Ventilation Limited Fire Principles
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Questions and Answers

What is a Ventilation Limited Fire?

  • A fire that is easily extinguished
  • A fire that produces no smoke
  • A fire that burns at a constant rate
  • A fire in which the heat release rate and fire growth are regulated by the available oxygen within the space (correct)

    • What are the 3 critical points of a Ventilation Limited Fire graph?

    Ignition, Fire under ventilated, Fire Dept. vents

    What is the flow path in a fire?

    The movement of heat and smoke from the higher pressure within the fire area toward the lower-pressure areas accessible by doors, window openings, and roof structures.

    What is a neutral plane?

    <p>The horizontal interface between the hot upper layer and the cool lower layer in a fire room or in a room into which there has been flow of the hot fire effluent.</p> Signup and view all the answers

    What is a fire plume?

    <p>The column of hot gases, flames, and smoke rising above a fire.</p> Signup and view all the answers

    The flow to and from a fire determines the _________________ and _________________ of fire growth.

    <p>magnitude, direction</p> Signup and view all the answers

    What is air entrainment?

    <p>The drawing of air into a fire or fire plume due to the buoyant flow of the plume.</p> Signup and view all the answers

    What are the 3 zones of a fire plume structure?

    <p>Always luminous flame zone (zone 1), Intermittently flaming zone (zone 2), Buoyant plume (zone 3)</p> Signup and view all the answers

    In what zone(s) of the fire plume structure are there high turbulence intensity?

    <p>Zones 2 &amp; 3</p> Signup and view all the answers

    In what zone(s) of the fire plume structure is there combustion?

    <p>Zones 1 &amp; 2</p> Signup and view all the answers

    In what zone(s) of the fire plume structure do the flames cease?

    <p>Zone 3</p> Signup and view all the answers

    What is the luminous flame zone (Zone 1)?

    <p>The zone that gases always accelerate upward toward.</p> Signup and view all the answers

    What is the intermittent flame zone (Zone 2)?

    <p>The zone that gases have a constant upward velocity.</p> Signup and view all the answers

    What is the buoyant plume zone (Zone 3)?

    <p>The zone that gases decrease with height.</p> Signup and view all the answers

    What is luminous flame height?

    <p>The distance between the base of a flame and the point at which the plume is luminous half the time and transparent half the time.</p> Signup and view all the answers

    How does the diameter of the plume change?

    <p>Increases at a rate directly proportional to the height.</p> Signup and view all the answers

    How does average midline temperature change with height?

    <p>Decreases at a rate inversely proportional to the 5/3 power of the height.</p> Signup and view all the answers

    How does average midline velocity change with height?

    <p>Decreases at a rate inversely proportional to the 1/3 power of the height.</p> Signup and view all the answers

    What is a ceiling jet (CJ)?

    <p>The radially outward flow under a ceiling resulting when a fire plume impinges on a ceiling.</p> Signup and view all the answers

    In a vent-limited fire, what 2 things happen?

    <p>Ideal gas law comes into play, Oxygen depletion.</p> Signup and view all the answers

    What does air entrainment depend on?

    <p>Entrainment rate is proportional to the burning rate of the fire and vertical distance between the base of the plume and the neutral plane.</p> Signup and view all the answers

    Heat loss from the hot layer to the ceiling creates ________ on rate of outflow.

    <p>drag</p> Signup and view all the answers

    Heat loss depends on what 3 things?

    <p>Thermal inertia of the walls, Heat capacity of upper-layer gas, Degree of turbulence in the upper layer.</p> Signup and view all the answers

    What is the stack effect in a tall building?

    <p>The vertical flow of air in a building, driven by vertical pressure differences developed by thermal buoyancy due to a difference between the building interior temperature and the outdoor temperature.</p> Signup and view all the answers

    True/False: The lowest zone is luminous; the gases accelerate upward.

    <p>True</p> Signup and view all the answers

    True/False: When a fire plume hits a ceiling, it spreads horizontally.

    <p>True</p> Signup and view all the answers

    What are the 3 concepts of reading smoke?

    <p>Smoke is fuel, The fuels have changed, Smoke has 'triggers'.</p> Signup and view all the answers

    What are the 4 steps to reading a fire?

    <p>Evaluate the key attributes, Weigh the Factors, Judge the Rate of Change, Predict the Event.</p> Signup and view all the answers

    What are the 4 key attributes of smoke?

    <p>Volume, Velocity (Pressure), Density, Color.</p> Signup and view all the answers

    What color is smoke that indicates early-stage heating?

    <p>White</p> Signup and view all the answers

    What color is smoke that comes from unfinished wood as it approaches late-stage heating?

    <p>Brown</p> Signup and view all the answers

    What color is smoke that is high-volume, turbulent, and ultra-dense, indicating impending autoignition?

    <p>Black</p> Signup and view all the answers

    What color is smoke from plastics and painted/stained surfaces?

    <p>Gray</p> Signup and view all the answers

    Study Notes

    Ventilation Limited Fire

    • Characterized by fire growth restricted by available oxygen.
    • Heat release rate directly correlates to oxygen supply.

    Critical Points of Ventilation Limited Fire

    • Key factors include ignition, fire under-ventilation, and fire department interventions.

    Flow Path

    • Describes heat and smoke movement from high-pressure fire areas to lower-pressure exits like doors and windows.

    Neutral Plane

    • The horizontal interface between hot upper gases and cooler lower layers in a fire environment.

    Fire Plume

    • Defined as the vertical column of hot gases, flames, and smoke emitted during a fire.

    Factors Influencing Fire Growth

    • Magnitude and direction of flow are essential in determining fire growth dynamics.

    Air Entrainment

    • The process by which air is drawn into a fire plume, influenced by the plume's buoyant movement.

    Zones of Fire Plume Structure

    • Three zones: luminous flame zone (constantly upward accelerating gases), intermittently flaming zone, and buoyant plume zone (ascending gases losing momentum).

    Turbulence Intensity

    • High turbulence is noted in zones 2 and 3, indicating chaotic fire behavior.

    Combustion Activity

    • Combustion occurs in zones 1 and 2, highlighted by the presence of flames.

    Flame Behavior in Fire Zones

    • Zone 3 is where flames cease, marking the end of active combustion.

    Characteristics of Flame Zones

    • Zone 1: Luminous flame zone; gases accelerate upwards.
    • Zone 2: Intermittent flaming; consistent upward velocity.
    • Zone 3: Buoyant plume; gases experience a decrease in height.

    Flame Height Measurement

    • Luminous flame height measures the distance from the flame base to a point where the plume is evenly luminous and transparent.

    Plume Diameter

    • Plume diameter increases proportionally to height, affecting dispersion.

    Temperature Distribution

    • Average midline temperature drops inversely proportional to height raised to 5/3.
    • Average midline velocity declines inversely proportional to height raised to 1/3.

    Ceiling Jet (CJ)

    • Radial outward flow beneath the ceiling caused by fire plume impacts.

    Vent-Limited Fire Dynamics

    • Involves application of the ideal gas law and oxygen depletion during combustion.

    Air Entrainment Rate

    • Proportional to both the burn rate and the vertical distance between the plume base and the neutral plane.

    Heat Loss Effects

    • "Drag" effects on outflow rate are influenced by heat loss to ceilings and upper walls.

    Heat Loss Determinants

    • Dependent on thermal inertia of walls, heat capacity of upper-layer gases, and turbulence degree in the upper layer.

    Stack Effect

    • The vertical airflow in tall buildings caused by temperature differences between indoors and outdoors.

    Smoke Characteristics

    • Reading smoke entails identifying its fuel properties, changes in fuel composition, and possible "triggers" for events.

    Steps to Reading a Fire

    • Evaluate key smoke attributes, weigh contributing factors, judge rate of change, and predict future fire behavior.

    Key Attributes of Smoke

    • Volume, velocity (pressure), density, and color essential for assessing fire conditions.

    Smoke Colors and Their Implications

    • White smoke: slow, low-pressure, indicates early heating stages.
    • Brown smoke: from unfinished wood, signifies late heating stages.
    • Black smoke: high volume, turbulent, indicates imminent autoignition.
    • Gray smoke: results from burning plastic and surfaces, due to moisture and hydrocarbons interaction.

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    Description

    This quiz explores the characteristics and critical aspects of ventilation limited fires. Key factors such as flow paths, neutral planes, and fire plumes are discussed, alongside elements influencing fire growth dynamics. Enhance your understanding of essential fire behavior concepts.

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