Ch. 2 Building Classifications and Structural Fire Resistance Flashcards
Factors that influence fire behavior
Basic building classifications
Occupancy classifications
Fire or fuel load
Fire resistance
5 major classifications
Type I - Fire resistive Type II - Noncombustible or protected noncombustible Type III - Exterior protected (masonry) Type IV - Heavy timber Type V - Wood frame
Classification can help …
… firefighters determine the likelihood of structural collapse under fire conditions. They also indicate the degree of occupant safety provided by the building’s construction
Classification and subclassifications of 3 digit numbers …
First digit - Fire resistance rating (in hours) of exterior bearing walls
Second digit - Fire resistance rating of structural frames or columns and girders that support loads of more than one floor
Third digit - Fire resistance rating of the floor construction
Type I (Fire Resistive)
Classified by the presence of noncombustibles structural components that have fire resistance ratings within a specified range.
Steel is a noncombustible …
… but not fire-resistive and must be protected to attain fire resistance
Fire resistance …
… increases structural integrity during a fire
Fire resistive …
… compartmentation provided by partitions and floors tends to limit or slow the spread of fire through a building.
Examples of variation in fire-resistance
Bearing walls, columns, and beams - 2 to 4 hours, as specified by the local code and the construction classification
Floor construction - 2 or 3 hours
Roof deck and construction supporting the roof - 1 to 2 hours
Interior partitions enclosing stairwells and corridors - as specified by the local code : usually 1 to 2 hours
Partitions separating occupancies or tenants - as specified by local code
Type I buildings …
…are most commonly constructed using a protected steel frame or reinforced concrete. Unprotected steel has no fire resistance. When steel is used in fire-resistive designs, it must be protected by an insulating material. The combination of the structural strength of steel and the insulation produce a fire-resistive structural assembly.
Combustible material permitted are . . .
Roof coverings Interior floor finishes Interior wall finishes and trims Doors and door frames Window sills and frames Platforms Nailing and flurring strips Light-transmitting plastics Foam plastics subject to restrictions
Type II Construction …
… allows a wider range of materials than Type I. In addition to steel and concrete block, glass and aluminum can be used with a limited structural role.
Some building codes …
… contain a provision to omit the fire-resistive rating for a roof construction for some occupancy types when the roof is located more than 20ft above the floor. This can cause a Type II (non-combustible) building to be classified and inspected as a Type I (fire-resistive), which can be significant in the event of a fire.
Type II - A (protected)
Require that structural components have one-hour fire resistance
Type II - B (unprotected)
… allows structural components to be unprotected, meaning the major structural components have NO fire-resistance. The use of unprotected steel is the most common characteristic of unprotected, noncombustible construction
The speed unprotected members will fail …
… depends on …
Ceiling height of the building
Size of the unprotected steel members
Intensity and duration of the exposing fire
Type III - Exterior Protected/Ordinary
Frequently constructed with exterior walls of masonry, but any noncombustible material with the required fire-resistance can be used for the exterior walls.
Type III Interior …
... structural components that are permitted to be partially or wholly combustible include : Walls Columns Beams Floors Roofs
Fundamental fire concern …
… with Type III construction is the combustible concealed spaces that are created between floor and ceiling joists and between studs in partition walls when they are covered with interior finish materials.
Type III confined spaces …
… must contain appropriate fire stops
Type IV Construction (mill construction) …
… is made of Heavy Timber. Like Type III construction, the exterior walls are normally made of masonry and the interior structural components are combustible
Main differences between Type III and Type IV
Type IV construction - beams, columns, floors, and roofs are made of solid or laminated wood with dimensions greater than in Type III construction.
Concealed spaces are not permitted between structural components in Type IV construction
Type IV does not use A and B subdivisions …
… designated 2HH is used instead.
Type V construction
All major structural components are permitted to be of combustible construction. Many are required to have a 1-hour fire-resistance for structural components
Fundamental problem with Type V construction …
… is the presence of extensive concealed voids.
Light frame construction …
… was introduced in 1830s and is considered “the common currency of small residential and commercial buildings in North America today”
Mixed construction …
… occurs where a new structure is built onto an existing structure of a different construction type
Building construction and occupancy classification …
… are used together in building codes to establish limitations on the permissible heights and open areas of buildings
12 Major Occupancy Classifications
Assembly Educational Day care Health Care Ambulatory health care Detention and correctional Residential Residential board and care Mercantile Business Industrial Storage
Fuel load …
…the total quantity of combustible material in a compartment
The fuel load contributes to …
… the calculation of the fire load, the maximum amount of heat that can be released if all fuel is consumed.
The fire load will vary …
… depending on the heat of combustion of the fuel load
The fire load can be used …
… as an estimate of the total potential heat release or thermal energy to which a building may be subjected to if all combustibles become fully involved in fire.
Buildings with combustible structural components …
… have an inherently greater fire load than noncombustible construction because the structural framing materials contribute a significant amount of fuel to a fire
