fire science chapter 4 building construction
live load
(1) items within a building that are movable but are not included as a permanent part of the structure; merchandise, stock, furnishings, occupants, FFs and the water used for fire suppression are examples of live loads (2) force placed upon a structure by the addition of people, objects or weather.
movable window configurations
-double-hung: has two sashes that can move past each other in a vertical plane -single-hung: has only one sash openable -casement: has a side-hinged sash that is usually installed to swing outward -horizontal sliding: has two or more sashes of which at least one moves horizontally within the window frame -awning: has one or more top-hinged outward-swinging sashes that are opened by unlatching and pushing or using the mechanical window crank -jalousie: includes a large number of narrow overlapping glass sections swinging outward -projecting: swings outward at the top or bottom and slides upward or downward in grooves. -pivoting: has a sash that pivots horizontally or vertically about a central axis.
factory-built homes
-manufactured homes: most common type. almost completely prefabricated prior to delivery and is the least expensive. the HUD code preempts all local building codes and is more stringent than model building codes -modular homes: must comply with the same local building codes as site-built homes. modular sections can be stacked vertically and horizontally in a variety of ways. -panelized homes: assembled on site from preconstructed panels made from insulation sandwiched between sheets of plywood -pre-cut homes: consists of individual parts that are custom cut and must be assembled on-site -hybrid modular homes: modular core units such as bathrooms or mechanical rooms are constructed in the factory, moved to the site and assembled. preconstructed panels are then added to the modules to compete the structure.
-open ceilings and other concealed spaces immediately whenever a fire is suspected of being in the overhead space. apply the following tactics:
-when responding to any structure where a fire has been reported, always check the ceiling prior to entering the building. -as you advance into the building, check the ceiling at intervals of ~20ft -when you enter another portion of the building, repeat the process -use extreme caution because opening concealed spaces can result in backdraft conditions -if smoke or fire is found above the ceiling, remove all ceiling tiles or material until the source is located -position between the nearest exit and the concealed space to be opened. -be aware of the position of other FFs in your area -do not allow the fire to extend over you or get between you and your exit path
Curtain wall
A nonload-bearing wall, often of glass and steel, fixed to the outside of a building and serving especially as a cladding.
hazards of truss systems
FF should take the following steps to minimize the risk of injury or death during structural fire fighting operations involving a roof or truss system: -know how to identify roof and floor truss construction -immediately report the presence of truss construction and fire involvement to the IC -use a thermal imager as part of the size-up process to help locate fires in concealed spaces -open ceilings and other concealed spaces immediately whenever a fire is suspected of being in the overhead space. *see next slide -undertand that fire-resistance ratings may not be truly representative of real-time fire conditions and the performance of truss systems may be affected by fire severity
engineered and truss construction
FFs must be aware of the danger posed by the increased use of engineered or lightweight construction and trussed support systems. experience has shown that unprotected engineered steel and wooden trusses can fail after 5-10min of exposure to fire. for steel trusses, 1000F is the critical temperature. metal gusset plates in wooden trussers can warp and fail quickly when exposed to heat. bowstring truss roofs became popular in the 1930s and are easily identified by the roof's arched or curved outline. the principles of bowstring truss construction are similar to other types of truss construction. web members used to form a series of triangles that transfer tension from the bottom cord and compression from the top chord of the truss onto the load-bearing walls. all trusses constructed prior to the 1960s have a common code deficiency: the bottom chord members may have inadequate tensile strength to support code-prescribed roof loads.
metals -steel
Steel is the primary material used in the construction of large modern buildings. Steel is also used for stairs, wall studs, window and door frames, and for balconies and railings. It is also used to reinforce concrete floors, roofs and walls. Steel structural members lengthen (elongate) when heated. A 50ft beam may elongate by as much as 4in when heated from room temperature to about 1000F. if the steel is restrained from movement at the ends, it buckles and fails somewhere in the middle. The failure of steel structural members can be anticipated at temperatures near or above 1000F. steel failure depends on many factors. For example, a lightweight steel truss will fail much quicker than a large, heavy I beam. To reduce the effect of heat on steel structural members, fireproofing materials such as sprayed-on concrete or sprayed-on insulation is used. It is important to remember the critical temperature for steel is 1000F; this temperature can easily be reached at ceiling level from the rising heat and smoke. Elongating steel can actually push out load bearing walls and cause a collapse. Also, if the walls are able to withstand the elongation, the steel will fail and sag somewhere in the middle, causing collapse of the upper floors or the roof. Water can cool steel structural members and stop elongation, which reduces the risk of a structural collapse.
lightweight steel truss
Structural support made from a long steel bar that is bent at a 90-degree angle with flat or angular pieces welded to the top and bottom
Metals - aluminum
The use of aluminum increased throughout the 20th century. Initial uses included decorative and functional uses including roofing, flashing, gutters, downspouts, window and doorframes, and exterior curtain wall panels. Aluminum is used in the construction of sun rooms, screened porches, car ports, and awnings found on residential structures. Aluminum studs have replaced wooden in many commercial and residential structures. Acoustical tile ceilings are supported by aluminum framing and support wires that can create entanglement hazard for FFs. Aluminum will be affected by heat more rapidly than steel.
other metals
Tin - has been used to produce metal ceiling tiles and is used as a roof covering Copper - found in wiring, pipes, gutters and other decorative elements lead - still found in pipes, flashing, and as a component of stained glass of leaded glass windows. these metals will fail when exposed to excessive amounts of heat
security
a common method for providing window security is to fasten metal bars or screens to the exterior of the window frame or to the building itself. when interior firefighting operations begin, security bars and grilles must be removed or disabled to ensure FF safety in case a rapid egress is required
metal doors
a common type of metal door is a hollow metal door made from steel or aluminum
doors - 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, and fire doors protecting openings that are not part of the required means of egress.
roof obstructions - photovoltaic roofs
a photovoltaic (solar energy) system produces clean and reliable energy that can be used in a wide range of applications. cells can be laid on top of a roof or embedded in the roof. the electricity generated by the operation of the solar system represents a significant hazard for FFs. even if power to the building is shut off, the panels retain a significant amount of electricity. research has shown that panels will continue to produce electricity even if they are fire damaged. it is not safe to break solar energy cells or skylights that are solar powered.
single use
a single-use structure must meet the building code requirements for its intended use. for instance, an office building must meet requirements found in the Business Occupancy Classification while an elementary school must meet the requirements of an Educational Occupancy. Requirements include exit access, emergency lighting, fire protection systems, construction type, and fire separation barriers, among many others. in many cases, a structure such as an industrial facility will contain multiple types of uses including storage, manufacturing, and offices. the structure is generally classified by its primary function.
parallel chord truss
a truss constructed with the top and bottom chords parallel. these trusses are used as floor joists in multistory buildings and as ceiling joists in buildings with flat roofs
wood panel and flush doors
a very 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 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. solid core doors are formed with an interior core of laminated blocks of wood, particleboard or mineral composition. the core is covered with two or three layers of surface material, which is usually plywood. a hollow-core door is constructed with spacers between the face panels to provide lateral support. 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
oriented strand board (OSB)
a wooden structural panel formed by gluing and compressing wood strands together under pressure. this material has replaced plywood and planking in the majority of construction applications. roof decks, walls, and subfloors are all commonly made of OSB
gypsum
aka drywall or Sheetrock, is an inorganic product from which plaster and wallboards are constructed. it is unique because it has a high water content that absorbs a great deal of heat as the moisture evaporates. the water content gives gypsum excellent heat-resistant and fire-retardent properties and is commonly used to insulate steel and structural members
pitched roofs
among the most common styles are thoe elevated in the center along a ridge line with a roof deck that slopes down to the eaves along the roof edges. most pitched-roof construction involves rafters or trusses made of wood or metal that run from the ridge line to the top of the outer wall at the eaves level. over these rafters, the roof decking (usually plywood) is applied at right angles. the finish may consist of shingles, asphalt roll roofing, metal panels, slate or tile
arched roofs
are ideal for some types of occupancies because they can span large open areas unsupported by columns, pillars, or posts. the rapid collapse of arched roofs involved in fire has contributed to many FF injuries and fatalities making them one of the most dangerous types of roof construction.
types of insulation
asbestos - mineral fiber used before 1970 for insulation and as a fire retardant. it is a known carcinogen. urea formaldehyde foam insulation (UFFI) - originally used in the 1970s for insulating walls, this material caused high levels of formaldehyde emissions when improperly installed mineral wool - includes slag wool and rock wool. it is becoming more popular as an insulation material cellulose - ~80% post-consumer recycled newspaper, the rest is fire-retardant chemicals. over time, cellulose loses its ability to be a fire retardant. it is also a respiratory irritant when inhaled cotton - type of insulation made up of cotton and polyester mill scraps, plastic fiber, and borates for fire resistance. it is as effective as fiberglass or cellulose and has fewer health risks straw - insulation used in the exterior walls of hybrid or natural (green) construction buildings and houses. it can be affected by moisture and may become infected by insects and vermin foam - foam insulation is applied in rigid boards called extruded and expanded polystyrene (EPS) or blown into wall cavities or voids in spray form. can irritate the respiratory system. there are several types of foam including polyisocyanurate, polyurethane, and polystyrene
unprotected stairs
because unprotected stairs are not enclosed with fire-rated construction, they may serve as a path of spread for fire and smoke. building codes typically allow the use of unprotected stairs in buildings when they connect only two adjacent floors above the basement level. these stairs are sometimes referred to as access or convenience stairs and can be used as part of an exit system in a two-story building
composite materials
being used more frequently than in the past. generally, composite materials are manufactured by combining two or more distinctly different materials. this process results in lightweight materials with high structural strength, resistance to chemical wear, corrosion resistant, and heat resistance. examples include: -finger-jointed timber: small pieces of wood that are joined into longer board using epoxy resins and glues -laminated timber: aka plywood or glulam wood, these materials are sheets of wood used for roof and floor decking, walls, and stair treads, among other uses -medium density fiberboard (MDF): another type of laminated wood product, MDF is closer in appearance and strength to hardwood. it is used for doors and door-surrounds, decorative moldings, rails, skirtings, and cornices -particle board: made from small particles and flakes generated in the manufacture of lumber, particle board is used for exterior and interior wall panels and furniture. urea formaldehyde is one of the types of glues used to manufacture particle board and can pose health hazard due to outgassing when heated -synthetic wood: this material, produced in sheets and boards, is manufactured from recycled plastic from liquid containers. primarily used for exterior rails, stairs and decks
dangerous building conditions - furnishings and finishes
besides the fuel load, the furnishings and interior finishes can contribute to fire spread and smoke production. the interior finishes include the window, wall, and floor coverings such as drapes, wallpaper, and carpet
US construction
both the IBC (international building code) and the NFPA classify buildings in five types of construction defined by the construction materials and their performance when exposed to fire. every building is composed of the following elements: structural frame, floor construction and roof construction
fire escapes
building codes have not permitted fire escapes in new construction for many decades. fire escapes that have been in place for many years may not be able to support the required live load created during an emergency evacuation or fire suppression operations. the best policy for FF is to use interior stairs if they are available, followed by fire department ground ladders and aerial devices to access upper floors
smokeproof stair enclosures
building codes require a smoke proof stair enclosure under certain circumstances such as stairs serving a high-rise building. stair enclosures using either active or passive smoke control may be defined as smoke proof. a mechanical ventilation system, activated by automatic fire/smoke detection equipment, actively keeps a stair enclosure free of smoke, even when a door is open to the fire floor.
type IV (heavy timber/mill construction)
characterized by the use of large-dimensioned lumber. as a general rule, these structural members will be greater than 8in in dimension with a fire-resistance rating of 2 hours. the dimensions of all structural elements must adhere to minimum dimension sizing. any other materials used in construction and not composed of wood must have a fire-resistance rating of at least 1 hour. type IV structures are extremely stable and resistant to collapse due to the sheer mass of their structural members. when involved in a fire, the heavy timber structural elements form an insulating effect derived from the timber's 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 to prevent fire travel. modern type IV construction materials may include small-dimensioned lumber that is glued together to form a laminated structural element (glulam element). these elements are extremely strong but the beams may fail when exposed to fire because the glue may be affected by the heat. - the high concentration of wood can contribute to the intensity of the fire once it starts -collapse of masonry walls can be caused by loss of structural integrity of timbers
type III (ordinary construction)
commonly found in older schools and mercantile, business and residential structures. requires that exterior walls and structural members be constructed of noncombustible materials. interior walls, columns, beams, floors, and roofs are completely or partially constructed of wood. may contain a number of conditions that can affect their behavior during a fire, including: -voids exist inside the wooden channels created by roof and truss systems and between wall studs that will allow for the spread of fire unless fire stops are installed in the void -older type III structures may have undergone renovations that have contributed to greater fire risk due to the creation of large hidden voids above ceilings and below floors that may create multiple concealed voids -structural components may have been removed to change the configuration, or to open up floor space, during renovations. this may reduce the load-carrying capacity of the supporting structural member -a change in building use or occupancy may result in additional loads that the building was not designed to carry -prefabricated wood truss system 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
flat roofs
commonly found on commercial, industrial, multifamily residential structures, and some single-family residences. generally has a slight slope toward the outer edge to facilitate drainage. the roof may be surrounded by parapet walls or divided by fire separation walls that extend from the foundation to above the roof
swinging fire doors
commonly used in stairwell enclosures or corridors that require a fire door. fire doors can either be 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 fire door to close, some type of detection device must first sense a fire or the smoke from a fire. the oldest and simplest device is a fusible link that melts from the heat of a fire. when a smoke detector is used to activate a fire door,the door closes more quickly.
rolling steel fire doors
commonly used to protect an opening in a fire wall in an industrial occupancy or an opening in a wall separating buildings into fire areas. 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 is constructed of interlocking steel slats with other operating mechanisms. it ordinarily closes under the force of gravity when a fusible link melts, but motor-driven doors are also available
type II (noncombustible or limited combustible)
composed of materials that will not contribute to fire development or spread. steel components used in type II do not need to be protected for the same lengths of time or have the same fire-resistance rating as type I. structures with metal framing members, metal cladding, or concrete-block construction of the walls with metal deck roofs is supported by unprotected open-web joists are the most common form of this construction type. the fire resistance rating is generally half that of type I, or 1 to 2 hours, depending on the component. these buildings are more prone to collapse because they are constructed of lighter-weight materials with lower fire-resistance ratings. you must always remember that the term noncombustible does not always reflect the true nature of the structure.
cockloft
concealed space between the top floor and the roof of a structure
fixed windows
consists only of a frame and a glazed stationary sash. the large windows found in mercantile occupancies and high rise office buildings are common examples of fixed windows
roof obstructions - permitted structural modifications
construction requirements are intended to provide occupants with the highest level of fire and life safety possible. over the life of a structure you can expect that modifications will be made to improve and update it. the modifications must meet the local building codes having been inspected and approved by the local building official.
means of egress
continuous and unobstructed way of exit travel from any point in a building or structure to a public way, consisting of three separate and distinct parts: exit access, exit and exit discharge
doors - revolving doors
designed to minimize the flow of air through a door opening to reduce building heating or cooling losses. a revolving door prevents the movement of hose or equipment into a building which can present a problem for FFs. furthermore, a crowd of people attempting to flee an emergency cannot move through revolving doors as quickly as they can through a comparable swinging door. to overcome these restrictions under emergency conditions, the wings of the revolving door are designed to collapse under pressure and provide an unobstructed opening.
building components - foundations
designed to support the weight of the building and all its contents. may be shallow or deep. a shallow foundation extends a few feet into the earth around the perimeter of the structure. the foundation sits on a footing made from poured, reinforced concrete or concrete blocks. the first floor is constructed upon the foundation, taking the form of a solid concrete slab or a stem wall with a wood or metal joist floor that creates a crawl space between the floor and the soil below. deep foundations are used to support the mass of a large area or tall building. deep foundations include piers or pilings driven into the soil, drilled shafts, caissons, helical piles, and earth-stabilized columns. multiple basement levels may also rest on the piers.
roof obstructions - non permitted modifications
even though permits and inspections are required by local ordinance, owners or occupants may make unapproved or non permitted modifications during construction or renovation that can inhibit effective ventilation and increase the risk of fire extension and structural collapse
spalling
expansion of excess moisture within masonry materials due to exposure to the heat of a fire, resulting in tensile forces within the material, causing it to break apart. the expansion causes sections of the material's surface to violently disintegrate, resulting in explosive pitting or chipping of the material's surface
exterior stairs
exterior stairs may either be open to the air or enclosed. enclosed exterior stairs must comply with requirements similar to those of interior protected stairs
building components - walls
exterior wall may be wood or metal siding attached to studs, a single layer of concrete blocks or logs. internal wall assemblies may be rated for a specified fire resistance time depending on the local building code. because masonry materials do not burn, a variety of masonry walls are used in the construction of fire walls. fire walls may be used as party walls 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 a structure. exterior walls and fire walls are the most difficult to penetrate when attempting to force entry into or escape an area.
fire doors
fire doors protect openings in fire-rated walls. the use of fire doors to block the spread of fire is an established fire-protection technique. 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 doors in their construction, their hardware, and the extent to which they may be required to close automatically. to qualify as a rated fire door, the entire assembly, including the door, hardware, door seal, and frame must pass a test by a third party testing agency. rated fire doors are identified with a label indicating the door type, the hourly rating and the identifying logo of the testing laboratory. it is not uncommon for the labels to be painted over in the course of building maintenance. most fire doors will be constructed of metal and may roll, slide, or swing into place when released
fire wall
fire-rated wall with a specified degree of fire resistance, built of fire-resistive materials and usually extending from the foundation up to and the through the roof of the building, that is designed to limit the spread of a fire within a structure
building components - floors/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. floors may be poured reinforced concrete; cellular concrete over metal decking; or finished wood, tile or carpet surface over a wood subfloor attached to metal or wood joists. ceilings are generally gypsum board, tin tiles, or lath and plaster attached to joists, roof trusses or beams. the ceilings in corridors that are designed as exit or egress passageways will have the same fire-resistance rating as the walls in that corridor. the material used to cover the floor is also rated to limit flammability in the corridor
construction, renovation and demolition hazards
for a variety of reasons, the risk of fire rises sharply when construction, renovation, or demolition is being performed in a structure. contributing factors are the additional fuel loads and ignition sources brought by building contractors and their associated equipment. some local fire codes mandate that standpipe systems must remain in operation during the demolition of multistory buildings although this is not always enforced.
dangerous building conditions - fuel loading
fuel load is the maximum heat that can be produced if all the combustible materials, both contents and building materials, in a given area burn. heavy fuel loading is the presence of large amounts of combustible materials in an area of a building. proper inspection and code enforcement prior to an incident is the most effective defense against these hazards
roof obstructions - cold roofs
generally found in cold, snowy climates to prevent ice damming and icicle formation at eaves. it is designed to prevent interior heat from escaping into the attic space thus melting the snow on the roof. the cold roof layering system design can create significant difficulty for FF during vertical ventilation operations
glass/fiberglass
glass is not typically used for structural support. conventional glass is not a barrier to fire extension. heated glass may break and shatter when it is struck by a cold fire stream. fiberglass is typically used for insulation purposes and is located between exterior and interior walls and between ceilings and roofs. although fiberglass is not flammable the materials used to bind the fiberglass may be combustible and difficult to extinguish
manufactured structures
home built in a factory and shipped to the location where it is installed. make up 25% of all housing sales in the US. they are not required to conform to the model building codes; they are required to conform to a US Dpt of housing and urban development standard that is similar to type V construction. manufactured homes built before 1976 have less fire resistance than those of current construction. lightweight building materials in some manufactured homes are susceptible to early failure in a fire. the use of these lightweight materials makes forced entry much easier. there has been a steady decline in fires in manufactured homes since 1980 due to: -factory-installed smoke alarms -use of flame-retardant materials in interior finishes, and 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)
ridge
horizontal line at the junction of the top edges of two sloping roof surfaces
purlin
horizontal member between trusses that supports the roof
structural collapse factors - construction type
in N America, examples of structural collapse involving high-rise buildings or type I construction buildings are very limited. church steeples, water tanks, chimneys, and false facades that extend above the top of the structure must be viewed as a potential collapse hazard even if the structure is not. all personnel must ensure the structural stability of the site before entering it. NIST and USFA tests indicate that in both residential and commercial structures there is very little difference between collapse times for steel bar joist-supported roofs and wood truss-supported roofs. both are prone to very rapid collapse. you must be aware that collapse of structures using lightweight construction can occur earlier in the incident and may not provide you with warning indicators listed above.
roof obstructions - security
in many communities, metal security bars or grilles are mounted over doors and windows to prevent illegal entry. this type of security will slow entry, create emergency exit hazards, and reduce the effectiveness of ventilation tactics
rafter
inclined beam that supports a roof, runs parallel to the slope of the roof and to which the roof decking is attached
roof penetrations and openings
include a variety of items that provide light, ventilation, access, vapor exhausts, or are part of the plumbing or HVAC systems. 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.
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. also, protected stairs generally serve two stories or more and are part of the required means of egress.
roof obstructions - green roofs
involves the use of the roof surface of a building for a rooftop garden. this increases the insulating effects between the building interior and the outside and it increases the air quality. a rooftop garden constitutes a dead load on the roof structural system, which must be capable of supporting the load. under fire conditions, the increased load can accelerate structural failure, particularly if the roof is combustible. they can also interfere with ventilation practices. 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 may be created by dry vegetation on the roof -the need for a clear space between vegetation and fire walls that penetrate the roof
dangerous building conditions - large, open spaces
large, open spaces contribute to the spread of fire throughout. in facilities with these, proper vertical tactical ventilation is essential for slowing the spread of the fire. in concealed spaces, fire can travel undetected, feeding on combustible exposed wood rafters
roof construction
made up of three main components including the roof supporting structure, the roof deck or sheathing and the roof covering
masonry
masonry includes bricks, stones and concrete blocks. Brick and stone are generally used to create veneer walls, which are decorative covers for wood, metal, and concrete-block load-bearing walls. masonry is minimally affected by fire and exposure to high temperatures. bricks rarely show any signs of loss of integrity or serious deterioration. stones and concrete may lose small portions of their surface when heated, a condition called spalling. concrete blocks may crack, but they usually retain most of their strength and basic structural ability. the mortar between the bricks, blocks and stone may be degraded by heat and may display signs of weakening.
doors - 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 very specific requirements and be tested and listed for use as a means of egress.
roof obstructions - rain roof
may be found on commercial buildings, schools and residential structures. generally, they are pitched roofs placed over older flat roofs for aesthetic purposes, to prevent leaks, channel moisture off the roof and as a more cost-effective alternative to repairing or resurfacing the original roof. the void created by a rain roof can conceal a fire and allow it to burn undetected. as the trusses are exposed to fire, they will weaken, increasing the potential for collapse of both the rain roof and the original roof. ventilating a rain roof will not remove smoke from the structure until the original roof is penetrated. however, you must not enter the void area to cut a hole in the original roof as this is extremely dangerous
windows
modern buildings often rely on their HVAC system 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. consequently, some buildings are designed with windows that cannot open 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. the term sash refers to a framed unit that may be included within a window frame and it may be fixed or movable.
roof obstructions - roof-mounted equipment
most commercial, industrial, institutional, educational, and some residential structures have equipment mounted on the roofs. this is particularly true of structures with flat roofs. these items add a live load to the dead load distributed on the roof, increase collapse hazards and add to the obstructions that will affect ventilation efforts.
glass doors
most commonly used in office and mercantile buildings. building codes require glass doors be made of tempered glass that resists breakage. in addition, various plastics such as Lexan or Plexiglas are often used in framed doors to provide additional security
horizontal sliding fire doors
often found in old industrial buildings and are usually held open by a fusible link, and slide into position along a track either by gravity or by use of a counterweight. also cannot be used to protect openings that are required as means of egress. 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 fire. the metals used include steel, galvanized sheet metal, and terneplate (a metal composed on tin and lead).
parapet
portion of the exterior walls of a building that extends above the roof. a low wall at the edge of the roof
lath and plaster
process in which horizontal wood strips called lath are nailed to wall studs and covered with a mixture of plaster to form an interior wall finish. generally found in building constructed prior to the 1950s. wire mesh was also used to replace the lath for ceilings in some houses. interior lath and plaster walls can be very difficult to penetrate with axes or hand tools. the walls can also conceal fire within the cavity between surfaces and add fuel to the fire in the form of the studs and lath
type I (fire resistive)
provides the highest level of protection from fire development and spread as well as collapse. all structural members are composed of noncombustible or limited-combustible materials with a high fire-resistive rating. structural components such as walls, floors and ceilings must be able to resist a fire for a period of 3 to 4 hours depending on the component. reinforced concrete, precast concrete and protected steel frame construction meet the criteria for type I construction. fire walls are used to limit fire spread through structures. these structures are often incorrectly referred to as being fireproof, but even though the structure will not burn, it may degrade from the effects of the fire. the following conditions may result from type I construction: -compartments can retain heat contributing to the potential for rapid fire development -roofs are extremely difficult to penetrate for the purpose of ventilation due to construction material and design -windows may be non operating, causing them to be difficult to open for ventilation.
fire-resistance rating
rating assigned to a material or assembly after standardized testing by an independent testing organization; identifies the amount of time a material or assembly will resist a typical fire, as measured on a standard time-temperature curve
reinforced concrete
reinforced concrete is internally fortified with steel reinforcement bars (rebar) or wire mesh. this gives the material the compressive strength (ability to withstand pressure on the surface) of concrete along with the tensile strength (ability to withstand being pulled apart or stretched) of steel. while reinforced concrete does perform well under fire conditions, it can lose strength through spalling. cracks and spalling in reinforced concrete surfaces are an indication that damage has occurred and that strength may be reduced. in addition, prolonged exposure to chemicals can cause the steel reinforcing bars to corrode and the concrete bond to weaken before any exposure to fire, significantly reducing the time to failure
doors - swinging doors
rotates around a vertical axis by means of hinges secured to the see jambs of the doorway framing. generally, swinging doors are required as exit doors as a means of egress, although other types of doors can be used under very specific conditions
doors - sliding doors
sliding doors are never allowed as a means of egress because they slow the travel of people through the door opening.
fire stop
solid materials such as wood blocks, used to prevent or limit the vertical and horizontal spread of fire and the products of combustion
stairs
stairs 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 that typically connect no more than two levels are called access or convenience stairs. although exterior fire escapes, escalators, and fixed ladders have been used as means of egress in the past, they are no longer allowed as a required means of egress from normally occupied spaces.
protected steel
steel structural members that are covered with either a fire-resistant spray-on fire proofing or fully encased in an Underwriter Laboratory (UL) tested and approved system
structural collapse
structural failure of a building or any portion of it resulting from a fire, snow, wind, water, or damage from other forces. collapse potential should be considered during preincident surveys and throughout the size-up process until the situation is mitigated
lightweight wood truss
structural supports constructed of 2x3in or 2x4in members that are connected by gusset plates
occupancy classifications
structures are also classified by their intended use or occupancy. occupancy classifications are defined by the building code and life safety code adopted by the AHJ. the three primary building codes in use in N America are NFPA 5000, IBC, and the National Building Code of Canada. structures may be divided into either single use occupancies or separated use occupancies
separated use
structures that contain multiple occupancies or use groups must meet the requirements for each individual occupancy classification. that is, in a strip mall, each space is classified by its use and separated from the other units by a fire-rated wall, as required by the building code.
canadian construction
the National Building Code of Canada (NBCC) defines three types of building construction: 1. combustible construction - does not meet the requirements for noncombustible construction 2. noncombustible construction - the degree of fire safety is attained by the use of noncombustible materials for structural members and other building assemblies 3. heavy timber construction - combustible construction in which a degree of fire safety is attained by placing limitations on the sizes of wood structural methods and the thickness and composition of wood floors and roofs; it also avoids concealed spaces under floor and roofs.
dangerous building conditions - roof coverings
the combustibility of a roof's surface is a basic concern to the fire safety of an entire community. wood shakes in particular, even when treated with fire retardant, can significantly contribute to fire spread
door construction/materials
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. aluminum and carbon steel are the metals most commonly used in doors, but stainless steel, bronze, and copper are also used.
eave
the edge of a pitched roof that overhangs an outside wall.
type V (wood or stick 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 which gives the appearance of type III construction while providing little additional fire protection or structural support to the structure. type V construction consists of framing materials that include wood 2x4 or 2x6in studs. most structures built in northern climates mandate 6in exterior wall cavities for increased insulation. the outside of the framing members is covered with any of the following: aluminum siding, shake shingles, wood clapboards, sheet metal, cement, stucco or other masonry products, plastic (vinyl) siding, planks, plywood, composite wood, styrofoam, veneers, asphalt siding *stucco is spread over a screen lattice that is attached to framing studs
roof decks
the portion of the roof between the roof supports and the roof covering. types of roof decks include: plywood sheathing, oriented strand board (OSB), wood tongue and groove, corrugated metal, sprayable concrete encapsulated polystyrene, reinforced concrete, and double tee preformed concrete. the components of roof decks include sheathing, roof planks or slabs, and purlins there are two types of concrete roofs typically in NA: precast and poured-in-place
roof coverings
the roof covering is the part of the roof exposed to the weather. materials include: wooden shingles or shakes, molded metal or rubber imitation shingles or tiles, asphalt shingles, asphalt sheets, terra-cotta or concrete tile, blown-on foam, built-up tar and gravel surfaces, metal roof systems or sheets, and composite materials
building components - roofs
the shape and construction of the roof is intended to provide drainage, support the weight of accumulations of snow, resist the effects of wind, and insulate the interior from external temperature changes. therefore, the geographic location of the structure can influence the type of roof. in general, there are three prevalent types of roof shapes: flat, pitched and arched
construction classifications
the type of building construction used in a structure is determined by the architect, structural engineer, or contractor. locally adopted building codes regulate the type of construction based on the intended use (referred to as occupancy classification), structure size,and the presence or lack of an automatic fire suppression system. the type of building construction is determined by the materials used in the construction and how well the materials resist exposure to fire. building codes are adopted by the AHJ and amended to meet local requirements. in the US there are currently two major model building codes, the NFPA 5000 Building construction and safety code and the International Code's Councils (ICC) international building code. factory-built homes are generally exempt from local building codes. they are instead regulated by the US federal gov through the dpt of housing and urban development. it is also that federal and state-owned buildings, including office, courthouses, university buildings, postal facilities, and other gov facilities may be exempt from local building requirements. because local AHJ can amend model codes to meet their needs, you must be familiar with the building codes adopted within your jurisdiction. you must also be aware that when existing building are renovated, the result may be a structure containing more than one construction method.
dangerous building conditions
there are two types of dangerous conditions that may be posed by a particular building: -conditions that contribute to the spread and intensity of the fire -conditions that make the building susceptible to collapse
roof supports
two general types used in residential and commercial construction: -beams are the sections of lumber located directly under the roof decking. on a pitched roof they extend from the ridge line or pole at the peak to each side wall. -roof truss assemblies may be conventional framing constructed on site or premanufactured assemblies built in a factory and shipped to the site. consist of top and bottom chords and webbing that extend from the peak to the walls. the ends are connected by a horizontal joist that also has supports between the joist and the rafters. wood trusses are assembled using metal gusset plates, also called gang nails. there are a variety of types of trusses including parallel chords, pitched chord and arched truss. the traditional wood-joisted roof uses solid wood joists that tend to lose their strength gradually when they are exposed to fire. this loss of strength results in the roofs becoming soft or "spongy" before failure. plywood or OSB used for roof sheathing can fail quickly and without warning because it is relatively thin. there has been an increased use of engineered or lightweight construction and trussed support systems in building construction. two of the most common types of engineered construction systems involve the use of lightweight steel or wooden trusses.
metals - iron
two types of iron can be found in buildings in N America: -cast iron - commonly used in the 19th century for structural support, beams and columns, for stairs, balconies, railings, and elevators, and for the facades of buildings. facades consisted of large exterior wall sections fastened to the masonry on the front of the building. cast iron stands up well to fire and intense heat, but it may crack or shatter when rapidly cooled with water. during a fire, bolts or other connections that hold cast iron components to the building can fail, causing them to fall. failure can also result from bolts rusting through or mortar becoming loose around the bolt -wrought iron: used in buildings of the early 1800s for nails, straps, tie rods, railings and beacons. today, wrought iron is used for decorations in the construction of gates, fences, and balcony railings. wrought iron is usually riveted or welded together while cast iron is bolted or screwed
plastic
used in many forms as a building material. on the exterior of buildings, vinyl sliding is used over older sliding, foam insulated panels, or other materials. water and sewer pipes are made from varying sizes of plastic pipe and fittings and are used to replace lead pipes. other decorative plastic materials include moldings, wall coverings, and mantel pieces. most plastic will melt and can contribute to the fuel load within a structure
sizing up existing construction
when sizing up a building, look for the following: -age of the building -construction materials -roof type -renovations or modifications -dead loads -number of stories -windows other items are important to observe during size-up, such as occupancy type adjacent exposures, the presence or lack of operational fire suppression systems, and fire conditions
wood
wood is the most common building material in North America and is the main component of a variety of structural assemblies. size and moisture content affect how wood reacts to fire conditions. the smaller the dimensions of the wood, the easier it is to ignite and the faster it will lose its structural integrity. lumber of smaller dimensions needs to be protected by gypsum drywall or other insulation to increase its resistance to heat or fire. the moisture content of wood affects the rate at which it burns. wood with a high moisture content (sometimes referred to as green wood) does not ignite as readily nor burn as fast as wood that has been kiln dried or dehydrated by exposure to air over long periods of time. wood can be pressure treated with fire retardants to reduce the speed at which it ignites or burns; however, they are not always totally effective in reducing fire spread. pressure treating wood also weakens the wood's load-carrying ability by as much as 25%. newer construction often contains composite building components and materials that are made of wood fibers, plastics and other substances joined by glue or resin binders. such materials include plywood, particleboard, fiberboard, oriented strand board and paneling. some of these products may be highly combustible, can produce significant toxic gases, or can rapidly deteriorate under fire conditions.
common building materials
wood, masonry, metals, reinforced concrete, gypsum, lath and plaster, glass/fiberglass, plastic, composite materials
