Ventilation 1. Introduction Ventilation: planned, methodical, systematic removal of pressure, heat,...

Ventilation 1

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

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

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 4

Gases Produced by Fire 5

Considerations for Proper Ventilation Heat tends to rise. Smoke collects under vertical obstructions. Mushrooms Fills the structure from highest point Vertical ventilation Horizontal ventilation 6

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

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. 8

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

Flashover Temperature increases When temperature reaches ignition point of any substance in the room, new combustion occurs. Chain reaction Very rapid fire spread 10

Backdraft (Smoke Explosion) Rapid ignition of smoke and unburned products of combustion With heat, pressure builds Smoke escapes Introduction of fresh air Ignition 11

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

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

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

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. 15

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

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

Cocklofts Major attack point for ventilation crew Especially in a top-floor fire or fire that has extended into that space 18

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

Voids in a typical structure that can trap heat and permit fire extension. 20

Voids in a typical structure that can trap heat and permit fire extension. 18.21 21

Air Movement Convection Conduction Radiation 22

Types of Ventilation Methods used individually or in combination Natural ventilation Mechanical ventilation 23

Smoke will be carried throughout the building to upper floors by normal air currents mixed in with the heat. 24

A smoke ejector exhaust fan placed in an opening will pull air through the fan as it ejects air out of the structure. 25

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

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

Mechanics of Ventilation Ventilation process Natural tendency of air 28

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

Horizontal Ventilation Same rules of vertical ventilation Both are a form of diffusion Openings are made Smoke and heat are channeled out 30

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

Ventilation Techniques Many techniques used to effect ventilation Simple and no tools Complex and dangerous, require sophisticated tools 32

Break Glass Quickest way to ventilate Best investment of time Time savings Glass dangers Wear protective equipment 33

Open Doors Opening a door exhausts huge volumes of smoke and heat built up. Keeping door on its hinges is a good practice. 34

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

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. 36

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

(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

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

(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

Iron or Halligan Tool brought down diagonally through the glass Sweep around the perimeter Short length a disadvantage Plan carefully to minimize risk 41

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

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

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 44

(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

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) 46

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

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

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

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

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. 51

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 52

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

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

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

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

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

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

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 59

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

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

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

Ventilate in the direction of the escape route so escape is not cut off. 63

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

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

Proper Supervision Conflicting options presented. Ensures effort is unified Brings experience to activity Prevents members from becoming too focused on mission 66

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

Access Initial size-up consideration First assess the needs of the ventilation objective. Access to rear yard Map out access strategy. 68

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 69

Height Be alert to structures ventilation needs. Sometimes necessary to cut a hole in an area out of reach Think proactively not reactively. 70

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

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

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

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

Cut a RoofOpen a Roof Cutting a roof and opening a roof are different operations. Cutting a roof Opening a roof 75

Factors Affecting Ventilation Partial openings Screens Type of roof material Construction features Building size Weather Wind direction 76

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

Airflow is reduced by friction. 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 79

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

Screens Presence of insect screens Failure to remove a screen Removal of window treatments Any obstruction reduces airflow 81

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

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 83

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

Weather Cool dry days Rainy humid days Snow Horizontal venting is not affected the same way. Positive pressure ventilation 85

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

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

Ventilation 1. Introduction Ventilation: planned, methodical, systematic removal of pressure, heat,...

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