f1re~~ protetion p1ann1ng report BUILDING CONSTRUCTION INFORMATION FROM THE CONCRETE AND MASONRY INDUSTRIES Signifiane of Fire Ratings for Building Constrution NO. 3 OF A SERIES The use of fire-resistive floors, roof, walls, beams, and olumns will tend to minimize the losses due to fire damage. Introdution Destrution resulting from unontrolled fires was the primary reason for adopting the first building odes. Beause building fires are a major hazard to life and property, building odes require that resistane to fire be onsidered in building design. Codes provide the means by whih strutural fire resistane is integrated into the design and onstrution of buildings. It is generally presumed that building omponents will perform satisfatorily for as long as their designated fire ratings indiate under atual fire onditions. However, this is not neessarily true. How are fire ratings determined? Standard laboratory tests have been developed to provide a means for evaluating the performane of building materials and strutural assemblies under fire exposure. Based on the findings from these tests, the fire endurane of the various strutural omponents that make up a building are determined. Beams, olumns, floors, roof deks, and wall systems are lassified as having fire endurane of one, two, three, or four hours, or frations thereof. This provides a omparison between different onstrutions, but does not neessarily mean that they will perform the same in an atual fire. Building odes employ this system of hourly fire ratings to speify the minimum requirements for the numerous elements of building onstrution. The required ratings are dependent upon the intended oupany, type of onstrution element, and building size that ombine to provide safety fators against potential fire hazards. Fire-test standards thus form the basis for testing building materials and assemblies in order to determine if they onform to the strutural protetion requirements for safeguarding lives and property from fire. In order to understand and evaluate the present North Amerian fire-test methods and test results, some important fators should be onsidered. This publiation will review these fators and suggest some of the additional information that is needed for a more omplete evaluation.
Standard Tests The fire-resistive property of an assembly of building omponents is determined in ompliane with the test methods of the Amerian Soiety for Testing and Materials known as ASTM E119, Standard Methods of Fire Tests of Building Constrution and Materials. Other standards, essentially alike, inlude the National Fire Protetion Assoiation, Standard Method No. 251; Underwriters Laboratories, UL 263; Amerian National Standards Institute, No. A2-1; and Underwriters Laboratories of Canada, ULC-S1 01. ASTM E119 ASTM E11 9 is a standard for firetesting suh onstrution asseml::>lies as walls, floors, roofs, beams, and olumns. The standard provides a ommon and uniform test method for the omparison of performane of assemblies for speifi onstrution uses. The standard fire test is based on exposing the test speimen to a fire having a standard relationship between duration and temperature. This relationship is known as the time-temperature urve. The onept was first introdued in the 1918 edition of ASTM Methods of Tests of Material and Constrution. At that time 12 urves were plotted indiating all the known temperature shedules in use. The present time-temperature urve was developed from those urves. No major hange has taken plae in the urve sine its adoption in 1918. The standard time-temperature fire urve represents ombustion of about 1 0 lb of wood with a heat potential of 8,000 Btu per pound) per square foot of exposure area per hour of test. The atual amount of fuel onsumed during a fire test is also ASTM E119 standard lime-temperature urve under whih tests are onduted The urve prov1des for an exposing fire of ontrolled extent and severity to be applied to the test speimen. 2,500... 2,000!! ~ ~ 1,500 ~ j g. ~ 1 1 000 ~.i! ~0 / / l----' --!--- 2 3 4 Test time, hr - dependent on the furnae design and on the heat apaity of the test assembly. A standard fire test is onduted by plaing the assembly in a test furnae. Floor and roof speimens are exposed to fire from beneath, beams from the bottom and sides, walls from one side, and olumns from all sides. The temperature is raised in the furnae over a given period of time in aordane with the ASTM E11 9 urve shown. This speified time-temperature relationship provides for a furnae temperature of 1,000 F at five minutes of the test, 1,300 F at 10 minutes, 1,700 F at one hour, and 2,000 F at four hours. The end point of the test is reahed and the fire endurane of the speimen is established when any one of the following ours: 1. The test assembly struturally fails to sustain the applied loads and physially ollapses. 2. Cotton waste plaed on the unexposed side of a floor or roof system is ignited through raks or fissures in the speimen. 3. The temperature of the unexposed surfae rises an average of 250 F above its initial temperature or 325 F at any loation. In addition, walls must sustain a hose stream test. In 1970, additional riteria on steel temperatures were added. Though the omplete requirements of E119 and the onditions of aeptane are muh too detailed for inlusion in this publiation, aeptane riteria for various assemblies are summarized graphially in Table 1. Design professionals, builders, and building and fire offiials reognize the fire-resistane ratings given to building assemblies based on these firetest riteria. Although two different assemblies may have the same fire ratings, their performane in a real fire situation an be different. The following onsiderations will help to explain why this is so. Separating End-Point Criteria Some fire-test standards, for example International Standard 834 of the International Organization for Standardization, permit separation of end-point riteria based on three prinipal onditions of aeptane: 1. Flame or gas passage 2. Heat transmission 3. Load-arrying apaity Eah of these riteria is given equal weight in North Ameria. The first end point reahed terminates the test. The fire endurane of the assembly is established from this single result regardless of how long it would take to reah the other end points. The first two riteria relate to the funtion of l 2
Table 1. Aeptane Criteria Reinforing Sustained Flame Hose steel Heat load passage stream temperature transmission Floors and Roofs a. Restrained b. Unrestrained Walls a. Bearing b. Nonbeanng Columns Beams a. Restrained J b. Unrestrained i * Beams spaed more than 4 It on enters. A test an be regarded as suessful if the onditions shown above are met. See ASTM E119 for details. 250 F ~ ABOVE NORMAL Heat Transmission versus Load-Carrying Capaity This hotel being onstruted of onrete will prov1de firesafety for guests. The load-arrying apaity of floors and walls is muh more than fire rating indiates. Tests of onrete or masonry walls and floors usually terminate beause of heat transmission. From firesafety standpoint it IS unreasonable to apply same rating to two assemblies when one has ollapsed and the other has only failed the heat-transmission ritenon. The ollapse of a bui lding is more serious than heat transmis SIOn through walls or roofs and the two should be onsidered separately. providing a barrier against spread of fire or transmission of exessive heat through the assembly while the third riterion relates to the strutural integrity of the assembly to resist fire exposure. Failure to meet the heat transmission riterion means that the average temperature on the unexposed side of the assembly has risen only 250 F, a lower heat than is often used for ooking food. Most building onstrution materials and building ontents will not burn at this temperature. Fire ratings ahieved by onrete and masonry assemblies are pratially always based on the heat-transmission end point. This means that the strutural integrity of the building is maintained during the test well beyond the time indiated by the fire rating. In an atual fire, maintenane of strutural integrity affords safety and protetion to fire-fighting personnel and equipment. Frequently the onrete and masonry suffer little more than superfiial damage in a fire and an readily be restored to use. Reporting the time required to reah the temperature end point and ontinuing the test beyond 3
An important fator in the use of negative furnae pressure during a fire test is the tendeny for q>oi air from the laboratory to leak into the furnae through raks or other openings in the furnae or speimen. Floor-eiling assemblies are examples of types of onstrution whose ratings ould be affeted by leakage during furnae tests. If ool air is drawn through the speimen it will result in lower plenum temperatures and higher fire-resistane ratings than would our without leakage. Also, materials that shrink in fires provide openings for air to ool framing materials during the test. Masonry walls are ideal for apartment onstrution. They provide a barrrer against the spread of fire while maintaining strutural integrity. that point would make possible the establishment of different, more realisti ode requirements based on the need for strutural integrity or the ontrol of the spread of a fire. Codes ould maintain high ratings for strutural integrity while modifying or waiving the heattransmission end-point requirement. The 1976 Wisonsin Administrative Code modifies the riterion in lnd 52.042 with the following general requirements: 5) The heat transmission requirements of ASTM E119 25b), with the exeption of high hazard areas, penal and health are failities, and warehouses for ombustible materials, may be redued to one-half of the hourly rating required by this ode, but not less than one hour. a) The fire-resistive rating for strutural integrity required by this ode shall be maintained where the heat transmission riteria has been redued. Negative Furnae Pressures HOT AIR & SMOKE _ Effet of Pressure in Fire Test Furnae The E119 standard does not speify negative or positive furnae pressures, but almost all tests in North Ameria are onduted with negative pressures. One obvious reason for this is to prevent the flow of hazardous fumes and smoke into the laboratory by foring suh emissions out the exhaust flue. In Europe the furnaes are required to operate with positive pressures and adequate safety devies. In atual building fires, positive pressures are developed by gas movements and heat. Positive pressures in the order of 0.5 psf have been observed. Considering all onditions of fire propagation, pressures in a building or ompartment an be quite variable, but will be positive in the immediate viinity of the fire. Positive Furnae Pressures Negative furnae pressure allows ool a1r from the laboratory to be drawn into the furnae. This will result 1n lower speimen temperatures than temperatures that our under realisti positive pressure. 4 H
Drop-in eilings are held in plae during fire tests by negative pressure. thus giving extra protetion that would not exist in an atual fire. Studies indiate that the fire-resistane rating obtained by tests onduted with negative furnae pressures may be a poor measure of atual performane in a building. Positive pressure is a more aurate dupliation of real fire onditions. North Amerian fire experts support the maintenane of positive pressure in fire testing as is done in Europe. The International Organization for Standardization requires positive pressure in test furnaes. When establishing required fire-resistane ratings for building assemblies. ode offiials should reognize the effet of negative test pressures on the results indiated by the standard North Amerian fire test. Fuel Consumed The furnae temperature is ontrolled by the standard time-temperature urve. As a result, the amount of fuel required by the exposing fire may depend on the properties of the test speimen. If the speimen itself burns. it ontributes to the furnae temperature and redues the amount of fuel needed to hold the desired time-temperature urve. In a real fire situation, a ombustible assembly adds to the fuel load and, therefore, to the intensity of the fire. If the speimen absorbs heat from the furnae fire as is the ase with onrete and masonry, a more intense exposing fire is needed to maintain the required furnae temperature in ontrast with a ombustible speimen that ontributes fuel to the furnae fire. The amount of fuel onsumed during a fire test is a good measure of the atual fire endurane of an assembly. An exposed onrete floor spei- men is likely to use 1 0% to 20% more fuel than that used during a test of the same floor with an insulated eiling protetion membrane and onsiderably more fuel than that used for testing a ombustible assembly. This fat is not reognized when assigning or speifying fire-resistane ratings. It should be. The more fuel input it takes to omplete a fire test. the more fire endurane a strutural assembly has. Sine different assemblies require different amounts of fuel to maintain the required time-temperature relationship, standard fire tests expose different speimens to varying energy inputs. Thus, when omparing different assemblies, it would be informative to onsider the amount of fuel used in eah test and that data should be reported. Rational Design Throughout the history of fire testing, tests on walls. floors. olumns. and roofs have demonstrated that onrete and masonry are highly fireresistant materials. Muh information has been developed from these tests about the fators that determine the fire resistane of onrete and masonry assemblies. In addition, a great deal of researh has been onduted on the behavior of onrete strutures during fire exposure. Due to the researh information and the analytial proedures available, it is now possible to alulate with reasonable auray the strutural fire endurane of onrete omponents of a building without laboratory firetesting. The proedure, known as the rational design or analysis method, eliminates or redues the need for ostly fire tests, and onsiders the effets on fire endurane of a large number of variables. The rational design method is beoming an aepted means of designing for fire protetion. An 1llustrat1on ol the amount ot fuel onsumed during a lire test. The more luel it takes, the more severe the f1re exposure and the more fire endurane a strutural assembly has. Conrete or Masonry Speimen Combustible Materials Speimen FUEL 5
Conlusions When evaluating the signifiane of fire ratings it is important to onsider how a speifi building assembly might behave if an atual fire were to our. Users of fire-test reports and fire ratings should be aware that limitations in testing proedures affet their appliability. Fire ratings do not tell the whole story. Building designers and building offiials should- Take into aount any data gathered beyond the initial end point and evaluate whether, from a firesafety standpoint, it is logial to apply the same rating to two assemblies, one of whih has ollapsed while the other failed only the heattransmission riterion in the same period oftime. Make allowanes for the fat that standard fire tests onduted under negative pressure result in higher fire ratings for some assemblies than would be ahieved under positive pressure. Consider this when omparing the fire ratings of various assemblies. Consider the amount of fuel used in the test and make this a fator in evaluating fire resistane and endurane of various assemblies. Use rational analytial proedures in determining fire endurane of onrete and masonry omponents, partiularly when preise listings of ratings are not readily available. This eliminates the need for firetesting those omponents. Rational design is a major step forward in designing for fire protetion. Referenes 1. ASTM Designation: E119-76, Standard Method of Fire Tests of Building Constrution and Materials, ASTM Book of Standards, Amerian Soiety for Testing and Materials, 1973. 2. Gustaferro, Armand H., "Temperature Criteria at Failure," Fire Test Performane, ASTM STP 464, Amerian Soiety for Testing and Materials, 1970, pages 68-84. 3. Siegel, L. G., "Effet of Furnae Design on Fire Endurane Test Results," Fire Test Performane, ASTM STP 464, Amerian Soiety for Testing and Materials, 1970, pages 57-67. 4. Salse, Eduardo, and Lin, Tung D., Strutural Fire Resistane of Conrete, Portland Cement Assoiation, 1976. 5. Gustaferro, Armand H., and Martin, Leslie D., Design for Fire Resistane of Preast, Prestressed Conrete, Prestressed Conrete Institute, 1977, 88 pages. Organizations represented on the CONCRETE AND MASONRY INDUSTRY FIRESAFETY COMMITTEE BIA Brik Institute.of Ameria CRSI Conrete Reinforing Steel Institute ESC&SI Expanded Shale Clay and Slate Institute NCMA National Conrete Masonry Assoiation NRMCA National Ready Mixed Conrete Assoiation PCA Portland Cement Assoiation PCI Prestressed Conrete Institute This publiation is intended for the use of professional personnel ompetent to evaluate the signifiane and limitations of its ontents and who will aept responsibility for the appliation of the material it ontains. The Portland Cement Assoiation dislaims any and all responsibility for appliation of the stated priniples or for the auray of the soures other than work performed or information developed by the Assoiation. PORTLAND CEMENT Iilli!] ASSOCIATION An OflloJniution of ement monufoturers to improve and extend the!ish of portlond ement ond onrete through sientifi ffleorh, engineering field work, ond m.trk.t development. 5420 Old Orhard Road, Skokie, Illinois 60077 Printed in U.S.A. SR179.01H