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14Ventilation

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Objectives (1 of 4)

• Define ventilation as it relates to fire suppression activities.

• List the effects of properly performed ventilation on fire and fire-suppression activities.

• Describe how fire behavior principles affect ventilation.

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Objectives (2 of 4)

• Describe how building construction features within a structure affect ventilation.

• List the principles, advantages, limitations, and effects of horizontal ventilation.

• List the principles, advantages, limitations, and effects of natural ventilation.

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Objectives (3 of 4)

• List the principles, advantages, limitations, and effects of mechanical ventilation.

• List the principles, advantages, limitations, and effects of negative-pressure and positive-pressure ventilation.

• List the principles, advantages, limitations, and effects of hydraulic ventilation.

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Objectives (4 of 4)

• List the principles, advantages, limitations, and effects of vertical ventilation.

• List safety precautions for ventilating roofs.

• List the basic indicators of roof collapse.

• Explain the role of ventilation in the prevention of backdraft and flashover.

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Introduction (1 of 2)

• Ventilation – The process of removing smoke, heat, and

toxic gases from a burning building and replacing them with cooler, cleaner, more oxygen-rich air

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Introduction (2 of 2)

• Primary method of fire spread is convection.

• Mushrooming occurs when the products of combustion reach the highest point.

• Products of combustion present a risk.

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Benefits of Proper Ventilation (1 of 2)

• Locate trapped occupants faster

• Fresh air to occupants

• Advance hose lines more rapidly and safely

• Reduce backdraft and flashover

• Limit fire spread

• Reduce property loss

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Benefits of Proper Ventilation (2 of 2)

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Backdraft (1 of 2)

• Occurs when building is charged with hot gases and oxygen has been consumed

• When air is introduced, fuel can ignite and explode.

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Backdraft (2 of 2)

• Release heat and unburned particles without allowing entry of clean air.

• Ventilate as high as possible.

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Flashover

• Needs both ventilation and cooling• Occurs when

– Air in room is very hot.– All combustibles in the space are near their

ignition point.

• Applying water cools the atmosphere.• Ventilation draws the heat and flames

away.

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Factors Affecting Ventilation (1 of 2)

• Convection– Heated gases will always follow the path of least

resistance.– Use this basic principle to cause the convection flow

to draw heated products out of the building.

• Mechanical ventilation activities– Negative-pressure– Positive-pressure– Hose streams

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Factors Affecting Ventilation (2 of 2)

• Wind and atmospheric forces– Wind speed and

direction– Temperature and

humidity

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Building Construction Considerations

• The way a building is constructed will affect ventilation operations.

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Fire-Resistive Construction• Construction design

– Structural components noncombustible– Compartmentalization

• Paths of fire spread– Heating, cooling, plumbing, electrical– Elevator shafts– Stairwells

• Roofs generally steel or concrete

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Ordinary Construction (1 of 2)

• Construction design– Exterior walls noncombustible– Interior walls/floors of wood– Roof is wood decking and structural support.

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Ordinary Construction (2 of 2)

• Paths of fire spread– Plumbing and

electrical chases– Void spaces in walls– Cockloft

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Wood-Frame Construction

• Exterior walls are combustible

• Paths of fire spread– Attics and cocklofts– Wood truss roofs and floors

• Construction types– Balloon-frame– Platform

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Ventilation and Tactical Priorities

• Ventilation is directly related to tactical priorities.

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Venting for Life Safety

• Life safety is the primary goal.

• Gives occupants a greater chance to survive

• Makes searches faster

• Limits fire spread to other occupants and fire fighters

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Venting for Containment

• Second highest priority is contain the fire and control the situation.

• Prevents fire spread

• Makes fire attacks easier

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Venting for Property Conservation

• Can significantly limit property damage

• Rapid ventilation reduces damage from smoke, heat, and water.

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Types of Ventilation

• Two basic types of ventilation– Horizontal

• Utilizes horizontal openings in a structure such as doors and windows

– Vertical • Involves openings in the roofs or floors

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Horizontal Ventilation (1 of 2)

• Commonly used in residential fires and room-and-contents fires

• Generally fast and easy to use

• Can be used from inside or outside the building

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Horizontal Ventilation (2 of 2)

• Most effective when opening is directly to outside

• More difficult when there are no openings

• Limits structural damage

• May utilize natural and mechanical methods

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Methods of Ventilation

• Natural– Depends on convection currents, wind, and

other natural air movement

• Mechanical– Uses mechanical means to augment natural

ventilation

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Natural Ventilation

• Used when air currents are adequate

• Used when ventilation is needed quickly

• Open leeward side of building first, then windward.

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Breaking Glass (1 of 2)

• General rules– Try to open first.– Wear full protective

clothing and eye protection.

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Breaking Glass (2 of 2)

• General rules (continued)– Ensure no one will be

struck by the glass.– Always use a tool.– Keep hands above or

to the side of the glass.

– Use a tool to clear remaining glass.

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Opening Doors

• Provide large openings.

• May compromise entry/exit points

• May be best for clean air points

• Good location for mechanical ventilation devices

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Mechanical Ventilation

• Methods of mechanical ventilation– Negative-pressure– Positive-pressure– Hydraulic

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Negative-Pressure Ventilation

• Ejectors• Limitations:

– Positioning– Power source– Maintenance– Air flow control

• Advantages– Explosion-proof

motors

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Positive-Pressure Ventilation

• Large, powerful fans • Advantages:

– Quick and efficient– Increased safety

• Disadvantages– May spread the fire– May increase carbon

monoxide levels

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Hydraulic Ventilation

• Fog or broken pattern• Advantages

– Move several thousand cubic feet of air per minute

• Disadvantages– Water damage– Safety hazards

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Vertical Ventilation (1 of 2)

• Releases combustion products vertically

• Occurs naturally if there is an opening

• May be assisted by mechanical means

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Vertical Ventilation (2 of 2)

• Make opening close to seat of fire

• Determine hottest point

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Safety Considerations (1 of 2)

• Structural stability of the roof

• Falling from the roof

• Two exit routes

• Opening should not be between fire fighters and exit.

• Have a charged hose line ready.

• Leave the area once done.

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Safety Considerations (2 of 2)

• “Sound” the roof• Walk on areas of

greatest support• Make cuts from

– Upwind– With clear exit path– While standing on firm

section

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Basic Indicators of Roof Collapse

• Spongy feeling

• Visible sagging

• Roof separating from the walls

• Structural failure in another portion of building

• Sudden increase in fire intensity

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Roof Construction

• Two components– Support structure

• Solid beams of wood, steel, or concrete• System of trusses of wood, steel, or wood and

steel

– Roof covering• Made of various weather-resistant materials• Supported by the roof decking

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Types of Roof Failures

• Support system failure– Supporting structure fails– Often a sudden and total collapse

• Roof covering failure– Burns through roof covering – Spreads out causing roof failure– In warmer climates burn through quickly; in

colder climates burn with little evidence

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Solid Beam vs. Truss

• Solid beam– Girders, beams, and

rafters

• Truss– Lightweight

components– Wood or steel bars– Triangular

configuration

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Roof Designs (1 of 2)

• Flat roofs– Can be constructed with many types of

supports, decking, and materials

• Pitched roofs– Have a visible slope for rain, ice, and snow

runoff

• Type of construction dictates how to ventilate

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Roof Designs (2 of 2)

• Arched roofs– Generally found in

commercial structures to create a large span without columns

– Use bowstring trusses in which fire can severely and quickly weaken structure

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Objectives of Vertical Ventilation

• Provide the largest opening

• Put in an appropriate location

• Use the least amount of time

• Use the safest technique

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Vertical Ventilation Assessment (1 of 2)

• Construction features• Indications of fire

damage• Safety zones and exit

paths• Built-in roof openings

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Vertical Ventilation Assessment (2 of 2)

• Locate at highest point and over seat of fire

• May need to cut an examination hole

• One hole is better than several small ones

• Minimum size 4' x 4'

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Tools Used in Vertical Ventilation

• Power saws

• Axes

• Halligan tools

• Pry bars

• Tin cutters

• Pike poles, other types of hooks

• Utility rope

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Types of Roof Cuts

• Rectangular cut

• Louver cut

• Triangular cut

• Peak cut

• Trench cut

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Rectangular Cut

• Requires four cuts completely through the decking

• Use care to not cut structural supports.

• Stand upwind and have a safe exit.

• Can use a triangular cut to help pry up

• If several layers exist, may have to peel a layer at a time

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Louver Cut

• Used for flat or sloping roofs with plywood decking

• Power saw or axe used to make the cuts

• Can quickly create a large opening

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Triangular Cut

• Used to prevent metal decking from rolling away as it is cut

• A saw or axe is used.• Several may be

needed because of their small size.

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Peak Cut

• Used for peaked roofs with plywood sheeting

• A tool is used to reveal the roof covering along the peak.

• A power saw or axe is used to make a series of vertical cuts.

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Trench Cut

• Used as a defensive tactic to stop the progress of a large fire in a narrow building

• Creates a large opening ahead of the fire

• “Writes off” part of the building

• Requires both time and manpower

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Special Considerations

• Obstacles preventing ventilation

• Concrete roofs

• Metal roofs

• Basement fires

• High-rise buildings

• Windowless buildings

• Large buildings

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Obstacles to Ventilation

• Poor access

• Multiple roofs and roof layers

• Sealed and boarded abandoned buildings

• Security measures such as steel bars and shutters

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Ventilating a Concrete Roof

• Found in commercial and industrial structures

• Generally flat and hard to breach

• May collapse from weakened support systems when exposed to fire

• Search for alternative openings

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Ventilating a Metal Roof

• Discoloration and warping may indicate seat of fire.

• As fire heats the metal deck, tar roof covering can melt and leak into the building.

• Metal can roll down and create a dangerous slide directly into the opening.

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Venting a Basement

• Usually few windows

• Usually requires both horizontal and vertical ventilation

• Fire fighters must descend the stairs through the venting combustion products.

• Make as many openings on one side and allow fire fighters to enter from the other

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High-Rise Buildings

• Many have hard to break sealed windows.

• Unique smoke patterns with stack effect.

• Newer buildings have smoke management in the HVAC.

• Designate one stairwell as a rescue route.

• Positive-pressure fans can keep smoke out of the stairs.

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Stack Effect Smoke Patterns

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Windowless Buildings

• Traps heat and smoke

• Treat similar to a basement fire.

• Ventilate high.

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Large Buildings

• More difficult than small ones

• Smoke cools as it travels, causing stratification.

• When possible, use interior walls and doors to create smaller areas.

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Summary (1 of 3)

• Ventilation provides many benefits.

• Several factors affect ventilation.

• Building construction affects ventilation.

• Ventilation is related to life safety, fire containment, and property conservation.

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Summary (2 of 3)

• Assessing the location and extent of smoke and fire will determine ventilation.

• The types of ventilation are horizontal and vertical.

• Horizontal ventilation uses horizontal openings in a structure.

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Summary (3 of 3)

• Vertical ventilation refers to the release of heat and smoke in a vertical direction.

• Many obstacles can be encountered during ventilation operations.

• Ventilation is a major consideration in backdraft and flashover.