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

18.5

Table 18-1 Gases Produced by Fire

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

18.7

Figure 18-1 Heat, smoke, and fire will follow the path of least resistance and find their way through any available opening.

18.8

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.

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 tunnel18.11

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

explosion18.12

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

18.15

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.

(A)

18.16

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.

(B)

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

18.20

Figure 18-10 Voids in a typical structure that can trap heat and permit fire extension.

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

18.25

Figure 18-12 Smoke will be carried throughout the building to upper floors by normal air currents mixed in with the heat.

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

18.27

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.

18.28

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.

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

18.32

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.

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 equipment18.34

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 out-

of-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

18.39

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.

(A) (B)

18.40

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.

(C) (D)

18.41

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.

(E) (F)

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

18.46

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.

(A) (B)

18.47

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.

(C) (D)

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

18.49

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.

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

18.52

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.

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 small18.55

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

18.57

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 hand-line should be in place below the opening to cut off any horizontal extension.

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

18.63

Figure 18-35 Ventilate in the direction of the escape route so escape is not cut off.

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 problems18.64

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 delayed18.75

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

18.78

Figure 18-38 Airflow is reduced by friction.

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

18.80

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.

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