Chapter 18
Ventilation
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
• Very complex subject area with
many facets
18.2
Principles, Advantages, and
Effects of Ventilation
• Ventilation: relief of products of
combustion
– Essential to fire suppression
• Benefits of ventilation:
– Deprives fire of ability to heat up structure
– Ventilation channels smoke out of the
structure
– Removal of smoke, heat, and toxic gases add
survival time to a potential victim
18.3
Heat, Smoke, and Toxic Gases
• When fire burns, air heats, expands, and
rises
– Exerts pressure on anything that surrounds it
• Fire spreads by convection and radiation
with rising of heated air
– Fire can spread by pressure
• Structures built today outfitted with heavy
insulation and tight weatherproof seams
• Many buildings have unopenable windows
– Ventilation important in these structures
18.4
Table 18-1 Gases Produced by Fire
18.5
Considerations for Proper
Ventilation
• Heat tends to rise, bringing smoke with it
• Smoke collects under vertical obstructions
– Mushrooms in all directions when it meets
obstruction
– Gradually fills the structure from highest point
• Vertical ventilation: removal of gases and
smoke through vertical channels
• Horizontal ventilation: channeling of
smoke and heat through horizontal
openings
18.6
Figure 18-1 Heat, smoke, and fire will follow the path of least
resistance and find their way through any available opening.
18.7
Figure 18-4 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.
18.8
Fire and Its By-Products
• During combustion, energy is released
from exothermic reaction as heat and light
• Ventilation removes harmful agents
• Carbon dioxide accelerates respiration
– Increases the rate of toxin absorption
• Ventilation prevents:
– Flashover and backdraft
– Smoke explosion
– Rollover/flameover
18.9
Flashover
• As trapped heat accumulates at the
ceiling, temperature increases
• When temperature reaches ignition
point of any substance in the room,
new combustion occurs
• Forms a chain reaction that causes
the entire room and all contents to
burn
• Very rapid fire spread
18.10
Backdraft (Smoke Explosion)
• Rapid ignition of smoke and unburned
products of combustion
– Result of introduction of oxygen into
environment
• With the heat, pressure builds in the
confined space
• When an opening is made a billow of
smoke escapes
• Tunnel of fresh air finds its way to the fire
• Ignition from seat of the fire burns back to
opening along air tunnel
18.11
Signs of a Potential Backdraft
• Short distance to opening
– Backdraft unspectacular
– Appears as if fire is flaring up
• Long distance to opening
– Amount of proper concentration from
opening to seat is greater
– Ignition travels greater distance and
amasses greater force
– Almost instantaneous reaction like an
explosion
18.12
Rollover/Flameover
• Heat brings products of combustion to
higher levels
– Usually accumulate near the ceiling
• Accumulated heat reaches ignition point
– Spread across room at ceiling level
• Fingers of flame reach across the room,
followed by a wall of flame
• Advancing hoseline disrupts the upper
thermal layer
– Disrupts the rollover phenomenon
18.13
What Needs to be Vented?
• Without ventilation, expanding heated
steam and smoke will roll over the wall of
water
– Drop down behind the hose team
• Long before entire building requires
venting, smaller voids and compartments
need to vent
– Exhaust increasing pressure and intensifying
heat
• If done in a timely manner, involvement of
entire building might be avoided
18.14
(A)
Figure 18-9 (A) 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.
18.15
(B)
Figure 18-9 (cont’d.) (B) 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.
18.16
Voids and Compartments
• All compartments treated with same
understanding
• Residential building is a large compartment
with many sub-compartments
– Example: apartments
• Each sub-compartment can be subdivided
– Example: rooms
• Each sub-compartment can be further
subdivided
– Example: closets
• Building might have eaves, peaks, gables,
etc.
18.17
Cocklofts
• Cockloft: space between ceiling of
top floor and bottom of roof
• Major attack point for ventilation
crew
– Especially in a top-floor fire or fire that
has extended into that space
18.18
Horizontal and Vertical Voids
• All heat follows the path of least resistance
• Unobstructed channel in form of horizontal
or vertical void
• Heat and fire extend without being seen
– Following pipe chases or electrical wire
pathways
• Ventilating these by opening at highest
points exposes extending fire for
extinguishment
– Trapped heat diffused into unheated spaces
• Minimizes risk of heating up a new portion
18.19
Figure 18-10 Voids in a typical structure
that can trap heat and permit fire extension.
18.20
Figure 18-10 (cont’d.) Voids in a typical structure that can trap
heat and permit fire extension.
18.21
Air Movement
• Convection
– Venting carries heat out to atmosphere
• Conduction
– Venting prevents heat from traveling to
uninvolved areas of the structure
• Radiation
– Venting delays or prevents exposed
material from reaching its ignition
temperature
18.22
Types of Ventilation
• Several methods used individually
or in combination
• Natural ventilation: open windows
and doors
• Mechanical ventilation: use smoke
fans and water to create air
movement
18.23
Natural
• Opening windows and doors provides
natural ventilation
– When time not essential; slower venting
operation
• Appropriate for light smoke condition
where incident is under control
• Method of choice for residual smoke
removal
• Cut a hole in the roof or break out windows
when greater volumes of smoke need to
be removed
18.24
Figure 18-12 Smoke will be carried
throughout the building to upper floors by
normal air currents mixed in with the heat.
18.25
Mechanical
• HVAC systems can be used for
ventilation in climate-controlled
buildings
• Smoke fans are placed in opening to
suck out smoke and heat
– Establish unobstructed path of airflow from
outside opposite the fan
– Disadvantage: fire crew exposed to smoke
and heat
• Air introduced via PPV fans or blowers
• Hydraulic ventilation: water creates air
movement
18.26
Figure 18-14 A smoke ejector exhaust fan
placed in an opening will pull air through the
fan as it ejects air out of the structure.
18.27
Figure 18-16 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.
18.28
Mechanics of Ventilation
• Entire ventilation process is the
movement of air from high-pressure
location to lower pressure
• Natural tendency of air is to move
from high pressure to lower
pressure
– Assists the firefighter in ventilation
18.29
Vertical Ventilation
• Based on the “heat rises” rule of physics
• Heat collects at upper levels and spreads
fire to those levels
• Opening vertical arteries releases pent-up
gases
– Reduces chance of fire spreading
• Heated air replaced with cooler air at lower
levels
– Improved conditions help crew in locating the
fire and searching for victims
18.30
Horizontal Ventilation
• Conforms to same rules of vertical
ventilation
• Both are a form of diffusion
– Molecules spill excess levels of high
concentrations into areas of low concentrations
– Molecules move laterally as well as vertically
– Molecules bounce off walls and move through
openings
• Openings are made
• Smoke and heat are channeled out
18.31
Figure 18-21 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.
18.32
Ventilation Techniques
• Many techniques used to effect
ventilation
• Some are simple and require no
tools
• Others are more complex and
dangerous to implement, and
require sophisticated tools
18.33
Break Glass
• Quickest way to open a building is to
break glass
• Best investment of time for results if
done properly
• Many windows can be broken in
time it takes to force one locked
door
• Glass can penetrate skin deep
enough to sever arteries and veins
• Wear protective equipment
18.34
Open Doors
• Opening a door will usually exhaust
huge volumes of smoke and heat
built up
• Keeping door on its hinges is a good
practice
– May need to close the door to limit fire
extension
18.35
Effects of Glass Panes
• Many windows have several panes of
glass separated by wood or aluminum
dividers
– Entire window should be removed
– Remove sash, cross members, etc.
• Remove all glass
– Sweep around perimeter with a tool
• Remove glass with a tool: two steps
– Break through glass from upper to lower sashes
– Sweep perimeter to remove remaining glass
18.36
Rope and a Tool
• When operating off a flat roof beyond
reach of a ladder
• Rope secured to the tool
• Turn of rope taken around firefighters hand
• Toss tool out as far as possible from
building in horizontal direction
• This technique leaves shards of glass in
place
– Does not remove screens, window shades or
curtains
– Effective when no other approach easily made
18.37
Hook or Pike Pole
• Length of pole keeps firefighter a
safe distance from falling glass
• Longer hook enables access to outof-reach windows
• Hook can also be used to extend
reach of firefighter attempting to
open or close a door
– Pry tool to remove roof material
– Used for other purposes that extend the
reach or remove firefighter from
dangerous positions
18.38
(A)
(B)
Figure 18-23 Making a ventilation hole requires some
preplanning. (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.
18.39
(C)
(D)
Figure 18-23 (cont’d.) (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.
18.40
(E)
(F)
Figure 18-23 (cont’d.) (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
ax to remove window glass, the flat side of the ax head
should be used, not the point or the striking surface.
18.41
Iron or Halligan
• Iron or Halligan tool brought down
diagonally through the glass
– Start at the upper corner
• Tool sweeps around the perimeter
to clean out any large shards
• Short length a disadvantage
– Places firefighter near flying glass
– Places firefighter in path of heat and
smoke
• Plan carefully to minimize risk
18.42
Ax
• Ax affords limited reach and places
firefighter in hazardous location
• Use an ax for venting glass
– Side of ax breaks the glass
• Do not use blade portion
– Use of striking head might cause
firefighter to lose grip on the handle
• This technique will not break
tempered glass
– Sharp pointed tool required
18.43
Portable Ladder
• Check for overhead obstructions
• Place ladder to side of window against
side of house
• Measure the base so that the tip will fall
into the glass at about 2/3 the height of the
window
• Reposition the ladder in front of the
window
– Perpendicular to the ground
• Shove the ladder into the building
– Tip of ladder crashes through upper pane
18.44
Negative Pressure Ventilation
• Negative pressure created on back side of
fan blade
• Place a fan in a window facing the outward
flow
• Heat and smoke trapped in the
compartment forced out
• Barrier must be created to separate
positively charged air from negatively
charged air
• Effective in limited access compartments
– Do not use during the attack
18.45
(A)
(B)
Figure 18-24 (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.
18.46
(C)
(D)
Figure 18-24 (cont’d.) (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.
18.47
Positive Pressure Ventilation
• Injects air into compartment and
pressurizes it
• Smoke and heat carried into areas of
lower pressure outside the structure
• Fans can be set up to augment one
another
• For every cubic foot of air injected into a
compartment, a cubic foot of air must be
ejected
• Most efficient when exhaust opening is ¾
to 1½ times the size of the entrance
opening
18.48
Figure 18-25 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.
18.49
Roof Ventilation
• Use penthouse doors, skylights, and
ventilation shafts for vertical ventilation
• Two types of vertical openings:
– Offensive
– Defensive
• Place offensive openings into structure
and evaluate need for defensive
ventilation
– Directly over the fire, if possible
• Strip cut (trench cut) is an example of
defensive ventilation
18.50
Expandable Cut
• Most efficient for time expended
• Produces as large a hole as needed
• Plan the cut so wind will blow smoke
away from work area
• Prevent damage to support rafters
or cross members
• One large opening produces more
airflow than several smaller holes
– Produces debris
18.51
Figure 18-29 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.
18.52
Two-Panel Louver Operation
• Used as an offensive heat hole
– Often on building construction that uses
plywood sheeting under paper as roof cover
• Based on a series of cuts beginning with
an outside cut
• Opening should be evaluated for
effectiveness
– If expansion needed, repeat steps for cut
• Last step: push in roofing pieces creating
louvers along the cut
18.53
Louver in Lieu
• Typically an offensive heat hole operation
placed into a panelized roof
• Performed by a minimum of three people
– Minimum of two saws, one rubbish or roof hook
• Placed in area of greatest smoke
pressurization
– While members are standing on purlins
• Members split into two teams
– Company Officer closest to means of access
and egress
18.54
Triangular Cut
• Roof supported by open web bar joist with
Q-decking is the best candidate for this
type of cut
• Span of web bar joist often exceeds 24
inches
• Opening can become a funnel if opened
using conventional square cuts
• Triangular cut will help support underlying
Q-decking because it is interlocked
– Tendency to sag reduced
• Holes will be relatively small
18.55
Strip Cut or Trench Cut
• Ventilates the cockloft area or open attic
space
• Offensive heat hole opening made
• Gases expanding under the roof are
vented to the atmosphere
– Not permitted to pass a chosen defensive line
• Building on fire side of the cut unsavable
• Hoseline positioned below the cut with
ceilings pulled down to expose the
opening
– Hoseline should not be operated from roof side
18.56
Figure 18-33 A trench cut is a defensive move.
Ceilings should be pulled below the cut to promote
vertical airflow through the trench. Additionally, a handline should be in place below the opening to cut off any
horizontal extension.
18.57
Inspection Cut
• First operation to be accomplished 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 by ventilation
crew
• First cut made at 45 degrees to a bearing
wall
– Followed by a cut opposite the first
– Triangular inspection completed with another
cut
18.58
Smoke Indicator Hole
• Only opening that will adequately
determine conditions directly below
firefighters
• Small triangular opening large
enough to push D-handle of a roof
hook through
– Small enough that a firefighter will not
put a foot through
• Placed in path of access and egress
every 15 to 20 feet of travel
18.59
Safety Considerations
• When considering placement of a
hole, 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
18.60
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
– Report to incident commander for
reevaluation if conditions are changing
out of sight
• Most incident commanders gladly
countermand in presence of new
information
18.61
Will the Escape Route Be Cut
Off?
• Individual safety of paramount importance
• When ventilating, 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 should be lighted at night if
possible
• Rooftop LCES primary responsibility of
person assigned to Roof Division or
Ventilation Group
18.62
Figure 18-35 Ventilate in the
direction of the escape route so
escape is not cut off.
18.63
Will Ventilation Endanger Others?
• Activity of one firefighter performing a
venting task must never endanger position
of another
• When opening a roof, advise everyone
else where the holes are
– Easy to fall into the fire
• Torn-up roofing material should be cleared
away as soon as possible to remove
tripping hazards
– Pile roofing in one place
• Think ahead of possible safety problems
18.64
Work in Teams
• Firefighter should never work alone
– Difficult for one person to be aware of
everything
• Affords opportunity for discussion
• Team member might make the
difference between being located in
a collapse
• Team member may make it possible
to remove a heavy obstruction
18.65
Proper Supervision
• There should be a person on the
scene to make decisions when
conflicting options presented
• Presence of supervision ensures
effort is unified
• Supervision brings experience to an
activity
• Prevents team members from
becoming too focused on mission
18.66
Obstacles to Ventilation
• Importance of ventilation cannot be
overstated
• Fire operations are unpredictable
• Firefighters confronted with
unforeseen circumstances that
delay ventilation activities
18.67
Access
• Access is an initial size-up consideration
• First assess the needs of the ventilation
objective
– Determine the route to be employed to reach
location of job performance task
• Example: adjoining building
• Access to rear yard might be impeded by
fences or dogs
– Alternative methods must be employed
• Map out access strategy for particular
building
18.68
Security Devices
• Security devices can impede ventilation in
access and timing
• Examples:
– Gates, screens, steel doors, and closed-up
windows
• Window openings may have been sealed
• Skylights may have been replaced with
plywood attached to inferior support
– No longer discernible
– Cause of firefighter deaths
18.69
Height
• Be alert to structure’s ventilation
needs
• Sometimes necessary to cut a hole
in an area out of reach
– Need for reach part of initial size-up
– Assume reach will be a problem
• Think proactively not reactively
18.70
Poor Planning
• Planning is an obstacle to ventilation
that can be addressed
• Time is not a luxury
– Planning must occur without delay
• Quick size-up and implementation of
a plan essential for timely ventilation
• If ventilation delayed, interior team
will suffer
– Backdraft, rollover, diminished survival
time, and arduous working conditions
18.71
Personnel Assignment
• Task assigned to shorthanded or
inexperienced crew will delay ventilation
• Safety an overriding concern
– Firefighter may be able to affect ventilation
while waiting for reinforcements
• Roof operation: two-person team can open
many openings quickly
• Structural components can be easily
opened or removed by individuals working
together
18.72
Unfamiliar Building Layout
• Floor layout can be confusing to the
firefighter
• Building layout can be an obstacle to
firefighter attempting to reach the rear
– Building wings, fences, lower floor extensions
– Buildings can have multiple doors on same floor
but serve three different levels
• Conduct “walkthroughs” and inspections
• Often same floor plan exists throughout
multistory building
18.73
Ventilation Timing
• Ventilation too early can lead to fire
extension
• Ventilation too late causes unnecessary
punishment to the interior forces
– Can prevent forward progress
• Vertical ventilation of firefighter access
holes is paramount
• Ventilation may have to be delayed if
occupants/firefighters are using stairs
18.74
Cut a Roof – Open a Roof
• Cutting a roof and opening a roof
are different operations
• Cutting a roof makes necessary cuts
to perform ventilation
• Once cuts made, roof can be
opened
• Opening refers to removal of roof
material
• Cuts may be made, and opening
time delayed
18.75
Factors Affecting Ventilation
• Several factors affect proper
ventilation, including the following:
–
–
–
–
–
–
–
Partial openings
Screens
Type of roof material
Wind direction
Weather
Building size
Construction features
18.76
Partial Openings
• Single opening has greater ventilation
capacity than multiple openings of
equivalent area
• Example: chimneys
– Greater the circumference of the vessel, the
less friction on the sides and the greater the
flow
• Many small holes have greater overall
length of perimeters
• The greater the perimeter, the more
opportunity to slow airflow
18.77
Figure 18-38 Airflow is reduced
by friction.
18.78
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
18.79
Figure 18-39 Airflow is greatest
through a window where glass is fully
removed. Screens, shades, curtains,
and window cross members should
also be removed.
18.80
Screens
• Presence of insect screens in a window
that has been broken out is magnified
– Screen is like a solid panel with hundreds of
holes
• Failure to remove a screen is like opening
100 windows and letting the shutter close
on 44 of them
• Removal of window treatments also
important
• Any obstruction reduces airflow
18.81
Roof Material
• Roof material may be several layers thick
• Kerf cut of the saw usually permits thin line
of smoke to vent
• When removing several layers of roofing,
cut should not penetrate the under-roof
area
• Corrugated metal roof:
– Kerf cut supplies oxygen
– Roof erupts into fire where roof weakened by
cuts
18.82
Dropped or Hanging Ceilings
• Dropped ceilings create impediments to
ventilation process
–
–
–
–
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 because
they are:
– Not always obvious
– Out of reach of roof firefighter
– Difficult to open
18.83
Building Size
• Building size affects ventilation
• In tall buildings, a neutral plane can occur
– Location where smoke collects instead of rising
• Factors that affect development of neutral
plane:
– Presence or absence of HVAC systems and
ducts
– Wind direction
– Presence of other buildings, and their height
– Outside temperature
– Presence or absence of smoke shafts
18.84
Weather
• On cool dry days, structures vent
quickly
• On rainy humid days, smoke lifts
slowly
• Snow impedes vertical venting
• Horizontal venting is not affected the
same way
• Use positive pressure ventilation
18.85
Opening Windows
• Simplest way to open a compartment
• One full sash opening better than two
equal in area
• Better in general to open top sash fully
• If smoke condition from door opening will
make room conditions worse, close door
and open window
• If two windows, open one at upper sash
and other at bottom sash
18.86
Lessons Learned
• Ventilation is a tool used in firefighting
– Must be understood and manipulated
• Proper use makes the difference between
extinguishing a fire and creating
conflagration
• Ventilation enables firefighter to make a
rescue
• Heat rises and cold air drops
– Heated air expands; cooled air contracts
• Airflow follows path of least resistance
– Can be artificially generated by mechanical
means
18.87