal Response Index - SprinklersThermal Response Index - Sprinklers

BSI 94/340340, “Draft Code of Practice for the Application BSI 94/340340, “Draft Code of Practice for the Application of Fire Safety Engineering Principles to Fire Safety in of Fire Safety Engineering Principles to Fire Safety in Buildings”, British Standards Institute, London, p 115 Buildings”, British Standards Institute, London, p 115 (1994) (1994)

Sprinkler Type TTyyppiiccaall RRTTII((mm11//22 ss11//22))

WWoorrssee SSaassee RRTTII((mm11//22 ss11//22))

Fast response 30 100Soldered link 150 N/A8 mm glass bulb 200 300


30

More Detailed Detector Response ModelMore Detailed Detector Response Model

RTI = response time index (m1/2 s1/2 )

C = conductivity factor (m1/2 / s1/2 )

• C is a measure of heat conduction from heat sensitive element to rest of heat detector or sprinkler

• RTI and C can be determined for a detector

• For C = 0, this model reduces to simpler model. Simple model is often accurate enough.

Dg

D Tu

cT

RTI

u

dt

dT1


31

Detector or Sprinkler in a ChannelDetector or Sprinkler in a ChannelDelichatsios (1981)Delichatsios (1981)

• In channel defined by corridor walls or ceiling beamsIn channel defined by corridor walls or ceiling beams

Eqn (2-Eqn (2-23)23)

Eqn (2-Eqn (2-24)24)

31

b

31

b

max

HH

Y 0.2exp

H 0.29

impT

T

61

maxmax102.0

b

HTHu


32

Detector or Sprinkler in a ChannelDetector or Sprinkler in a ChannelDefinition of termsDefinition of terms

• TTmaxmax = Gas temperature near ceiling (K or °C) = Gas temperature near ceiling (K or °C)

• TTimpimp = Gas temperature where it impinges on ceiling = Gas temperature where it impinges on ceiling

(K or °C). Given by Alpert Eqn (2-13).(K or °C). Given by Alpert Eqn (2-13).

• uumaxmax = Gas velocity near ceiling (m s = Gas velocity near ceiling (m s-1-1))

• H = Height of ceiling above fire source (m)H = Height of ceiling above fire source (m)

• Y = Distance along channel Y = Distance along channel from point of impingementfrom point of impingement (m) (m)

• 2 2 llbb = Width of channel (m) = Width of channel (m)

• hhbb = Depth of channel (m) = Depth of channel (m)


33

Detector or Sprinkler in a ChannelDetector or Sprinkler in a Channel

Limits of ApplicationLimits of Application

• For corridors correlations hold providedFor corridors correlations hold provided

Y > Y > llbb (gas is flowing along channel) (gas is flowing along channel)

(a)(a)

llbb > 0.2 H (ceiling jet impingement within channel) (b) > 0.2 H (ceiling jet impingement within channel) (b)

• For beams must also haveFor beams must also have

hhbb / H > 0.1 ( / H > 0.1 (llbb / H) / H)1/31/3 (no spillage under beams) (no spillage under beams) (c) (c)

or combining (b) and (c)or combining (b) and (c)

hhbb / H > 0.17 / H > 0.17


34

Time Dependent FiresTime Dependent Fires

• In small room with slowly growing fire, Alpert’s In small room with slowly growing fire, Alpert’s (steady-state) correlations can ue used with(steady-state) correlations can ue used with

• In large industrial facilitiesIn large industrial facilities– Travel time of fire gases from burning item to Travel time of fire gases from burning item to

detector or sprinkler may be detector or sprinkler may be 10 s 10 s– If fire grows rapidly, steady-state model may If fire grows rapidly, steady-state model may

yield overly conservative resultsyield overly conservative results

Q tQ


35

tt22 Fire Growth Fire Growth

• Growth of fire can often be characterized as Growth of fire can often be characterized as

Eqn (2-25)Eqn (2-25)

ttii = time of “ignition” (s) = time of “ignition” (s)

= growth coefficient (kW s= growth coefficient (kW s-2-2))

• “Design” Fires, NFPA 72, National Fire Alarm Code

Slow

Medium Eqn (2-Eqn (2-26)26)

Fast

Ultra-fast

2

ittQ

2 t00469.0Q2 t01876.0Q

2 t20117.0Q

2 t30029.0Q


36

Example of tExample of t22 Fire Fire


37

Transient Ceiling JetsTransient Ceiling JetsHeskestad and Delichatsios (1978) Heskestad and Delichatsios (1978)

• AssumedAssumed

• Dimensionless timeDimensionless time

• Dimensionless gas travel time Dimensionless gas travel time (fire source to ceiling location)(fire source to ceiling location)

• ForFor TTmaxmax = u = umaxmax = 0 = 0

2tQ

tH

0.489t*4/5

1/5

H

r1 0.954t

*

g

t*

g

* t


38

Transient Ceiling JetsTransient Ceiling Jets Heskestad and Delichatsios (1978)Heskestad and Delichatsios (1978)

Eqn (2-27)Eqn (2-27)

Eqn (2-28) Eqn (2-28)

34

**

5/3

5/2

max

313.0188.014.7

Hr

tt

HT g

32

**

63.0

5/15/1

max

313.0188.0)/(29.0

H

rtt

Hr

Hu g

t*

g

* t


39

Transient Ceiling JetsTransient Ceiling JetsHeskestad and Delichatsios (1978)Heskestad and Delichatsios (1978)

• ForFor TTmaxmax = u = umaxmax = 0 = 0

• ForFor Early on, fire is small & transport time Early on, fire is small & transport time relatively long, transient effects are relatively long, transient effects are prominent. Eqns prominent. Eqns (2-27 & 28) apply.(2-27 & 28) apply.

• ForFor Later, fire is large & transport time Later, fire is large & transport time relatively short, transient correlations relatively short, transient correlations revert to revert to Heskestad and Delichatsios Heskestad and Delichatsios steady-state correlations (p 2-23 & 25)steady-state correlations (p 2-23 & 25)

t*

g

* t

t*

g

* t

t*

g

* t


40

Example:Example: Sofa p 2-35 with t Sofa p 2-35 with t ii = 0 in room with H = 5 m. = 0 in room with H = 5 m.

Calculate Calculate TTmaxmax and u and umaxmax for r = 4 m and t = 120 s. for r = 4 m and t = 120 s.

11.41 120 5

)1736.0( 0.489t*

4/5

1/5

72.15.0

4.01 0.954t

*

g

10.22

5.04.0

0.3130.188

1.7211.41

313.0188.0

**

Hr

ttg


41



TTmaxmax = 84 K +293 K = 377 K = 104°C = 84 K +293 K = 377 K = 104°C

K 8410.220.5

)1736.0(14.7

34

5/3

5/2

maxT

m/s 2.610.22)0.5/0.4(

)0.5()1736.0(29.0

32

63.0

5/15/1

maxu


42



Steady-state: Heskestad & Delichatsios (p 2-23 & 25) Steady-state: Heskestad & Delichatsios (p 2-23 & 25) 34

3/5

3/2

max

313.0188.0

175.2

H

rH

QT

K 104

5.04.0

0.3130.188

1

5.0

)120 x (0.17362.75

34

5/3

2/32

max

T


43



Steady-state: Heskestad & Delichatsios (p 2-23 & 25) Steady-state: Heskestad & Delichatsios (p 2-23 & 25)

uumaxmax = 2.8 m / s = 2.8 m / s

32

63.0

3/1

3/1

max

313.0188.0

1179.0

H

rH

r

H

Qu


44

Thermal Response of Heat Detectors & SprinklersThermal Response of Heat Detectors & Sprinklers• Simple model (convective heating)Simple model (convective heating)

= = -1-1 (T (Tgg - T - TDD)) Eqn (2- Eqn (2-

19)19)

• No simple solution when TNo simple solution when Tgg and u are time-dependent and u are time-dependent

• Must solve numerically (with computer)Must solve numerically (with computer)

dt

dTD


45

Detector Response for Simple Time-Dependent TDetector Response for Simple Time-Dependent Tgg(t) (t)

Assuming u is Relatively ConstantAssuming u is Relatively Constant

• Eqn (2-19) Eqn (2-19) = - = - -1-1 {(T {(TDD - T - T) - (T) - (Tgg - T - T)})}

• If (TIf (Tgg - T - T) = ) = t t = - = - -1-1 {(T {(TDD - T - T) - ) - t t

} }

• Solution is (TSolution is (TDD - T - T) = ) = { t - { t - [ 1 - exp (- t / [ 1 - exp (- t / ) ] }) ] }

• If If is small & time of activation >> is small & time of activation >> then for t >> then for t >>

(T(TDD - T - T) = ) = { t - { t - }}

dt

T-TdD

dt

T-TdD


46

Confined CeilingsConfined Ceilings

• For large industrial or warehouse facilities, models for For large industrial or warehouse facilities, models for unconfined ceiling jet flows are often sufficientunconfined ceiling jet flows are often sufficient

• In small rooms or for long times after ignition in large In small rooms or for long times after ignition in large industrial or warehouse facilities, ceiling jet can become industrial or warehouse facilities, ceiling jet can become completely immersed in hot smoky layercompletely immersed in hot smoky layer

• Hence ceiling jet entrains hot gas rather than cool air Hence ceiling jet entrains hot gas rather than cool air temp of ceiling jet higher than for unconfined ceilingtemp of ceiling jet higher than for unconfined ceiling

• Reduction in activation time of sprinkler or heat detectorReduction in activation time of sprinkler or heat detector• To predict properties of ceiling jet, must know temp of hot To predict properties of ceiling jet, must know temp of hot

layer & height of interface between hot layer and cool layerlayer & height of interface between hot layer and cool layer• Analytical and computer models are available for such Analytical and computer models are available for such

scenariosscenarios


47

Ceiling FlamesCeiling Flames


48


• Flame impinges on ceiling & spreads out radially, even Flame impinges on ceiling & spreads out radially, even if ceiling is non-combustibleif ceiling is non-combustible

Heskestad & Hamada ( 93 to 760 kW)Heskestad & Hamada ( 93 to 760 kW)

Flame extension, rFlame extension, rff (m) (m)

rrf f = 0.95 (= 0.95 (ll - H) - H) Eqn (2- Eqn (2-

29)29)

Heskestad flame length (burning in open)Heskestad flame length (burning in open)

ll = 0.235 - 1.02 D = 0.235 - 1.02 D Eqn (2-Eqn (2-3) 3)

Q

Q

2/5


49


• Ceiling flames may ignite combustible or damage non-Ceiling flames may ignite combustible or damage non-combustible ceiling elements, cables and pipescombustible ceiling elements, cables and pipes

• Ceiling flames enhance thermal radiation to floorCeiling flames enhance thermal radiation to floor– augment burning rate of burning itemaugment burning rate of burning item– augment flame spread over burning itemaugment flame spread over burning item– augment heating or remote combustibles (targets)augment heating or remote combustibles (targets)


50

Ceiling Flame Increases Flame Spread & BurningCeiling Flame Increases Flame Spread & Burning• Consider burning of 0.76 m x 0.76 m slab of PMMA in an Consider burning of 0.76 m x 0.76 m slab of PMMA in an

enclosure allowing air access from four sidesenclosure allowing air access from four sides• Max rate of burning ~ 3 x open-burning rateMax rate of burning ~ 3 x open-burning rate• Achieved in approximately 1/3 the timeAchieved in approximately 1/3 the time


51

Flames in a CornerFlames in a Corner

• For flames above a burning object located against a For flames above a burning object located against a wall or in a corner (of non-combustible materials)wall or in a corner (of non-combustible materials)– asymmetric and therefore reduced entrainment of asymmetric and therefore reduced entrainment of

air have a major impact on the flame dynamicsair have a major impact on the flame dynamics– flame length is increasedflame length is increased


52

Temperature above fires in 1.22 m high wood pallets (x)Temperature above fires in 1.22 m high wood pallets (x)


53

ReferencesReferences• D. Drysdale, An Introduction to Fire Dynamics,Wiley, 1999, Chap 4

• B. Karlsson and J.G. Quintiere, Enclosure Fire Dynamics, CRC Press, 2000, Chap. 4

• R.L. Alpert, “Ceiling Jet Flows”, SFPE Handbook of Fire Protection Engineering, 3rd Ed., 2002

Carleton University, 82.583 (CVG****), Fire Dynamics II, Winter 2003, Lecture # 2 1 Fire Dynamics II...

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Transcript of Carleton University, 82.583 (CVG****), Fire Dynamics II, Winter 2003, Lecture # 2 1 Fire Dynamics II...