lecture_1

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Carleton University, 82.583 (CVG****), Fire Dynamics II,

Winter 2003 Lecture # 1

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Fire Dynamics II

Lecture # 1Introduction / Enclosure Phenomena

Jim Mehaffey

82.583 or CVG****



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Fire Dynamics II82.583 or CVG****

• Lectures: Wednesdays 5:30 - 8:30 p.m.• Location: Room 404, Southam Hall• Lecturer: Dr. Jim Mehaffey, Forintek

Tel: (613) 523-0927Fax: (613) [email protected]

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Recommended Text Books• Dougal Drysdale, An Introduction to Fire Dynamics,

Wiley, 1999• Björn Karlsson and James G. Quintiere, Enclosure

Fire Dynamics, CRC Press, 2000• SFPE Handbook of Fire Protection Engineering, 3rd

Ed., 2002

Lecture Noteshttp://www.carleton.ca/~ghadjiso/



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82.575 Fire Dynamics I• Introduction to basic chemistry & physics of fire• Simple mathematical models describing fires

developing in the open

82.583 Fire Dynamics II• How are basic chemistry & physics altered

when fire develops within an enclosure• Simple mathematical models describing fires

developing in enclosures

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82.579 Introduction to Fire Protection Engineering (1998, 1999 & 2000)

• 82.579 = Fire Dynamics I + Fire Dynamics II, but delivered in one term, not two terms



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Fire Dynamics II - Course DescriptionCourse addresses the dynamics of fires in buildings. Phenomena that govern ignition, fire growth and severity, temperature and pressure development, toxicity and visibility are investigated. Fire Dynamics IIbuilds on basic concepts presented in Fire Dynamics I. The way containment modifies fire processes is highlighted. Particular emphasis is placed on the reaction of people, buildings and building components to exposure by fire. This basic background provides a foundation for beginning the process of designing a fire safe building.

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Enclosure Fire Dynamics• Fires develop differently in an enclosure than in

the open • Limited supply rate of oxygen causes a

reduction in the rate of burning• Trapping of heat in the enclosure causes an

increase in the rate of burning • Enclosure fire dynamics is a competition

between these two effects



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Proposed Course Outline

• Lecture 1: Introduction / Enclosure Phenomena

• Lecture 2: Ceiling Jets & Ceiling Flames

• Lecture 3: Accumulation or Smoke Filling

• Lecture 4: Vent Flows

• Lecture 5: Chemistry of Room Fire Combustion

• Lecture 6: Smoke and Heat Venting

Winter Break: February 17-23

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Proposed Course Outline (continued)

• Lecture 7: Heat Flow Calculations

• Lecture 8: Flame Spread & Burning Rates

• Lecture 9: Room-fire Dynamics

• Lecture 10: Pre-flashover Fire

• Lecture 11: Post-flashover Fire

• Lecture 12: Backdrafts & Explosions



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Grading– Problem Sets: 60% – Final Exam: 40%

Problem Sets– Number 1: Distributed during Lecture 3 – Number 2: Distributed during Lecture 6 – Number 3: Distributed during Lecture 8 – Number 4: Distributed during Lecture 10

Final ExamFor evaluation purposes only. Not returned to students.

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Introduction / Enclosure PhenomenaOutline

• How does confinement impact fire dynamics?• What types of models, in addition to those we

have seen for fires burning in the open (in Fire Dynamics I) will be needed to describe building fires?

• We’ll look at the details of these new models in subsequent lectures.



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Consider an Unconfined Fire Plume (1)

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Unconfined Fire Plume• Properties of an unconfined fire plume depend on

– Rate of heat release– Diameter of fire base

• Models are available (Fire Dynamics I) to predict– Flame length– Axial temperature as a function of height– Upward axial velocity as a function of height– Virtual point source (of buoyant plume)– Radius (of buoyant plume)– Total upward mass flow (of buoyant plume)– Concentration of CO & soot (in buoyant plume)



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Consider a Fire Plume Confined by a Ceiling

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

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

– Rate of heat release– Diameter of fire base– Height of ceiling

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

they are subjected to max. temp & velocity



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Lecture 2: Ceiling Jets & Ceiling Flames• Take a deeper look at unconfined ceiling jets

– review various models for ceiling jets– what do temperature and velocity profiles below the

ceiling look like (will the sprinkler be located where maxima in temperature & velocity occur)?

– what happens if the rate of heat release is strongly time-dependent?

– what if the ceiling jet is immersed within a hot upper layer?

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Consider a Ceiling Flame



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Lecture 2: Ceiling Jets & Ceiling Flames• For ceiling flames

– model flame extension under the ceiling– investigate the impact of flame extension under a

ceiling on radiant heat transfer to (and rate of burning of) the burning object

****************************************************************• For flames above a burning object located against

a wall or in a corner– investigate the effect of asymmetric and reduced

entrainment of air on flame dynamics

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Development of a Hot Smoke Layer



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Development of a Hot Smoke Layer• Ceiling jet eventually reaches enclosure walls• Hot gas is forced downward along wall• Hot gas is buoyant so flow turns upward• Layer of hot gas forms under ceiling

Lecture 3: Accumulation or Smoke Filling• Models for rate of descent of the hot layer• Properties of hot layer (temperature, gas & soot

concentrations)

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Interaction with Openings• If there is an opening to an adjacent room or to

the outdoors, the hot layer flows out of the opening when it descends to top of opening

• Heat in enclosure break windows and thereby create an opening as fire develops

• Hot gas exits from upper part of opening and fresh air enters through lower part



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Lecture 4: Vents Flows• Models for rate of exit of hot gas from enclosure

through an opening• Models for rate of entry of air into enclosure

through an opening• Model for maximum possible rate of heat

release for a ventilation-controlled fire

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Rate of Ventilation of Fire• Fires burning in the open are well-ventilated. Air can

readily approach a fire from all sides.• Fires burning within enclosures often burn in poorly-

ventilated conditions.

Lecture 5: Chemistry of Room Fire Combustion• Models to predict impact of reduced ventilation on:

– effective heat of combustion– yields of combustion products (CO, CO2, soot)



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Lecture 6: Smoke and Heat Venting• In an enclosure fire, smoke and heat in the hot upper

layer are dangerous for occupants, fire fighters, expensive equipment and / or stored goods

• For these reasons either natural or mechanical venting is sometimes employed to keep the upper layer above a predetermined height

• Models to predict size of openings required or rate of mechanical venting needed to meet design objectives

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Lecture 7: Heat Flow Calculations



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Lecture 8: Flame Spread & Burning Rates• Models for predicting how thermal radiation

from hot upper layer can– Increase rate of flame spread across combustibles– Increase rate of burning of combustibles

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Lecture 9: Room-fire Dynamics



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Lecture 9: Room-fire Dynamics• Flashover: Transition from burning of one or a

few objects to full room involvement

• Fire development: experimental findings• Impact of ventilation and boundary types

• Fire growth: combustible linings

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Lecture 10: Pre-flashover Fire• Models for rate of heat release required for

flashover to occur

• Models for time to flashover

• Models for temperature in hot smoky layer



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Lecture 11: Post-flashover Fire• Models for rate of heat release

• Models for hot gas temperature in enclosure

• Models for response of structural elements and enclosure boundaries

• Rational requirements for fire resistance

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Lecture 12: Backdrafts & Explosions• Explosions:

– Fuel and air premixed– Following ignition rapid combustion– Deflagration (flame propagates through mixture)– Large pressure rise– Enclosure walls & ceiling may not be able to

withstand pressure → explosion– Explosion venting



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Lecture 12: Backdrafts & Explosions• Backdrafts:

– Limited ventilation → large quantity of unburnt “gas”– When opening suddenly introduced, inflowing air

mixes with “gas” creating flammable mixture– Ignition source ignites flammable mixture, resulting

in an extremely rapid burning– Expansion due to heat released expels burning

“gas” through opening & causes fireball outside enclosure

– Draftdrafts can be extremely hazardous

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Lecture 12: Backdrafts & Explosions• BLEVE: Boiling Liquid Expanding Vapour Explosion

– Propane is a liquid under atmospheric conditions– Liquified by application of pressure & stored in tank – In tank, liquid & vapour at equilibrium, with vapour

at high pressure– If tank immersed in fire, heat causes evaporation of

liquid and higher vapour pressure– Activates relief valve (turbulent jet flame)– Pressure may still rise and fire may weaken metal

casing.– Tank ruptures → BLEVE



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Kemano Public Safey Initiative

• Remote company town closed: July 2000

• Firefighter training & fire research

• Forintek invited to participate

• Partners: National Research Council Weyerhaeuser

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• 6 fire experiments were conducted in one-and two-family houses

• Fires allowed to grow and challenge houses’ wood-frame structures

• No (or delayed) fire suppression

• Temperatures measured at 50 locations in rooms and assemblies

The Fire Test Program

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• First item ignited: plastic waste-paper basket filled with polyurethane chips and shredded paper

• Waste-paper basket in contact with upholstered furniture or mattress

• Intent: quickly establish a large fire that challenges the wood-frame structure

Ignition Source



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The Ignition Source

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Rate of Heat Release: Ignition Source

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0 20 40 60 80 100 120 140

Time (s)

Heat

Rel

ease

Rat

e (k

W)



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• Living room fully furnished

• Walls: wood studs protected by regular gypsum board

• Ceiling: wood joists protected by regular gypsum board

• Doors covered / windows partially open

Fire Test # 1

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• Same as Fire Test # 1 except:

Walls and ceiling protected by fire-rated gypsum board

Fire Test # 2



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Purposes:

• Compare abilities of wood-frame walls and ceilings protected by regular & fire-rated gypsum board to contain fire in room of origin

• Generate data to validate computer models predicting thermal response of fire-rated wood-frame assemblies

Fire Tests # 1 & 2

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Fire Test 2

Video Clip



44S-987

Fire Exposures

0.0

200.0

400.0

600.0

800.0

1000.0

1200.0

0.0 10.0 20.0 30.0 40.0 50.0 60.0

Time (min)

Tem

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(o C)

Living Room Fires - Duplex

ASTM E 119 & CAN/ULC-S101

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15.9-mm Type X gypsum boardnearly withstands room burnout

Kemano Fire Tests

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