Transcript of Ventilation 1. Introduction Ventilation: planned, methodical, systematic removal of pressure, heat,...
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- Ventilation 1
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- Introduction Ventilation: planned, methodical, systematic
removal of pressure, heat, smoke, gases, and flame Essential part
of tactical and strategic objectives Late application of proper
ventilation subjects firefighters to extreme circumstances. Complex
subject area with many facets 2
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- Principles, Advantages, and Effects of Ventilation Ventilation
Essential to fire suppression Benefits: Deprives fire of ability to
heat up structure Channels smoke out of the structure Removal of
smoke, heat, and toxic gases add survival time to a potential
victim 3
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- Heat, Smoke, and Toxic Gases When fire burns, air heats,
expands, and rises. Convection Radiation Structures built today
Heavy insulation Tight weatherproof seams Windows that do not open
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- Gases Produced by Fire 5
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- Considerations for Proper Ventilation Heat tends to rise. Smoke
collects under vertical obstructions. Mushrooms Fills the structure
from highest point Vertical ventilation Horizontal ventilation
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- Heat, smoke, and fire will follow the path of least resistance
and find their way through any available opening. 7
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- Air movement is created by water application. Openings in back
of the nozzle team will create airflow from behind in the direction
of the hose team. It can be a source of fresh cool air, or it can
pull fire to the nozzle from behind. Indiscriminate ventilation can
be a liability. Careful assessment and proper timing are important.
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- Fire and Its By-Products During combustion, energy is released
from exothermic reaction: Heat Light Harmful agents Carbon dioxide
Ventilation prevents: Flashover and backdraft Smoke explosion
Rollover/flameover 9
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- Flashover Temperature increases When temperature reaches
ignition point of any substance in the room, new combustion occurs.
Chain reaction Very rapid fire spread 10
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- Backdraft (Smoke Explosion) Rapid ignition of smoke and
unburned products of combustion With heat, pressure builds Smoke
escapes Introduction of fresh air Ignition 11
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- Signs of a Potential Backdraft Short distance to opening
Unspectacular Flaring up Long distance to opening Proper
concentration from opening to seat is greater Greater force
Instantaneous reaction 12
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- Rollover/Flameover Heat brings products of combustion to higher
levels. Accumulated heat reaches ignition point. Flame reaches
across the room, followed by a wall of flame. Advancing hoseline
disrupts the upper thermal layer. 13
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- What Needs to be Vented? Without ventilation Expanding heated
steam and smoke will roll over the wall of water. Before building
requires venting, voids and compartments need to vent. If timely,
involvement of building might be avoided. 14
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- Applying water to the upper levels of a thermal layer will cool
and disrupt the rollover effect that is apt to occur with the
proper conditions. Ventilation is critical when this is done.
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- 18.16 As a hose team advances into the fire and sprays water in
droplet form, it creates a wall of water and disrupts the high-heat
thermal layer and cools the upper levels of the compartment. Water
absorbs heat as it turns to steam, expanding 1,700 times as it
does. If there is no path for the expanding water/steam conversion,
it will take the path of least resistance, in this case over the
wall of water and the nozzle team. The water movement will then
pull any heat from the back of the nozzle team and roll over on top
of it. 16
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- Voids and Compartments All compartments treated with same
understanding Residential building is a large compartment with many
sub- compartments. Each sub-compartment can be subdivided. Each
sub-compartment can be further subdivided. Eaves, peaks, gables,
etc. 17
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- Cocklofts Major attack point for ventilation crew Especially in
a top-floor fire or fire that has extended into that space 18
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- Horizontal and Vertical Voids Heat follows the path of least
resistance. Unobstructed channel in form of horizontal or vertical
void Heat and fire extend without being seen. Ventilating
horizontal and vertical voids 19
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- Voids in a typical structure that can trap heat and permit fire
extension. 20
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- Voids in a typical structure that can trap heat and permit fire
extension. 18.21 21
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- Air Movement Convection Conduction Radiation 22
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- Types of Ventilation Methods used individually or in
combination Natural ventilation Mechanical ventilation 23
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- Smoke will be carried throughout the building to upper floors
by normal air currents mixed in with the heat. 24
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- A smoke ejector exhaust fan placed in an opening will pull air
through the fan as it ejects air out of the structure. 25
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- Positive pressure literally pressurizes the structure and
forces smoke out any path of least resistance. Almost the same
effect would occur if a light breeze were blowing directly into the
structure from one side and venting out the other side. 26
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- PPV can be used in a positive pressure attack (PPA) mode; the
incident commander must avoid PPV use during the following
conditions: Imminent or confirmed rescue of a firefighter or
civilian Working fire attack Unknown location of fire Inability to
provide a proper exhaust point Structure that presents an
over-pressurization or hostile event indicator 27 Mechanical
Ventilation
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- Mechanics of Ventilation Ventilation process Natural tendency
of air 28
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- Vertical Ventilation Heat rises rule of physics Collects at
upper levels and spreads fire to those levels Opening vertical
arteries Heated air replaced with cooler air 29
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- Horizontal Ventilation Same rules of vertical ventilation Both
are a form of diffusion Openings are made Smoke and heat are
channeled out 30
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- Heated air has more agitation in its molecules, causing
internal pressure in a compartment. This will, in turn, create
greater velocity when air exits an opening. Normal diffusion takes
much longer to occur when only natural air movement and currents
are employed. 31
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- Ventilation Techniques Many techniques used to effect
ventilation Simple and no tools Complex and dangerous, require
sophisticated tools 32
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- Break Glass Quickest way to ventilate Best investment of time
Time savings Glass dangers Wear protective equipment 33
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- Open Doors Opening a door exhausts huge volumes of smoke and
heat built up. Keeping door on its hinges is a good practice.
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- Effects of Glass Panes Many windows have several panes of
glass. Separated by wood or aluminum dividers Remove all glass.
Remove glass with a tool. Break through glass from upper to lower
sashes. Sweep perimeter to remove remaining glass. 35
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- Rope and a Tool When operating off a flat roof Rope secured to
the tool Turn of rope around firefighters hand Toss tool out in
horizontal direction. This technique leaves shards of glass.
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- Hook or Pike Pole Length keeps firefighter safe Enables access
to out-of-reach windows Hook also used to extend reach of
firefighter attempting to open or close a door 37
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- (A) Firefighters should make the hole so that heat, smoke, and
possibly flame do not envelop them. (B) When working off a ladder,
the same general precautions are necessary. Firefighters must be
secured to the ladder before performing any action. (A)(B) Making a
ventilation hole requires some preplanning. 38
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- 18.39 (C) When venting from above, firefighters use the wind to
their advantage and stand off to one side so that they are not
standing in the path of any initial billow of heat. (D) When
pulling off roof boards, firefighters should work in the clear air
with the wind blowing smoke away, and be careful with roof debris.
It will most likely be hidden in the smoke. (C)(D) Making a
ventilation hole requires some preplanning. 39
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- (E) When removing a skylight, firefighters work with the wind
at their backs. It is sometimes less work to lift off the entire
housing than to break out each individual pane of glass. (F) When
using an axe to remove window glass, the flat side of the axe head
should be used, not the point or the striking surface. (E)(F)
Making a ventilation hole requires some preplanning. 40
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- Iron or Halligan Tool brought down diagonally through the glass
Sweep around the perimeter Short length a disadvantage Plan
carefully to minimize risk 41
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- Axe Affords limited reach Places firefighter in hazardous
location Use an axe for venting glass Do not use blade portion Will
not break tempered glass 42
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- Portable Ladder Overhead obstructions Side of window Measure
the base so that the tip will fall into the glass at about 2/3 the
height of the window. Reposition the ladder. Shove the ladder into
the building. 43
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- Negative Pressure Ventilation Created on back side of fan blade
Place a fan facing the outward flow. Heat and smoke Positively
charged air and negatively charged air Limited access compartments
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- (A) When using an exhaust fan, it is important to cover the
openings around the unit. (B) When covering any opening around the
exhaust fan, the vacuum necessary to operate efficiently will be
created and the exhausted air will not be sucked back around the
fan. (A) (B) 45
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- 18.46 (C) When using an exhaust fan in a door, the air will
circulate from the exhaust side into the intake side if no
provision is made to block that flow. (D) Through the use of
plastic, tarps, or even a piece of plywood, the air is prevented
from being pulled back into the intake side of the fan. (C)(D)
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- Positive Pressure Ventilation Injects air into compartment and
pressurizes Smoke and heat carried outside the structure Fans set
up to augment one another For every cubic foot of air injected into
a compartment, a cubic foot of air must be ejected. Exhaust opening
size 47
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- With positive pressure ventilation, the theory is to actually
pressurize the compartment and then the smoke and heat will
actually be pushed out another opening. To be effective, certain
actions must be taken. (1) The blower or fan must be placed a short
distance from the opening so that a cone of air is created that
just barely exceeds the opening being used. (2) The exhaust opening
should be smaller than the introduction opening for maximum
efficiency. That opening size depends on the number of blowers and
their capacity. There are many variations where this practice can
be effective. 48
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- Roof Ventilation Use penthouse doors, skylights, and
ventilation shafts Two types of vertical openings Place offensive
openings into structure Evaluate need for defensive ventilation
Strip cut (trench cut) 49
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- Expandable Cut Efficient for time expended Large a hole as
needed Plan the cut Prevent damage to support rafters or cross
members One large opening produces more airflow than several
smaller holes. 50
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- The initial hole was cut and the lid lifted off in one piece.
In the foreground, the cuts of the second hole can be seen along
the right side of the hole. This type of roof, called an inverted
roof, consists of a flimsy under-roof support system while the
actual weight-carrying members exist at the occupancy ceiling
level. This photo illustrates how little support is available.
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- Two-Panel Louver Operation Offensive heat hole Based on a
series of cuts Begins with an outside cut Opening should be
evaluated for effectiveness Push in roofing pieces creating louvers
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- Louver in Lieu Offensive heat hole operation Placed into a
panelized roof Minimum of three people Area of greatest smoke
pressurization Members split into two teams 53
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- Triangular Cut Best candidate for this type of cut Roof
supported by open web bar joist with Q-decking Span of web bar
joist Opening can become a funnel Triangular cut will help support
underlying Q-decking Holes relatively small 54
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- Strip Cut or Trench Cut Ventilates the cockloft area or open
attic space Offensive heat hole Gases expanding under the roof are
vented. Building on fire side of the cut unsavable Hoseline
positioned below the cut 55
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- A trench cut is a defensive move. Ceilings should be pulled
below the cut to promote vertical airflow through the trench.
Additionally, a hand-line should be in place below the opening to
cut off any horizontal extension. 56
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- Below Grade or Basement Ventilation Creates many challenges
Locate exterior openings prior to entry Use roof ventilation
techniques on ground floor if no exterior openings Critical to
begin ventilation as early as possible 57 18.57
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- Inspection Cut First operation on a flat roof Determines: Roof
covering and depth of covering Roof sheeting material Rafter
direction Conditions directly below firefighters Types of
operations to be done First cut at 45 degrees to a bearing wall
Followed by a cut opposite the first Triangular inspection
completed with another cut 58
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- Smoke Indicator Hole Will adequately determine conditions
directly below firefighters Small triangular opening Placed in path
of access and egress 4.5 to 6 metres (15 to 20 feet) of travel
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- Safety Considerations Consider benefit gained against liability
created. In some cases, it is best not to vent at that location.
Example: Do not vent if venting would expose a victim and rescuer
on a ladder to danger. 60
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- Will Ventilation Permit the Fire to Extend? No justification
for permitting a fire to extend in order to complete a task Order
may be given without full understanding of the consequences
Incident commanders and new information 61
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- Will the Escape Route Be Cut Off? Individual safety Keep an eye
toward escape. When venting a series of windows, firefighter must
work toward the escape point. Should always be two easily
recognizable ways off a roof Escape routes lighted at night Rooftop
LCES 62
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- Ventilate in the direction of the escape route so escape is not
cut off. 63
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- Will Ventilation Endanger Others? Activity of one firefighter
must never endanger position of another. When opening a roof,
advise everyone else where the holes are. Torn-up roofing material
should be cleared away. Tripping hazards Think ahead of safety
problems. 64
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- Work in Teams Never work alone. Opportunity for discussion
Might make the difference between being located in a collapse May
make it possible to remove a heavy obstruction 65
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- Proper Supervision Conflicting options presented. Ensures
effort is unified Brings experience to activity Prevents members
from becoming too focused on mission 66
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- Obstacles to Ventilation Importance cannot be overstated. Fire
operations are unpredictable. Firefighters confronted with
unforeseen circumstances that delay ventilation activities 67
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- Access Initial size-up consideration First assess the needs of
the ventilation objective. Access to rear yard Map out access
strategy. 68
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- Security Devices Security devices Access Timing Examples Gates,
screens, steel doors, and closed-up windows Window openings sealed
Skylights replaced with plywood attached to inferior support
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- Height Be alert to structures ventilation needs. Sometimes
necessary to cut a hole in an area out of reach Think proactively
not reactively. 70
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- Poor Planning Planning is an obstacle to ventilation. Time is
not a luxury. Quick size-up Implementation of a plan essential If
ventilation delayed, interior team will suffer Backdraft Rollover
Diminished survival time Arduous working conditions 71
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- Personnel Assignment Task assigned to shorthanded or
inexperienced crew will delay ventilation Safety an overriding
concern Roof operation Two-person team can open many openings
quickly Structural components easily opened or removed by
individuals working together 72
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- Unfamiliar Building Layout Confusing floor layout Building
layout can be an obstacle. Building wings Fences Lower floor
extensions Multiple doors on same floor Walk-throughs and
inspections Often same floor plan exists throughout multistory
building 73
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- Ventilation Timing Ventilation too early Ventilation too late
Vertical ventilation of firefighter access holes is paramount.
Ventilation may have to be delayed if occupants/firefighters are
using stairs. 74
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- Cut a RoofOpen a Roof Cutting a roof and opening a roof are
different operations. Cutting a roof Opening a roof 75
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- Factors Affecting Ventilation Partial openings Screens Type of
roof material Construction features Building size Weather Wind
direction 76
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- Partial Openings Single opening has greater ventilation
capacity than multiple openings of equivalent area Chimneys Greater
the circumference, the less friction and the greater the flow Many
small holes have greater overall length of perimeters. The greater
the perimeter, the more opportunity to slow airflow. 77
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- Airflow is reduced by friction. 78
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- Partially Broken Windows Windowpane that is broken and many
shards of glass left in place Area of opening reduced Presence of
shards creates more perimeter opening distance 79
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- Airflow is greatest through a window where glass is fully
removed. Screens, shades, curtains, and window cross members should
also be removed. 80
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- Screens Presence of insect screens Failure to remove a screen
Removal of window treatments Any obstruction reduces airflow
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- Roof Material Roof material may be several layers thick. Kerf
cut When removing several layers, cut should not penetrate the
under-roof area. Corrugated metal roof 82
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- Dropped or Hanging Ceilings Dropped ceilings: Trapped air
pockets conceal fire and smoke. Raging fire will not vent through
roof opening. Several hanging ceilings may be in place. Space
between ceilings collects gases. Dropped ceiling are hazardous Not
always obvious Out of reach of roof firefighter Difficult to open
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- Building Size Building size affects ventilation. In tall
buildings, a neutral plane can occur. Factors affect development of
neutral plane: HVAC systems and ducts Wind direction Presence of
other buildings Outside temperature Smoke shafts 84
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- Weather Cool dry days Rainy humid days Snow Horizontal venting
is not affected the same way. Positive pressure ventilation 85
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- Opening Windows Simplest way to open a compartment One full
sash opening better than two Open top sash fully If smoke condition
from door opening will make room conditions worse, close door and
open window. Two windows, open one at upper sash and other at
bottom sash 86
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- Lessons Learned Ventilation is a tool used in firefighting.
Must be understood and manipulated Proper use the difference
between extinguishing a fire and creating conflagration Ventilation
enables firefighter to make a rescue. Heat rises and cold air drops
Airflow follows path of least resistance 87