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Section - Building Construction BUILDING CONSTRUCTION INTRODUCTION The most important reason for understanding building construction is safety Firefighters should be able to identify the types of building construction, associated terminology, and type of roof, to know when it is no longer safe to remain in or on the building Firefighters must be familiar with the basics of building construction and how a fire in a particular building can affect its structural integrity Knowing common building construction terminology will allow firefighters to understand and interpret building construction experts who may be called to a structure fire Firefighters must also have an understanding of the major roof types and be aware of their associated strengths and weaknesses When attacking a fire, this knowledge will make it easier to avoid serious injury or fatalities due to the hazards intrinsic to a particular roof type Buildings may collapse for a variety of reasons including stress, poor construction, or deterioration Firefighters should be aware of the potential and imminent indicators of building collapse They should be able to inspect a building and identify those indicators which may lead to building collapse, both under normal conditions and during fire suppression operations These indicators, in some cases, may be avoided or alleviated Firefighters must know what to under these circumstances and when it is no longer safe to remain in, on, or near the building An example might include the steady build-up of the water level when fighting an internal structure fire It may be possible to reduce the amount of water on the floor by either knocking out the lower windows at floor level or by drilling holes in the floor Another important aspect of building construction that firefighters must be concerned with is building classifications and the basic differences between each type Since buildings vary in type, design, and construction methods each will have its own unique fire problems and hazards Therefore, firefighters who are familiar with the type of building classification and associated collapse hazards will a better job of containing the structure fire and they will be safer firefighters 9-1 Section - Building Construction OBJECTIVES • Identify and describe common terms utilized in wood frame construction • Recognize and describe various types of walls found in typical building construction • Identify major types of roof styles and associated roof coverings • Identify design causes of structural collapse and some major warning signs of potential structural collapse during fire operations • Describe the indications of imminent building collapse which might be noted during an emergency These may include: a b c d e f g h • Identify the five major types of building construction and the collapse hazards of each • Identify the structural features which may influence fire spread and safety, which would include: a b c d e 9-2 Ankle-deep water on the floors Holes in the floor Sagging floors Sliding sheets of plaster Rising plaster dust Steel beams exposed to intense heat and fire Spongy floors and roof Burned-out trusses Fire walls, doors, windows, shutters, partitions, stops Curtain boards Venting devices (smoke and heat) Fire exits and escapes Fire and smoke dampers • Identify in high-rise construction the two different types of frame work for high-rise construction • Identify construction methods used in tilt-up construction Section - Building Construction TERMINOLOGY The following dwelling cutaway, overviews examples of construction terminology and techniques that are useful in developing a basic knowledge of construction fundamentals 9-3 Section - Building Construction Definitions of Wall Types Bearing Wall: A bearing wall is capable of supporting a vertical load, such as a floor or a roof, in addition to its own weight Non-bearing Wall: This wall is not designed to support a vertical load Exterior Wall: An exterior wall separates the interior from the exterior of a building Such a wall is usually exposed to the outside, though not always It forms the extent or boundary of the building Interior Wall: This wall will be wholly within a building and will not be exposed to weather Party Wall: A party wall usually separates two buildings of distinct ownership and lies on the lot dividing line between the two properties This wall can be either bearing or non-bearing Fire Wall: This type of wall is erected to prevent the spread of fire It must have sufficient fire resistance to withstand the effects of the most severe fire that could occur in the building As well, it must provide a complete barrier to the spread of fire Any openings in this type of wall must be properly protected One-Hour Wall: This is a term often used in the fire service There are 83 different ways to construct a typical one-hour wall as described in Chapter 43, Table 43-A, of the Uniform Building Code A typical one-hour wall will be non-bearing and will consist of either: • 2"x4" wood studs, 16 inches centered, with both sides covered by one layer of 5/8" type “X” gypsum wallboard • 1/4" “Tin Can” metal studs, 24 inches centered, with both sides covered by one layer of 5/8" type “X” gypsum Partition: This is an interior wall, one story or less in height, which separates two areas A partition can be either bearing or non-bearing Fire Partition: This is a partition that will inhibit the spread of fire but does not qualify as a fire wall Curtain Wall: A curtain wall is an exterior, non-bearing wall more than one story in height It is usually supported by the structural frame Panel Wall: This is an exterior wall one story in height In a multistory building, panel walls must be supported at each floor level 9-4 Section - Building Construction Parapet Wall: This is defined as the portion of wall that extends above the roof of a building Shear Wall: This type of wall is erected to assist in resisting the force of wind It is built within the building and usually is part of some required enclosure, such as an elevator or stair shaft This is a bearing wall Veneer Wall: This is an exterior wall created to improve the appearance of a building It is constructed from a variety of materials including marble, brick, stone, or steel The most common veneered wall is brick on a wood frame These walls are unsupported and are only as strong as the underlying wall During a fire, these walls can become very unsafe Basic Roof Types The following roof types summarize the majority of different types of roofs found within the city of San Diego and surrounding areas There are several others, but in general they are a variation of these types Each type will be covered in detail further on within this section 9-5 Section - Building Construction Description: “A” frame configuration Conventional or ordinary construction consists of a ridge board, rafters from the ridge board down to and across the outside walls (studs) Ridge and rafters are usually 2x6 inches or larger Rafters are usually 16 inches to 24 inches “on center” Additional support is provided by collar beams and ceiling joists The roof is constructed in semi-flat to steep pitches Strengths: Ridge board, rafters (if 2x6 inches or larger) and the area where rafters cross the outside walls Hazards: Older gables may use 2x4 inch rafters Newer roofs use 3/8 or 1/2 inch plywood as a decking instead of 1x4 inch or 1x6 inch stripping Plywood will burn and fail at a faster rate, offers little resistance to fire, and is difficult to remove for ventilation purposes 9-6 Section - Building Construction Description: Similar to gable roof, but no “A” frame configuration Ends of roof terminate in “hip” configuration Conventional or ordinary construction consists of ridge pole (board), hip rafters from the ridge pole down to and across the corners at the outside walls Valley rafters are utilized where two roof lines are joined together Ridge and rafters are usually 2x6 inches or larger Rafters are usually 16 to 24 inches “on center” Various degrees of pitch are utilized HIP ROOF Strengths: Ridge pole, valley rafters, hip rafters, and the area where rafters cross the outside walls Hazards: Similar to gable roofs, utilization of 2x4 inch rafters and 3/8 or 1/2 inch plywood as a decking Roofs with a steep pitch will require roof ladders to conduct ventilation operations If the roof is finished with tile, it becomes slippery when wet and offers little footing when dry 9-7 Section - Building Construction CORRUGATED ROOF Description: Fast and inexpensive to erect whether large or small Corrugations consist of steel, aluminum, or fiberglass over a wood or metal substructure Corrugated steel is often utilized, usually 18 to 20 gauge thickness (About the thickness of an American car fender, 0475".) Strengths: Ridge and area where roof crosses the outside bearing walls Hazards: Corrugations may be steel, aluminum, or fiberglass Expect rapid failure of these materials when exposed to heat or fire Some buildings utilize plastic or fiberglass panels in the roof as skylights Personnel should consider this roof extremely hazardous for ventilation operations 9-8 Section - Building Construction Description: Steel or wood substructure covered by corrugated metal “Robertson Decking”; an air-entrained mixture of sand, cement, and occasionally pea gravel is pumped on top of the corrugated metal decking and wire mesh to a thickness of about to inches Composition roofing material is utilized as a final layer Strengths: Lightweight concrete surfaces offer a strong, hard surface Structurally sound and resilient to fire Hazards: Difficult to penetrate with chain-saw or rotary saw with a masonry blade Use a rotary saw with carbide-tipped wood blade to cut ventilation holes 9-9 Section - Building Construction SAWTOOTH ROOF Description: Constructed in commercial buildings to yield additional light and ventilation Constructed with rafters of 2x8 inches or larger, and utilizes wood and/ or metal supports for bracing to provide additional strength Vertical portion is usually “wired” glass with opening panes Sloping portion is covered with 1x6 inch sheathing or plywood and composition roofing material Strengths: Substructure constructed from adequate (2x8 inch, 2x10 inch, etc.) lumber Easy to ventilate-open the hinged panes of glass Consider the area where rafters cross or are tied into the vertical walls as strong areas Hazards: Newer sawtooth roofs are covered with 1/2 inch plywood Plywood decking provides little resistance to fire - 10 Section - Building Construction decking is nailed down, this construction is very unstable Common on center spacing for this construction is feet Half-inch plywood is utilized for the decking Used in floor and roof systems Strengths: Consider the perimeter of the building where the roof ties into the exterior walls as a strong area Hazards: What there is to burn consists of a 3/8 inch plywood stem and 2x3 or 2x4 inch chords It will take little time for the 3/8 inch plywood to burn, weaken and cause collapse of the chords and the roof Buildings will be found with open and unprotected chords Common practice is to run heating and air conditioning ducting of various sizes through the stems which removes a good percentage of the stem and gives fire horizontal access to adjacent “I” beams As with other lightweight roofs, depth of cuts for ventilation purposes is critical COLLAPSE HAZARDS OF THE FIVE STANDARD TYPES OF BUILDING CONSTRUCTION Type I, Fire-Resistive Construction There are two basic types of fire-resistive construction: reinforced concrete buildings and structural steel buildings Both are designed to resist fire which burns out an entire floor without spreading flames to other floors or collapsing the structure However, during serious fires a collapse danger does exist with both types of construction In reinforced concrete buildings, heated concrete ceilings collapse on top of firefighters; in steel skeleton buildings, heated concrete floors buckle upward Both of these structural failures are caused by spalling, the rapid expansion of heated moisture inside the concrete Small amounts of moisture, normally trapped inside concrete, expand when heated by fire and create an internal pressure within the concrete This pressure can cause heavy sections of concrete to crack away from a ceiling and collapse down onto fire operations or on top of a firefighter This type of collapse occurs in a building without a suspended ceiling, where the concrete ceiling above the fire is directly exposed to flames below In steel skeleton construction, the under side of each floor is not concrete; each floor consists of light-gauge corrugated steel sheet which supports several inches of concrete floor above it Heat from a fire reaching the under-side of the corrugated steel is conducted through the concrete floor directly above The moisture in the concrete above the steel is heated, and the internal pressure develops in the concrete above Consequently, the expanding concrete buckles upward suddenly to 12 inches Type II, Non-Combustible/Limited Combustible There are three basic types of non-combustible buildings: The metal-frame structure covered by metal exterior walls, the metal-frame structure enclosed by concrete - 24 Section - Building Construction block, non-bearing exterior walls; the concrete block bearing walls supporting a metal roof structure On all three types, the steel roof support system may be either one of the following: a system of solid steel girders and beams, lightweight openweb bar joist, or a combination of both The collapse danger to a firefighter from a non-combustible building is roof cave-in from the unprotected steel open-web bar joist The main disadvantage of the open-web bar joists is its susceptibility to damage by a fire in the combustible contents inside the building Tests have shown that unprotected lightweight open-web bar joist can fail when exposed to fire for five to ten minutes This possibility makes it extremely dangerous for a firefighter to operate on a roof supported by steel open-web bar joists which are being heated by flames The open-web bar joist is the main structural hazard of non-combustible construction Type III, Ordinary Construction The ordinary constructed building called “brick-and-joist” has exterior walls of masonry with wood floors and roof This construction method was used to build many of the public, commercial, and multiple dwellings throughout the country The structural hazard of an ordinary constructed building is the parapet wall, the portion of the masonry wall that extends above the roof line The collapse danger of the parapet wall is one of the reasons why the area directly in front of a fire building is so dangerous, and why firefighters are urged either to move inside the doorway or away from the front of the building altogether There are several design features relating to ordinary construction which warrant close observation These include efflorescence, parging, and spreaders Efflorescence results when large amounts of soluble salts are used in mortar and excessive water penetrates the masonry Efflorescence appears as a white powdery substance on the wall and indicates weakened mortar Parging is the plastering over of a masonry wall with concrete It is frequently a cosmetic fix for an unattractive, deteriorated wall A wall out of alignment is always a sign of danger Spreaders are intended to spread the load among one or more structural members and are frequently used to support a wall in trouble They are often indicated on the outside of a wall by a circle, star, channel, or other device; arranged in a pattern they usually serve a decorative purpose When placed at random, these spreaders provide additional strength to the wall Type IV, Heavy Timber Construction Falling masonry walls which crash to the ground and spray bouncing chunks of bricks and mortar along the street or pavement are the structural hazards of heavy timber buildings This type of construction does not collapse during the early stages of a fire when interior firefighting is taking place However, after several hours, its floors will collapse and the free-standing walls will fall into the street and on to the roofs of lower buildings nearby Consequently, withdrawing to protect exposures is the strategy used at a fire involving heavy timber construction when the initial attack fails - 25 Section - Building Construction Type V, Wood-Frame Construction The structural hazard of a wood frame building is the combustible bearing wall constructed of 2x4 inch wood studs A wood frame building is a bearing wall structure The two side walls are usually bearing (that is, supporting a load other than their own weight); the front and rear walls are usually non-bearing The structural supports of the side bearing walls are only 2x4 inches in size and roof joists also 2x10 inches Firefighters should know that wood-frame buildings use smaller structural members to support larger structural members, and the weak link in this design is smaller structural supports, the 2x4 inch bearing walls Failure of a bearing wall will trigger simultaneous failure of the floors and roof TOP PLATES KICKER BLOCK HEADER STUD TRIMMER FIRE BLOCKING DIAGONAL BRACING - 26 SILL TRIMMER 10 SOLE PLATE 11 SUBFLOORING 12 FLOOR JOIST 13 HERRINGBONE BRIDGING 14 CRIPPLE STUDS Section - Building Construction STRUCTURAL COLLAPSE There are many causes of structural collapse in buildings Failure can result from architectural faults in the original construction, the age of the building, slip-shod repairs, and heavily-laden floors Firefighters must be able to identify the indications of potential and imminent collapse for the safety of both themselves and others at an incident Design Faults in Construction The potentially worst faults in building construction are unprotected vertical shafts and openings This includes stair shafts, vents, pipe chases, and atriums These open shafts are dangerous because they may allow a fire to expose other floors of the building, and in the case of vents a chimney effect can result, fueling the fire Combustion products can sweep up from the original fire and involve other areas of the building This fault is responsible for the greatest loss of life not only because people can be overcome by smoke but also because exits from the building are made inaccessible Large, unprotected floor areas are also responsible for building collapse under fire conditions Floors without physical barriers can become completely engulfed by fire Because there is nothing to stop the progress of fire, a draft effect is created moving the fire across the floor When a floor becomes enveloped in flame, firefighters find it difficult to fight the fire due to intense heat Firefighting under these circumstances is accomplished through halls, doors, and windows and in the case of very large floors, the fire will be extremely difficult to contain because the fire hose stream cannot reach the center of the floor Building collapse can result from the high temperatures which unprotected metal structures may endure during a fire Steel is used frequently in building construction for reasons of strength, elasticity, and cost The problem arises when the metal is subjected to temperatures of over 1,000 degrees The steel will expand and possibly disrupt other structural components Under even higher temperatures, the metal can give way completely Firefighters should be aware that when comparing steel and wood, where the structural members are of equal strength, a wooden support will resist fire much better than steel Large wooden members will burn slowly and resist fire for longer periods of time than unprotected steel, which has a poor record of withstanding fire Other faults pointing to the possible collapse of buildings are alterations of structural supports, bracing old supports with steel rods (i.e., look for “stars” on the outside of the building), steel angle iron used to reinforce the three walls, and overly-laden floors Such alterations eliminate, or cheaply substitute, structural supports to gain more usable room or to save money - 27 Section - Building Construction Indicators of Possible Collapse During fire operations, firefighters may observe events which could lead to collapse of the structure For example, lack of water drainage on the floor greatly increases the risk of collapse Two inches of water on a floor 40x80 feet will add more than 15 tons of weight to the floor Note- a 250 gpm nozzle can deliver one ton of water per minute The following list of events should serve as warnings of imminent building collapse and firefighters observing any of these during fire operations must leave the building and report conditions to the company officer • • • • • • • • • • • • • • • Ankle-deep water on the floor A large fire which has been out of control for more than 20 minutes Steel beams that have been exposed to extreme heat and fire Excessive water buildup Sagging or bulging floors and walls Rising dust, indicating movement of the building, floor, or roof Holes in the floor Cracks in the walls, floors, or roof Smoke and/or water leaking through the walls Burned out trusses or I-beams Sliding sheets of plaster Walls or columns out of plumb (square) Interior explosions, rumblings, noises, or heavy gusts of smoke Spalling Interior collapse BUILDING INTERIORS There are three principal elements which determine the fire resistance of a building: the fire resistance of the building itself, contents or processes within the building, and the characteristics of the interior finish of the building The interior finishes include but are not limited to: wood, plywood, plywood paneling, plaster, gypsum wallboard, fibrous ceiling tiles, plastics, and a variety of wall coverings Surface coatings may also exist such as paint, varnish, and acoustic spray which will add to fire characteristics Interior finishes can affect a fire in four ways: - 28 They may influence the rate at which the fire build-up reaches “flash over” They can contribute to fire extension by allowing the flame to spread over its surface Section - Building Construction They may add to the intensity of the fire by contributing additional fuel They can add toxic gas and smoke which will contribute to life and property hazards Once a fire has gained some headway, the upper portion (ceiling) will become extremely hot as the gases fill it If this area becomes hot enough, the gases may ignite This is commonly referred to as “flashover” Thermal radiation emanates from the combustion, heating the materials in the area rapidly When the combustible materials have become heated to their ignition temperatures, simultaneous ignition will occur An interior finish which absorbs and holds heat would be more preferable because it would inhibit flashover for a longer period of time A term referred to as “flameover” can occur if material is combustible Flameover is defined as the rapid spread of fire over one or more surfaces For example, a combustible surface may allow the fire to spread over it rapidly permitting it to reach other material If the finished material is of a combustible nature it will not inhibit the fire and it will only serve to fuel it Many burning interiors are dangerous not only because of the heat factor but also due to the smoke and toxic gases they release In fact, fire tests have shown a greater threat to life because of toxicity and smoke inhalation Firefighters must always wear SCBAs when fighting interior fires so they are not overwhelmed by toxic gas or smoke - 29 Section - Building Construction TILT-UP CONSTRUCTION Tilt-up construction, or tilt slab as it is sometimes called, is constructed by casting wall panels on the ground along the outside perimeters of a building When the panels are cured, they are tilted up into place and tied together The individual wall panels (load-bearing or non-load bearing) are usually pinned together by connectors The fire resistance of the completed structure is dependent upon the protection afforded to the connectors Connectors are set into the precast element, and mating connectors are provided on the structures to which it is to be attached Bolts and nuts may be used, or the connections may be welded The recess provided for the joists is then dry- packed with a stiff mortar Often no protective covering is provided for the connectors; it may not even be required Once the walls are standing, the builder carefully braces the walls with tormentors or braces This is required for stability until the roof is in place and tied in, thus stabilizing the building The roof may be of any type construction If the roof is made of wood and is involved in fire it may simply burn away, leaving the concrete panels free standing as a vertical cantilever If this occurs, beware of the possibility of the walls collapsing Other hazards involve concrete which may spall from the bottom of Tbeams exposing the tendons to their failure temperature, or if steel is used it may elongate This elongation may push the walls down Consequently, when dealing with tilt-up construction and a building heavily involved in fire, great care must be taken to ensure proper placement of personnel and equipment HIGH-RISE CONSTRUCTION The construction industry today uses two different types of framework for high-rise structures: structural steel, and reinforced concrete Buildings with a reinforced concrete framework are made either by connecting large sections of concrete called - 30 Section - Building Construction “precast”, which includes plain concrete, reinforced concrete and pre-tensioned concrete, or by building one monolithic structure of reinforced concrete called “castin-place” Cast-in-place concrete includes plain concrete, reinforced concrete, and post-tensioned concrete By this method, tons of concrete are poured into wooden forms, creating a solid reinforced concrete skeleton structure of floors and supporting columns A cast-in-place concrete building is built on the site, floor by floor Steel reinforcing rods and wires are strategically placed inside wood forms, which act as molds to shape the poured concrete into floors and columns When completed, the cast-in-place structure is one solid, concrete structure reinforced by steel The hardened concrete provides the compressive strength to the structure, and the steel reinforcement supplies the tensile strength to the concrete After each floor is poured and hardened, the form work and the supporting shoring are disassembled and rebuilt to receive the concrete for the next higher floor This process is repeated for each additional floor In some so-called “fast-track” construction projects, one concrete floor is poured every 48 hours Although it takes approximately 27 days for concrete to reach its maximum strength, the high-rise building construction process cannot wait that long for each floor to harden After 48 hours, a concrete floor, depending upon the type of concrete and the temperature, can have sufficient strength to enable the wood formwork below to be removed and reconstructed above Even though the formwork is removed, bracing remains below the freshly poured concrete floors for support, and portable steel jacks or timber columns will continue to support several floors below Construction engineers state that within 24 hours of pouring, the entire concrete floor can collapse on firefighters if the wood formwork below has been destroyed by fire At this time it is most dangerous for a fire to occur in the formwork; however, even the concrete floors in place for 48 hours or more, without the formwork below, can collapse in small sections if they are heated by a scrap lumber fire Consequently, the fire department faces problems with concrete construction in three distinct areas: collapse during construction with no fire, fire during construction, and fire in a completed, occupied building When structural steel is used in high-rise construction, fireproofing is often applied to meet the standards required by the local building codes While there is no such thing as a truly fireproof building, the term has survived as the designation of the system by which steel is insulated Fireproofing of steel is classified as individual or membrane Individual fireproofing provides protection for each piece of steel In one method, steel is encased in a structure Concrete, terra cotta, metal lath and plaster, brick and gypsum board are materials commonly used This method is called encasement In another method, fireproofing is directly applied to the steel, usually by spraying Materials are asbestos fiber (no longer used), an intumescent coating containing - 31 Section - Building Construction non-combustible fibers which smell and char when exposed to flame, and cementatious coatings Membrane fireproofing does not protect individual members In one method, wire lath and cement plaster are used In another method, the fireproofing of the floor is accomplished by a rated floor-ceiling assembly The efficiency of fireproofing depends first on the competence of the subcontractor and the willingness of the builder to demand quality work It further depends on the building department staff who inspect the original installation to determine that fireproofing and fire protection are not compromised This is particularly important in the case of sprayon fireproofing and membrane-floor and ceiling assemblies Finally, it is a serious error to consider all high-rise buildings as a single problem There are firesignificant construction differences among high-rises The particular buildings within San Diego must be studied in detail to determine the particular potential modes of building failure STRUCTURAL FEATURES WHICH INFLUENCE FIRE SPREAD In a study carried out by the NFPA, it was found that inferior construction, unprotected openings, large open areas, and inoperative fire doors were major determinants in the amount of damage done to a structure and its interior in fire conditions These features were found to contribute to the spread of fire Furthermore, it was determined that the speed of flame spread over a substance is directly influenced by the amount of flammable vapors released by combustible materials when they are heated, their texture, and thickness The following structural features will help limit the spread of fire if they are constructed properly (i.e., they not violate the building code) For more information on these features and other lesscommon ones, refer to the current Uniform Building Code Fire Walls Fire walls are typically constructed of concrete, structural clay tiles, or some other structurally sound and non-combustible material and must have a fire-resistive rating of at least one hour Fire walls must be able to remain intact if and when there is collapse on either side A fire wall will be continuous from the foundation to a parapet above the roof line of the building The height of the parapet portion is dictated to be at least 30 inches above the roof line In addition, these walls must have a minimum thickness dictated by the type of construction (refer to Chapter 43, Table 43-A of the Uniform Building Code) All fire walls must have parapets, wing walls, be attached to the foundation, and have fire- resistive ratings as required by location, type of construction, and occupancy Openings in fire walls must conform to the requirements of the building - 32 Section - Building Construction Some of the code violations firefighters may encounter when dealing with fire walls include: inferior construction materials, lack of thickness in the wall, no parapets, and openings that are not correctly constructed, inoperative, or blocked open Firefighters should always inspect fire walls during pre-fire planning and inspections to determine aspects of construction and imperfections which may create hazards during a fire Fire Partitions Fire partitions are installed as a impedence to fire spread, but are not considered a fire wall They are constructed of non-combustible or protected combustible materials and are attached or supported by structural components having a fireresistant rating equal to or better than the fire partition (usually one to two hours) As with fire walls, openings must conform to the requirements set forth to provide adequate fire protection The fire resistance of a fire partition will be governed by the type of construction used in the building Openings in Fire Walls and Partitions There are six different classifications for fire-protective openings Depending upon the type of building construction and the hazards which may be present, openings must provide protection equal to or greater than the wall or partition Three-Hour Protection: These openings are often given a class rating of “A” and must provide three hours of fire protection equally on both sides These enclosures cannot contain any glass and are located in walls that separate buildings or separate buildings into fire areas One-to 1/2-Hour Protection: These enclosures protect openings into vertical shafts (e.g., stairwells and elevator shafts) and are often classified with a rating of “C” As well, one to 1/2 hour protection must be provided in exterior wall openings Exterior wall openings are often referred to as Class “D” openings 45-Minute Protection: These enclosures must provide 3/4 of an hour protection against fires The openings they protect are usually located in corridors and room partitions, generally considered Class “C” and in exterior walls that are subject to light or moderate exposure to fire (Class “E” and “F”) - 33 Section - Building Construction Fire Doors Typically, fire doors are used for the protection of both vertical and horizontal openings Fire doors can be horizontal or vertical sliding, single or double swinging, or overhead rolling Any of these door types may or may not be counterbalanced Often, fire doors are either self-closing or automated Self-closing doors will return to a closed position after opening Automated doors may remain open after opening them, but will close when heat or smoke actuates the closing mechanism Fire doors must not be locked though they may be latched In addition, these doors should never be blocked, wedged or in a state that would prevent them from closing Automatic closing doors must be kept in proper working order at all times If fire doors contain glass, it must be at least 1/4 inch thick and must be safety protected with wire Fire doors can be considered safe if they contain a current label from the “Underwriters Laboratories” or “Factory Mutual Laboratories” as evidence of testing For more information refer to NFPA Standard # 80 - 34 Section - Building Construction Fire Windows and Fire Shutters For these types of enclosures to be effective in containing fire spread, they must be properly maintained and serviced Often these openings are associated with exterior wall openings (Class “E” and “F”) with labels stating “Inspected Fire Window for Light Exposures” Fire windows must be constructed of wired glass, /4 inch or greater in thickness There are locations where fire windows are covered by shutters (i.e., at threequarter, one-, and 1/2 hour openings) The shutters must carry a rating equal to or greater than the wall opening they are protecting These fire shutters must either remain closed or must close automatically under fire conditions Once closed, fire shutters must remain secure to be considered effective in reducing fire spread Of the different types of fire shutters, the automatic rolling shutters installed over windows on the interior side of the building are considered the most useful and practical Curtain Boards (Draft Curtains) Curtain boards are most generally found in large open areas of buildings Their major purpose is to direct fire and smoke into a pre-designed area for rapid ventilation At the same time, they are designed to prohibit flame and smoke spread in other directions This is especially useful in sprinklered buildings to avoid water damage in unaffected areas, as the operation of the sprinklers can be localized to the fire area For these fire-resistive structures to be considered effective they cannot be spaced more than 250 feet apart for low and moderately heated occupancies In buildings that are subject to high heat sources, curtain boards must not be spaced any further than 100 feet apart The depth of a curtain board must be a minimum of six feet but in some cases (under severe fire hazards) may be doubled or as close as feet from the floor Ventilation Devices These systems are designed to complement other fire safe-guards and are not replacements for fire protection devices Vents are very useful in smoke and heat dissipation, especially in buildings where vapors and dusts are highly combustible For a venting system to be considered effective, it should be free of any human element Rather, it should be automatic using fusible links, hinged dampers, and counterweights that are heat reactive Types of vents include: monitor controlled, continuous gravity, unit type, sawtooth roof skylights, and exterior wall openings Monitors usually make use of fusible links which are effective from as low as 165°F to 212 ° F or higher, if so required The fusible links operate vent doors that may be glass, metal panels, or louvered when heat containment is not a factor Continuous gravity vents are narrow slot openings which are attached to weather hoods on the roof Many will have movable shutters which will open automatically in the event of a fire This style of vent is most common in buildings where high heat production is of concern - 35 Section - Building Construction Unit-type vents are lightweight metal frames or housings with built-in shutters that open in the event of high heat or fire (e.g., fusible links) This type of structure is most commonly associated with curtain boards Sawtooth roof skylights are sashes of glass usually non-wired which can be opened to form a vent Often this style of venting device must be operated manually and is influenced by wind direction and force Exterior wall openings are most effective in structures where heat and smoke not have to travel more than 60 feet They are usually characterized by louvered, open vents but can also remain closed and automatically open in the event of fire Fire Exits and Escapes Buildings and structures must have appropriate fire escapes and exits in accordance with the location, size, occupancy, type of construction, and fire protection available Fire escapes and exits must be correctly marked, lighted in reduced visibility areas, and indicate the most accessible route to safety Furthermore, they cannot be obstructed in any way that would prohibit the swift evacuation of the occupants These exits cannot be locked while the building is occupied and must remain open from the direction of occupant departure The width of the exit must not be less than 28 inches, large enough for a single file line of people to escape freely For more information on fire escapes and exits firefighters should refer to NFPA 101, the Life Safety Code, and Uniform Building Code, Appendix III (d) Fire and Smoke Dampers These are used to restrict fire and smoke to the involved area and away from unaffected areas Fire and smoke dampers operate much like venting devices but in the opposite manner: instead of allowing smoke to dissipate these devices will close under fire conditions Like automatic vents, many are controlled by fusible links, heat actuating switches, and in some cases, smoke detectors Fire dampers are generally automated and once closed, will remain closed until manually opened These devices are required in a number of circumstances which include: • • • • • Where a duct passes through a fire-protected wall or partition or roof At fresh air intakes At branches in the main duct Vertical ducts passing through fire-resistive floors When ducts have openings installed in a fire-resistive ceiling There are other circumstances where fire dampers will be required and a number of exceptions pertaining to particular situations For more information on fire dampers, firefighters should refer to NFPA 90A, 90B & 91 - 36 Section - Building Construction Smoke dampers are commonly required in air conditioning systems and are intended to interrupt the flow of air or smoke through the system when the air conditioner is shut down Fire Stops Fire stops are utilized to prevent fire spread within the hollow walls, floors, and other internally open areas within a building or structure They are usually pieces of wood (2x4 inch) placed between wall studs, partitions, ceiling planks, etc., to cut off any draft within the hollow areas When fire stops are not used it's probable that a fire could rage through the structure, burning unexposed internal areas before it is ever discovered The minimum fire stopping would include isolation of all hollow walls at the floors and ceilings, isolation of the ceilings at the walls and curtain boards For more information on fire stopping refer to NFPA 101 (6-13) Fire Loads A comprehensive understanding of building construction requires basic knowledge of the concept of loads and how they are applied There are several types of loads: designed loads are those the building architect anticipated and planned for; and conversely, undesigned loads are unanticipated Undesigned loads can be concentrated or applied to a relatively small area, or equally distributed over a larger surface These loads can be further subdivided into dead and live loads.A dead load is the weight of the building and any part of a structure which is permanently attached to it ( dead loads may also be considered static, as they are relatively unchanging) A live load is not built in and can be categorized as an impact load (if it is in motion when applied) A suspended load is held in place by attachment to a building component above it Any load can change in nature when portions of the building fail For example, a large printing press permanently attached to the third floor would be considered a dead load; should the floor fail, the falling press would become an impact load upon those floors beneath it Loads are applied in three ways: an axial load passes through the center of mass of the supporting element perpendicular to the cross section; an eccentric load is one perpendicular to the cross section of the supporting element that does not pass through the center of mass; a torsional load is one parallel to the cross section of the supporting member which does not pass through the long axis These loads are applied through three forces: compression tends to push or squeeze a material together; tension tends to pull materials apart; and shear tends to break material by causing its molecules to slide past one another Building materials are also classified as brittle (weak in tension and shear and tend to break without bending), or ductile ( tend to deform before breaking) - 37 Section - Building Construction REFERENCES Building Construction for the Fire Service, Francis L Brannigan, NFPA, Quincy, Massachusetts 1993 Collapse of Burning Buildings, Vincent Dunn, New York, 1988 Fire Protection Handbook, NFPA, Quincy, Massachusetts, 1981 Ventilation Methods and Techniques, John Mittendorf, Los Angeles, 1988 Uniform Building Code (UBC), Western Fire Chiefs, 1982 - 38 ... most common veneered wall is brick on a wood frame These walls are unsupported and are only as strong as the underlying wall During a fire, these walls can become very unsafe Basic Roof Types... roofing material is utilized as a final layer Strengths: Lightweight concrete surfaces offer a strong, hard surface Structurally sound and resilient to fire Hazards: Difficult to penetrate with... hinged panes of glass Consider the area where rafters cross or are tied into the vertical walls as strong areas Hazards: Newer sawtooth roofs are covered with 1/2 inch plywood Plywood decking provides