Chapter 13 Ventilation - PowerPoint Presentation

Chapter 13 Ventilation

Knowledge Objectives Describe the characteristics of a ventilation-limited fire. Describe the impact of door control on ventilation. Describe the impact of ventilation location. Describe the impact of ventilation hole size. Describe the impact of wind on fire behavior. Describe the impact of exterior suppression on fire behavior.

Knowledge Objectives Describe the importance of including ventilation considerations in a size-up. Describe how the location, size, and stage of fire affect ventilation operations. Describe how the characteristics of different construction types affect ventilation operations. Describe the importance of the timing and coordination of ventilation and suppression.

Knowledge Objectives Describe steps that can be taken to minimize backdrafts and flashovers. List the two basic types of ventilation. Explain how horizontal ventilation removes contaminated atmosphere from a structure. List the two methods of horizontal ventilation. Explain how natural ventilation removes contaminated atmosphere from a structure.

Knowledge Objectives Describe the techniques used to provide natural ventilation to a structure. Explain how mechanical ventilation removes contaminated atmosphere from a structure. Describe the techniques used to provide mechanical ventilation to a structure. Describe how negative-pressure ventilation removes contaminated atmosphere from a structure.

Knowledge Objectives Describe the techniques used to provide negative pressure ventilation to a structure. Describe how positive-pressure ventilation removes contaminated atmosphere from a structure. Describe the techniques used to provide positive-pressure ventilation to a structure. Describe how hydraulic ventilation removes contaminated atmosphere from a structure.

Knowledge Objectives Describe the techniques used to provide hydraulic ventilation to a structure. Describe how vertical ventilation removes contaminated atmosphere from a structure. Describe how to ensure fire fighter safety during vertical ventilation operations. Identify the warning signs of roof collapse. Describe the components and characteristics of roof assemblies.

Knowledge Objectives List the differences in solid-beam construction and truss construction in roofs. Explain how roof construction affects fire resistance. List the basic types of roof design. Describe the characteristics of flat roofs. Describe the characteristics of pitched roofs. Describe the characteristics of curved roofs. Describe the techniques of vertical ventilation.

Knowledge Objectives List the tools utilized in vertical ventilation. List the types of roof cuts utilized in vertical ventilation operations. Describe the characteristics of a rectangular or square cut. Describe the characteristics of a seven, nine, eight (7, 9, 8) rectangular cut. Describe the characteristics of a louver cut. Describe the characteristics of a triangular cut.

Knowledge Objectives Describe the characteristics of a peak cut. Describe the characteristics of a trench cut. Describe the special considerations in ventilating basements. Describe the special considerations in ventilating concrete roofs. Describe the special considerations in ventilating metal roofs.

Knowledge Objectives Describe the special considerations in ventilating high-rise buildings. Describe the special considerations in ventilating windowless buildings. Describe the special considerations in ventilating large buildings. Explain how to ensure that ventilation equipment is in a state of readiness.

Skills Objectives Break glass with a hand tool. Break a window with a ladder. Deliver negative-pressure ventilation. Deliver positive-pressure ventilation. Perform hydraulic ventilation. Operate a power saw. Make a rectangular cut to deliver vertical ventilation.

Skills Objectives Make a seven, nine, eight (7, 9, 8) rectangular cut to deliver vertical ventilation. Make a louver cut to deliver vertical ventilation. Make a triangular cut to deliver vertical ventilation. Make a peak cut to deliver vertical ventilation. Make a trench cut to deliver vertical ventilation. Perform a readiness check on a power saw. Maintain a power saw.

Introduction Ventilation Controlled and coordinated removal of heat and smoke from a structure Replaces escaping gases with cooler, cleaner, oxygen-rich air Must be planned and systematic

Effects of VentilationHelps remove hot gases from fire compartment Makes it easier to locate the seat of the fire Improves visibility Contributes to: Faster and safer knockdown More effective fire suppression Improved efficiency of searching Quickly adds oxygen to a fire if performed or timed poorly

Basic Steps of VentilationStep one:Determine need for ventilation. Assess location and amount of ventilation needed. Coordinate ventilation operations with other parts of fire suppression operations.

Basic Steps of VentilationStep two:Mechanical operations Opening or closing doors and windows Opening skylights Cutting openings in the roof Questions to ask before beginning mechanical operations: Why am I ventilating? Where do I want to accomplish the ventilation? When do I want to perform the ventilation?

Ventilation-Limited and Fuel-Limited FiresVentilation-limited fire Large quantities of thermal energy Can rapidly convert to active burning if oxygen is added Fuel-limited fire Limited amount of fuel available for burning Sufficient oxygen for fire growth Any opening establishes a potential flow path

Flow PathAreas where heat, smoke, and air flow from areas of higher pressure to areas of lower pressureCan be unidirectional or bidirectional Determined by Building design Which doors and windows are open to the outside

The Impact of Door ControlLimiting air inlet limits fire’s ability to grow Maintain control of front door Fire fighter may be stationed at front door to maintain partial door closure Closing interior doors can also help limit fire growth. © Jones & Bartlett Learning. Photographed by Glen E. Ellman

The Impact of Ventilation LocationLocation of ventilation openings Influences how fast a fire reacts to changes in ventilation Determines how effective the opening is at removing hot gases and smoke from the fire location Ventilating directly over the fire Produces the fastest impact on behavior of fire Exhausts greatest amount of combustion products Should be performed with coordinated water application

The Impact of Ventilation LocationOther factors that affect how fast fire responds to oxygen Stage the fire is in Whether fire is vent-limited or fuel-limited Number and size of ventilation inlets and outlets Shape of ventilation openings Temperature of fire room Configuration of walls Amount and type of contents in fire flow path

The Impact of Ventilation Hole SizeFire studies conducted by UL demonstrate that Larger-sized vertical ventilation openings do not localize growth of the fire Vertical ventilation alone does not reduce temperatures in the fire building

The Impact of Ventilation Hole SizeWhen performing ventilation in coordination with an exterior fire attack: Vertical ventilation by itself does not usually have a positive effect on ventilation-limited fire. Vertical ventilation in coordination with exterior application of water as close to fire as possible: Improves visibility Reduces temperature in fire compartment Temporarily limits fire growth A larger hole is more effective in lowering temperature.

The Impact of WindWind Can rapidly change the direction, speed, and flow path of a fire Provides unlimited oxygen through open windows and doors on the upwind side of a burning building © Jones & Bartlett Learning.

The Impact of WindRemember to:Keep wind at your back during a fire attack. Avoid ventilating on the upwind or downwind side of a fire (unless it is part of a well-organized suppression effort).

The Impact of Exterior SuppressionVentilation-limited fires Minimal cooling effect from ventilation alone Ventilation without suppression can cause flashover. Use a coordinated attack with ventilation and water application from a safe distance. Removes large amounts of highly flammable fuels Helps improve visibility within the fire building Improves fire fighter safety Increases potential for occupant survival

The Impact of Exterior SuppressionTransitional attack Offensive fire attack initiated by quick, indirect, exterior attack into the fire compartment Initiates cooling and darkens fire Perform prior to entry, search, and suppression Does not reduce importance of proper ventilation

The Impact of Exterior SuppressionProviding ventilation without close coordination can contribute to fire growth © Jones & Bartlett Learning.

Size-Up and VentilationDuring size-up, consider: Location, size, and stage of the fire Fire department arrival time Building size, shape, and construction type Potential for rescue and for building collapse Amount of fuel in the building contents Impact of modern versus traditional contents Type of fire attack that can be used Potential ventilation locations

Location, Size, and Stage of FireSmoke can provide clues Very hot fire Smoke moves quickly Cooler fire Smoke moves slowly and gently Might hang low to the ground Little or no smoke Small fire in incipient stage Fire has exhausted most of its fuel supply Courtesy of District Chief Chris E. Mickal /New Orleans Fire Department, Photo Unit.

Modern ConstructionBuilt with new-growth lumber and lightweight components Provides: More fuel Fuels that reach flashover faster Fuels that generate greater amounts of energy Building components that fail sooner Often tightly sealed from the outside Contributes to higher interior temperatures

Type I Construction (Fire-Resistive)Structural components made of noncombustible materials Spaces divided into compartments Fire can still spread through Openings for mechanical systems Plumbing and electrical chases Elevator shafts and stairwells Exterior windows

Type I Construction (Fire-Resistive)Vertical extensionFire spreads from floor to floor through exterior windows Also known as auto-exposure © Jones & Bartlett Learning.

Type I Construction (Fire-Resistive)Engineered designs to assist fire fighters with ventilation Smoke and heat vents in the ventilation system Positive pressure stairwells and elevator shafts HVAC (heating, ventilation, and air conditioning) systems designed to be used to pressurize floors or areas Openings for skylights or HVAC ducts in roofs supported by concrete or steel decking

Type II Construction (Noncombustible)Structural components made of noncombustible materials May include fire walls Common in single-story warehouse buildings Horizontal ventilation Limited to existing doors Vertical ventilation Attempt only with aerial platforms or ladders May be difficult or impossible with metal roof decking

Type III Construction (Ordinary)Exterior walls made of noncombustible or limited-combustible materials Wood used for Interior walls and floors Decking and structural support of roof Horizontal ventilation through windows and doors Vertical fire extension possible through interior stairwells and other openings

Type III Construction (Ordinary)Coordinated suppression and vertical ventilation are essential to extinguishing attic fires. Courtesy of District Chief Chris E. Mickal /New Orleans Fire Department, Photo Unit.

Type IV Construction (Heavy Timber)Exterior walls masonry constructionWood interior walls, columns, floors, and roof Difficult to ignite, but can burn for many hours Often converted into smaller compartments Vertical openings for elevators and stairs Usually contain many windows

Type V Construction (Wood Frame)Exterior walls not required to be constructed of masonry or noncombustible materials Common features Void spaces Modern, fast-growth lumber Lightweight wood-truss roofs Manufactured I-beam floors

Type V Construction (Wood Frame)Older Type V buildings Assembled with balloon-frame construction Allows fire to spread to attic very quickly Modern Type V construction Platform-frame construction Lightweight components

Timing and Coordination of Ventilation and SuppressionLimiting air entering fire compartment limits fire’s ability to grow Keep ventilation openings closed until prepared to apply water. Change from ventilation-limited stage to fuel-limited stage by applying water. Three Ws of ventilation When Where Why

Minimizing Backdrafts and Flashovers Exercise great caution when conditions indicate backdraft or flashover is possible. Use transitional attack. Apply water from safe location as close to fire as possible. Makes ventilation more effective © Jones & Bartlett Learning.

Backdrafts and VentilationBackdraft can occur when Building is charged with hot gases. Most available oxygen has been consumed. Introduction of oxygen can cause explosion. Fire fighters must release as much heat and unburned products of combustion as possible. Fire fighters should open hose streams as soon as fire or high temperatures are encountered.

Flashovers and VentilationFlashover Transition from a fire that has grown by igniting one type of fuel to another to a fire where all exposed surfaces have ignited Recognize conditions of potential flashover. Do not enter an environment if signs of impending flashover are present. Use a transitional attack to cool the fire compartment, vent, and then enter.

Types of Ventilation Two basic types of ventilation Horizontal Uses horizontal openings in a structure such as doors and windows Vertical Involves openings in the roofs or floors

Types of Ventilation Can be natural or mechanical Natural: Depends on convection currents and other natural forces Mechanical: Uses fans or other powered equipment Can also be intentional or accidental Intentional: Planned and done on purpose Accidental: Window or door fails or is mistakenly left open

Horizontal Ventilation Uses horizontal openings in a structure Commonly used in residential fires and room-and-contents fires Generally fast and easy to use Can be used from inside or outside the building Courtesy of District Chief Chris E. Mickal /New Orleans Fire Department, Photo Unit.

Horizontal Ventilation Most effective when opening is directly to outside More difficult when there are no openings Limits structural damage May include both natural and mechanical methods

Natural Ventilation Depends on convection currents, wind, and other natural air movements Used when Air currents are adequate to move contaminated atmosphere out of the building. Ventilation is needed quickly. Open upwind side of building first, then open downwind side

Natural Ventilation Breaking glass May be necessary if window cannot be opened and need for ventilation is urgent Must communicate with officer first Use tool to clear glass. Make sure no one will be hit by falling glass. © Jones & Bartlett Learning

Natural Ventilation Breaking glass from a ladder Position ladder on upwind side. Make tip of ladder even with top of window. Climb to position level with window. Lock into ladder for safety. Use hand tool to break window and clear glass.

Natural Ventilation Breaking a window with a ladder Requires proper ladder selection Raise ladder into top half of window or raise next to window to determine proper height. Roll ladder into window, draw back at tip, and forcibly drop into top third of window. Objective is to push broken glass into window opening

Natural Ventilation Opening doors Provide large openings May compromise entry/exit points Open only when host line is charged and attack team is ready to advance Good location for mechanical ventilation devices

Mechanical Ventilation Uses large high-powered fans or other powered equipment Methods Negative-pressure ventilation Positive-pressure ventilation Hydraulic ventilation

Negative-Pressure Ventilation Smoke ejectors Used to exhaust products of combustion Create negative pressure Usually 16 to 24 in. (40-60 cm) in diameter Powered by electricity, gasoline, or water pressure Courtesy of Super Vacuum Mfg. Co., Inc.

Negative-Pressure Ventilation Limitations Positioning Power source Maintenance Air flow control Advantages Explosion-proof motors

Positive-Pressure Ventilation Uses large, powerful fans to force fresh air into a structure Usually set up at exterior doorways © Jones & Bartlett Learning

Positive-Pressure VentilationMust provide outlet or exhaust opening to release positive pressure Ineffective if building is not intact Consider force and direction of wind Multiple fans for very large structures © Jones & Bartlett Learning

Positive-Pressure VentilationAdvantages Can be set up by one fire fighter very quickly Fire fighter does not have to enter hazardous atmosphere Quick and efficient Can help confine fire Increases safety Does not require as much cleaning and maintenance

Positive-Pressure Ventilation Disadvantages May spread the fire if used improperly Very noisy May increase carbon monoxide levels Hot motors unsafe to use when flammable or combustible vapors are present Some fans will not start if tipped down while getting it out of the apparatus.

Hydraulic Ventilation Uses water stream from hose line to exhaust smoke and heated gases Narrow fog or broken-pattern stream Most useful for clearing a room after the fire is under control © Jones & Bartlett Learning

Hydraulic Ventilation Disadvantages Must enter heated, toxic environment to use May deplete needed water supplies May cause excessive water damage May create safety hazard in cold weather Ventilation should be created before hose line advances into fire area.

Vertical Ventilation Releases combustion products into atmosphere vertically Occurs naturally if an opening is above the fire May be assisted by mechanical means Most often involves operations on the roof Courtesy of Captain David Jackson, Saginaw Township Fire Department.

Vertical Ventilation Openings should be made as close to seat of fire as possible. Signs of hottest point Smoke from roof area Melted asphalt shingles Steam coming from roof Must be a horizontal intake vent to admit air Horizontal vents on floor above fire can vertically vent the fire.

Vertical Ventilation Safety considerations Perform only when necessary. Assess roof components. Risk of roof collapse Determine type of roof construction beforehand. Danger of falling Reduces risks to fire fighters inside building Should always be performed quickly and efficiently Should always have two safe exit routes Opening should not be between fire fighters and exit.

Vertical VentilationSafety considerations (cont’d) Have charged hose line ready. Leave area once done. Path should follow areas of greatest support. Be aware of surroundings. Plan order of cuts carefully. Stay upwind. Maintain clear exit path. Stand on firm section of roof. © craig robinson / iStockphoto.com .

Basic Indicators of Roof Collapse Roof collapse Greatest risk when performing vertical ventilation Signs of impending roof collapse Visible sagging Roof separating from the walls Structural failure of any portion of building Sudden increase in fire intensity High heat indicators on a thermal imager

Roof Construction Roof support system Provides structural strength Must be able to bear weight of rain or snow accumulation May be constructed of Solid beams System of trusses Combination of wood and steel © Jones & Bartlett Learning

Roof Construction Roof decking Portion of roof between roof supports and roof covering Composed of rigid material such as Wooden boards Plywood sheets Metal panels

Roof Construction Roof covering Weather-resistant surface of roof May have several layers Materials may include Shingles and composite materials Tar and gravel Rubber Foam plastics Metal panels

Roof Construction Solid-beam vs. lightweight construction Can be impossible to determine by appearance Solid-beam construction Girders, beams, or rafters Larger and heavier Lightweight construction Trusses or engineered systems (I-joists) © Jones & Bartlett Learning. Photographed by Glen E. Ellman . © Jones & Bartlett Learning. Photographed by Glen E. Ellman .

Roof Construction Lightweight construction c an fail completely when One smaller component is weakened One connection between components fails Series of trusses usually fails in rapid succession

Roof ConstructionLightweight construction not necessarily bad or inherently weak Trusses may be made of individual steel bars or angle sections. Should assume modern construction uses lightweight construction for roof supports Courtesy of Captain David Jackson, Saginaw Township Fire Department.

Roof Construction Effects of roof construction on fire resistance Type of material used affects time it takes for fire to burn through roof. Most roofs eventually fail with fire exposure. Local climate conditions help indicate roof strength. Strong construction and more insulation in snowy climates Very light construction in warmer climates

Roof Design Flat roofs Usually have slight slope May be solid components Beams or trusses run from load-bearing wall to load-bearing wall Decking usually constructed of multiple layers May have parapet wall © Jones & Bartlett Learning. Photographed by Glen E. Ellman

Roof Design Pitched roofs Visible slope for rain, ice, and snow runoff Can be supported by trusses or series of rafter and beams Often have layer of solid sheeting or wooden boards covered with weather-resistant membrane and outer covering

Roof Design Type of construction dictates ventilation method for pitched roofs Tin and slate roofs Break tiles and push through laths Tin roofs Cut and peel back Wood roofs Cut, chop, or saw Ground or aerial ladder can be used to access lower part of roof

Roof Designs Curved roofs Generally found in commercial structures Steel or wood bowstring trusses or arches Wood, plywood, or corrugated steel sheets Layered roof covering Structure may not be evident from inside Should be identified and documented during preincident planning surveys © NicVW / Alamy Images.

Vertical Ventilation Techniques Vertical ventilation objectives Provide largest opening Put in appropriate location Use least amount of time Use safest technique

Vertical Ventilation Techniques Roof openings that can provide vertical ventilation: Built-in roof openings Examination openings Primary expendable openings Defensive secondary openings

Vertical Ventilation Techniques Initial assessment Note construction features and indications of fire damage. Establish safety zones and exit paths. Identify built-in roof openings.

Vertical Ventilation Techniques Do not conduct ventilation operations in unsafe locations. Use visible cues to pinpoint best location to vent. May need to make examination holes. Use power saw to make kerf cut. © Jones & Bartlett Learning

Vertical Ventilation Techniques Determine the most appropriate type of opening to make Built-in rooftop openings Skylights Rooftop stairway exit doors Louvers Ventilators © Jones & Bartlett Learning. Photographed by Glen E. Ellman

Vertical Ventilation Techniques Cutting one large hole better than several small ones Make a hole of the same size in ceiling below to allow heat and smoke to escape. © Jones & Bartlett Learning

Tools Used in Vertical Ventilation Power saws Axes Halligan tools Pry bars Tin cutters Pike poles and other types of hooks Utility rope Self-Contained Breathing Apparatus (SCBA) and full personal protective equipment (PPE)

Types of Roof Cuts Roof construction is major consideration Rectangular or square cut Requires four cuts completely through the decking Avoid cutting through structural supports. Stand upwind with two unobstructed exit routes. First and last cuts should be parallel to and just inside roof supports. If several layers exist, may have to peel a layer at a time

Types of Roof Cuts Seven, nine, eight (7, 9, 8) rectangular cut Effective ventilation method for large commercial buildings with flat roofs Seven cuts produced Results in 4-ft by 8-ft (1.2-m by 2.4-m) ventilation hole

Types of Roof Cuts Louver cut Used for flat or sloping roofs with plywood decking Power saw or axe used to make: Two parallel cuts perpendicular to roof supports Cuts parallel to roof supports Cut sections are tilted Can quickly create a large opening

Types of Roof Cuts Triangular cut Prevents metal decking from rolling away as it is cut Saw or axe used to cut triangle-shaped section of decking May need several because of small size

Types of Roof Cuts Peak cut Used for peaked roofs with plywood sheeting Hand tool is used to reveal roof covering along peak Power saw or axe is used to make series of vertical cuts between supports Individuals panels may be Struck with an axe and louvered Pried up with a hook

Types of Roof Cuts Trench cut (strip cut) Creates large opening ahead of fire Used as defensive tactic Made from one exterior wall across to the other Begins with two parallel cuts spaced 2 to 4 ft (0.6 to 1.2 m) apart Short perpendicular cuts every 4 ft (1.2 m) Secondary cut used to limit fire spread Requires time and personnel

Special Considerations Common obstacles Poor access or obstructions Security measures Boarded or sealed window openings Multiple roofs and roof layers

Ventilating Basements Applying water down interior stairway while advancing to seat of fire not safe Use of interior stairs for ventilation for basement fires not safe Ventilate through exterior windows or doors when possible Courtesy of NIST.

Ventilating Concrete Roofs Generally flat and hard to breach May collapse from weakened support systems when exposed to fire Few options Should use alternative openings

Ventilating Metal Roofs Discoloration and warping May indicate seat of fire Lightweight steel bar joists Can sag or collapse in a fire Tar roof covering Can melt and leak through joints Metal from roof deck can roll down when cut Creates dangerous slide into opening

Ventilating High-Rise Buildings Sealed windows often hard to break Unique patterns of smoke movement Can be trapped on individual floors Can move up or down vertical shafts Newer buildings may have smoke management capabilities in HVAC system Stack effect may occur Response to differences in temperature inside and outside building

Ventilating High-Rise Buildings Winter stack effect Cold outer atmosphere and heated interior Smoke rises quickly through vertical openings © Jones & Bartlett Learning

Ventilating High-Rise Buildings Summer stack effect Hot outer atmosphere and cooled interior Smoke pushes down vertical openings © Jones & Bartlett Learning

Ventilating High-Rise Buildings Situation can change as fire produces sufficient heat to alter building’s temperature profile. Cooled smoke may “sit” in one location. Managing air movement in stairways and elevator shafts is key. Designate at least one evacuation stairwell. Use positive-pressure fans to keep smoke out.

Ventilating Windowless Buildings Two risks Traps heat and products of combustion No secondary exit route Ventilation approach similar to basements Use existing openings and make new openings. © olaf schlueter / Shutterstock , Inc.

Ventilating Large Buildings More difficult than ventilating small ones Smoke cools as it travels or is exposed to sprinkler suppression system Causes stratification Difficult to clear Use interior walls and doors to create smaller area when possible Can use several fans in series or in parallel lines to clear smoke

Equipment Maintenance Keep equipment in good repair and operate at peak efficiency. Read and follow manufacturer’s instructions. Rotate unused fuel regularly. Practice using ventilation tools.

Summary Ventilation is the controlled and coordinated removal of heat and smoke from a structure. Effective ventilation not only removes heat and smoke, it also replaces the escaping gases with cooler, cleaner, and oxygen-rich air. Fire size-up needs to include the type of ventilation that is appropriate for the fire conditions and a plan to implement ventilation operations in coordination with other fire-suppression activities.

Summary Before ventilating, fire fighters must first determine if they are dealing with a ventilation-limited fire or a fuel-limited fire. If the fire is ventilation-limited, supply oxygen. If the fire is fuel-limited, establish a flow path. Uncoordinated ventilation can cause rapid fire growth. Factors that influence the effectiveness of ventilation operations include door control, the ventilation location relative to the fire, the ventilation hole size, the impact of wind, and the impact of exterior suppression on fire behavior.

Summary Modern construction practices contribute to ventilation-limited fires and rapid heat build-up. Backdrafts and flashovers can be minimized through the use of a transitional fire attack that is coordinated with appropriate ventilation.

Summary Horizontal ventilation takes advantage of the doors, windows, and other openings at the same level as the fire. In some cases, fire fighters make additional openings in a wall to provide horizontal ventilation. Horizontal ventilation is commonly used in residential fires, room-and-contents fires, and fires that can be controlled quickly by the attack team.

Summary Vertical ventilation refers to any opening that allows the products of combustion to travel up and out. It involves making openings in roofs or floors so that heat, smoke, and toxic gases can escape from the structure in a vertical direction. Pathways for vertical ventilation can include ceilings, stairwells, exhaust vents, and roof openings such as skylights, scuttles, or monitors. Additional openings can be created by cutting holes in the roof or the floor and making sure that the opening extends through every layer of the roof or floor. The choice of roof openings depends primarily on the building’s roof construction.

Summary Mechanical ventilation includes negative-pressure ventilation, positive-pressure ventilation, and hydraulic ventilation. Negative-pressure ventilation uses smoke ejectors to exhaust smoke and heat from a structure. It can be used to move smoke out of a structure after a fire. Positive-pressure ventilation uses fans to introduce clean air into a structure and push the contaminated atmosphere out. It can be used to reduce interior temperatures and smoke conditions in coordination with a fire attack or clear a contaminated atmosphere after a fire has been extinguished. Hydraulic ventilation moves air using fog or broken-pattern fire streams to create a pressure differential behind and in front of the nozzle. It is most useful in clearing smoke and heat out of a room after the fire is under control.

Summary Before performing vertical ventilation, fire fighters must evaluate all pertinent safety issues and avoid unnecessary risks. The biggest risk is roof collapse. Assess the roof for roof scuttles, heat vents, plumbing vents, louver ventilation, solar panels, and fan shafts to prevent tripping or falling from the roof.

Summary When working on a roof, have two safe exit routes. A second ground ladder or aerial device should be positioned to provide a quick escape route. The ventilation opening should never be located between the exit route and the ventilation crew.

Summary Fire fighters who are assigned to vertical ventilation tasks should always be aware of the condition of the roof. They should immediately retreat from the roof if they notice any of the following signs: Visible indication of sagging roof supports Any indication that the roof assembly is separating from the walls, such as the appearance Structural failure of any portion of the building, even if it is some distance from the ventilation operation A sudden increase in the intensity of the fire from the roof opening High heat indicators on a thermal imaging device of fire or smoke near the roof edges

Summary The three major components of roof construction are roof support structures, roof decking, and roof coverings. The roof support system provides the structural strength to hold the roof in place. The structural system is either solid-beam or lightweight construction. The roof covering is the weather-resistant surface and may consist of many layers. The roof decking is a protective layer between the support structures and the coverings.

Summary Roof designs include flat roofs, pitched roofs, and curved roofs. Flat roof construction is similar to floor construction. It can be supported by solid components or by trusses. Flat roofs often have vents, skylights, scuttles, or other features that penetrate the roof deck. Removing the covers from these openings provides vertical ventilation without the need to make cuts through the roof deck. Pitched roofs have a visible slope. They can be supported by trusses or a system of rafters and beams. Many of these roofs have a layer of solid sheeting covered by a weather-resistant membrane and outer covering. The roof construction material dictates how to ventilate the roof. Curved roofs create large open spans without the use of columns. They are often supported with bowstring trusses or arches. The collapse of a bowstring truss is usually very sudden.

Summary The types of vertical ventilation openings include the following: Built-in roof openings Inspection openings Primary (expandable) openings Secondary (defensive) openings

Summary Some commercial or industrial structures have concrete roofs. There are few options for ventilating these structures. Use alternative ventilation openings such as vents or skylights. Metal roofs conduct heat and are often supported by lightweight steel metal joists. Both horizontal and vertical ventilation can be required to vent a basement.

Summary HVAC systems may be used to ventilate high-rise buildings. To ensure successful ventilation operations, all equipment and tools must be in a ready state and properly maintained.