IFSTA 7th ch 3.docx

There may be structures within your jurisdiction that are hundreds of years old and are located next to ones constructed in the past year (Figure 3.1). Each will conform to a different building code intended to provide a certain level of fire safety and structural stability. Each will be constructed...

There may be structures within your jurisdiction that are hundreds of years old and are located next to ones constructed in the past year (Figure 3.1). Each will conform to a different building code intended to provide a certain level of fire safety and structural stability. Each will be constructed from the building materials and architectural design common to the period of construction. In addition, older structures may have been renovated with engineered lumber or modern insulation systems. You must know the materials used to construct the buildings in your response area, their construction classifications, and the components that make up the structures. You must also know how the building's design and construction affect fire behavior and development inside the structure. Construction Classifications Locally adopted building codes regulate the type of construction based on the intended use (also known as occupancy classification), structure size, and the presence or lack of an automatic fire suppression system. The construction materials and their resistance to fire exposure determine the type of building construction (Figure 3.2). The authority having jurisdiction (AHJ) adopts and amends building codes to meet local requirements. Some building codes are locally developed although most are based on nationally accepted model building codes. In the United States, there are currently two major model building codes, NFPA 5000, Building Construction and Safety Code®, and the International Code Council's (ICC) International Building Code® (IBC*). In Canada, to enact building and fire regulations, the provinces, territories, and municipalities pass legislation that references the relevant National Model Construction Codes or provincial code. The following sections describe the general characteristics of each construction type specified in the model building codes for the U.S. and Canada. While minor differences exist between the model building codes, generally these construction types are common to each. Because local AHJs can amend model codes to meet their needs, you must be familiar with the building codes adopted within your jurisdiction. United States Construction Both the NEPA and the IBC® classify buildings in five types of construction (Type I through Type V). The types are further divided into subcategories, depending on the code and construction type. The construction materials and their performance when exposed to fire define each construction type. Type / (Fire-Resistive) Type I construction (also known as fire-resistive construction) provides the highest level of protection from fire spread as well as structural collapse. All structural members are composed of noncombustible or limited-combustible materials with a high fire-resistive rating so that the structural members do not add to the fuel load. Type I construction can be expected to remain structurally stable longer than other construction types during a fire and is considered to be the most collapse resistant. Reinforced concrete, precast concrete, and protected steel frame construction meet the criteria for Type I construction (Figure 3.3). Type I structures are often incorrectly referred to as being fireproof. While the structure will not burn, the structure may degrade from the effects of fire. Type I construction provides structural stability should a fire occur; however, the addition of combustible materials such as contents, furniture, and interior finishes can generate sufficient heat over time to weaken the building's structural integrity. During a fire in a Type I structure, firefighters may experience the following conditions:   Compartments can retain heat, contributing to the potential for rapid fire development.   Roofs may be extremely difficult to penetrate for ventilation purposes due to construction material and design.   Windows may be nonoperating, causing them to be very difficult to open for ventilation. Type Il (Noncombustible) Buildings classified as Type II construction (also known as noncombustible construction) are composed of materials that will not contribute to fire development or spread. Type II construction materials do not meet the stricter requirements of those materials used in the Type I building classification but still do not add to the fuel load (Figure 3.4). Steel components used in Type Il do not need to be protected for the same lengths of time or have the same ire-resistance rating as Type I. The most common form of this construction type includes metal framing mem-pers, metal cladding, or concrete-block wall construction and unprotected, open web joists supporting metal roof decks. These buildings are more prone to collapse than Type I, because they are constructed of lighter-weight materials with lower fire-resistance ratings. Type Ill (Ordinary Construction) Type III construction (also known as ordinary construction) is commonly found in mercantile, business, and residential structures and older schools. This construction type requires that exterior walls and structural members be constructed of noncombustible or limited combustible materials. Interior walls, columns, beams, floors, and roofs are completely or partially constructed of wood  Type III buildings may contain a number of conditions that can influence fire behavior, including the following:   Void spaces inside the wooden channels that roof and truss systems create between wall studs are less protected than in Type I and II construction. Fire will spread through these spaces unless fire stops are installed in the void    Prefabricated wood truss systems similar to those used in Type V construction may also be found in new Type III structures. These systems may fail quickly when exposed to fire  Type IV (Heavy Timber) Type IV construction (also known as heavy timber construction) is characterized by the use of large-dimensioned lumber or laminated wood. These dimensions vary depending on the particular building code in use at the time of construction. The dimensions of all structural elements, including columns, beams, joists, and girders, must adhere to minimum dimension sizing. Type IV structures are extremely stable and resistant to collapse due to the sheer mass of their structural members. When involved in a fire, it is the timbers' own char that reduces heat penetration to the inside of the beam. Exterior walls are constructed of noncombustible materials. Interior building elements such as floors, walls and roofs are constructed of solid or laminated wood with no concealed spaces. This lack of voids or concealed spaces helps prevent unseen fire travel. Modern Type IV construction materials may include small-dimensioned lumber glued together to form a laminate structural element (sometimes called glue-laminated or glulam elements). These elements are extremely strong and are commonly found in churches, auditoriums, and other large facilities with vaulted or curved ceilings. Glue-laminated beams (glulam beams) may fail when exposed to fire because the heat may affect the glue holding the laminates together. Type IV buildings may contain the following conditions that can affect their behavior during a fire:   The high concentration of wood can contribute to the intensity of a fire once it starts.   Collapse of masonry walls can be caused by loss of structural integrity of timbers. Type V (Wood Frame) Type V construction is commonly known as wood frame. The exterior load-bearing walls are composed entirely of wood. A veneer of stucco, brick, or stone may be constructed over the wood framing. These veneers offer the appearance of Type III construction but provide little additional fire protection or structural support. Two examples of this type of construction are single-family residences and some multistory apartment buildings. Type V construction consists of framing materials that include wood 2 x 4 or 2 x 6-inch studs. The outside of the framing members is covered with any number of materials exterior siding. Depending upon the siding material, siding can either contribute to exterior fire spread or help to minimize fire spread. Nails, screws, or glue may be used to attach exterior siding. In the case of stucco, it is spread over a screen lattice that is attached to the framing studs. Modern siding such as vinyl siding adds another petroleum-based fuel to the structural fire load. Vinyl siding is likely to produce dense, dark, oily, toxic smoke and will melt away from the side of the building. The siding covers combustible insulation or sheathing which becomes exposed to fire as the siding melts. These combustible materials may contribute to rapid fire development on the exterior of the structure and may extend fire spread to the interior. Some structures include 6-inch exterior wall cavities for increased insulation. Homes with increased energy efficiency may use exterior insulation to provide the same or similar increased insulation. Type V construction includes the use of a prefabricated wood truss system in place of solid floor joists. The truss system creates a large, open void between the floors of a structure, rather than the closed channel system found with solid wood floor joists. When wood I-beams are used, they are usually constructed of a central piece of thin plywood or wood composite, glued to two, 2 x 4-inch pieces, forming the top and bottom of the truss. These wood I-beams may have numerous holes cut in them to allow for electric, communication, and utility lines to be extended through them. Under fire conditions these plywood I-beams fail and burn much more rapidly than solid lumber. Adhesives and other industrial glues are used more frequently in modern Type V construction to connect engineered structural members. Research shows that adhesives are no more or less reliable than other construction methods. Size-up, duration of the fire, and fireground actions at the scene are more important indicators of structural collapse than the construction methods used. Factory-Built Homes Factor built homes (also known as manufactured, prefabricated, modular and industrialized housing) are structures that are partially or completely built in a factory and shipped to the location on which they are to be installed. Factory built homes take many forms and include mobile homes that have an axle assembly under the frame. Houses may also be constructed from steel shipping containers. Each container is a separate module connected to others to construct a complete house. Manufactured (Mobile) Homes Manufactured homes are the most common type of factory-built homes, almost completely prefabricated prior to delivery, and the least expensive. Manufactured homes usually have wheels and a permanent steel undercarriage and are towed behind a transport vehicle for delivery. They normally range from one-section single-wide homes to three-section triple-wide homes. Manufactured homes are not required to conform to the model building codes. They are required to conform to a U.S. Department of Housing and Urban Development (HUD) standard that is similar to Type V construction. The HUD code preempts all local building codes and is more stringent than model building codes. The HUD code is based on performance standards and tends to encourage construction innovations. The manufactured home's fire resistance will vary depending on age. Factory-built homes constructed before 1976 have less fire resistance than those of current construction. Lightweight building materials in some factory-built homes are susceptible to early failure in a fire. The use of lightweight materials does make forced entry much easier because walls can be quickly breached. The heat that the building's burning contents produces will cause these materials to ignite or melt rapidly. These contents have the same fuel loads as those found in conventional structures. Factory-built homes may be anchored directly to a concrete slab or have open crawl spaces beneath them, the latter of which provides an additional source for oxygen during a fire. Fire may spread more quickly through manufactured homes because of fewer internal walls to create compartments and interior finishes which add to the fuel load. The fire may become ventilation-limited quickly as a result. With adequate ventilation, fire spread will be even faster. An NFPA analysis of fires in residential occupancies indicates a steady decline in fires in manufactured homes since 1980. The analysis compares manufactured homes built before the HUD standard was enacted in 1976 (prestandard) and those constructed after 1976. Reductions in fire loss and residential fatalities can be attributed to construction requirements that include:   Factory-installed smoke and carbon monoxide alarms   Use of flame-retardant materials in interior finishes   Use of flame-retardant materials around heating and cooking equipment   Installation of safer heating and cooking equipment   Installation of gypsum board rather than wood paneling in interior finishes   Factory-installed fire suppression systems (sprinklers) Other Types of Factory-Built Homes Factory built homes are constructed in a variety of ways. Based upon the method of construction, factory-based homes may be referred to as any of the following: Modular homes - Modular or sectional homes must comply with the same local building codes caste. built homes. Only about 6 percent of all factory-built structures are modular homes. Modular sections tan te stacked vertically and connected horizontally in numerous ways. The modular section is transported to the sie and then attached to a permanent foundation, which may include a full basement.   Panelized homes - Panelized homes are assembled on-site from pre-constructed panels made of foam insulation sandwiched between sheets of plywood. The individual panels are normally 8 feet wide by up to 40 feet long. The bottom edges of the wall panels are recessed to fit over the foundation sill. Each panel includes wiring chases. Because the panels are self-supporting, framing members are unnecessary.   Pre-cut homes - Pre-cut homes consist of individual parts that are custom cut and must be assembled on-site. Pre-cut homes come in a variety of styles including:   Pole houses   Post-and-beam construction   Log homes   A-frames   Geodesic domes Hybrid modular structure - One of the most recent developments in factory-built homes, the hybrid modular structure includes elements of both the modular design and the panelized design. Modular core units such as bathrooms or mechanical rooms are constructed in the factory, moved to the site and assembled. Pre-constructed panels are then added to the modules to complete the structure. Floors, Ceilings, and Walls Floors and ceilings form the bottom and top of a compartment with the walls forming the sides. Understanding the construction of each can help firefighters understand how these components influence, fire behavior and fire fighting within compartments.  Floors and Ceilings Floors at ground level may consist of a concrete slab or a floor assembly made up of joists and decking over a crawl space or basement. Upper floors of a multistory building consist of the joists and decking with the ceiling attached to the bottom. The top level of a building consists of a ceiling, joists or rafters and the roof above. The space between the floor/ceiling or ceiling/roof may contain:   Duct work or open return air plenum   Electrical or communications wiring   Water or natural gas pipes   Pipes for a fire suppression system   Recessed lighting and audio speakers   Fiberglass, cellulose, or foam insulation beneath the roof or under the floors to act as soundproofing NOTE: Some states and local jurisdictions have passed laws and ordinances that require buildings other than single-family dwellings to display a warning placard indicating the type of floor or ceiling truss system used in the structure. If your jurisdiction has this requirement, you must be familiar with it and look for the placards when you respond to a structure fire. Floor and ceiling assemblies may be constructed of a combination of materials. Floors may be:   Poured reinforced concrete   Cellular concrete over metal decking   Finished wood, tile, or carpet surface over a wood subfloor attached to metal or wood joists Ceilings are generally:   Gypsum board   Tin tiles   Lath and plaster attached to joists, roof trusses, or beams The ceilings in corridors that are designated as exit or egress passageways will have the same fire-resistance rating as the walls in that corridor. The material used to cover the floors in high occupancy structures is also rated to limit flammability in the corridor. Ratings are indicated in hours. Walls Walls define the perimeter of the building, as well as divide it into compartments or rooms. Exterior walls may be wood or metal siding attached to:   Studs   A single layer of concrete   Concrete blocks   Logs Wall assemblies consist of a bottom plate, top plate, vertical studs, and horizontal braces sandwiched between two surfaces made of gypsum or lath and plaster. The cavity that the two surfaces forms may be a void or contain some form of insulation. Insulation may also be installed on the exterior of the wall. Fire walls provide separation to meet the requirements of a specified fire-resistance rating. Fire wall assemblies include the wall structure, doors, windows, and any other protected openings meeting the required protection-rating criteria. Fire walls may be used to separate two adjoining structures or two occupancy classifications within the same structure to prevent the spread of fire from one to the other. Fire wall assemblies can also divide large structures into smaller portions and contain a fire to a particular portion of the structure. However, when owners and contractors make unprotected penetrations through these walls for pipes, wires, and ducts, the protection that fire walls provide can be reduced or eliminated. Heat, smoke, and flames can pass through these openings, spreading the fire into compartments that might otherwise have been protected. Exterior walls and fire walls are the most difficult to penetrate when attempting to force entry into an area or to escape an area. Skills required for forcing entry through walls are included in Chapter 9, Forcible Entry. Basements and Stairs Basements and stairs present unique challenges for firefighters. Fire in basements can damage floor joists and load-bearing walls that support the upper floor and structure. Stairs can provide a flow path for the movement of air, fire gases, and smoke throughout a structure. Additionally, stairs present a fall danger during low-visibility conditions. Basements A basement is a floor of a structure that is either partially or fully below-grade level. Single-story basements can also be constructed on shallow foundations. Basements often serve as storage or utility spaces for the structure and house HVAC, breaker box, water heater, and other utility distribution units. Fires in basements may be more hazardous than in other compartments because of limited means of ingress/egress and limited ventilation. Being partially or fully underground can limit access to the basement. Walk-out or "daylight" basements are part of a structure built on a slope so that one or more sides of the basement may have a door or windows to the exterior. The upper portion of some basements extends above ground level and may have windows around the above-ground perimeter to allow light into the basement. Some basements are only accessible through interior stairwells; others have both interior and exterior stairs. Basements may be unfinished, lacking drywall on exposed wall studs and ceiling joists. The absence of drywall reduces the fire resistance of the studs and joists making the structural members part of the fuel load in the space. If these members fail, the floor above will collapse into the basement. Stairs Stairs provide access to, or egress from, different levels of a structure. Stairs in commercial and multifamily residential buildings that are a part of the required means of egress must provide protection for the occupants as they travel to safety. Stairs meeting these requirements are called protected or enclosed because they are built to resist the spread of fire and smoke. Stairs that are not required to be a part of the means of egress system and typically connect no more than two levels are called access or convenience stairs. Stairs can be classified as either interior or exterior stairs, depending on their location. The design or layout of a set of stairs may take any of several different forms. Although exterior fire escapes, escalators, and fixed ladders have been used as a means of egress in the past, they are no longer allowed as a required means of egress from normally occupied spaces. Protected Stairs Interior protected stairs are critical components of the life safety system of a building. Protected stairs are enclosed with fire-rated construction, usually with either a 1- or 2-hour rating, depending on building height. Protected stairs generally serves two stories of ground deep art of the required means of egress. They are the primary egress paths from floors above or below ground level and can adversely affect the safety of occupants if they do not maintain a breathable atmosphere. Firefighters should control the doors on protected stairs to of the in the integrity of the stairwell. Sometimes securing stairway doors open may facilitate either ventilation of a structure or evacuation of occupants. Only secure the doors in the open position when doing so will not endanger occupants or firefighters using the stair-well. High-rise structures may have pressurization or other methods for protecting stairwells that will fail if stair-are left open. Exterior Stairs Exterior stairs may be either open to the air or enclosed. Enclosed exterior stairs must comply with requirements similar to those of interior protected stairs. Open stairs are naturally ventilated but may be partially enclosed from the weather. They typically have at least two adjacent sides open to natural ventilation. Unprotected Stairs Because unprotected stairs are not enclosed with fire-rated construction, they may serve as a flow path for fire and smoke. They will not protect anyone using them from exposure to the products of combustion. Building codes typically allow the use of unprotected stairs in buildings when they connect only two adjacent floors above the basement level. Roofs The primary function of the roof is to protect the structure and its contents from the effects of weather. The shape and construction of the roof is intended to provide drainage, support the weight of accumulations of snow, and resist the effects of wind. Therefore, the geographic location of the structure can influence the type and construction of the roof. Penetrations or openings in the roof are indications of the general arrangement of the rooms within and may be used to assist in vertical ventilation during a fire. NOTE: Building owners or occupants may make unapproved or nonpermitted modifications to roofs during construction or renovation. Roof Types In general, you will encounter three prevalent types of roof shapes: flat, pitched, and arched. Some buildings have a combination of these roof designs. Some of the more common styles that compose these types are: Pitched Hip Gambrel Shed Mansard Lantern Sawtooth Butterfly Less common styles are sawtooth and butterfly roofs. Residential structures may have a combination of these styles which can contribute to voids underneath and limit the ability of firefighters to access areas under the roof. Flat Roofs Flat roofs are commonly found on commercial, industrial, and multifamily residential structures, as well as on some single-family residences. Flat roofs generally have a slight slope to facilitate drainage. Chimneys, vent pipes, shafts, scuttles, and skylights are common features that penetrate through flat roofs. Parapet walls may surround flat roofs. Fire separation walls may divide the roof from neighboring roofs. These fire walls extend from the foundation to above the roof. Obstructions that may also be located on roofs include: Water tanks   HVAC equipment   Antennas   Solar panels   Signs Pitched Roots There are a number of pitched roof styles. Among the most common are those elevated in the center along a ridge line with a roof deck that slopes down to the eaves along the roof edges. Shed roofs are pitched along one edge and the deck slopes down to the eaves at the opposite edge. Most pitched-roof construction involves beams or trusses that run from the ridge line to the top of the outer wall at the eaves level. These beams or trusses can be made of wood or metal. The roof decking or sheathing material, usually plywood or oriented strand board (OSB), is applied at right angles over these beams, sometimes over the entire roof. In other applications, decking consists of boards or planks set with a small space between them. This is commonly called skip sheathing. Pitched roofs usually have a covering of roofing paper applied before the finish surface is laid. The finish may consist of the following:   Wood or asphalt shingles   Asphalt roll roofing   Metal panels   Slate   Tile Arched Roots Arched roofs are ideal for some types of occupancies because they can span large open areas unsupported by columns, pillars, or posts. Arched roofs were primarily constructed from the late 1800s to the mid-1900s due to the availability of inexpensive lumber. The design of an arched roof depends primarily on the exterior walls to support the weight of the roof. Types of arched roofs include ribbed, pleated barrel, diagonal grid (Lamella) and bowstring as illustrated. Roof Construction Roofs are made up of three main components including the roof supporting structure, the roof deck or sheathing, and the roof covering. On some types of structures, such as single-family residences, the roof covering is the most visible component when viewed from the outside. On other types of structures, a view of the entire roof may be obstructed by the height of the building, parapet walls, or adjacent buildings. When viewed from inside, the roof supports and deck may be visible or covered by a ceiling assembly which creates a void that may be a few inches (millimeters) or many feet (meters) in depth. Roof Supports There are two general types of roof supports used in residential and commercial construction: beams and truss assemblies. Beams are the sections of lumber located directly under the roof decking. On-pitched roofs, they extend from the ridge line or pole at the peak to each side wall. On flat roofs, the beam extends from wall to wall. The beam may be exposed or concealed behind a ceiling. Box beams and I-beams, also referred to as wide flange beams, are manufactured from plywood and are often used in conjunction with wood joists to support flat roofs and floors. These beams provide adequate structural strength under normal conditions, but the thin web portion of plywood I-beams makes them susceptible to early failure in a fire. Roof truss assemblies may be conventional framing constructed on site or pre-manufactured in a factory and shipped to the site. Trusses constructed on site take longer to build and consist of top and bottom chords and webbing that extend from the peak to the walls. A horizontal joist with supports between the joist and the rafters connects the ends. Wood trusses are assembled using metal gusset plates (gang nails) that only penetrate about ⅜ inch into the wood. As wood burns away from the plates during a fire, the plates fall out and are no longer a structural support for the truss.  Much like engineered box beams or I-beams, trusses created from engineered materials are also susceptible to early failure. The open web design of truss joists permits the rapid spread of fire in directions perpendicular to the truss joist instead of simply along the long dimension of the member. Truss types include parallel chords, pitched chords, and arched chords, not to be confused with bowstring trusses. The parallel chord truss, constructed of wood or metal, is generally used to support flat roofs and floor assemblies. Engineered construction systems are manufactured from smaller pieces of wood or light gauge steel to form trusses that weigh less than traditional systems made from solid wood or heavy gauge steel. Lightweight construction is becoming more common, and other than Type I and Type IV construction, it can be found in:   Homes   Apartments   Small commercial buildings   Warehouses Two of the most common types of engineered construction systems involve the use of lightweight steel or wooden trusses. Lightweight steel trusses are made from long steel chords that are either straight or bent up to 90 degrees with either flat or tubular members in the web space. Flat roofs are also supported by open-web steel joists and steel beams. Depending on the fuel load within the structure, unprotected lightweight open-web joists can be expected to fail quickly in a fire. Roof Decks The roof deck is the portion of roof between the roof supports and the roof covering. Types of roof decks found in North America include:   Plywood sheathing   Oriented strand board (OSB)   Wood tongue and groove   Corrugated metal   Sprayable concrete encapsulated polystyrene   Reinforced concrete   Double tee preformed concrete The components of roof decks include sheathing, roof planks or slabs, and purlins. Sometimes, as in concrete deck roofs, the roof deck serves as the roof support. In other cases, the roof covering and the deck are the same. Corrugated steel decking is frequently used in applications where it serves as both the deck and the exterior roof covering. If a multistory building is to have a flat roof, the usual practice is to use the same structural system for the roof and the floors because it is more economical. Therefore, a building with wood-joisted floors usually will have a wood-joisted roof system and a steel-framed building will have a steel roof. It is possible to encounter exceptions to this rule, especially where a story has been added to an older building. There are two basic types of concrete roofs common in North America: cast-in-place and precast. Cast-in-place concrete is placed into forms at the building site as a wet mass and hardens in prepared forms. Cast-in-place concrete permits the designer to cast the concrete in a wide variety of shapes. This type of concrete roof does not develop its design strength until after it has been placed in the location where it will be used. Precast concrete roof units are widely used because they can be fabricated off-site and hauled to the construction site ready for use. Precast roof slabs are available in many shapes, sizes, and designs. Lightweight concrete roofs are one particular variety of precast construction. These roofs have gypsum plaster and Portland cement mixed with aggregates, such as perlite, vermiculite, or sand to form lightweight concrete. Lightweight, precast planks are manufactured from this material, and the slabs are reinforced with steel mesh or rods. Time, corrosion, moisture, or exposure to heat may cause concrete to separate from metal reinforcement and degrade its structural integrity. Lightweight concrete roofs are usually finished with roofing felt and hot tar to make them watertight. These roofs are extremely difficult to penetrate when performing vertical ventilation. Roof Coverings The roof covering is the part of the roof exposed to the weather. Roof-covering materials include (Figure 3.28):   Shingles:   Asphalt   Wooden or shake   Fiberglass   Rubber   Solar   Asphalt sheets   Terracotta, concrete, slate, or synthetic membrane tiles   Blown-on foam   Built-up tar and gravel surface   Metal roof systems or sheets Composite Materials  Roof Penetrations and Openings Roof penetrations and openings include items that provide light, ventilation, access, vapor exhausts, or are part of the plumbing or HVAC systems. Roof openings may be locked or secured in some manner. Roof penetrations and openings include (Figure 3.29):   Scuttle hatches   Skylights   Monitors   Automatic smoke vents   Ventilation shafts   Ventilation fans   Penthouse or bulkhead doors   Chimneys   HVAC exhausts   Bathroom vent pipes   Attic vents   Dormers  Penetrations can indicate the location of some types of rooms such as bathrooms or mechanical spaces. Monitors, smoke and attic vents, scuttle hatches, and skylights may be used to gain access to attics and cocklofts and may be used to provide an exit point for some types of ventilation. Roof Modifications Roof modifications should be identified during preincident surveys, the initial size-up, and at other times in case the structure needs to be ventilated. Roof modifications include:   Green roofs   Cold roofs   Photovoltaic roofs   Rain or snow roofs   Security   Structural modifications   Roof-mounted equipment Green Roots A green roof involves the use of the roof surface of a building for a rooftop garden. A rooftop garden constitutes a dead load on the roof structural system, which must be capable of supporting the load. The layer of earth required for a rooftop garden can range from a few inches (millimeters) to 1 to 2 feet (300 to 600 mm). This dead load can vary from 20 to 150 pounds per square foot (1 to 7.5 kPa). The structural engineer can account for this load in the structural plans for new construction. However, when a garden is planned for an existing roof, the existing structural system must be analyzed to ensure its adequacy. Under fire conditions, the increased load can accelerate structural failure, particularly if the roof is combustible. Green roofs can also interfere with ventilation practices and fire location indicators. Other concerns include:   The effects of high-velocity winds and uplift wind pressures   Roof drainage which can add weight to the roof creating a collapse hazard   The exposure hazard that dry vegetation on the roof may create   The need for a clear space between vegetation and fire walls that penetrate the roof Cold Roofs A cold roof system is generally found in cold, snowy climates to prevent ice damming and icicle formation at eaves. A cold roof system is designed to prevent interior heat from escaping into the attic space, thus melting the snow on the roof. The installation requires a sheathing layer to be installed above the top chord of the truss or rafter. A membrane (similar to Tyvek" is installed above the sheathing layer to prevent condensation buildup. Then two layers of 1 x 4-inch (25 by 100 mm) parallel spacers are installed above the membrane to create a 3-inch (75 mm) void air space which acts as insulation against the warm air from the home. A second layer of sheathing is installed above the parallel spacers. The roof covering system is applied next. This type of roof can create significant difficulty for firefighters during vertical ventilation operations. Photovoltaic Roofs A photovoltaic (PV) system (solar energy) produces clean and reliable energy useful for many applications. Photovoltaic cell panels can be laid on top of a roof or embedded in the roof (Figure 3.30). The electricity that the photovoltaic system generates presents a significant hazard for firefighters. Even if power to the building is shut off, the panels retain a significant amount of electricity. If light is available - even light from fire apparatus headlights or lighting equipment - the panels will continue to produce power. Research has shown that panels will also continue to produce electricity even if they are fire damaged. It is not safe to break photovoltaic cells or solar-powered skylights. Solar panels, like other elements on a roof, may not be visible from the ground on a building with a flat roof. The panels also present a significant tripping and falling hazard. Because of the hazards these systems present, it is crucial that fire departments identify their presence during preincident planning. Rain or Snow Roofs Rain roofs, also called snow roofs, may be found on commercial buildings, schools, and residential structures. These assemblies are pitched roofs built over older flat roofs for:   Aesthetic purposes   Leak prevention   Directing moisture off the roof   An alternative to repairing or resurfacing the original roof Rain roofs are also built over mobile homes to provide a more permanent appearance. They may be constructed from lightweight metal panels and trusses to form a peak or simply a second flat roof surface made from wood and roofing materials. The void that the rain roof creates can conceal a fire and allow it to burn undetected (Figure 3.31). As trusses are exposed to fire, they weaken, increasing the potential for collapse of both the rain roof and the original roof. HVAC units may also be hidden from view under the rain roofs, adding to the collapse potential. Ventilating a rain roof will not remove smoke from within the structure until the original roof is penetrated. Firefighters should not enter the void area to cut a hole in the original roof because they can:   Become trapped in the void.   Be overcome by the heat and smoke trapped in the void.   Fall through a weakened original roof.   Be caught in an extreme fire condition as the heated gases mix with fresh air. Roof Security Wired glass may be installed for security purposes in rooftop skylights. This type of glass is difficult to penetrate and takes time to remove. Firefighters may encounter other types of roof security. For example, store owners may install iron plates on the roof of a grocery store to prevent break-ins. During a subsequent fire, the weight of the plates can cause the roof to collapse. Installations like this can also prevent timely tactical vertical ventilation. Thorough preincident surveys should uncover barriers like these. Roof-Mounted Equipment Most commercial, industrial, institutional, educational, and some residential structures have equipment mounted on the roofs, especially on flat roofs. These items add to the load distributed on the roof, increase collapse hazards, and add to the obstructions that can affect ventilation efforts. Some items may also be found on flat roofs underneath rain roofs. Roof-mounted equipment includes (Figure 3.32):   HVAC units   Water towers   Telecommunications equipment   Telephone towers   Radio transmission equipment   Television antennas and satellite dishes   Advertising signs or billboards   Recreation areas   Wind generators   Electrical transformers   Derricks, hoists, and cranes   Winches   Steeples, minarets, spires, and crosses   Electrical lines and weather heads Many firefighters have been injured and killed because roof-mounted equipment has caused the collapse of a fire-weakened roof. Being aware of fire behavior and how it affects a building as well as the general design and construction of the fire building can help keep you safe. Doors Doors vary widely in operation, style, design, and construction. Doors are a tool for fire and flow path control. Doors are generally classified by the way that they operate. The following types of doors are commonly used in modern building construction:   Swinging   Sliding   Folding   Vertical   Revolving Doors can also be classified by style and construction material. Door styles are mainly of interest to an architectural designer. However, the construction material of a door influences its effectiveness as a fire barrier and the degree to which it can be forced open during an emergency. Doors are constructed from wood, metal, and glass. Wood doors may be panel or flush designs and may contain glass components. Aluminum and carbon steel are the most commonly used metals, but stainless steel, bronze, and copper are also used. In addition, doors are sometimes manufactured with a veneer of hardboard, fiberglass, or plastic. Swinging Doors A swinging door rotates by means of hinges secured to the side jambs of the doorway or on pivot posts supported at the top and bottom. A swinging door can be either single or double leaf. A door of this type may also be single acting (swinging in one direction), or double acting (swinging in two directions). Swinging doors are usually required as exit doors in a means of egress, although other types of doors can be used under specific conditions. Sliding Doors A sliding door is suspended from an overhead track and uses steel or nylon rollers. Floor guides or tracks are usually provided to prevent the door from swinging laterally. A sliding door can be designed for surface sliding, pocket sliding, or bypass sliding. A sliding door eliminates a door swing that might interfere with the use of interior space. A pocket sliding door, which slides into a wall assembly, is frequently used within residential units because it is out of sight when open. Sliding doors are also used for elevators, power-operated doors in storefront entrances, and fire doors to protect openings that are not a part of the means of egress. Sliding doors are never allowed as a part of a means of egress because they slow the travel of people through the door opening. Folding Doors A folding door is hung from an overhead track with rollers or glides similar to those used by a sliding door. A folding door can be either bifolding or multifolding. Folding doors may be found in residential occupancies, in places of assembly to divide large conference areas into smaller rooms, and as horizontal fire doors. Horizontal fire door assemblies must meet specific requirements and be tested and listed for use as a means of egress. Vertical Doors A door that opens in a vertical plane is known as an overhead door and is often found in industrial occupancies for applications such as :   Loading dock doors   Garage doors   Freight elevator doors   Fire doors protecting openings that are not part of the required means of egress A vertical operating door can be a simple single leaf that is raised in vertical guides along the edge of the doorway, or it can consist of two or more horizontal panels. Vertical rolling doors that consist of interlocking metal slats are commonly used in factories and warehouses. A door that operates vertically is usually provided with some type of counterbalance mechanism, either weights or springs, to help overcome the weight of the door. A vertical door can be raised manually, mechanically via chain hoist, or power-operated. Revolving Doors A revolving door is constructed with three or four sections or wings that rotate in a circular frame. A revolving door is designed to minimize the air flow through a door opening to reduce building heating or cooling losses. In a fire situation, revolving doors can prevent the movement of hose or equipment into a building. In addition, a crowd of people fleeing an emergency cannot move through a revolving door as quickly as they can through a swinging door. To overcome these restrictions, the wings of the revolving door are designed to collapse under pressure and provide an unobstructed opening. Several types of mechanisms hold the wings of revolving doors in place within the door unit. Old models use simple chain keepers or stretcher bars between the wings while new models use spring-loaded, cam-in-groove hardware. Most models employ a collapsing mechanism that allows the wings to open to a book-fold position when the wings are pushed in opposite directions. Wood Panel and Flush Doors A common type of swinging door is the wood panel door. A panel door consists of vertical and horizontal members that frame a rectangular area. Thin panels of wood, glass, or louvers are placed within the framed rectangular area. A flush door (sometimes referred to as a slab door) consists of flat face panels that are the full height and width of the door. The panels are attached to a solid or hollow core. A flush door can be designed with openings to accommodate glass vision panels or ventilation louvers. In the past, flush doors were constructed from one solid piece or slab of wood. Today, a flush door is constructed of wood components finished to present a smooth, unbroken surface on both sides. Solid-core doors are formed with an interior core of laminated blocks of wood, particleboard, or a mineral composition. The core is covered with two or three layers of surface material, which is usually plywood. If a wood solid-core door is intended for exterior application where security is a concern, a layer of sheet metal may be attached to the exterior surface. This added layer makes forcing the door more difficult. A hollow-core door is constructed with spacers between the face panels to provide lateral support. The interior spacers consist of a grid or honeycomb of wood, plastic, or fiberboard. Hollow-core doors are less expensive and lighter than solid-core doors. They have minimal thermal or sound-insulating value and usually are used for interior applications. Solid-core doors are better fire barriers than either panel doors or hollow-core doors. A solid-core door that has not been specifically designed as a fire door will act as a significant barrier to fire if it is closed at the time of the fire. Glass Doors Glass doors are used in both exterior and interior locations. They are found in almost all occupancies, but they are most commonly used in office and mercantile buildings. Glass doors can be either framed or frameless. A frameless glass door consists of a single sheet of glass to which door hardware such as handles are attached. In a framed door, the glass is placed in and surrounded by a metal or wood frame with the required door hardware attached to the frame. Building codes require glass doors to be made of tempered glass that resists breakage. Various plastics such as Lexan® or Plexiglas* are often used in framed doors to provide additional security. Metal Doors A common type of metal door is a hollow door made from steel or aluminum (Figure 3.40). A hollow metal door can be either panel or flush and is normally 1¾ inches (45 mm) thick. A flush door consists of smooth sheet metal face panels 1o inch (1 mm) thick. Vertical sheet metal ribs within the door spaced 6 to 8 inches (150 mm to 200 mm apart separate the face panels of a steel door. A sound-deadening material can be placed between the ribs. An aluminum flush door usually has a core of hardboard and honeycomb-patterned paper. A metal door can also be constructed of heavy corrugated steel. In this type of door, a steel frame supports one or two corrugated sheets. A door made with two corrugated sheets has an interior core material such as Styrofoam. Fire Doors Fire doors protect openings in fire-rated walls and block the spread of fire within a structure. Modern fire doors are found in all types of occupancies. When properly maintained and operated, fire doors are very effective at limiting the spread of fire and total fire damage. Fire doors differ from ordinary (nonfire) doors in their construction, their hardware, and the extent to which they may be required to close automatically. The construction and operation of fire doors depend on the type of occupancy, the amount of space around the door opening, and the required fire protection rating for the doo. Most fire doors will be constructed of metal and may roll, slide, or swing into place when released. Special types of fire-rated fire doors are available for:   Freight and passenger elevators   Security (bullet-resisting doors)   Service counter openings   Dumbwaiters   Chute openings Overhead Rolling Steel Fire Doors An overhead rolling steel fire door is commonly used to protect a fire wall opening in an industrial occupancy or an opening in a wall separating buildings into fire areas. An overhead rolling steel fire door may be used on one or both sides of a doorway or other wall opening (Figure 3.42). One architectural advantage of an overhead rolling fire door is that it is relatively inconspicuous and does not use wall space next to the opening. This type of door cannot be used on any opening that is required to be part of the means of egress. This type of door ordinarily closes under the force of gravity when a fusible link melts, but motor-driven doors are available. An overhead rolling door is constructed of interlocking steel slats with other operating components such as:   Releasing devices   Governors Counterbalance mechanisms Wall guides Horizontal Sliding Fire Doors Horizontal sliding fire doors are often found in old industrial buildings, are usually held open by a fusible link, and slide into position along a track either by gravity or by the force of a counterweight. Horizontal sliding doors cannot be used to protect openings in walls that are required parts of a means of egress. Several different materials are used to construct horizontal sliding fire doors. A common type of sliding fire door is a metal-covered, wood-core door. The wood core provides thermal insulation, while the sheet metal covering protects the wood from the fire. Because wood undergoes thermal decomposition when exposed to heat, a vent hole is usually provided in the sheet metal to vent the gases of decomposition. The metals used to cover the wood core include steel, galvanized sheet metal, and terneplate (a metal composed of tin and lead). Fire doors made with terneplate are commonly referred to as tin-clad doors, although the metal used is not pure tin. Swinging Fire Doors Swinging fire doors are commonly used in stairwell enclosures or corridors that require a fire door. A swinging fire door has the disadvantage of requiring a clear space around the door to ensure closure. However, a swinging door is a good choice when the door is located in a corridor where it must remain open during normal day-to-day operations. To perform its function, a swinging fire door must be closed during a fire. However, it is normally desirable for fire doors to remain open or to be easily opened to allow for ordinary movement of building occupants. Fire doors can be either automatic or self-closing. An automatic door is normally held open and closes automatically when an operating device is activated. A self-closing door is normally closed and will return to the closed position if it is opened and released. For a swinging fire door to close, some type of detection device must first sense a fire or the smoke from a fire. The oldest and simplest detection device is a fusible link that melts from the heat of a fire. Fusible links have the advantage of being inexpensive, relatively rugged, and easy to maintain. However, because they depend on heat from a fire, they are slower to operate than devices that react to smoke or the rate-of-temperature increase. A significant amount of smoke may flow through a door opening before a fusible link can release a fire door. When a smoke detector is used to activate a fire door, the door closes more quickly. It also permits easy testing of the fire door. A smoke detector costs more and requires periodic cleaning. As with all smoke detectors, they must be properly positioned with respect to dead air spaces or ventilation ducts. Some fire doors are designed to close when any component of the fire alarm system is activated. Windows Windows have long been relied upon as a means of light, ventilation, access, and rescue. However, modern buildings often rely on their HVAC systems for ventilation and artificial lighting for illumination. Elimination of windows that can be opened enhances energy efficiency in buildings because it reduces air infiltration around windows. Some buildings are designed with windows that cannot be opened or without windows altogether, resulting in increased difficulties for tactical ventilation and fire suppression team access. A window consists of a frame, one or more sashes, and all necessary hardware to make a complete unit. A window frame includes the members that form the perimeter of a window, and it is fixed to the surrounding wall or other supports. The term sash refers to a fixed or movable framed unit that may be included within a window frame. The frame is composed of the sill, side jambs, and head jamb. The sill is the lowest horizontal member of the window frame and supports the weight of the hardware and sash. All windows contain glass, known as glazing. The glass may be single-, double-, or triple-glazed. There may be one thickness of glass, two thicknesses separated by an inert gas, or three thicknesses separated by voids filled with gas. Some window and door panels may also have retracting shades located in the void. Windows can be broadly classified into fixed (nonoperable) or movable (operable). Windows that contain both fixed and movable characteristics are generally included in the movable classification. Fixed Windows A fixed window consists only of a frame and a glazed stationary sash. A fixed window can be used alone or in combination with movable windows. The large windows found in mercantile occupancies and high-rise office buildings are common examples of fixed windows. They are also referred to as display windows, picture windows, and deadlights. Fixed windows may be found in many applications including over and around doors, in skylights, and in residential applications.  Movable Windows Movable windows are designed in several common configurations:   Double-hung - Has two sashes that can move past each other in a vertical plane. A double-hung window is commonly used in residential occupancies because it permits circulation through the top and bottom of the window opening. Balancing devices consist of counterweights, springs, or a spring-loaded coiled tap to hold the movable sashes at the desired position. Windows that use counterweights are found in old buildings.   Single-hung - Has only one openable sash. Balancing devices consist of counterweights, springs, or a spring-loaded coiled tap to hold the movable sash at the desired position.   Casement - Has a side-hinged sash that is usually installed to swing outward. It may contain one or two operating sashes and can be opened fully by unlatching and pushing or using the mechanical window crank for ventilation.   Horizontal sliding — Has two or more sashes of which at least one moves horizontally within the window frame. In a three-sash design, the middle sash is usually fixed; in a two-sash unit, one or both sashes may be movable.   Awning - Has one or more top-hinged, outward-swinging sashes that are opened by unlatching and pushing or using the mechanical window crank. This arrangement permits the window to be open during rain. Hopper windows are similar in design to awning windows except they are hinged at the bottom.   Jalousie - Includes a large number of narrow overlapping glass sections swinging outward (the same basic concept as the awning window). The individual pieces of glass are about 4 inches wide. An operating mechanism supports the glass sections at their ends. Jalousie windows are popular architecturally because the amount of opening can be varied for ventilation without admitting rain. Projecting — Swings outward at the top or bottom and slides upward or downward in grooves. A push bar that usually operates the projected window is notched to hold the window in place.   Pivoting - Has a sash that pivots horizontally or vertically on a central axis. Part of a pivoting window swings inward and part swings outward when it is opened. A window of this design provides the full area of the window opening for ventilation. Security Windows Windows may also provide an access point for intruders. Consequently, security is frequently provided for windows, especially windows that are accessible from the ground or adjacent roofs. A common window security method is to fasten metal bars or screens to the exterior of the window frame or to the building itself. The metal bars fastened to the building may be embedded in masonry or mounted on hinges and locked with padlocks or other locking devices. Security windows are available with movable sashes and fixed bars so that the windows can be opened for ventilation while maintaining security of the premises. Security bars or grilles have a negative effect on fire and life safety. They can prevent the escape of trapped occupants or firefighters and can slow the access time for firefighters. Security bars and grilles must be removed or disabled when interior operations begin to ensure firefighter safety in case a rapid egress is required. Rolling Steel Shutters Much like overhead rolling steel fire doors, rolling steel shutters may also be used to protect a fire wall opening in an industrial occupancy or an opening in a wall separating buildings into fire areas. Rolling steel shutters block interior window openings, such as office windows overlooking a factory floor. Rolling steel shutters have the same operating components as rolling steel doors. These shutters ordinarily close under the force of gravity when a fusible link melts, but motor-driven shutters are available.