ROOF OPERATIONS - LA County Firefighters

1 roof OPERATIONS . COURSE OUTLINE. Introduction PART I-Phases of Structure Fires PART II- roof Construction PART III-Tactical Considerations PART IV-Ventilation Methods INTRODUCTION. A considerable portion of the annual loss of life and property is a direct result of the lack of timely, effective ventilation 80% of all fire fatalities are due to smoke inhalation More than one-half of the nations fire loss is a direct result of smoke and heat damage Ventilation has a direct effect on all aspects of fire fighting strategies PART I. PHASES OF STRUCTURE FIRES. PHASES OF STRUCTURE FIRES. Structure fires progress through three basic phases: Incipient or Beginning Phase Steady State or Free-Burning Phase Hot Smoldering Phase Phases of Fire THE INCIPIENT / BEGINNING PHASE. Oxygen content approximately 21%. Carbon dioxide, sulfur dioxide, carbon monoxide and water vapor produced. The flame temperature can be above 1000.

2 Degrees, while room temperature may only be slightly elevated. Phases of fire STEADY STATE / FREE-BURNING PHASE. Adequate oxygen and fuel sustain free- burning and fire growth to the point of full involvement of area/room. Mushrooming Flashover Phases of Fire STEADY STATE / FREE-BURNING PHASE. Mushrooming Smoke and gases are heated. If confined to a room or building, they will rise to the uppermost level. Cooler air is displaced down towards the fire, providing oxygen and sustaining combustion. As circulation occurs, heated smoke and gases build internal pressure that continue to rise and spread laterally. Phases of Fire STEADY STATE / FREE-BURNING PHASE. Flashover A simultaneous ignition over the surface of the room or area. Occurs when the heat from the fire raises the temperature of the contents to their ignition temperatures. The ignition happens in an instant. Effects may be deadly to Firefighters Phases of Fire HOT SMOLDERING PHASE.

3 If the free-burning state remains un-vented, the fire progresses into the hot smoldering phase. Low oxygen levels with little or no flame production. Temperatures in excess of 1000 degrees. Dense black smoke, that pressurizes the area. Intense heat continues to vaporize lighter fuels. These gases greatly increase the chance of a backdraft. Phases of Fire HOT SMOLDERING PHASE. Backdraft A confined area that is teeming with pressurized, heated and flammable gases. The introduction of oxygen to this fuel-rich environment will result in an explosion of significant intensity. Effects may be deadly to Firefighters Part II. roof . CONSTRUCTION. roof Construction The Firefighters ability to safely and efficiently ventilate a building through the roof will depend to some degree on his understanding of roof construction It is essential that Firefighters become familiar with the existing and newly constructed buildings within their response area roof Construction Conventional VS.

4 Lightweight CONVENTIONAL. CONSTRUCTION. roof Construction Conventional Construction Structural members depend on size for strength. Less surface area exposed to fire. The larger the size of a structural member, the longer it will take to fail when exposed to fire. Potentially longer burn time results in a greater window of safety for fire fighters. roof Construction Arched Trusses Buildings built during the 1930's and 1940's commonly used truss construction. Truss members have the same strength relationships as lightweight only much stronger. roof Construction Bridge Trusses Buildings built in the 1920's-1940's not as common as the arch Roofs vary in size and slightly in design Top surface is basically a flat roof roof Construction Conventional Residential roof Construction Conventional Residential roof Construction RAFTERS AND SPACE. SHEETING. roof Construction Conventional Construction Firefighter Concerns Generally sound construction Strongest areas of these roofs are ridges, hips, valleys, over trusses and where rafters cross outside walls Size of structural member dictates fire exposure time prior to failure Heat holes are acceptable and preferred with this type of construction roof Construction LIGHTWEIGHT.

5 CONSTRUCTION. roof Construction Lightweight construction: Does not derive its strength from size. Strength obtained from multiple members in compression and tension. Involves the use of less fire resistive materials. Provides less time to ventilate before the roof becomes unstable. roof Construction Lightweight Construction General Rules Expect early and complete collapse No heat holes Cut vent holes well ahead of fire 3/8-1/2 decking offers little resistance to fire Time on these roofs is very limited roof Construction Major types of Lightweight roof construction Metal Gusset Plate Trusses. Wooden I Beam. Open Web Truss. Open Web Steel Joist Panelized roof Construction Metal Gusset Plate Trusses: Common in residential and commercial buildings. Usually 2 x 4 lumber butt jointed and held together by metal gusset plates commonly known as gang nail which are 3/8 in depth. Characterized by a top (compression) chord and bottom (tension) chord.

6 Spans up to 80' with trusses 2' on center roof Construction Lightweight Commercial Metal gusset plate roof Construction Metal Gusset Plates roof Construction Metal Gusset Plates Burn test-structural collapse 1min. 20 direct flame impingement roof Construction Metal Gusset plates Firefighter Concerns Gusset plates increase charring at joints resulting in failure Bottom chord or web failure causes truss failure Open space between chords promotes fire spread roof Construction Wooden I Beam: Top and bottom chord of 2 x 3 or 2 x 4 . The stem is normally 3/8 plywood or OSB glued in place. Common spacing is 2' on center. Strongest location is where the roof meets the exterior wall. roof Construction Wooden I Beam roof Construction Wooden I Beam Burn test-structural collapse 3 min. 15. sec. With direct flame impingement. roof Construction Wooden I Beam Firefighter Concerns Stem has very little relative mass and burns to failure quickly.

7 Poke through construction reduces truss strength and promotes fire spread roof Construction Open Web Trusses: Wooden top and bottom chord cross connected by steel tube web members. 2x3 or 2x4 chords with spans of up to 70'. Normal spacing is 2' on center. Strongest location is where the roof meets the exterior wall. roof Construction Open web Free hanging bottom cords roof Construction Open Web Trusses: Structural collapse 4 min. 30 sec. With direct flame impingement. roof Construction Open Web Trusses Firefighting Concerns This is the most lightweight of truss construction Steel is good conductor of heat Open space between cords promotes fire spread roof Construction Open Web Steel Joist Steel top and bottom chords usually 1/8 angle iron Webs 1/8 angle iron or 5/8 solid bars Corrugated metal decking is commonly used with these trusses Often configured in a panelized . fashion roof Construction Open Web Steel Joist roof Construction Open Web Steel Joist roof Construction Open Web Steel Joist Firefighter Concerns Steel exposed to heat can distort and fail Consider rotary saws with carbide blades for cutting steel decking Fire may travel in horizontal openings of metal decking roof Construction Panelized Construction Consist of large, laminated beams spaced 12'.

8 To 40'. Beams can span well over 100'. Purlins with metal hangers on 8' centers. Purlins may be timber or truss design 2 x 4 rafters 2' on centers. Decking is usually 1/2 plywood. roof Construction Panelized Construction roof Construction PANELIZED SKELETON. roof Construction Panelized roofs: Structural collapse 5 min. 20 sec. With direct flame impingement roof Construction Panelized Construction Firefighter Concerns Steel beam supports weaken and fail resulting in sudden collapse of large portions of roof Foil insulation adds to fire spread Strongest areas are over beams, purlins and perimeter of building roof CONSTRUCTION. roof Styles and Designs roof Styles There are three basic styles of roof design Pitched roofs Arched roofs Flat roofs roof Styles Pitched roof Design Gable Hip Shed Bridge Truss Mansard Gambrel roof Styles Gable Basic A-frame design with the roof pitched in two opposing planes. May utilize conventional or lightweight construction.

9 Covered by shake, tile, rock, composition, etc. and supported by sheathing or plywood. roof Styles PITCHED roof LINES. roof Styles Pitched roof with dormers roof Styles Hip Similar to the gable roof , but lacks the A- frame configuration. Two sets of opposing pitches where the roof slopes down to meet every outside wall. May utilize conventional or lightweight construction. roof Styles Hip roof roof Styles Shed This style is essentially half a gable roof . May utilize conventional or lightweight construction. roof Styles Bridge Truss Easily identified by its characteristic sloping ends. Wooden truss members are 2 x 12 . and constitute a heavy grade of construction. Rafters are 2 x 6 or larger and covered by 1 x 6 sheathing and composition. Bridged truss concealed by supported facade roof Styles Bridged Truss roof Styles Bridge Trusses roof Styles Bridge Trusses roof Styles Mansard This roof has a double slope on each of its four sides.

10 The lower slope is steeper than the upper slope. roof Styles Arched roof Design Ribbed arch Lamella roof Bowstring arch Gambrel Pitched roof with two plans on each side Lower plans are steeper than upper plan Difficult to ladder, roof ladder usually required Lower plan may make up interior wall Gambrel roof Styles Ribbed Arch Truss Similar to Bridge Truss except that the top chord is arched. Large wooden members of 2 x 12 to 2 x 14 . Rafters (2 x 6 or more) are covered with 1 x 6 . sheathing and composition roofing material. Early collapse is not a primary concern. roof Styles Arched Truss Roofs roof Styles Arched Trusses roof Styles Arched Trusses roof Styles Arched Truss This roof predictably fails in sections. roof Styles Lamella Roofs Egg-crate, geometric or diamond-patterned roof . roof decking is 1 x 6 sheathing. Common on gymnasiums, supermarkets and recreational buildings. Total roof collapse may occur if fire removes more than 20% of roof structure.