Structural Fire Protection - AISC Home

1 Got questionsabout fireprotection? Check out thishandy tear-outguide! December 2002 Modern Steel ConstructionFarid AlfawakhiriChristopher HewittRobert SolomonAISC engineers and a representative from the NFPA provideanswers to questions about the materials, components andsystems designed to provide life safety and structuralintegrity during questions answeredStructural FireProtectionWhat is a fire load? Where dofire loads primarily come fromin buildings? fire loads account for all com-bustible building contents, including fur-nishings, equipment, and combustibleconstruction components. Most of abuilding s fire load results from contentsthat have been introduced after theconstruction is complete.

2 The fire loadis usually expressed in terms of the wood-equivalent weight of com-bustible building contents per unit build-ing-floor area in psf. The actual weightof combustible contents is adjusted tothe wood-equivalent weight based onthe estimated potential heat of contentsnormalized to the potential heat ofwood (8000 Btu/lb). Alternatively, thefire load could be expressed in terms ofthe potential heat of building contentsper unit building-floor area in fast does a conventionalfire spread? The rate at which a fire spreads andgrows in a building depends on manyfactors: the combustion properties of theconstruction materials building furnishings and contents ventilation conditions room geometry and configuration timely detection and effectiveness offire suppression response by occu-pants and/or firefighters availability and effectiveness of au-tomatic fire detection and suppres-sion systems availability and effectiveness of firebarriers At what temperature does atypical fire burn?

3 The duration and the maximum tem-perature of a fire in a building compart-ment depend on the amount andconfiguration of available combustibles,ventilation conditions, properties of thecompartment enclosure, and weatherconditions. The maximum temperatureof a fully developed building fire willrarely exceed 1800 F. The average gastemperature in a fully developed fire isnot likely to reach 1500 F. Tempera-tures of fires that have not developed topost-flashover stage will not exceed1000 is thermal mass ?Thermal mass is used sometimesfor effective specific heat or heat ca-pacity. Effective specific heat inBtu/(lb F) is the amount of energy, perunit mass of material, required to raisethe temperature of the material by onetemperature unit.

4 Similarly, effective-heat capacity in Btu/(ft3 F) is theamount of energy, per unit volume ofmaterial, required to raise the tempera-ture of the material by one temperatureunit. For most construction materials,specific heat and heat capacity values(as well as thermal conductivity values)are temperature dependent. Thismeans that these values change in thetemperature range associated withbuilding fires (50 F to 1800 F), be-cause many materials undergo physic-ochemical changes at elevatedtemperatures. These thermal proper-ties are also sensitive to the testingmethod used, and different sources listvarying values of material properties forthe same is a heat sink?

5 Where arethey found?A heat sink refers to anything ab-sorbing large amounts of heat throughphysical and/or chemical containing large amounts ofchemically combined water in theirstructure, like gypsum or concrete , canform heat sinks. They absorb significantamounts of heat due to the energy con-sumed in the water-evaporationprocess. Materials with high thermalconductivity and high effective-heat ca-pacity will also act as heat sinks. Mate-rials with low thermal conductivity willreflect and not absorb is flashover?Flashover is an abrupt transitionfrom the burning of a small number ofitems in the room, or a small portion ofthe room, to full-room involvement in afire.

6 Room- fire flashover is a state inwhich all the combustible contents ofthe room experience a nearly simulta-neous ignition. Most fires never reachflashover because they are extin-guished before this can occur. Somefires self extinguish when the air supplyis insufficient, or when the fire has alow-enough energy source to preventignition of multiple time to flashover depends onmany factors, such as the properties ofcombustibles, the size of the room andventilation conditions. In larger rooms,the time to flashover will usually belonger. In well-ventilated large prem-ises, like open parking garages andlarge atriums, flashover is is also unlikely to occur insprinklered can one find the thermalconductivity or thermal resist-ance values of different fire -pro-tective materials?

7 A good source is the third edition(2002) of the SFPE Handbook of fire Protection Engineeringby the So-ciety of fire Protection Engineers( ). For some materials, in-formation might be is the meaning of fire re-sistant ? Is it the same thing as fireproof ? fire resistanceis the ability of build-ing components and systems to per-form fire -separating and/or load-bearing functions under fire building components andsystems are those with specified fire -resistance ratings based on fire -resist-ance tests. These ratings, expressed inminutes and hours, describe the timeduration for which given building com-ponents and systems maintain specificfunctions while exposed to simulatedfire events.

8 Various test protocols de-scribe the procedures to evaluate theperformance of doors, windows, walls,floors, beams and term fireproofis a misnomer nothing is truly fireproof. All construc-tion materials, components andsystems have limits and can be ir-reparably damaged by steel a fire -resistant systemor material? fire -resistance ratings are assignedto construction components and sys-tems, not materials. Materials are clas-sified for their combustion properties,and steel is non-combustible. Steel alsoexhibits other valuable Structural anddurability properties. It is used in manyfire-resistant building components andsystems, where load-bearing struc-tural-steel members are insulated fromthe thermal effects of a Steel Construction December 2002 What are spray-applied fire -pro-tective materials made of?

9 Spray-applied fire -protective materi-als fall into two broad categories: mineralfiber and cementitious. These materialsare based on proprietary formulations,supplied in a dry form, and must bemixed and applied according to themanufacturer s mineral-fiber mixture combinesfibers, mineral binders, air and water. Itis usually spray-applied. The dry mix-ture of mineral fibers and bindingagents is fed to a spraying is added to the mixture in thenozzle as it is sprayed onto the metalsurface. In its final, cured form, the min-eral-fiber coating is lightweight, non-combustible, chemically inert and apoor conductor of heat (a low thermalconductivity insulator).

10 Cementitious coatings incorporatelightweight aggregates, like perlite orvermiculite, in a heat-absorbing matrixof gypsum and/or Portland formulations also use magne-sium oxychloride, magnesium oxysul-fate, calcium aluminate or ammoniumsulfate. Various additives and foamingagents can be added to the coatings are often classi-fied by their density (as low, mediumand high).Other than spray-applied fire -protective materials, whatother materials/methods can beused to fire protect steel? concrete and masonry encase-ments are traditional fire -protective ma-terials that can be used. Gypsum-boardand mineral-board products, ceramic-wool wraps, and various intumescentcoatings are common itself is an effective fire -protectivematerial when used in sheet form toprovide a protective and reflectiveshield for other materials.