Fireground Support Operations (1st Edition)



Fireground Support Operations (1st Edition)

Chapter 8 - Vertical Ventilation

"By The Numbers"

▪ It is recommended that a clear space of 10 feet be around the operator of a cutting tool.

▪ An advantage of rubbish hooks for stripping roofing is that it has 2 hooks to grab the roofing (some have D-handles for more advantage).

▪ Considerations for vertical ventilation include:  safety, 2nd means of egress, attack/protection lines ready, weather, loads/obstructions on roof, reading roofs, locating seat of fire, coordination with attack crews, using existing roof openings, cutting 1 large hole, enlarging original opening, roof construction, type, and condition, and elapsed time into incident.

▪ Monitors with solid sides have at least 2 opposite sides hinged at the bottom and are held closed at the top with a fusible link (open during fire).

▪ Clerestory windows are a row of windows installed on a vertical wall between 2 offset roof sections.

▪ A roof that decreases 5 inches vertically for each 1 foot horizontally is called a 5 in 12 roof.

▪ Roofs designed to withstand heavy snow loads might have a 12 in 12 pitch (45 degree angle).

▪ Ridge and rafters of gable roofs are often 2 x 6 inch if built on site and 2 x 4 inch if prefabricated.

▪ Rafters are commonly spaced 16 to 24 inch on center.

▪ Valley rafters are used where 2 ridgelines intersect.

▪ Hip roofs consist of a ridge beam with rafters running perpendicular to the ridge and hip rafters running from the ridge beam at a compound angle of 45 degrees laterally, and a lesser angle down to and beyond the outside walls.

▪ Shed roofs are 1/2 of a gabled roof.

▪ Shed roofs slope only from 1 side.

▪ Shed roofs may be constructed of mono-pitch trusses which have only 1 web member (collapse prone).

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

▪ Wood bridge trusses are usually made from 2 x 12 inch lumber, and vertical metal tie rods for support, while the joists are 2 x 6 inch or 2 x 8 inch covered with 1 x 6 inch sheathing.

▪ Bridge truss spacing may be as much as 16 to 20 feet on center.

▪ Mansard roofs have a double slope on each of the 4 sides.

▪ Mansard roofs pitch at 2 angles, instead of a constant angle.

▪ The difference in the mansard and modern mansard is they way the 4 sides meet in the middle.

▪ In a modern mansard roof, 4 steeply sloped sides rise to meet a flat top called a deck.

▪ Gambrel roofs are essentially a gable type with 2 different slopes on each side of the peak (lower slope steeper than upper slope).

▪ Rafters of sawtooth roofs are 2 x 8 inch lumber or larger, with wood or metal support bracing.

▪ Butterfly roofs resemble 2 opposing shed roofs that meet at the lower edges in the middle of the building.

▪ Tracking elapsed time into an incident at 5-, 10-, 15-, and 20-minute intervals is a way of tracking collapse hazards of roofs.

▪ Ventilation openings in roofs should at least 4 x 4 feet and in many cases may need to be larger.

▪ 1 large ventilation opening is better than several small openings.

▪ Flat roofs have a slight slope (2 in 12 pitch or less) from the front toward the rear.

▪ Inverted roofs differ from conventional flat roofs in that the main roof joists are set at the level of the ceiling, and a framework of 2 x 4 inch members is constructed above the main joists.

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

▪ It is difficult and time consuming to cut concrete roofs over 4 inches thick.

▪ Poured gypsum roofs consist of bar joists or I-beams with gypsum-covered brackets tack welded to the joists and a layer of gypsum cement on top up to 2 1/2 inches thick with wire mesh reinforcement.

▪ Firefighters may have to cut 1 or more inspection (AKA smoke indicator) holes to find the seat of the fire.

▪ Heavy fire conditions can quickly burn through 2 x 4 inch support members.

▪ On flat roofs, the 1st cut for a ventilation hole should be made across the leeward end, followed by the parallel cuts (approx. 4 feet), then pull back covering.

▪ Louver vents on flat roofs can be accomplished by making a 4th cut to connect the parallel cuts.

▪ At least 2 sides of a roof monitor should be removed when used for ventilation.

▪ Typical arches are spaced on 16 to 20 foot centers.

▪ The chords of bowstring arch members are usually laminated 2 x 12 inch or larger lumber and rafters are usually 2 x 10 inches covered with 1 x 6 inch sheathing and roofing material.

▪ Lamella roof framework is 2 x 12 inch wood members bolted together at intersections with steel gusset plates with 1 x 6 inch planking and composition roofing material on top.

▪ In many modern buildings, heavy timber and 1 x 6 inch sheathing have given way to laminated beams and 2 x 4 inch lumber covered with 1/2 inch plywood or OSB, regardless of building size.

▪ Panelized roofs consist of laminated beams, commonly 6 x 36 inches, that span the length or width of the building.

▪ Beams in panelized roofs may have lengths well in excess of 100 feet and may be spaced 12 to 14 feet apart with wooden purlins, usually 4 x 12 inches with metal hangers installed on 8 foot centers between and perpendicular to the beams.

▪ Wooden joists in panelized roofs, usually 2 x 4 inches by 8 feet, are installed with metal hangers on 2 foot centers between and perpendicular to purlins.

▪ Plywood or OSB (4' x 8' x 1/2") is nailed over the panelized roof framework (composition shingles on top).

▪ A 3-layer, laminated insulation is used on the underside of panelized roof decking.

▪ Wooden parallel roof trusses are held together with gusset plates (AKA gang nails) with 3/8 inch prongs most common.

▪ Web members on combination wood/metal trusses are usually 1 inch cold-rolled steel tubing with ends pressed into a semicircular shape (punched to receive connecting pins).

▪ Normal spacing of combination wood/metal trusses is 2 feet on center.

▪ Bar joists can support metal deck roofs for spans up to 144 feet.

▪ The most common pitched roof trusses are prefabricated of 2 x 4 inch lumber held by gusset plates at intersections.

▪ In pitched roof trusses, spans of up to 55 feet are possible using 2 x 4 inch components.

▪ The most common spacing for pitched roof trusses is 2 to 4 feet on center with 1/2 inch sheathing of plywood or OSB.

▪ Wooden I-beams consist of a top and bottom chord and a solid 3/8 inch plywood or OSB web.

▪ Chords of wooden I-beams may be 2 x 3 inch, 2 x 4 inch, or wooden laminate called "micro-lam".

▪ Roof coverings consist of 1 or more layers of underlayment (AKA substrate) as a vapor barrier.

▪ Roof coverings are classified in NFPA 203, Guidelines on Roof Coverings and Roof Deck Construction.

▪ Wood shingles/shakes are usually nailed to 1 x 4 inch or 1 x 6 inch planked sheathing with a space of about 1 inch between planks (AKA skip or spaced sheathing).

▪ Most common composition roofing is 36 inches in width.

▪ Melted roofing tar is "hot mopped" onto 1 or more layers of tar paper and is topped with pea-sized gravel or crushed slag to complete tar and gravel roofs.

▪ Urethane/isocyanate foams may be in the form of 4 x 8 foot sheets of foam or foam sealed in 1 or more layers of a roof covering.

▪ Concrete, clay, or ceramic tile roofs have tiles which are usually flat, interlocking pieces that hook over 1 x 2 inch battens (AKA furring strips) nailed to sheathing or rafters.

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

▪ Light-gauge metal/fiberglass roofs consist of aluminum, fiberglass, or 18- to 20-gauge steel panels over wood or metal substructure (may be corrugated, ribbed, or shaped to simulate tiles/shakes).

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

▪ One type of steel clad roof uses 1/4 inch thick by 2 inches wide steel strips laid side-by-side with a 2nd layer at right angles welded at intersections (leaves small openings of 6 to 8 inches), then lag bolted to the joists below.

▪ Another type of steel clad roof consists of 4 x 8 foot sheets of steel (1/8 to 1/4 inch thick) welded together to form a continuous steel layer.

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

▪ A 1/4 inch steel plate weighs about 10 lbs./ft.2.

▪ Most roof assemblies employ a parallel rafter system spaced from 12 to 24 inches on center, spanning the shortest distance between bearing walls (exception = panelized roofs).

▪ When sounding a roof fails, a chain/rotary saw can be used to cut diagonally, 45 degrees, to any exterior wall and blade will usually encounter a rafter before cut is 3 feet long.  If rafter direction is still unknown, then cut parallel to sidewall 2 to 3 feet.  Complete triangle cut to determine spacing.

▪ One 8 x 8 foot hole is equal to four 4 x 4 foot holes.

▪ With rafter spacing of 2 feet on center, a center-rafter cut (AKA cutting the rafters) will yield a 4 x 4 foot opening.

▪ Trench vents are approximately 4 feet wide and span the width of the building.

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