1. Chapter 18
Ventilation

2. 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

3. 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

4. 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

5. Table 18-1 Gases Produced by Fire

6. 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

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

8. Figure 18-4 Air movement is created by water application
Figure 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.

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. (A)
Figure (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.

16. (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 16

17. 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. 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

19. 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

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

21. Figure 18-10 (cont’d.) Voids in a typical structure that can trap heat and permit fire extension.
18.21

22. Air Movement Convection Conduction Radiation
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

23. 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

24. 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

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

26. 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

27. Figure A smoke ejector exhaust fan placed in an opening will pull air through the fan as it ejects air out of the structure.

28. Figure 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.

29. 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

30. 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

31. 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

32. Figure 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.

33. 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

34. 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

35. 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

36. 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

37. 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

38. 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

39. (A)
(B)
Figure 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.

40. (C)
(D)
Figure (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

41. (E)
(F)
Figure (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.

42. 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

43. 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

44. 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

45. 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

46. (A)
(B)
Figure (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.

47. (C)
(D)
Figure (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

48. 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

49. Figure 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.

50. 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

51. 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

52. Figure 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.

53. 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

54. 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

55. 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

56. 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

57. Figure 18-33 A trench cut is a defensive move
Figure 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.

58. 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

59. 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

60. 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

61. 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

62. 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

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

64. 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

65. 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

66. 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

67. Obstacles to Ventilation
Importance of ventilation cannot be overstated
Fire operations are unpredictable
Firefighters confronted with unforeseen circumstances that delay ventilation activities

68. 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

69. 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

70. 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

71. 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

72. 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

73. 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

74. 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

75. 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

76. 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

77. 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

78. Figure 18-38 Airflow is reduced by friction.

79. 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

80. Figure Airflow is greatest through a window where glass is fully removed. Screens, shades, curtains, and window cross members should also be removed.

81. 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

82. 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

83. 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

84. 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

85. 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

86. 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

87. 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