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Review of compartmentation: requires assemblies to achieve fire-resisting ratings.
Review IBC Table 601 "Fire resistive rating requirements for building elements (hours)"
Examine the footnotes to Table 601:
For example, compare Type V-A (using sprinklers to avoid 1-hr construction) versus Type V-B (using sprinklers for bonus area and height): Assume Group B occupancy and no frontage increase:
Note that heavy timber consists of big wooden cross-sections as follows:
Mass timber buildings, e.g., made with cross-laminated timber, offer another possibility for wood-framed tall buildings, typically governed by heavy timber rules.Examples of various assemblies are given: see chapter 7, IBC, or product literature for gypsum board, masonry units, etc. Typical 1-hour partition assemblies can be fabricated with normal wood or steel studs and 1 layer each side of 5/8" thick "firecode" gypsum board fastened according to the specifications. For a 2-hour rating, one typically uses 2 layers of gypsum board each side, etc. Masonry units (or concrete) is also commonly used for 1-, 2-, 3-, or 4-hour-rated assemblies. For hollow block, manufacturers provide "equivalent" thicknesses so that their ratings can be computed. Sprayed-on or troweled-on cementitious fireproofing is commonly used for steel elements. Shaftwall, where gypsum board can be applied from one side of a shaft (the side with a floor to stand on...) was illustrated. Some images follow:
Changes to the requirements for shaft enclosures (exit stairs, etc.) as a result of recommendations made in the aftermath of the World trade Center collapse:
In the latest versions of the IBC (Chapter 4), enclosures for interior exit stairways and elevator hoistway enclosures shall have impact-resistant construction board, concrete, or masonry materials. This applies to high-rise buildings (buildings with an occupied floor located more than 75 feet above the lowest level of fire department vehicle access) of Risk Category III or IV (see Section 1604.5 of the 2015 IBC), and to all high-rise buildings that are more than 420 feet in building height.
Fire-rated glass types
Firestopping (fire safing) is an increasingly important component of assemblies, to close of gaps and holes, especially at penetrations of conduit, pipes, etc., and at floor-curtain wall intersections.
Lack of proper fire safing was also reported in the Grenfell Tower fire in which 71 people died (London in June, 2017). "The cavity barriers, which are supposed to expand and seal the gap between concrete floors, were the wrong size. The ones installed, according to the investigation, were able to close a gap of 25 millimeters, but the size of the actual gaps in between floors is 50 millimeters. In addition to the size discrepancy, some barriers were installed incorrectly, the report notes." (from Durability + Design, April 18, 2018)
Reasons for exterior cladding fires and their prevention:
Flame spread or surface burning characteristics rating must be considered and tested: it is a ranking derived by laboratory standard test methodology of a material's propensity to burn rapidly and spread flames.
Combustibility is a measure of how easily a substance will set on fire, through fire or combustion. This is an important property to consider when a substance is used for construction or is being stored.
NFPA 285, referenced in the IBC: Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Non-Load-Bearing Wall Assemblies Containing Combustible Components, provides a standardized fire test procedure for evaluating the suitability of exterior, non-load bearing wall assemblies and panels used as components of curtain wall assemblies that are constructed using combustible materials or that incorporate combustible components for installation on buildings where the exterior walls are required to be non-combustible. Assemblies (not just materials) must be tested to ensure that fire will not spread over the exterior cladding. Some combustible materials — water-resistive barriers or WRBs and foamed insulation — are allowed in exterior wall assemblies where this is otherwise prohibited (Types I – IV construction) but only if they pass NFPA 285.
References (pdf): John Valiulis, Building Exterior Wall Assembly Flammability: Have We Forgotten the Past 40 Years? | Owens-Corning Enclosure Solutions | Joseph Lstiburek, BSI-098: Great Fire of London
Some notes from the John Valiulis reference:
NFPA 285 does not apply to Type V buildings. Therefore, it applies to all other construction types: I, II, III, and IV.
Mostly, these exterior fires have nothing to do with the combustible interior contents of the building. Hence, having interior fire sprinklers is mostly useless in preventing such exterior cladding fires.
IBC generally looks at individual combustible components as well as the total assembly.
For each component, there are typically flame spread limits and cone calorimeter heat release limits. There are also exceptions, e.g., NFPA 285 compliance not required for combustible exterior cladding not higher than 40 feet above grade.[This exception shows up in Chapter 14 - Exterior Walls.]
Special restrictions for Metal Composite Panels (MCP) and fiber-reinforced plastic (FRP) were added to the 2009 IBC. And restrictions on the use of high pressure laminates (HPL) and water-resistive barriers (WRB) were added to the 2012 IBC.
Some testing not required with certain WRBs when they are the only combustible materials in the wall (e.g., where there is no combustible rigid insulation).
Some people and corporations within the building industry have tried to water down these requirements; their so-called Code change proposals for the 2015 and 2018 IBC were rejected. However, they have had limited success within the local Code adoption process, e.g., in the Washington, D.C. 2013 Building Code.
A comprehensive discussion of exit stairs as defined in the IBC can be found here.Means of egress is continuous and unobstructed path of travel from any point in a building to a public way. It consists of 3 basic parts:
Notes on egress:
"The Fire, Buildings and City Planning Departments [in NYC] are writing rules to govern what are called occupant-evacuation elevators — cars that can, in special circumstances, be used to move people down in an emergency."
"That would upend decades of codes and practices based on the notion that elevators are perilous and undependable in fires or other emergencies. Experts who have spent years studying building evacuations believe that approach has become outmoded and is in itself potentially dangerous as extremely tall skyscrapers increasingly pierce the New York skyline."
"Some requirements that the city is expected to impose for evacuation elevators have been anticipated in elevators at 3 and 4 World Trade Center. The floors in front of the elevator doors are raised slightly, to protect the hoist ways from water from sprinklers or firefighters' hoses. The capacity of the emergency generators was increased to provide uninterrupted service to those cars. The cars stop at every floor. Hoist ways are within cores protected by reinforced concrete walls at least 18 inches thick." [NY Times, March 18, 2015]
Here's a short (2 minute) video showing some egress and guard rail issues in E. Sibley Hall, Cornell Univeristy:
Disclaimer: Students are responsible for material presented in class, and required material described on course outline. These notes are provided as a tentative outline of material intended to be presented in lectures only; they may not cover all material, and they may contain information not actually presented. Notes may be updated each year, and may or may not apply to non-current versions of course.
first posted Sept. 11, 2012 | last updated: Sept. 11, 2017
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