Ventilation

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Ventilation

• Essentials of Fire Fighting
• NFPA 1001
• Ventilation Practices SFFMA 8-1.1,1.2,1.7,1.8

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Definition

• Ventilation - The systematic removal of heated
  air, smoke, and gases from a structure and
  replacement with cooler air.

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Early ventilation methods

• From the earliest times, man has recognized that
  heated air, gases, and smoke rises. Cave
  dwellers and Indians practiced ventilation
  techniques by creating natural vents in the roofs
  of their caves, igloos, and tents. Early
  settlers vented their wood fires through
  stovepipes and chimneys, and ventilated their
  homes through doors and windows.

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Early ventilation methods - cont

• Today, when these natural means are unavailable,
  unworkable, or ineffective, mechanical fans
  kitchen and bathroom ventilators and louvered
  attic ventilators are often built-in as a way
  of assisting nature.
• However, built-in ventilation systems are
  generally not powerful enough to handle the
  tremendous heat, smoke, and gasses given off in a
  structural fire. It is at this point that the
  firefighter must step in and provide other means
  of ventilation.

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Types of Ventilation

• Vertical ventilation
• Horizontal ventilation
• Forced ventilation
• Mechanical positive pressure
• Mechanical negative pressure
• Hydraulic
• Built-in ventilation systems

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How has modern technology increased the emphasis
on ventilation?

• Increased fuel load in all occupancies due to
  increased use of plastics and other synthetic
  materials.
• More products of combustion.
• More dangerous products of combustion.

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Backdraft

• Introduction of oxygen causes fire of explosive
  force

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Characteristics of potential backdraft

• Pressurized smoke exiting small openings
• Black smoke becoming dense gray-yellow
• Confinement and excessive heat
• Little or no visible flame
• Puffs of smoke leaving building
• Smoke-stained windows
• Muffled sounds
• Rapid inward suction of air when opening is made

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Flashover

• Simultaneous ignition of all combustibles in room
• High heat from floor to ceiling

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Flashover potential

• Heat buildup
• Room contents heated to ignition temperature

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Reasons for Ventilation

• Saving lives
• Aid rescue operations
• Reduce flashover potential
• Reduce backdraft potential
• Suppressing Fire
• Aid in attack and extinguishment
• Control fire spread
• Reducing damage
• Enable property conservation

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Factors for Ventilating

• Is there a need for ventilation at this time?
• Where is ventilation needed?
• What type of ventilation should be used?

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Is there a need for ventilation at this time?

• Need based on heat, smoke, and gas conditions
  within the structure, structural conditions, and
  life hazards.

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Where is ventilation needed?

• Decision based on construction features, building
  contents, exposures, extent of fire, location of
  fire, top or vertical openings, and cross or
  horizontal openings.

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What type of ventilation should be used?

• Natural or mechanical, horizontal or vertical,
  hydraulic.

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What life safety hazards are likely to be found
in an unvented burning structure in which smoke
and gases have accumulated?

• Obscurity caused by dense smoke
• Presence of toxic gases
• Lack of oxygen
• Presence of flammable gases
• Danger of backdraft, flashover, and rollover

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Remember

• The smoke density, behavior, and color can aid in
  making a ventilation decision.

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What building factors aid the firefighter in
determining whether to use horizontal or vertical
ventilation?

• The number and size of wall openings
• The number of stories, staircases, shafts,
  dumbwaiters, ducts, and roof openings
• The availability and involvement of exterior fire
  escapes and exposures

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Problems to consider when ventilating a high-rise
building

• Number of occupants
• Number of internal vertical openings
• Smoke/fire gas stratification
• Number of personnel (four to six times as great
  as for a residential fire)
• Communication and coordination among personnel
• Roof ventilation

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Problems posed by basements

• Need to descend through heat and smoke to reach
  the seat of the fire
• Outside entrances blocked or secured for
  protection against burglars
• Impractically or difficulty of natural ventilation

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Problems posed by windowless buildings

• Adversely affect fire fighting and ventilation
  operations
• Ventilation may be delayed, allowing the fire to
  gain headway or to create backdraft conditions
• Usually require mechanical ventilation for smoke
  removal
• May be able to use built-in ventilation system

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Factors affecting where to ventilate

• Availability of natural openings
• Location of fire
• Building construction
• Wind direction
• Phase of fire
• Building condition
• Building contents

• Signs of possible roof collapse
• Consequences to fire
• Consequences to exposures
• Attack crews readiness
• Ability to protect exposures

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Remember

• Vertical ventilation usually means opening the
  roof or existing roof openings to allow heated
  gases and smoke to escape to the atmosphere

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Different roof types

• Flat
• Mansard
• Shed
• Butterfly
• Hip
• Gable
• Lantern
• Gambrel
• Arch

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Note

• Existing roof openings should be used for
  vertical ventilation whenever possible. The
  openings may not be large enough and may have to
  be supplemented with additional openings

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Cautions

• In addition to the existing openings already
  discussed, the flat roofs found most commonly on
  commercial, industrial, and apartment buildings,
  may also contain such obstacles as satellite
  dishes, electrical and guy wires, television
  antennas, heating and air conditioning equipment,
  water towers, swimming pools, roof gardens,
  clotheslines, and pet cages

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Flat roof constructions
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What is the best way for the fire department to
determine roof materials and construction details?

• Through inspection and pre-incident planning
  surveys

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Pitched roof construction
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Arched roof construction
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What is trench (or strip) ventilation?

• Cutting a large hole or trench at least 4 feet
  (1.3m) wide and extending from one exterior wall
  to the opposite exterior wall to stop the spread
  of fire

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When and where is trench ventilation most
commonly used?

• Most commonly used on low, widely expansive
  occupancies such as schools, shopping malls, and
  motels

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Why is vertical ventilation of critical
importance when attacking a basement fire?

• Commonly, the first extension from a basement
  fire will be in the attic, particularly in very
  old buildings with balloon frame construction

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What are some ways in which a basement can be
directly ventilated?

• Horizontal ventilation through ground-level
  windows or below-ground-level windows in wells
• Through interior vertical shafts such as
  stairwells and hoistway shafts
• Through a hole in the floor near a ground-level
  door or window, using mechanical ventilation to
  force the smoke from the floor opening out the
  exterior opening

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Upsetting vertical ventilation

• Improper use of forced ventilation
• Excess breakage of glass
• Fire streams directed into ventilation holes
• Breakage of skylights
• Explosions
• A burn-through
• Additional openings between attack team and upper
  opening

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Caution

• Be careful when projecting a stream downward
  through a vertical opening. Elevated streams
  projected just above the horizontal plane are
  effective in subduing sparks and flying brands
  rising from the ventilation opening and in
  reducing the heat of the thermal column.

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Caution

• Never project a stream through the ventilation
  hole while firefighters are still inside the
  building because such action stops the
  ventilation process and places interior crews in
  serious danger

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Note

• Vertical ventilation is not the solution to all
  ventilation problems because often its
  application would be impractical or impossible.
  In these cases, other strategies, such as
  horizontal ventilation should be considered

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Definition

• Horizontal Ventilation The venting of heat,
  smoke, and gases through wall openings such as
  windows and doors.

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Examples of structures that lend themselves to
horizontal ventilation

• Residential buildings in which the fire has not
  involved the attic
• The involved floors of multistory structures
  below the top floor or the top floor if the
  attic is uninvolved
• Buildings with large, unsupported, open spaces
  under the roof and structural weakness

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Factors to consider when using horizontal
ventilation

• The importance of weather conditions
• Routing of heat and gases as it relates to
  occupant safety and exposures
• The ignition hazard to higher portions of the
  fire building posed by rising heated gases
• The placement of charged lines
• Precautions against upsetting horizontal
  ventilation

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Horizontal ventilation being interrupted by a
firefighter
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Forced ventilation

• To this point, ventilation has been considered
  from the standpoint of the natural flow of air
  currents and the currents created by fire
• Forced ventilation is accomplished mechanically
  (with blowers or ejectors) and hydraulically
  (with fog streams)

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Safety measures that should be used when using
blowers or ejectors

• Clear personnel from the area before starting
• Do not place where clothing, draperies, or
  curtains can be drawn into the fan
• Avoid the discharge stream because of heat and
  particles that may be projected by the venting
  equipment

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Advantages of forced ventilation

• Ensures more positive control
• Supplements natural ventilation
• Speeds ventilation process
• Allows for safer and more rapid rescue
• Reduces smoke damage
• Promotes good public relations

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Disadvantages of forced ventilation

• May cause fire to intensify and spread
• Is dependent on a power source
• Requires special equipment

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What are the primary differences between negative
and positive-pressure ventilation?

• Negative-pressure ventilation
• Positive-pressure ventilation

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Negative-pressure ventilation

• Pressure inside the building is lower than
  outside the building air is pulled from the
  windward side through the building and exhausted
  on the leeward side

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Positive-pressure ventilation

• Pressure inside the building is greater than that
  outside the building air is generally blown into
  the building from the windward side and exits on
  the leeward side

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Note

• If the prevailing wind cannot be used (i.e., fire
  is on the windward end of the building), positive
  pressure has proven effective against winds of up
  to 25 mph. As winds exceed 25 mph, efficiency is
  reduced accordingly

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Hydraulic ventilation

• Forced ventilation used to clear a structure of
  heat, smoke, steam, and gases following the
  initial knockdown of the fire
• Takes advantage of the air that is drawn into a
  fog stream to help push the products of
  combustion out of the structure

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How wide must the fog pattern be in hydraulic
ventilation?

• Wide enough to cover 85 to 90 percent of the
  window or door opening through which the smoke
  will be pushed

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What is the closest the nozzle tip should be to
the ventilation opening?

• No closer than 2 feet (0.6 m) from the opening

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The end