Transcript Chapter14
14 Ventilation 14 Objectives • Define ventilation as it relates to fire suppression activities. • List the effects of properly performed ventilation on fire and fire suppression activities. • Describe how fire behavior principles affect ventilation. • Describe how building construction features within a structure affect ventilation. • Define horizontal and vertical ventilation. • List the principles, advantages, limitations, and effects of horizontal/vertical/mechanical/natural ventilation. • List the principles, advantages, limitations, and effects of positivepressure, negative-pressure and hydraulic ventilation. • List safety precautions for ventilating roofs. • List the basic indicators of roof collapse. • Explain the role of ventilation in the prevention of backdraft and flashover. 2 14 Introduction • Ventilation – The process of removing smoke, heat, and toxic gases from a burning building and replacing them with cooler, cleaner, more oxygen-rich air • Primary method of fire spread is convection • Mushrooming occurs when the products of combustion reach the highest point. • Products of combustion present a risk to fire fighters and occupants. 3 14 Benefits of Proper Ventilation • • • • • • Locate trapped occupants faster Fresh air to occupants overcome by smoke Advance hose lines more rapidly and safely Reduce backdraft and flashover Limits fire spread Reduces property loss Vented structure Unvented structure 4 14 Factors Affecting Ventilation • Convection currents • Mechanical ventilation activities – Negative-pressure – Positive-pressure – Hose streams • Wind and atmospheric forces – Wind speed and direction – Temperature and humidity 5 14 Building Construction • The way a building is constructed will affect ventilation operations. Fire-Resistive Construction • Construction design - Structural components noncombustible - Compartmentalization • Paths of fire spread – Heating, Ventilation, and Air Conditioning – Stairways – Elevator shafts • Roofs generally of steel or concrete 6 14 Wood-Frame Construction Ordinary Construction • Construction design – Exterior walls noncombustible – Interior walls/floors of wood – Roof is wood decking and structural support • Construction design – Similar to ordinary but exterior walls are combustible • Paths of fire spread • Paths of fire spread – Plumbing and electrical chases – Void spaces in walls – Cockloft – Attics and cocklofts – Wood truss roofs and floors • Construction types – Balloon-frame – Platform 7 14 Ventilation and Tactical Priorities • Ventilation is directly related to tactical priorities. Venting for Life Safety • • • • Life safety is the primary goal. Gives occupants a greater chance to survive Makes searches faster Limits fire spread to other occupants and fire fighters Venting for Confinement • • • Second highest priority is contain the fire and control the situation Prevents fire spread Makes fire attacks easier 8 Venting for Property Conservation • • Limits amount of damaged areas Rapid removal limits amount of permanent damage. 14 Location and Extent of Smoke and Fire Conditions • Factors to consider – – – – • Where to ventilate Size of the fire Stage of combustion Location within the building Available ventilation options – As close to the fire as possible • Determine fire size, intensity, and fuel – Light smoke, moving lazily—small fire of ordinary combustibles – Large amount of black rolling smoke— petroleum base fire – Hotter the fire, the faster the smoke moves – Cool days may cause smoke inversion. – Sprinkler activation may cause the smoke to cool and act as a fog. 9 • Directly over the seat • Through an open door or window that opens outside – If unable to vent close to the fire • Predict how location will affect the fire • Anticipate fire spread and locate hose lines for protection 14 Types of Ventilation • Two basic types of ventilation – Horizontal • Utilizes horizontal openings in a structure such as doors and windows – Vertical • Involves openings in the roofs or floors 10 14 Horizontal Ventilation • Commonly used in – Residential fires – Room-and-contents fires – Fires that can quickly be controlled • Generally fast and easy to use • Can be used from inside or outside the building • Most effective when opening is directly to outside • More difficult when there are no openings • Limits structural damage • May utilize natural and mechanical methods 11 14 Methods of Ventilation • Natural – Depends on convection currents, wind, and other natural air movement – Used when air currents are adequate – Used when ventilation is needed quickly – Open leeward side of building first, then windward. • Mechanical – Uses mechanical means to augment natural ventilation 12 14 Breaking Glass • General rules – Try to open first. – Wear full protective clothing and eye protection. – Ensure no one will be struck by the glass. – Always use a tool. – Keep hands above or to the side of the glass. – Use a tool to clear remaining glass. 13 14 Opening Doors • • • • Provide large openings May compromise entry/exit points May be best for fresh air points Good location for mechanical ventilation devices 14 14 Mechanical Ventilation • Methods of Mechanical Ventilation – Negative-pressure – Positive-pressure – Hydraulic 15 14 Negative-Pressure Ventilation • Uses fans called ejectors to exhaust smoke and heat • Limitations: – – – – Positioning Power source Maintenance Air flow control • Advantages – Explosion-proof motors 16 14 Positive-Pressure Ventilation • Uses large, powerful fans to force fresh air into a structure. • Advantages: – Quick and efficient – Increased safety • Disadvantages – May spread the fire – May increase carbon monoxide levels 17 14 Hydraulic Ventilation • Uses a fog or broken pattern stream to create a pressure differential • Advantages – Can move several thousand cubic feet of air per minute – Does not require specialized equipment • Disadvantages – Water damage – Safety hazards 18 14 Vertical Ventilation • Releases combustion products vertically • Occurs naturally if there is an opening • May be assisted by mechanical means • Usually involves making openings in roof • Make opening close to seat of fire • Determine hottest point 19 14 Safety Considerations • • • • • • • • • Structural stability of the roof Falling from the roof Two exit routes Not getting opening between you and the exit Have a charged hose line Leave the area once done “Sound” the roof Walk on areas of greatest support Make cuts from – Upwind – With clear exit path – While standing on firm section 20 14 Basic Indicators of Roof Collapse • • • • Spongy feeling Visible sagging Roof separating from the walls Structural failure in another portion of building • Sudden increase in fire intensity 21 14 Roof Construction • Two components – Support structure • Solid beams of wood, steel, or concrete • System of trusses of wood, steel, or wood and steel – Roof covering • Made of various water repellant materials • Supported by the roof decking 22 14 Types of Roof Failures • Support system failure – Supporting structure fails – Often a sudden and total collapse – Areas with heavy snow loads more prone • Roof covering failure – Burns through roof covering close to seat of fire – Spreads out causing roof failure – Areas with light snow loads more prone 23 14 Solid Beam vs. Truss • May not be able to tell by looking • Solid beam – Girders, beams, and rafters • Truss – Lightweight components, often 2" x 4" wood with gussets or staples – Steel bars welded together – Triangular configuration 24 14 Roof Designs • Flat roofs – Can be constructed with many types of supports, decking, and materials • Pitched roofs – Have a visible slope for rain, ice, and snow runoff • Arched roofs – Generally found in commercial structures to create a large span without columns 25 14 Objectives of Vertical Ventilation • • • • Provide the largest opening Put in an appropriate location Use the least amount of time Use the safest technique 26 14 Vertical Ventilation Assessment • • • • • • • • Construction features Indications of fire damage Safety zones and exit paths Built-in roof openings Locate at highest point and over seat of fire May need to cut an examination hole One hole is better than several small ones Minimum size 4' x 4' 27 14 Tools Used in Vertical Ventilation • • • • • • • Power saws Axes Halligans Pry bars Tin cutters Pike poles and other types of hooks Utility rope 28 14 Types of Roof Cuts • • • • • Rectangular cut Louver cut Triangle cut Peak cut Trench cut 29 14 Rectangular or Square Roof Cut • Requires four cuts completely through the decking • Use care to not cut structural supports. • Stand upwind and have a safe exit. • Can use a triangle cut to help pry up • If several layers exist, may have to peel a layer at a time 30 14 Louver Roof Cut • Used for flat or sloping roofs with plywood decking • Power saw or axe used to make the cuts • Can quickly create a large opening 31 14 Triangle Roof Cut • Used to prevent metal decking from rolling away as it is cut • A saw or axe is used. • Several may be needed because of their small size. 32 14 Peak Roof Cut • Used for peaked roofs with plywood sheeting • A tool is used to reveal the roof covering along the peak. • A power saw or axe is used to make a series of vertical cuts between the supports. 33 14 Trench Roof Cut • Used as a defensive tactic to stop the progress of a large fire in a narrow building • Creates a large opening ahead of the fire • “Writes off” part of the building • Requires both time and manpower 34 14 Special Considerations • • • • • • • Obstacles preventing ventilation Concrete roofs Metal roofs Basement fires High-rise buildings Windowless buildings Large buildings 35 14 Obstacles to Ventilation • Poor access • Multiple roofs and roof layers • Sealed and boarded abandoned buildings • Security measures such as steel bars and shutters • Concrete roofs • Metal roofs 36 14 Ventilating a Concrete Roof • Found in commercial and industrial structures • Generally flat and hard to breach • May collapse from weakened support systems when exposed to fire • Search for alternative openings 37 14 Ventilating a Metal Roof • Discoloration and warping may indicate seat of fire. • As fire heats the metal deck, tar roof covering can melt and leak into the building. • Metal can roll down and create a dangerous slide directly into the opening. 38 14 Venting a Basement • Usually few windows • Fire will quickly spread • Usually requires both horizontal and vertical ventilation • Fire fighters must descend the stairs through the venting combustion products. • Make as many openings on one side and allow fire fighters to enter from the other 39 14 High-Rise Buildings • Many have hard to break sealed windows. • They create unique smoke patterns with the stack effect. • Newer buildings have smoke management in the HVAC. • Designate one stairwell as a rescue route. • Positive-pressure fans can keep smoke out of the stairs. 40 14 Stack Effect Smoke Patterns 41 14 Windowless Buildings • Traps heat and smoke with no secondary exit • Treat similar to a basement fire. • Ventilate high and use mechanical assistance. • May need to – use existing roof openings, cut new ones – reopen boarded windows/doors or make new openings 42 14 Large Buildings • More difficult than small ones • Smoke cools as it travels, causing stratification. • When possible, use interior walls and doors to create smaller areas. 43 14 Backdraft • May occur when building is charged with hot gases and most of oxygen has been consumed • When air is introduced, fuel can ignite and explode. • Prevent by releasing heat and unburned particles without allowing fresh air • Ventilate as high as possible. • Once flaming begins, fire fighters may enter. 44 14 Flashover • Needs both ventilation and cooling • Occurs when – air in room is very hot and – all combustibles in the space are near their ignition point • Applying water cools the atmosphere • Ventilation draws the heat and flames away 45 14 Summary (1 of 2) • Ventilation provides many benefits. • Several factors affect ventilation. • Building construction affects ventilation operations. • Ventilation is related to life safety, fire containment, and property conservation. • Assessing the location and extent of smoke and fire will determine ventilation operations. • The types of ventilation are horizontal and vertical. 46 14 Summary (2 of 2) • Horizontal ventilation uses horizontal openings in a structure. • Vertical ventilation refers to the release of heat and smoke in a vertical direction. • Many obstacles can be encountered during ventilation operations. • Ventilation is a major consideration in backdraft and flashover. 47