Chapter 18

Chapter 18 Ventilation11IntroductionVentilation: planned, methodical, systematic removal of pressure, heat, smoke, gases, and flameEssential part of tactical and strategic objectivesLate application of proper ventilation subjects firefighters to extreme circumstances.Complex subject area with many facets22Principles, Advantages, and Effects of VentilationVentilationEssential to fire suppressionBenefits: Deprives fire of ability to heat up structureChannels smoke out of the structureRemoval of smoke, heat, and toxic gases add survival time to a potential victim33Heat, Smoke, and Toxic GasesWhen fire burns, air heats, expands, and rises.Convection RadiationStructures built today Heavy insulationTight weatherproof seamsWindows that do not open44Gases Produced by Fire

55Considerations for Proper VentilationHeat tends to rise.Smoke collects under vertical obstructions.Mushrooms Fills the structure from highest pointVertical ventilationHorizontal ventilation66Heat, smoke, and fire will follow the path of least resistance and find their way through any available opening.

77Air 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.

8Fig from p. 5718Fire and Its By-ProductsDuring combustion, energy is released from exothermic reaction: Heat LightHarmful agents Carbon dioxideVentilation prevents:Flashover and backdraftSmoke explosionRollover/flameover

99FlashoverTemperature increasesWhen temperature reaches ignition point of any substance in the room, new combustion occurs.Chain reactionVery rapid fire spread1010Backdraft (Smoke Explosion)Rapid ignition of smoke and unburned products of combustionWith heat, pressure builds Smoke escapesIntroduction of fresh air Ignition1111Signs of a Potential BackdraftShort distance to openingUnspectacularFlaring upLong distance to openingProper concentration from opening to seat is greaterGreater forceInstantaneous reaction1212Rollover/FlameoverHeat 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.1313What Needs to be Vented?Without ventilationExpanding 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.1414Applying 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.

151518.16As 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.

1616Voids and CompartmentsAll compartments treated with same understandingResidential 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.1717CockloftsMajor attack point for ventilation crewEspecially in a top-floor fire or fire that has extended into that space1818Horizontal and Vertical VoidsHeat follows the path of least resistance.Unobstructed channel in form of horizontal or vertical voidHeat and fire extend without being seen.Ventilating horizontal and vertical voids1919Voids in a typical structure that can trap heat and permit fire extension.

2020Voids in a typical structure that can trap heat and permit fire extension.

18.212121Air MovementConvectionConductionRadiation2222Types of VentilationMethods used individually or in combinationNatural ventilationMechanical ventilation2323Smoke will be carried throughout the building to upper floors by normal air currents mixed in with the heat.

2424A smoke ejector exhaust fan placed in an opening will pull air through the fan as it ejects air out of the structure.

2525Positive 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.

2626PPV 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 civilianWorking fire attackUnknown location of fireInability to provide a proper exhaust pointStructure that presents an over-pressurization or hostile event indicator

27Mechanical Ventilation27Mechanics of VentilationVentilation process Natural tendency of air2828Vertical VentilationHeat rises rule of physicsCollects at upper levels and spreads fire to those levelsOpening vertical arteries Heated air replaced with cooler air2929Horizontal VentilationSame rules of vertical ventilationBoth are a form of diffusionOpenings are madeSmoke and heat are channeled out3030Heated 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.

3131Ventilation TechniquesMany techniques used to effect ventilationSimple and no toolsComplex and dangerous, require sophisticated tools3232Break GlassQuickest way to ventilate Best investment of time Time savingsGlass dangers Wear protective equipment3333Open DoorsOpening a door exhausts huge volumes of smoke and heat built up.Keeping door on its hinges is a good practice.3434Effects of Glass PanesMany windows have several panes of glass. Separated by wood or aluminum dividersRemove all glass.Remove glass with a tool.Break through glass from upper to lower sashes.Sweep perimeter to remove remaining glass.3535Rope and a ToolWhen operating off a flat roofRope secured to the toolTurn of rope around firefighters handToss tool out in horizontal direction.This technique leaves shards of glass.3636Hook or Pike PoleLength keeps firefighter safeEnables access to out-of-reach windowsHook also used to extend reach of firefighter attempting to open or close a door3737(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.383818.39(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.3939(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.4040Iron or HalliganTool brought down diagonally through the glass Sweep around the perimeterShort length a disadvantagePlan carefully to minimize risk4141AxeAffords limited reach Places firefighter in hazardous locationUse an axe for venting glassDo not use blade portionWill not break tempered glass4242Portable LadderOverhead obstructionsSide of windowMeasure 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.4343Negative Pressure VentilationCreated on back side of fan bladePlace a fan facing the outward flow.Heat and smokePositively charged air and negatively charged airLimited access compartments4444(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)454518.46(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)4646Positive Pressure VentilationInjects air into compartment and pressurizes Smoke and heat carried outside the structureFans set up to augment one anotherFor every cubic foot of air injected into a compartment, a cubic foot of air must be ejected.Exhaust opening size4747With 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.

4848Roof VentilationUse penthouse doors, skylights, and ventilation shaftsTwo types of vertical openingsPlace offensive openings into structure Evaluate need for defensive ventilationStrip cut (trench cut)4949Expandable CutEfficient for time expendedLarge a hole as neededPlan the cutPrevent damage to support rafters or cross membersOne large opening produces more airflow than several smaller holes.5050The 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.

5151Two-Panel Louver OperationOffensive heat holeBased on a series of cuts Begins with an outside cutOpening should be evaluated for effectivenessPush in roofing pieces creating louvers5252Louver in LieuOffensive heat hole operation Placed into a panelized roofMinimum of three peopleArea of greatest smoke pressurizationMembers split into two teams5353Triangular CutBest candidate for this type of cutRoof supported by open web bar joist with Q-deckingSpan of web bar joistOpening can become a funnelTriangular cut will help support underlying Q-deckingHoles relatively small5454Strip Cut or Trench CutVentilates the cockloft area or open attic spaceOffensive heat holeGases expanding under the roof are vented.Building on fire side of the cut unsavableHoseline positioned below the cut5555A 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.

5656Below Grade or Basement VentilationCreates many challengesLocate exterior openings prior to entryUse roof ventilation techniques on ground floor if no exterior openingsCritical to begin ventilation as early as possible5718.57Inspection CutFirst operation on a flat roofDetermines:Roof covering and depth of coveringRoof sheeting materialRafter directionConditions directly below firefightersTypes of operations to be doneFirst cut at 45 degrees to a bearing wallFollowed by a cut opposite the firstTriangular inspection completed with another cut5858Smoke Indicator HoleWill adequately determine conditions directly below firefightersSmall triangular openingPlaced in path of access and egress4.5 to 6 metres (15 to 20 feet) of travel5959Safety ConsiderationsConsider 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.6060Will Ventilation Permit the Fire to Extend?No justification for permitting a fire to extend in order to complete a taskOrder may be given without full understanding of the consequencesIncident commanders and new information6161Will the Escape Route Be Cut Off?Individual safetyKeep 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 roofEscape routes lighted at nightRooftop LCES6262Ventilate in the direction of the escape route so escape is not cut off.

6363Will 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 hazardsThink ahead of safety problems.6464Work in TeamsNever work alone.Opportunity for discussion Might make the difference between being located in a collapseMay make it possible to remove a heavy obstruction6565Proper SupervisionConflicting options presented.Ensures effort is unifiedBrings experience to activityPrevents members from becoming too focused on mission6666Obstacles to VentilationImportance cannot be overstated.Fire operations are unpredictable.Firefighters confronted with unforeseen circumstances that delay ventilation activities6767AccessInitial size-up considerationFirst assess the needs of the ventilation objective.Access to rear yardMap out access strategy.6868Security DevicesSecurity devices Access TimingExamplesGates, screens, steel doors, and closed-up windowsWindow openings sealedSkylights replaced with plywood attached to inferior support6969HeightBe alert to structures ventilation needs.Sometimes necessary to cut a hole in an area out of reachThink proactively not reactively.7070Poor PlanningPlanning is an obstacle to ventilation.Time is not a luxury.Quick size-up Implementation of a plan essentialIf ventilation delayed, interior team will sufferBackdraftRolloverDiminished survival timeArduous working conditions7171Personnel AssignmentTask assigned to shorthanded or inexperienced crew will delay ventilationSafety an overriding concern Roof operation Two-person team can open many openings quicklyStructural components easily opened or removed by individuals working together 7272Unfamiliar Building LayoutConfusing floor layoutBuilding layout can be an obstacle. Building wingsFencesLower floor extensionsMultiple doors on same floorWalk-throughs and inspectionsOften same floor plan exists throughout multistory building 7373Ventilation TimingVentilation too earlyVentilation too late Vertical ventilation of firefighter access holes is paramount.Ventilation may have to be delayed if occupants/firefighters are using stairs.

7474Cut a RoofOpen a RoofCutting a roof and opening a roof are different operations.Cutting a roofOpening a roof7575Factors Affecting VentilationPartial openingsScreensType of roof materialConstruction featuresBuilding sizeWeatherWind direction7676Partial OpeningsSingle opening has greater ventilation capacity than multiple openings of equivalent areaChimneysGreater the circumference, the less friction and the greater the flowMany small holes have greater overall length of perimeters.The greater the perimeter, the more opportunity to slow airflow.7777Airflow is reduced by friction.

7878Partially Broken WindowsWindowpane that is broken and many shards of glass left in placeArea of opening reducedPresence of shards creates more perimeter opening distance7979Airflow is greatest through a window where glass is fully removed. Screens, shades, curtains, and window cross members should also be removed.

8080ScreensPresence of insect screens Failure to remove a screenRemoval of window treatmentsAny obstruction reduces airflow8181Roof MaterialRoof material may be several layers thick.Kerf cutWhen removing several layers, cut should not penetrate the under-roof area.Corrugated metal roof

8282Dropped or Hanging CeilingsDropped 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 hazardousNot always obviousOut of reach of roof firefighterDifficult to open8383Building SizeBuilding size affects ventilation.In tall buildings, a neutral plane can occur.Factors affect development of neutral plane:HVAC systems and ductsWind directionPresence of other buildingsOutside temperatureSmoke shafts8484WeatherCool dry daysRainy humid daysSnowHorizontal venting is not affected the same way.Positive pressure ventilation8585Opening WindowsSimplest way to open a compartmentOne full sash opening better than twoOpen top sash fullyIf 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 sash8686Lessons LearnedVentilation is a tool used in firefighting.Must be understood and manipulatedProper use the difference between extinguishing a fire and creating conflagrationVentilation enables firefighter to make a rescue.Heat rises and cold air dropsAirflow follows path of least resistance8787