Transcript Ventilation PowerPoint

14
Ventilation
14
Objectives (1 of 3)
• 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.
• Describe how building construction features
within a structure affect ventilation.
2
14
Objectives (2 of 3)
• Define horizontal ventilation.
• List the principles, advantages, limitations,
and effects of horizontal ventilation.
• List the principles, advantages, limitations,
and effects of vertical ventilation.
• List the principles, advantages, limitations,
and effects of natural ventilation.
• List the principles, advantages, limitations,
and effects of mechanical ventilation.
3
14
Objectives (3 of 3)
• List the principles, advantages, limitations,
and effects of positive-pressure and negativepressure ventilation.
• List the principles, advantages, limitations,
and effects of hydraulic 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.
4
14
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
5
14
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 to fire
fighters and occupants.
6
14
Benefits of Proper Ventilation
(1 of 2)
• Locate trapped occupants faster
• Fresh air to occupants overcome by
smoke
• Advance hose lines more rapidly and
safely
• Reduce backdraft and flashover
• Limits fire spread
• Reduces property loss
7
14
Benefits of Proper Ventilation
(2 of 2)
Unvented structure
Vented structure
8
14
Factors Affecting Ventilation
(1 of 2)
• Convection currents
• Mechanical ventilation activities
– Negative-pressure
– Positive-pressure
– Hose streams
9
14
Factors Affecting Ventilation
(2 of 2)
• Wind and
atmospheric forces
– Wind speed and
direction
– Temperature and
humidity
10
14
Building Construction
• The way a building is constructed will
affect ventilation operations.
11
14
Fire-Resistive Construction
• Construction design
– Structural components noncombustible
– Compartmentalization
• Paths of fire spread
– Heating, Ventilation, and Air Conditioning
– Stairways
– Elevator shafts
• Roofs generally of steel or concrete
12
14
Ordinary Construction
• Construction design
– Exterior walls noncombustible
– Interior walls/floors of wood
– Roof is wood decking and structural support
• Paths of fire spread
– Plumbing and electrical chases
– Void spaces in walls
– Cockloft
13
14
Wood-Frame Construction
• Construction design
– Similar to ordinary but exterior walls are
combustible
• Paths of fire spread
– Attics and cocklofts
– Wood truss roofs and floors
• Construction types
– Balloon-frame
– Platform
14
14
Ventilation and Tactical Priorities
• Ventilation is directly related to tactical
priorities.
15
14
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
16
14
Venting for Confinement
• Second highest priority is contain the
fire and control the situation
• Prevents fire spread
• Makes fire attacks easier
17
14
Venting for Property
Conservation
• Limits amount of damaged areas
• Rapid removal limits amount of
permanent damage.
18
14
Location and Extent of Smoke
and Fire Conditions (1 of 3)
• Factors to consider
– Size of the fire
– Stage of combustion
– Location within the building
– Available ventilation options
19
14
Location and Extent of Smoke
and Fire Conditions (2 of 3)
• Where to ventilate
– As close to the fire as possible
• Directly over the seat
• Through an open door or window that opens
outside
– If unable to vent close to the fire
• Predict how location will affect the fire
• Anticipate fire spread and locate hose lines for
protection
20
14
Location and Extent of Smoke
and Fire Conditions (3 of 3)
• Determine fire size, intensity, and fuel
– Light smoke, moving lazily—small fire of
ordinary combustibles
– Large amount of black rolling smoke—
petroleum base fire
– Hotter the fire, the faster the smoke moves
– Cool days may cause smoke inversion.
– Sprinkler activation may cause the smoke
to cool and act as a fog.
21
14
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
22
14
Horizontal Ventilation (1 of 2)
• Commonly used in
– Residential fires
– Room-and-contents fires
– Fires that can quickly be
controlled
• Generally fast and easy
to use
• Can be used from
inside or outside the
building
23
14
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
24
14
Methods of Ventilation
• Natural
– Depends on convection currents, wind, and
other natural air movement
• Mechanical
– Uses mechanical means to augment
natural ventilation
25
14
Natural Ventilation
• Used when air currents are adequate
• Used when ventilation is needed quickly
• Open leeward side of building first, then
windward.
26
14
Breaking Glass
• General rules
– Try to open first.
– Wear full protective
clothing and eye
protection.
– 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.
27
14
Opening Doors
•
•
•
•
Provide large openings
May compromise entry/exit points
May be best for fresh air points
Good location for mechanical ventilation
devices
28
14
Mechanical Ventilation
• Methods of Mechanical Ventilation
– Negative-pressure
– Positive-pressure
– Hydraulic
29
14
Negative-Pressure Ventilation
• Uses fans called
ejectors to exhaust
smoke and heat
• Limitations:
–
–
–
–
Positioning
Power source
Maintenance
Air flow control
• Advantages
– Explosion-proof motors
30
14
Positive-Pressure Ventilation
• Uses large, powerful
fans to force fresh air
into a structure.
• Advantages:
– Quick and efficient
– Increased safety
• Disadvantages
– May spread the fire
– May increase carbon
monoxide levels
31
14
Hydraulic Ventilation
• Uses a fog or broken
pattern stream to create
a pressure differential
• Advantages
– Can move several
thousand cubic feet of air
per minute
– Does not require
specialized equipment
• Disadvantages
– Water damage
– Safety hazards
32
14
Vertical Ventilation (1 of 2)
•
•
•
•
Releases combustion products vertically
Occurs naturally if there is an opening
May be assisted by mechanical means
Usually involves making openings in
roof
33
14
Vertical Ventilation (2 of 2)
• Make opening close
to seat of fire
• Determine hottest
point
34
14
Safety Considerations (1 of 2)
•
•
•
•
Structural stability of the roof
Falling from the roof
Two exit routes
Not getting opening between you and
the exit
• Have a charged hose line
• Leave the area once done
35
14
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
36
14
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
37
14
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 water repellant materials
• Supported by the roof decking
38
14
Types of Roof Failures
• Support system failure
– Supporting structure fails
– Often a sudden and total collapse
– Areas with heavy snow loads more prone
• Roof covering failure
– Burns through roof covering close to seat of fire
– Spreads out causing roof failure
– Areas with light snow loads more prone
39
14
Solid Beam vs. Truss
• May not be able to tell
by looking
• Solid beam
– Girders, beams, and
rafters
• Truss
– Lightweight components,
often 2" x 4" wood with
gussets or staples
– Steel bars welded
together
– Triangular configuration
40
14
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
41
14
Roof Designs (2 of 2)
• Arched roofs
– Generally found in
commercial
structures to create a
large span without
columns
42
14
Objectives of Vertical Ventilation
•
•
•
•
Provide the largest opening
Put in an appropriate location
Use the least amount of time
Use the safest technique
43
14
Vertical Ventilation Assessment
•
•
•
•
•
•
•
•
Construction features
Indications of fire damage
Safety zones and exit paths
Built-in roof openings
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'
44
14
Tools Used in Vertical Ventilation
•
•
•
•
•
•
•
Power saws
Axes
Halligans
Pry bars
Tin cutters
Pike poles and other types of hooks
Utility rope
45
14
Types of Roof Cuts
•
•
•
•
•
Rectangular cut
Louver cut
Triangle cut
Peak cut
Trench cut
46
14
Rectangular or Square Roof 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 triangle cut to help pry up
• If several layers exist, may have to peel
a layer at a time
47
14
Louver Roof 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
48
14
Triangle Roof 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.
49
14
Peak Roof 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 between the
supports.
50
14
Trench Roof 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
51
14
Special Considerations
•
•
•
•
•
•
•
Obstacles preventing ventilation
Concrete roofs
Metal roofs
Basement fires
High-rise buildings
Windowless buildings
Large buildings
52
14
Obstacles to Ventilation
• Poor access
• Multiple roofs and roof layers
• Sealed and boarded abandoned
buildings
• Security measures such as steel bars
and shutters
• Concrete roofs
• Metal roofs
53
14
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
54
14
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.
55
14
Venting a Basement
• Usually few windows
• Fire will quickly spread
• 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
56
14
High-Rise Buildings
• Many have hard to break sealed windows.
• They create unique smoke patterns with the
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.
57
14
Stack Effect Smoke Patterns
58
14
Windowless Buildings
• Traps heat and smoke
with no secondary exit
• Treat similar to a
basement fire.
• Ventilate high and use
mechanical assistance.
• May need to
– use existing roof
openings, cut new ones
– reopen boarded
windows/doors or make
new openings
59
14
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.
60
14
Backdraft
• May occur when building is charged with hot
gases and most of oxygen has been
consumed
• When air is introduced, fuel can ignite and
explode.
• Prevent by releasing heat and unburned
particles without allowing fresh air
• Ventilate as high as possible.
• Once flaming begins, fire fighters may enter.
61
14
Flashover
• Needs both ventilation and cooling
• Occurs when
– air in room is very hot and
– all combustibles in the space are near their
ignition point
• Applying water cools the atmosphere
• Ventilation draws the heat and flames
away
62
14
Summary (1 of 2)
• Ventilation provides many benefits.
• Several factors affect ventilation.
• Building construction affects ventilation
operations.
• Ventilation is related to life safety, fire
containment, and property conservation.
• Assessing the location and extent of smoke
and fire will determine ventilation operations.
• The types of ventilation are horizontal and
vertical.
63
14
Summary (2 of 2)
• Horizontal ventilation uses horizontal
openings in a structure.
• 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.
64