Fireground Support Operations (1st Edition)



Fireground Support Operations (1st Edition)

Chapter 8 - Vertical Ventilation

Test Review

▪ Ventilation is not a method of fire extinguishment (only influences fire).

▪ Almost any forcible entry tool may be used for vertical ventilation.

▪ The most common cutting tools for vertical ventilation are:  rotary saw, chain saw, and pick-head axe.

▪ Gasoline-powered tools should be run briefly on the ground, shut off, then hoisted aloft.

▪ Rotary saws should be rocked slowly forward until the blade contacts the roof, then is drawn back toward the operator to complete cuts.

▪ If a rafter is encountered with a rotary saw, rock the saw backward to clear the rafter.

▪ With a rotary saw, it is more difficult to feel rafters than with a chain saw.

▪ Chain saws are usually the preferred tool for cutting roofs.

▪ Chain saws used for forcible entry usually have carbide-tipped cutting chains (cuts through nails/light gauge metal).

▪ Chain saws may have an adjustable depth gauge to prevent cutting rafters.

▪ Chain saws are drawn back toward the operator to make a cut.

▪ Steps for checking a chain saw prior to use include:  check chain oiler, increase to cutting speed, use only the last few inches of the bar to cut.

▪ Chain saws are generally safer than rotary saws because they do not twist when revved.

▪ Many chain saws have chain brakes to stop movement if the saw "bucks" out of a cut.

▪ To keep both hands free for work, some firefighters wear axes in scabbards strapped to their waists.

▪ Pick-head axes can be used to scrape away pea gravel to allow cutting with a power saw.

▪ When cutting a roof with an axe, cut as close to the rafters as possible (minimizes deflection of axe).

▪ The safest way to cut with an axe is short, controlled strokes, with the axe cutting the side of the feet.

▪ When shingles are present, strike with the pick of an axe and remove shingles prior to cutting.

▪ Shingles can be removed from skip-sheathed roofs with the point of an axe.

▪ The angle of the cut with an axe should not be toward the firefighter's feet.

▪ The most common stripping tools are:  pick-head axe, pike pole, and rubbish hook.

▪ Sledgehammers work as stripping tools for tile/slate roofs (breaks them).

▪ To strip sheathing, firefighters should face leeward, insert a stripping tool, and pull covering while backing away.

▪ An advantage of pike poles in stripping roofing is greater distance from the ventilation opening.

▪ Short, controlled blows with a sledgehammer will shatter tile/slate roofing (flat/pick-head axe may also be used).

▪ type, and condition, and elapsed time into incident.

▪ Roof construction type and condition help determine visibility, footing, and stability.

▪ Observing weather includes temp, humidity, visibility, and wind direction/speed.

▪ Vertical ventilation directly over the seat of the fire is preferred, ONLY if it is safe.

▪ Obstructions on roofs include:  solar panels, HVAC units, vents, etc.

▪ Firefighters are usually standing on roofs that have been weakened by the fire below.

▪ Firefighters, before standing on a roof, should:  read (observe condition) and sound (test condition) the roof.

▪ Firefighters should sound roofs with a hand tool as they advance (except for tile/slate roofs).

▪ High parapets may cause falling onto roofs, while low parapets may cause trip hazards.

▪ Firefighters should never be on a roof without PPE, SCBA, and PASS (officer must have radio).

▪ Truck companies are responsible for performing vertical ventilation when deemed necessary.

▪ Burning buildings should be laddered on all sides when resources permit.

▪ Aerial devices should be positioned for greatest advantage.

▪ To read a roof means to observe certain construction features and other signs of potentially unsafe conditions.

▪ When reading a roof, observe:  age, type, supporting member locations, type/condition of roof coverings, and live/dead loads on roof.

▪ Vents, skylights, and other features penetrate roofs between rafters.

▪ Weathering of roofs often reveal rafter locations.

▪ Factors to consider before getting onto a roof include:  sagging, roof vents "getting taller", water/snow, fire/smoke from roof vents, heavy dead/live loads, and drop-offs.

▪ Thermal imaging camera can locate roof supports.

▪ Roofs should be struck with the blunt end of a tool when "sounding" (solid over supports, bounces or feels softer between supports - hollow sound).

▪ Roofs with several layers of shingles may not respond to "sounding" methods.

▪ Tile/slate roofs cannot be sounded.

▪ When vertically ventilating, place ladders away from windows and electrical wires.

▪ When working from ladders on a roof, work between an unsafe area and the egress.

▪ Firefighters should continually sound/read roofs during operations.

▪ Generally, the strongest roof points are directly over roof supports, at ridges and valleys, and where the roof meets the outside walls.

▪ The weakest points of a roof are between supports.

▪ Roof supports always run perpendicular to the outside walls.

▪ Firefighters should never walk diagonally across a roof.

▪ Roof ladders should not be used on fire-weakened roofs to distribute weight over a larger area.

▪ Ventilation should be performed with wind at the firefighter's back (not always possible with windward side fire).

▪ If roof stability is questionable, ventilation work should be done from aerial devices.

▪ Assess wind direction/intensity, size/type of roof, and time to cut opening, when determining need for a charged hoseline on roofs.

▪ Charged hoselines may not be needed to protect vent crews on single-family residences (short time to cut hole).

▪ Hose streams used to cool the thermal column exiting ventilation openings should be directed horizontally or at a slight upward angle, NEVER into the opening.

▪ Existing roof openings such as scuttle hatches, penthouses, skylights, monitors, turbine vents, light and/or ventilations shafts, ridge vents, and clerestory windows may sometimes be used for ventilation.

▪ All roof exiting openings with the exception of light and ventilation shafts are likely to be locked.

▪ Scuttle hatches are normally square or rectangular metal-covered hatches to provide exit from cocklofts or attics onto the roof (often accessed with ladders from top floor or attic).

▪ Penthouses (AKA bulkheads) often enclose tops of stairways that terminate on the roof, and usually have a metal-clad door of standard size.

▪ Some skylights are thermoplastic and are designed to melt out from the heat of fire.

▪ On corrugated metal roofs, translucent fiberglass panels may act as skylights.

▪ Some skylights can be tilted open for ventilation.

▪ Monitor vents are square or rectangular and penetrate roofs of single- or multi-story buildings to provide additional natural light and/or ventilation.

▪ Monitors may have metal, glass, wired glass, or louvered sides.

▪ Removing turbine (AKA rotary vane) vents for ventilation can reduce efficiency of ventilation.

▪ Light/ventilation shafts act as natural chimneys during a fire.

▪ To break windows from a roof, a tool may be tied to a rope, thrown outward from the wall, allowing it to strike the window below.

▪ Some newer pitched roof buildings have narrow, plastic attic vents running the entire length of the ridge, and may be used for ventilation by pulling the vent.

▪ Clerestory windows make excellent ventilation openings (economical to repair).

▪ The angle or degree of slope (pitch) of pitched roofs varies with climate and aesthetic considerations.

▪ Pitch is expressed in inches of fall per horizontal foot.

▪ Pitched roofs are usually supported by wooden or metal rafters, laminated beams, or trusses.

▪ In post-and-beam construction, ceilings are often omitted and rafters become part of the interior decor.

▪ Attic spaces of pitched roofs may be vented by louvers at each end gable, turbine vents, or ridge vents.

▪ Hip roofs are a type of pitched roof that has no gables and is vented with turbine, eyebrow, or ridge vents.

▪ The most common pitched roofs are gable, hip, lantern, and shed styles (other types are bridge truss, mansard, modern mansard, gambrel, sawtooth, and butterfly).

▪ Gable roofs are perhaps the most common roof style, and is found on small residential/commercial structures.

▪ The pitch of gable roofs varies from almost flat to very steep.

▪ The strongest support locations of gable roofs are the point where rafters meet the outside walls and the ridge beam.

▪ A-frame gable roofs consist of rafters that run perpendicular to the ridge beam and down to and beyond the outside walls.

▪ Trussed pitched roofs are designed to cover considerable spans (rafters of timber or metal).

▪ Hip roofs are similar to gable roofs except the ends terminate in a "hip" rather than gable.

▪ The strongest parts of hip roofs are the ridges, valleys, hips, and at the outside walls.

▪ Lantern roofs consist of a high gabled roof with vertical wall above a downward-pitched shed roof section on either side (found on barns, churches, rural-style commercial buildings).

▪ Aerial devices may be needed to ventilate lantern roofs.

▪ Bridge trusses (heavy-duty) have sloping ends with the top chord shorter than bottom.

▪ The strongest areas of bridge truss roofs are the perimeter where the bottom chord rests on the outside bearing walls.

▪ Expect early failure of bridge truss roofs.

▪ A true mansard roof forms a slight hipped peak or ridge.

▪ Modern mansards have a flat central portion.

▪ Modern mansard roofs utilize bridge or K trusses as support members.

▪ Expect early failure of modern mansard roof.

▪ Modern mansard roofs may include overhangs that form concealed spaces (fire/smoke spread).

▪ Gambrel roofs are most often found on barns and outbuildings.

▪ Preferred method for ventilating gambrel roofs is via aerial device.

▪ Sawtooth roofs are common to industrial and institutional buildings to maximize light/ventilation.

▪ Firefighters who fall on butterfly roofs are not in danger of sliding off the edge.

▪ One of the major hazards of pitched roofs is steepness and lack of secure footing.

▪ Pitched roofs should be vented at the highest point on the leeward side directly over the fire or as close as safely possible.

▪ When working from a roof ladder, a pick of a Halligan or axe can be imbedded into a roof for an additional foothold.

▪ After cutting a ventilation opening, long pike poles or rubbish hooks can be used to remove ceiling to complete the opening.

▪ Flat roofs are more common on mercantile and industrial buildings, multiple dwellings, and apartment complexes than on single-family dwellings.

▪ Flat roofs are commonly penetrated by multiple existing roof openings (scuttles, vents, etc.).

▪ Flat roofs may be surrounded by mansard-type facades or parapets.

▪ Flat roofs may have many dead loads (HVAC, water tanks, etc.).

▪ Flat roofs are commonly supported by horizontal joists or rafters similar to joists in floor systems.

▪ Structural elements of flat roofs include wood, concrete, or metal substructure covered with sheathing.

▪ Flat roofs often have a concealed space between the roof and ceiling of the top floor below it (AKA cockloft, attic, crawl space, or interstitial space).

▪ Common styles of flat roofs include inverted, rain, wooden deck, modern mansard, and panelized roofs.

▪ The surface of inverted flat roofs feel "springy" or "spongy" when walked on.

▪ Inverted roofs have a concealed space of several feet in height between ceiling and roof.

▪ Unprotected structural members within the concealed space of inverted roofs are exposed on all 4 sides (severe fire damage possible).

▪ "Rain roofs" can be found over any type of roof and consists of a roof built on a raised framework above the framework of the original roof (creates concealed space).

▪ Rain roofs are common on buildings with flat or arched roofs.

▪ Wooden deck roofs present a hazard if lightweight plywood or OSB decking is used (panel 3/8" to 5/8" offer little fire resistance).

▪ Metal deck roofs consist of metal bar joists, which usually run across the narrow dimension of the building, and metal decking laid perpendicular to the joists (spot welded).

▪ Large metal deck roofs consists of large beams that either run across the narrow dimension of the building or parallel to the long dimension, and bar joists that run perpendicular to the beams.

▪ The most common concrete roof is lightweight concrete poured over metal decking.

▪ Also common are concrete roofs consisting of precast Double-T panels.

▪ Some concrete roofs have built-in "knock-out" panels to make an opening.

▪ Lightweight concrete roofs may be cut using a rotary saw with a masonry blade.

▪ Poured gypsum roofs are easily cut with power saws and a metal-cutting blade.

▪ Modern mansard roofs have a perimeter which is steeply pitched and a top that is flat.

▪ Some modern mansards are only facades (wall with triangular cross section) which creates a depressed area on top ranging from a few feet to several feet (fall hazard when stepping onto obscured roof).

▪ Modern mansards with facades have an uninterrupted concealed space (fire spread hazard).

▪ Vent pipes appear to be getting taller when a roof is actively sagging.

▪ Patches of melting snow can sometimes identify hot spots.

▪ Thermal imagers not only show hot spots but also show direction of roof supports.

▪ Metal access ladders on the sides of structures should not be used by firefighters (age/weathering).

▪ Guard dogs, razor ribbon, and barbed wire is sometime present on roofs.

▪ Cutting a ventilation hole on flat roofs is usually the most effective way method of ventilation.

▪ Tar coverings tend to "gum up" a chain saws, so rotary saws may be a better choice.

▪ Ventilation holes in flat roofs should be cut parallel to rafters and perpendicular to the walls.

▪ Locating rafters and purlins can be done by sounding or buy cutting diagonally until a member is met, then cut again to determine rafter direction.

▪ Pause after breaking out the 1st pane of a skylight to make sure interior personnel heard the warning that the skylights were being broken.

▪ Arched roofs are typically used to support roofs with large, open spaces (i.e.-sports arena).

▪ Arched roofs may use bowstring trusses, steel arches, concrete, or laminated wood.

▪ Steel arches can be made of plate girders or trusses.

▪ Wood arches are laminated and glued at a factory.

▪ Vertical and horizontal forces of arched roofs are resisted by abutments or buttresses at the ends of the arch.

▪ Arches contain hinges to allow for thermal expansion/contraction, and are found at the top of the arch or at the abutments.

▪ Bowstring arch roofs are commonly found in older bowling centers and supermarkets.

▪ Bowstring arch roofs have a wooden bottom chord or steel rod for lateral support (turnbuckles maintain tension).

▪ Tie rods of bowstring arch roofs are prone to early collapse (outer walls fall outward).

▪ Lamella roofs are a geometric, egg-crate or modified diamond-pattern framework with plank sheathing.

▪ The perimeter of a lamella roofs is the strongest.

▪ The single biggest hazard of arched roofs is danger of sudden and total collapse.

▪ It is recommended to work from aerial devices when ventilating arched roofs.

▪ Arched roofs should be ventilated at top of arch directly over the fire or with a narrow strip along the centerline of the roof.

▪ Conventional openings in arched roofs can be cut perpendicular to and between main arch supports.

▪ Louver vents in arched roofs can usually be made faster.

▪ Beams of panelized roofs are supported at the ends by pilasters, wood or steel posts, or saddles.

▪ The strongest parts of a panelized roof are the beams, purlins, and perimeter where roof meets exterior walls.

▪ Insulation of panelized roofs consists of a tar-impregnated layer covered on both sides by aluminum foil (during fire foil peels away, tar disintegrates).

▪ All trusses are designed as a series of triangles (strongest geometric shape known).

▪ All trusses have a top and bottom chord with connection components known as the "web".

▪ The most common types of roof trusses are parallel and pitched.

▪ Parallel roof trusses consist of metal or wood/metal combination.

▪ Top and bottom chords of parallel roof trusses are parallel to each other (reduces weight).

▪ For combination wood/metal trussed roofs, the area where the roof meets exterior walls is strongest.

▪ All metal parallel trusses are known as bar joists.

▪ Metal parallel trusses consist of "zig zag" web members with top/bottom chords made of opposing angle iron.

▪ Pulling on the bottom chord of parallel roof trusses during overhaul can cause collapse.

▪ Pitched roof trusses are named depending on configuration.

▪ Common pitched truss configurations are the Howe, Pratt, and Fink trusses.

▪ Pitched roof trusses are normally only supported by outside bearing walls.

▪ Truss clips may be present on pitched roof trusses where the truss meets interior partition walls.

▪ With pitched roof trusses, unless gusset plates are corner nailed, they offer less fire resistance than conventional "stick-built" roof systems (early collapse possible).

▪ The most common type of substrate is tar paper (AKA roofing felt).

▪ The most common roof coverings for pitched roofs are:  wood shingles/shakes, composition shingles/roll roofing, tile/slate, and light-gauge metal/fiberglass.

▪ The most common roof coverings on flat roofs are:  tar and gravel, urethane/isocyanate foam, synthetic membrane, and steel.

▪ Cedar and redwood are the most common wood shingles (highly combustible).

▪ Wood shingles are sawn from large rectangular blocks, while shakes are much thicker and are split from large blocks of wood (less uniform shape).

▪ Wood shingles/shakes can be stripped by pulling an axe laterally in quick, short strokes.

▪ Wood shakes/shingles are very slippery when wet.

▪ Composition roofing has an asphalt base with granular mineral coating (fire retardant).

▪ A flat shovel works best to strip composition shingles.

▪ Composition shingles tend to "gum" up power saw blades.

▪ Tar and gravel roofs (AKA built-up roofs), are common on flat or nearly flat roofs.

▪ Urethane/isocyanate foams produce toxic gases when cut (wear SCBA).

▪ Some roofs have liquid elastomers (rubber-like substances) sealed with flexible, water-resistant synthetic membranes (AKA single-ply roofs) made of neoprene, PVC, chlorinated polyethylene, or bituminous sheets reinforced with polyester or fiberglass (toxic when cut).

▪ Synthetic membrane roofs are sealed by heating the underside with an electric heat sealer gun or propane torch.

▪ Terra-cotta tile (AKA Spanish tile) roofs consist of either semicircular or S-shaped tiles nested on a roof, usually over a single layer of tar paper/wood sheathing.

▪ Slate roofs are most common on churches (usually nailed to roof sheathing).

▪ If walking on roof tiles, step only on the lower half of the tiles to prevent breakage.

▪ Light-gauge metal/fiberglass roofs are prone to early collapse.

▪ Steel clad roofs tend to promote flashover/backdraft, impede ventilation, and increase collapse potential.

▪ Steel clad roofs are topped with hot tar for weatherproofing.

▪ Once on a roof, firefighters should maintain contact with the ladder and "bounce" on the roof to get a feel for the support of the roof.

▪ Always work backward toward an area of safety when making ventilation cuts.

▪ Cutting louver vents is often the fastest and most efficient way of opening a roof.

▪ In the most common louver vent cut, the longest cuts are parallel to the rafters.

▪ Another method of louver vent is called dicing (AKA rolling the rafters) and consist of making the longest cuts perpendicular to the rafters.

▪ Trench (AKA strip) ventilation is primarily a defensive maneuver.

▪ Trench ventilation will help confine a fire to a single section of a building by preventing horizontal spread.

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