80A-A2001-rop

377

Report of the Committee on

Exposure Fire Protection

Edward J. Kaminski, ChairSchirmer Engr Corp., IL [SE]

Peter J. Barbadoro, Fire Smart Bldg. Tech. Inc., MA [IM]Kenneth E. Bland, American Forest & Paper Assn., DC [M]Russell P. Fleming, Natl Fire Sprinkler Assn., NY [M]Gene L. Hortz, Rohm and Haas Co., PA [M]Yvonne M. Keafer, Sedgwick James of PA, Inc., PA [I]Joseph J. Messersmith, Jr., Portland Cement Assn., VA [M]Igor Oleszkiewicz, Natl Research Council of Canada, ON [RT]Donald Lee Parsley, Parsley Consulting Engr, CA [SE]Mark J. Petrone, Conneticut Interlocal Risk Mgmt. Agency, CT [I]James W. Quinnette, Nuclear Service Organization, DE [I]Robert J. Richter, Construction Domain Consultant, VA [SE]Christopher A. Spencer, FM Global, MA [I]

Alternates

Richard J. Davis, FM Global, MA [I] (Alt. to C. A. Spencer)Gene B. Endthoff, Natl Fire Sprinkler Assn., IL [M] (Alt. to R. P. Fleming)Andrew Kim, Natl Research Council of Canada, ON [RT] (Alt. to I. Oleszkiewicz)Stephen V. Skalko, Portland Cement Assn., GA [M] (Alt. to J. J. Messersmith, Jr.)E. Hayden Smith, Nuclear Service Org., DE [I] (Alt. to J. W. Ouinnette)

Staff Liaison: James D. Lake

Committee Scope: This Committee shall have primaryresponsibility for documents on protection of buildings from fireexposure, excluding installation details for outside sprinklers,which are handled by the Technical Committee on AutomaticSprinklers.

This list represents the membership at the time the Committee wasballoted on the text of this edition. Since that time, changes in themembership may have occurred. A key to classifications is found at thefront of this book.

The Report of the Technical Committee on Exposure FireProtection is presented for adoption.

This Report was prepared by the Technical Committee onExposure Fire Protection and proposes for adoption, a completerevision to NFPA 80A, Recommended Practice for Protection ofBuildings from Exterior Fire Exposures , 1996 edition. NFPA 80A-1996 is published in Volume 11 of the 2000 National Fire Codesand in separate pamphlet form.

This Report has been submitted to letter ballot of the TechnicalCommittee on Exposure Fire Protection, which consists of 13voting members. The results of the balloting, after circulation ofany negative votes, can be found in the report.

NFPA 80A May 2001 ROP Copyright 2000, NFPA

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(Log #CP2)80A- 1 - (1-1): AcceptSUBMITTER: Technical Committee on Exposure Fire ProtectionRECOMMENDATION : Revise Scope as follows: This recommended practice addresses separation distancesbetween buildings to limit exterior fire spread based on exterioropenings and other construction features.SUBSTANTIATION: More accurately describes the document.COMMITTEE ACTION: Accept.NUMBER OF COMMITTEE MEMBERS ELIGIBLE TO VOTE: 13VOTE ON COMMITTEE ACTION: AFFIRMATIVE: 10 NOT RETURNED: 3 Barbadoro, Parsley, Richter

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(Log #CP3)80A- 2 - (1-2): AcceptSUBMITTER: Technical Committee on Exposure Fire ProtectionRECOMMENDATION : Revise the purpose of the document asfollows: These recommendations are intended to provide a reasonablelevel of protection for combustibles within and on the exterior of abuilding exposed to an external building fire contemplatingeffective fire fighting activity.SUBSTANTIATION: More accurately describes the purpose ofthe documentCOMMITTEE ACTION: Accept.NUMBER OF COMMITTEE MEMBERS ELIGIBLE TO VOTE: 13VOTE ON COMMITTEE ACTION: AFFIRMATIVE: 10 NOT RETURNED: 3 Barbadoro, Parsley, Richter

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(Log #CP4)80A- 3 - (1-3 Noncombustible Materials): AcceptSUBMITTER: Technical Committee on Exposure Fire ProtectionRECOMMENDATION : Revise definition of NoncombustibleMaterials as follows: Noncombustible Materials: A material that, in the form in whichit is used and under the conditions anticipated, will not ignite,burn, support combustion, or release flammable vapors whensubjected to fire or heat. Materials that are reported as passingASTM E 136, Standard Test Method for Behavior of Materials in aVertical Tube Furnace at 750C, shall be considerednoncombustible materials.SUBSTANTIATION: This is the preferred definition from theNFPA Glossary of Terms.COMMITTEE ACTION: Accept.NUMBER OF COMMITTEE MEMBERS ELIGIBLE TO VOTE: 13VOTE ON COMMITTEE ACTION: AFFIRMATIVE: 10 NOT RETURNED: 3 Barbadoro, Parsley, Richter

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(Log #CP5)80A- 4 - (1-3 Pilot Ignition): AcceptSUBMITTER: Technical Committee on Exposure Fire ProtectionRECOMMENDATION : Revise the definition of Pilot Ignition asfollows: Pilot Ignition*. The ignition of a material by radiation where alocal high temperature igniting source is located in the stream ofgases and volatiles issuing from the exposed material. A-1-3 Pilot Ignition. In practice, a glowing ember or a flash offlame might constitute the high temperature ignition source, whichoften serves to ignite the flammable gases and volatiles. This mechanism differs from spontaneous ignition by radiationin which there is no local high temperature igniting source and forwhich higher intensities of radiation are necessary. [1-3]SUBSTANTIATION: This action removes the explanatorylanguage from the current definition and places in the Annex.COMMITTEE ACTION: Accept.NUMBER OF COMMITTEE MEMBERS ELIGIBLE TO VOTE: 13VOTE ON COMMITTEE ACTION: AFFIRMATIVE: 10 NOT RETURNED: 3 Barbadoro, Parsley, Richter

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(Log #CP6)80A- 5 - (2-2.3): AcceptSUBMITTER: Technical Committee on Exposure Fire ProtectionRECOMMENDATION : Revise paragraph to read as follows: Percent of Opening in Exposing Wall Area. The percent ofopening in the exposing wall area is the percentage of the exposingwall made up of doors, windows, or other openings within theassumed height and width of the exposing fire. Walls without theability to withstand fire penetration for more than 20 minutesshould be treated as having 100-percent openings. Walls havingthe ability to withstand fire penetration for more than 20 minutes,but less than the expected duration of the fire, should be treated ashaving 75-percent openings or actual percentage of openings,which ever is greater.SUBSTANTIATION: This change clarifies that the use of lessthan the actual opening percentage should not be recommended.COMMITTEE ACTION: Accept.NUMBER OF COMMITTEE MEMBERS ELIGIBLE TO VOTE: 13VOTE ON COMMITTEE ACTION: AFFIRMATIVE: 10 NOT RETURNED: 3 Barbadoro, Parsley, Richter

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(Log #CP7)80A- 6 - (2-2.5): AcceptSUBMITTER: Technical Committee on Exposure Fire ProtectionRECOMMENDATION : Revise paragraph as follows 2-2.5 Width/Height or Height/Width. 2-2.5.1 The width versus height or height versus width should bedetermined as a measure of the configuration of the exposing faceexpressed as a ratio. 2-2.5.2 The larger of the values w/h or h/w should be used.SUBSTANTIATION: Clarifies the intent for the use of ratios.COMMITTEE ACTION: Accept.NUMBER OF COMMITTEE MEMBERS ELIGIBLE TO VOTE: 13VOTE ON COMMITTEE ACTION: AFFIRMATIVE: 10 NOT RETURNED: 3 Barbadoro, Parsley, Richter

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(Log #CP9)80A- 7 - (2-3, A-2-3): AcceptSUBMITTER: Technical Committee on Exposure Fire ProtectionRECOMMENDATION : Reorganize this paragraph and theappendix note as follows: 2-3* Determination of Separation Distances. 2-3.1 To determine distances, the lesser dimension of eitherwidth (w) or height (h) should be multiplied by the guide numberand 1.5 m (5 ft) added to the result. 2-3.2 Where the I value for the combustible materials used isindicated by appropriate tests to be less than 12.5 kW/m2 (0.3cal/cm2/sec or 66 Btu/ft2/min) or where I is indicated to begreater than 12.5 kW/m 2 (0.3 cal/cm2/sec or 66 Btu/ft2/min)and where there are no openings in the facade of the exposedbuilding, the percentage openings should be adjusted bymultiplying by the ratio of 12.5 kW/m2/I (0.3 cal/cm2/sec/I or 66Btu/ft2/min/I). 2-3.3 Recommended separation distances contemplate firedepartment response. Where no organized fire-fighting facilitiesare available, the distances derived from guide numbers in Table4.3(c) should be increased by a factor of up to 3. Add the following paragraphs at the begining of A-2-3:Table 2-3 determines the separation distance necessary betweentwo buildings so that pilot ignition of the exposed building or itscontents is unlikely, assuming no means of protection are installedin connection with either building. Guide numbers are obtainedfrom this table. Table 2-3 is based on a maximum tolerable level of incidentradiation (I) at the facade of an unprotected exposed building of12.5 kW/m2 (0.3 cal/cm2/sec or 66 Btu/ft2/min). This assumesthat the facade is constructed of typical cellulosic materials.SUBSTANTIATION: Separate the various recommendations andplace the explanatory material in the appendix.COMMITTEE ACTION: Accept.NUMBER OF COMMITTEE MEMBERS ELIGIBLE TO VOTE: 13VOTE ON COMMITTEE ACTION: AFFIRMATIVE: 10 NOT RETURNED: 3 Barbadoro, Parsley, Richter

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(Log #CP8)80A- 8 - (Table 2-4): AcceptSUBMITTER: Technical Committee on Exposure Fire ProtectionRECOMMENDATION : Revise table as follows: Table 2-4 Minimum Separation Distance for Exposing Buildingswith Combustible/Nonrated Roof Assemblies

Number of Stories Horizontal SeparationLikely to Contribute Distance or Height ofto Flaming through Protection abovethe Roof Exposing Fire

(m) (ft)1 7.5 252 10 333 12.5 414 15 49

SUBSTANTIATION: These are logical conversions based on thesubjectivity of the basis of the original table.COMMITTEE ACTION: Accept.NUMBER OF COMMITTEE MEMBERS ELIGIBLE TO VOTE: 13VOTE ON COMMITTEE ACTION: AFFIRMATIVE: 10 NOT RETURNED: 3 Barbadoro, Parsley, Richter

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(Log #CP10)80A- 9 - (4-2.2(d)): AcceptSUBMITTER: Technical Committee on Exposure Fire ProtectionRECOMMENDATION : Revise the note in the SeparationDistance Adjustment column to read reduce in accordance with2-3.2.SUBSTANTIATION: Table 2-3 is not the correct reference. Thereference should be to the paragraph.COMMITTEE ACTION: Accept.NUMBER OF COMMITTEE MEMBERS ELIGIBLE TO VOTE: 13VOTE ON COMMITTEE ACTION: AFFIRMATIVE: 10 NOT RETURNED: 3 Barbadoro, Parsley, Richter

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(Log #CP11)80A- 10 - (4-2.3(e) (New) ): AcceptSUBMITTER: Technical Committee on Exposure Fire ProtectionRECOMMENDATION : Add new subparagraph as follows: (e) Install listed automatic window sprinklers in accordance with their listings reduce 50 percentSUBSTANTIATION: To recognize the use of a potentialalternative technology based on the recent listings of automaticsprinklers for window protectionCOMMITTEE ACTION: Accept.NUMBER OF COMMITTEE MEMBERS ELIGIBLE TO VOTE: 13VOTE ON COMMITTEE ACTION: AFFIRMATIVE: 10 NOT RETURNED: 3 Barbadoro, Parsley, Richter

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(Log #CP12)80A- 11 - (4-2.4(f) (New) ): AcceptSUBMITTER: Technical Committee on Exposure Fire ProtectionRECOMMENDATION : Add new subparagraph as follows: (f) Install listed automatic window sprinklers in accordance with their listings reduce to 1.5m (5ft)SUBSTANTIATION: To recognize the use of a potentialalternative technology based on the recent listings of automaticsprinklers for window protectionCOMMITTEE ACTION: Accept.NUMBER OF COMMITTEE MEMBERS ELIGIBLE TO VOTE: 13VOTE ON COMMITTEE ACTION: AFFIRMATIVE: 10 NOT RETURNED: 3 Barbadoro, Parsley, Richter

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(Log #CP13)80A- 12 - (4-2.5(f) (New) ): AcceptSUBMITTER: Technical Committee on Exposure Fire ProtectionRECOMMENDATION : Add new subparagraph as follows:

(f) Install listed automatic window sprinklers in accordance with their listings reduce 75 percentSUBSTANTIATION: To recognize the use of a potentialalternative technology based on the recent listings of automaticsprinklers for window protectionCOMMITTEE ACTION: Accept.NUMBER OF COMMITTEE MEMBERS ELIGIBLE TO VOTE: 13VOTE ON COMMITTEE ACTION: AFFIRMATIVE: 10 NOT RETURNED: 3 Barbadoro, Parsley, Richter

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(Log #CP1)80A- 13 - (Entire Document): AcceptSUBMITTER: Technical Committee on Exposure Fire ProtectionRECOMMENDATION : The Technical Committee on ExposureFire Protection proposes a complete revision to NFPA 80A,Recommended Practice for Protection of Buildings from ExteriorFire Exposures, 1996 edition, as shown at the end of this report.This includes a restructure of the entire document to comply withthe NFPA Manual of Style as follows: 1. Chapter 1 to contain administrative text only. 2. Chapter 2 to contain only referenced publications cited in themandatory portions of the document. 3. Chapter 3 to contain only definitions. 4. All mandatory sections of the document must be evaluated forusability, adoptability, and enforceability language. Generatenecessary committee proposals. 5. All units of measure in document are converted to SI unitswith inch/pound units in parentheses. 6. Appendices restructured and renamed as Annexes.SUBSTANTIATION: To address new technologies in exposurefire protection and editorial restructuring, to conform with the2000 edition of the NFPA Manual of Style.COMMITTEE ACTION: Accept.NUMBER OF COMMITTEE MEMBERS ELIGIBLE TO VOTE: 13VOTE ON COMMITTEE ACTION: AFFIRMATIVE: 10 NOT RETURNED: 3 Barbadoro, Parsley, Richter

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NFPA 80A

Recommended Practice for

Protection of Buildings from Exterior Fire Exposures

2001 Edition

NOTICE: An asterisk (*) following the number or letterdesignating a paragraph indicates that explanatory material on theparagraph can be found in Annex A. Information on referenced publications can be found in Chapter2.

Chapter 1 Administration

1.1 Scope. This recommended practice addresses separationdistances between buildings to limit exterior fire spread based onexterior openings and other construction features.

1.2 Purpose . These recommendations are intended to provide areasonable level of protection for combustibles within and on theexterior of a building exposed to an external building fire,contemplating effective fire-fighting activity.

1.3 Application The hazards of exposure to a structure fromadjacent exposing fires and the multiple conditions under whichsuch exposure can occur make it impossible to develop a table,formula, or set of rules that adequately covers all conditions. Theuser of this recommended practice should become familiar withthe general theory of radiation exposure hazard as outlined inA.3.1.2, Exposure Severity.


380

1.4 Units and Formulas. Metric units of measurement in thisrecommended practice are in accordance with the modernizedmetric system known as the International System of Units (SI).The liter unit, which is outside of but recognized by SI, iscommonly used in fire protection and is therefore used in thisrecommended practice. In this document, values formeasurements are expressed in SI units followed by an equivalentEnglish unit. The first stated value should be regarded as therecommendation because the given equivalent value might beapproximate.

Chapter 2 Referenced Publications

2.1 The following documents or portions thereof are referencedwithin this recommended practice and should be considered partof the recommendations of this document.

2.1.1 NFPA Publications. National Fire Protection Association,1 Batterymarch Park, P.O. Box 9101, Quincy, MA 02269-9101.

NFPA 13, Standard for the Installation of Sprinkler Systems, 1999edition.

NFPA 80, Standard for Fire Doors and Fire Windows, 1999 edition.

NFPA 255, Standard Method of Test of Surface BurningCharacteristics of Building Materials, 2000 edition.

Fire Protection Handbook, 18th ed., 1997.

2.1.2 Other.

McGuire, J. H., Fire and the Spatial Separation of Buildings,reprinted from Fire Technology, vol. 1, no. 4, November 1965, pp.278287. Technical paper No. 212, NRC 8901, February 1966,National Research Council of Canada, Division of BuildingResearch, Ottawa.

2.2 Bibliography.

2.2.1 Books.

Bird, E. L., and Docking, S. J., Fire in Buildings, Van Nostrand,New York.

Giedt, W. H., Principles of Engineering Heat Transfer, VanNostrand, New York, 1957.

Gross, D., and Robertson, A. F., Experimental Fire inEnclosures, Fire Research, Tenth Symposium (International) onCombustion, Combustion Institute, Pittsburgh, PA, 1965, pp. 931942.

Thomas, P. H., Size of Flames from Natural Fires, Colloquiumon Modeling Principles, Ninth Symposium (International) onCombustion, Academic Press, New York, 1963, pp. 844859.

Wilkes, G. B., Heat Insulation, Wiley, New York, 1950.

2.2.2 Journal Articles.

Conflagrations in America Since 1900, NFPA Quarterly, vol. 44,no. 4, Part 2, April 1951.

Eickner, H. W., Basic Research on the Pyrolysis and Combustionof Wood (Technical Paper 107, Forest Products Laboratory, U.S.Department of Agriculture, Oct. 1961), Forest Products Journal, vol.12, no. 4, April 1962, pp. 194199.

Lawson, D. I., Ignition of Wood by Radiation, British Journal ofApplied Physics, vol. 3, no. 9, September 1952, pp. 288292.

Los Angeles Fire Department, Operation School Burning, No. 2,1961.

Moysey, E. B., Space Separation for Prevention of Farm FireSpread, Fire Technology, vol. 1, no. 1, February 1965, pp. 6268.

Moysey, E. B., and Muir, W. E., Pilot Ignition of BuildingMaterials by Radiation, Fire Technology, vol. 4, no. 1, February1968, pp. 4650.

Nelson, H. E., Radiant Energy Transfer in Fire ProtectionEngineering Problem Solving, Fire Technology, vol. 4, no. 3, August1968, pp. 196205.

Salzberg, F. and Waterman, T. E., Studies of Building Fires withModels, Fire Technology, vol. 2, no. 3, August 1966, pp. 196203.

Shorter, G. W. et al., The St. Lawrence Burns, NFPA ReprintQ53-17, Quarterly of the National Fire Protection Association, vol. 53,no. 4, April 1960, pp. 300316.

Simms, D. L., On the Pilot Ignition of Wood by Radiation,Combustion and Flame, vol. 7, no. 9, September 1963, pp. 253261.

Simms, D. L. and Law, M., The Ignition of Wet and Dry Wood byRadiation, Combustion and Flame, vol. 11, no. 5, October 1967, pp.377388.

2.2.3 Proceeding.

Muir, W. E., Moysey, E. B., and Scott, W. A., Ignition of SomeBuilding Materials, Canadian Society of Agricultural Engineers,June 2830, 1966.

2.2.4 Reports.

Browne, F. L., Theories of the Combustion of Wood and ItsControl, Report No. 2136, December 1958, Forest ProductsLaboratory, U.S. Department of Agriculture, Madison, WI.

Bruce, H. D., Experimental Dwelling-Room Fires, Report No.1941, April 1959, reaffirmed 1965, Forest Products Laboratory, U.S.Department of Agriculture, Madison, WI.

Butcher, E. G., Chitty, T. B., and Ashton, L. A., TheTemperatures Attained by Steel in Building Fires, Fire ResearchTechnical Paper No. 15, 1966, Ministry of Technology and FireOffices Committee, Joint Fire Research Organization, HerMajestys Stationery Office, London.

Fire Research 1958, Report of the Fire Research Board with the Report ofthe Director of Fire Research for the year 19581959, Department ofScientific and Industrial Research and Fire Offices Committee, HerMajestys Stationery Office, London (out of print).

Ingberg, S. H., Fire Resistance Classifications of BuildingConstructions, Building Materials and Structures Report BMS 92,October 1942, U.S. Department of Commerce, National Bureau ofStandards, Washington, DC.

Ingberg, S. H., Dunham, J. W., and Thompson, J. P.,Combustible Contents in Buildings, Building Materials andStructures Report BMS 149, July 1957, U.S. Department ofCommerce, National Bureau of Standards, Washington, DC.

Keough, J. J., Diagrams for the Approximate Assessment ofRadiation Exposure Hazards from Fires in Buildings, UP 153, July1963, Commonwealth Experimental Building Station,Commonwealth Department of Works, Chatswood, N.S.W.,Australia.

Langdon-Thomas, G. J. and Law, M., Fire and the ExternalWall, Fire Note No. 8, 1966, Ministry of Technology and FireOffices Committee, Joint Fire Research Organization, HerMajestys Stationery Office, London.

Law, M., Heat Radiation from Fires and Building Separation,Fire Research Technical Paper No. 5, 1963, Department ofScientific and Industrial Research and Fire Offices Committee,Joint Fire Research Organization, Her Majestys Stationery Office,London.

Law, M., Radiation from Fires in a Compartment, Fire ResearchTechnical Paper No. 20, 1968, Ministry of Technology and FireOffices Committee, Joint Fire Research Organization, HerMajestys Stationery Office, London.

Life Hazard of Interior Finishes (Development of Method),Report No. 11760, June 1950, and Life Hazard Tests on WoodInterior Finish, Report No. 11975, Oct. 1951, Factory MutualLaboratories, reproduced 1952, National Lumber ManufacturingAssociation, Washington, DC.

Copyright 2000, NFPA

381

McGuire, J. H., Heat Transfer by Radiation, Fire ResearchSpecial Report No. 2, 1953, Department of Scientific and IndustrialResearch and Fire Offices Committee, Her Majestys StationeryOffice, London.

McGuire, J. H., Ignition of Materials Behind Common 1/8-inch-Thick Window Glass, Technical Note No. 456, September 1965,National Research Council of Canada, Division of BuildingResearch, Ottawa.

Ross, D., Field Burnout Tests of Apartment Dwelling Units,Building Science Series No. 10, September 1967, U.S. Departmentof Commerce, National Bureau of Standards, Washington, DC.

Scott, W. A., Spacing of Farm Buildings for Fire Control, 1964,University of Saskatchewan.

Yokoi, S., Study of the Prevention of Fire Spread Caused by HotUpward Current, Report No. 34, November 1960, BuildingResearch Institute, Ministry of Construction, Japan.

Chapter 3 Definitions

3.1 General Terms. The definitions contained in this section shallapply to the terms as used in this recommended practice. Whereterms are not included in this section, common usage of the termshall apply.

3.1.1 Exposure. The heat effect from an external fire that mightcause ignition of, or damage to, an exposed building or itscontents.

3.1.2* Exposure Severity. The intensity of an exposing fire.

3.1.3 Noncombustible Material. A material that, in the form inwhich it is used and under the conditions anticipated, will notignite, burn, support combustion, or release flammable vaporswhen subjected to fire or heat. Materials that are reported aspassing ASTM E 136, Standard Test Method for Behavior of Materialsin a Vertical Tube Furnace at 750C, are considered noncombustiblematerials. (220:3.1)

3.1.4* Pilot Ignition. The ignition of a material by radiation wherea local high-temperature igniting source is located in the stream ofgases and volatiles issuing from the exposed material.

3.2 NFPA Official Definitions.

3.2.1* Approved. Acceptable to the authority having jurisdiction.

3.2.2* Authority Having Jurisdiction. The organization, office, orindividual responsible for approving equipment, an installation, ora procedure.

3.2.3 Should. Indicates a recommendation or that which is advisedbut not required.

Chapter 4 Classification of Exposures and RecommendedSeparation Distances

4.1 Exposures. Two types of exposure should be considered, asdescribed in 4.1.1 and 4.1.2.

4.1.1 Exposure to Radiation. Exposure to radiation results from anyof the following:

(1) Radiant energy passing through windows or other openingsin the faade of a burning building (2) Flames issuing from the windows of a burning building (3) Flames issuing from the burning faade of a building

4.1.2 Exposure to Flames. Exposure to flames results from flamesissuing from the roof or top of a burning building in cases wherethe exposed building is higher than the burning building.

4.2 Exposure from Buildings of Greater or Equal Height.

4.2.1 Where a building is exposed by a building of greater or equalheight, only the thermal radiation from the walls or wall openingsof the exposing building should be considered.

4.2.2 Separation distances should be determined so that pilotignition of the exposed building or its contents is unlikely,assuming no means of protection are installed in connection witheither building.

4.3 Minimum Separation Distance.

4.3.1 General. The minimum separation distances betweenbuildings should be determined using 4.3.2 through 4.3.8 andTables 4.3.7.3 and 4.3.8.2

4.3.2 Width of Exposing Fire.

4.3.2.1 The width of the exposing fire should be considered to bethe length in meters (feet) of the exposing wall between interiorfire separations or between exterior end walls where no fireseparations exist.

4.3.2.2 Fire separations (such as partition walls or fire walls)should have sufficient fire resistance to contain the expected fire.

4.3.3 Height of Exposing Fire.

4.3.3.1 The height of the exposing fire should be regarded as theheight in meters (feet) of the number of stories involved in theexposing fire, considering such factors as the buildingconstruction, closure of vertical openings, and fire resistance offloors.

4.3.3.2 The relevant fire separations should have a fire resistancesufficient to contain the expected fire.

4.3.4 Percentage of Opening in Exposing Wall Area. Thepercentage of opening in the exposing wall area should beregarded as the percentage of the exposing wall made up of doors,windows, or other openings within the assumed height and widthof the exposing fire.

4.3.4.1 Walls without the ability to withstand fire penetration inexcess of 20 minutes should be treated as having 100 percentopenings.

4.3.4.2 Walls having the ability to withstand fire penetration for notless than 20 minutes but not exceeding the expected duration ofthe fire should be treated as having 75 percent openings or theactual percentage of openings, whichever is greater.

4.3.5 Severity.

4.3.5.1 Three levels of exposure severity should be assumed: light,moderate, and severe. Two of the important properties influencingfire severity are as follows:

(1) The average combustible load per unit of floor area (2) The characteristics and average flame spread ratings of theinterior wall and ceiling finishes

4.3.5.2 Tables 4.3.5.2(a) and 4.3.5.2(b) should be used to assessseverity based on these properties, and the more severe of the twoclassifications should govern.

Table 4.3.5.2(a) Severity of Fire LoadFire Loading of

Floor AreaClassification

ofkg/m2 lb/ft 2 Severity034 07a Light3573 815 Moderate74 16 Severe

aExcluding any appreciable quantities of rapidly burningmaterials such as certain foamed plastics, excelsior, orflammable liquids. Where these materials are found insubstantial quantities, the severity should be classified asmoderate or severe.

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Table 4.3.5.2(b) Severity of Interior Wall and Ceiling FinishAverage Flame Spread Ratingof Interior Wall and Ceiling

Finish1

Classificationof

Severity 2

025 Light2675 Moderate 76 Severe

1See NFPA 255, Standard Method of Test of Surface BurningCharacteristics of Building Materials.2Where only a portion of the exposing building hascombustible interior finish (e.g., some rooms only, ceilingonly, some walls only), this factor is considered whenjudging severity classification.

4.3.6 Width/Height or Height/Width.

4.3.6.1 Width versus height, w/h, or height versus width, h/w ,should be determined as a measure of the configuration of theexposing face and should be expressed as a ratio.

4.3.6.2 The larger of w/h or h/w values should be used.

4.3.7* Determination of Separation Distances .

4.3.7.1 To determine distances, the lesser dimension of eitherwidth, w , or height, h, should be multiplied by the guide numberand 1.5 m (5 ft) added to the result.

4.3.7.2 Where the I value for the combustible materials used isindicated by appropriate tests not to exceed 12.5 kW/m2 (0.3cal/cm2sec or 66 Btu/ft2min), or where I is indicated to be notless than 12.5 kW/m2 (0.3 cal/cm2sec or 66 Btu/ft2min) andthere are no openings in the facade of the exposed building, thepercentage openings should be adjusted by multiplying by the ratioof 12.5 kW/ m2I (0.3 cal/cm2secI or 66 Btu/ft2minI).

4.3.7.3 Recommended separation distances assume fire departmentresponse. Where no organized fire-fighting facilities are available,the distances derived from the guide numbers in Table 4.3.7.3should be increased by a factor of 3 or less.

4.3.8* Exposure from Buildings of Lesser Height.

4.3.8.1 Where the exposing building is of lesser height than theexposed building, the separation distance should first bedetermined from Table 4.3.7.3.

4.3.8.2 Where the roof assembly of the exposing building iscombustible and has no fire resistance rating, means of protectionshould be provided above the roof level of the exposing building inaccordance with Table 4.3.8.2.

Table 4.3.8.2 Minimum Separation Distance for ExposingBuildings with Combustible/Nonrated Roof Assemblies

Number of Stories Likelyto Contribute

to Flaming

Horizontal SeparationDistance or Height of

Protection Above ExposingFire

Through the Roof (m) (ft)1 7.5 252 10 333 12.5 414 15 49

4.3.8.3 Where separation distances derived from Table 4.3.7.3 donot exceed the distances indicated in Table 4.3.8.2, means ofprotection should be applied on the exposed building wall to aheight equal to the separation distance, commencing at the heightof the roof of the exposing building.

4.3.8.4 Where the roof of the exposing building has a fire resistancerating sufficient to contain the expected fire (based on the fireloading within the area), no exposure hazard is considered to existthroughout the roof.

4.3.8.5 Where the roof has a fire resistance rating less thannecessary to contain an expected fire, means of protection shouldbe provided in accordance with Table 4.3.8.2, taking intoconsideration the fire stability of the roof assembly involved, thefuel it could contribute, including roof insulation and covering,and its tendency to inhibit flaming through the roof.

4.3.8.6 Subject to 4.3.8.4 and 4.3.8.5, the number of storiesexpected to contribute to flaming through the roof should beconsidered to be the top story together with those stories that aresuccessively located beneath the top story and are not separatedfrom it, as indicated in 4.3.3.

4.3.8.7 High attic spaces should be counted as a story, subject to4.3.8.4 and 4.3.8.5. Where the height of the attic is low,interpolation between the values provided in Table 4.3.8.2 shouldbe made.

Chapter 5 Means of Protection

5.1 Types. Various means of protecting buildings from fire damageresulting from exterior exposure, listed as follows in no specificorder with regard to adequacy, should be considered:

(a) Buildings(1) Clear space between buildings(2) Total automatic sprinkler protection

(b) Walls(1) Blank walls of noncombustible materials(2) Barrier walls (self-supporting) between the building and

exposure(3) Extension of exterior masonry walls to form parapets or

wings(4) Automatic outside water curtains for combustible walls

(c) Wall Openings(1) Elimination of openings by filling with equivalent

construction(2) Glass block panels in openings(3) Wired glass in steel sash (fixed or automatic closing) in

openings(4) Automatic or deluge sprinklers outside over openings(5) Automatic (rolling steel) fire shutters on openings(6) Automatic fire doors on door openings(7) Automatic fire dampers on wall openings

5.2 Additional Protection.

5.2.1 Additional means of protection that can be developed, suchas double-glazed glass in metal sash, flame-retardant coatings, andother arrangements, also should be considered.

5.2.2 Any additional means of protection should be approvedbefore being implemented.

5.3 Evaluation of Protection. In evaluating the suitability of any ofthe types of protection specified in Section 5.1, the adverse effectsof convected heat, flame impingement, and small flying brandsassociated with winds, as well as the beneficial effects of firedepartment operations, have been considered. Large flying brandshave not been considered.

5.4 Selecting the Means of Protection. The means of protectionselected should be approved for the individual application andshould be installed in accordance with appropriate standards (e.g.,fire doors installed in accordance with NFPA 80, Standard for FireDoors and Fire Windows; automatic sprinklers installed inaccordance with NFPA 13, Standard for the Installation of SprinklerSystems).

5.5 Manual Operation. Manually operated window shutters orsprinklers should not be used. The excessive time needed to closeor activate them at the time of a fire incident and the fact that theproperty exposed could be vacant or uninhabited at the time of thefire incident make their value questionable.

5.6 Application of Means of Protection. The various means ofprotection to reduce the separation distances indicated in Table4.3.7.3 and Table 4.3.8.2 should be applied in accordance with theguidelines provided in 5.6.1.

Tab

le 4

.3.7

.3 G

uid

e N

um

bers

for

Min

imu

m S

epar

atio

n D

ista

nce

s

Seve

rity

W

idth

/H

eigh

t or

Hei

ght/

Wid

th

Perc

enta

ge o

f O

pen

ings

1G

uid

e N

um

ber

[mu

ltip

ly b

y le

sser

dim

ensi

on, a

dd

5 f

t (1

.52

m),

to

obta

in b

uil

din

g-to

-bu

ild

ing

sep

arat

ion

]

Lig

ht

Mod

erat

e Se

vere

1.

0 1.

3 1.

6 2.

0 2.

5 3.

2 4

5 6

8 10

13

16

20

25

32

40

20

10

5 0.

36

0.40

0.

44

0.46

0.

48

0.49

0.

50

0.51

0.

51

0.51

0.

51

0.51

0.

51

0.51

0.

51

0.51

0.

51

30

15

7.5

0.60

0.

66

0.73

0.

79

0.84

0.

88

0.90

0.

92

0.93

0.

94

0.94

0.

95

0.95

0.

95

0.95

0.

95

0.95

40

20

10

0.76

0.

85

0.94

1.

02

1.10

1.

17

1.23

1.

27

1.30

1.

32

1.33

1.

33

1.34

1.

34

1.34

1.

34

1.34

50

25

12.5

0.

90

1.00

1.

11

1.22

1.

33

1.42

1.

51

1.58

1.

63

1.66

1.

69

1.70

1.

71

1.71

1.

71

1.71

1.

71

60

30

15

1.02

1.

14

1.26

1.

39

1.52

1.

64

1.76

1.

85

1.93

1.

99

2.03

2.

05

2.07

2.

08

2.08

2.

08

2.08

80

40

20

1.22

1.

37

1.52

1.

68

1.85

2.

02

2.18

2.

34

2.48

2.

59

2.67

2.

73

2.77

2.

79

2.80

2.

81

2.81

100

50

25

1.39

1.

56

1.74

1.

93

2.13

2.

34

2.55

2.

76

2.95

3.

12

3.26

3.

36

3.43

3.

48

3.51

3.

52

3.53

60

30

1.55

1.

73

1.94

2.

15

2.38

2.

63

2.88

3.

13

3.37

3.

60

3.79

3.

95

4.07

4.

15

4.20

4.

22

4.24

80

40

1.82

2.

04

2.28

2.

54

2.82

3.

12

3.44

3.

77

4.11

4.

43

4.74

5.

01

5.24

5.

41

5.52

5.

60

5.64

100

50

2.05

2.

30

2.57

2.

87

3.20

3.

55

3.93

4.

33

4.74

5.

16

5.56

5.

95

6.29

6.

56

6.77

6.

92

7.01

60

2.26

2.

54

2.84

3.

17

3.54

3.

93

4.36

4.

82

5.30

5.

80

6.30

6.

78

7.23

7.

63

7.94

8.

18

8.34

80

2.63

2.

95

3.31

3.

70

4.13

4.

61

5.12

5.

68

6.28

6.

91

7.57

8.

24

8.89

9.

51

10.0

5 10

.50

10.8

4

100

2.96

3.

32

3.72

4.

16

4.65

5.

19

5.78

6.

43

7.13

7.

88

8.67

9.

50

10.3

3 11

.15

11.9

1 12

.59

13.1

51 W

her

e th

e p

erce

nta

ge o

f op

enin

gs o

r w

idth

/h

eigh

t or

hei

ght/

wid

th r

atio

is b

etw

een

tab

le v

alu

es p

rovi

ded

, in

terp

olat

ion

bet

wee

n r

esp

ecti

ve g

uid

e n

um

bers

sh

ould

be

mad

e. S

eeA

.4.3

.7 f

or t

reat

men

t of

un

equ

ally

dis

trib

ute

d w

ind

ows.


384

5.6.1 Separation Adjustments. Tables 5.6.1(a) through 5.6.1(e)should be used for adjusting the separation distances derived fromTable 4.3.7.3 and Table 4.3.8.2.

Table 5.6.1(a) Frame or Combustible Exposed Exterior Walls

Means of ProtectionSeparation Distance

AdjustmentReplace with blank fire-resistivewall (3-hour minimum)

Reduce to 0 m (0 ft)

Install automatic deluge watercurtain over entire wall with nowindows, with wired glass windows,or with windows closed by 3/4-hourprotection

Reduce to 1.5 m (5 ft)

Install automatic deluge watercurtain over entire wall withordinary glass windows

Reduce by 50 percent

Table 5.6.1(b) Frame or Combustible Exposed Exterior Wall[I Greater than 12.5 kW/m2 (0.3 cal/cm2sec or 66

Btu/ft 2min)] with Openings


AdjustmentReplace with blank fire-resistivewall (3-hour minimum)




Install automatic deluge watercurtain over entire wall withordinary glass windows


Close all wall openings withmaterial equivalent to wall, or closewith 3/4-hour protection andeliminate combustible projectionsthat have I less than wall

Reduce in accordancewith 4.3.7.2

Table 5.6.1(c) Noncombustible Exposed Exterior Wall (FireResistance Less Than 3 Hours)


AdjustmentReplace wall with blank fire-resistive wall (3-hour minimum)


Close all wall openings withmaterial equivalent to wall, or closewith 3/4-hour protection andeliminate combustible projections




Install automatic deluge watercurtain on all wall openingsequipped with ordinary glass andon combustible projections


Install listed automatic windowsprinklers in accordance with theirlistings


Table 5.6.1(d) Veneered Exposed Exterior Wall[Combustible Construction Covered by a Minimum of 100

mm (4 in.) of Masonry]


AdjustmentReplace wall with blank fire-resistive wall(3-hour minimum)


Close all wall openings with 3/4-hour protection and eliminatecombustible projections


Close all wall openings withmaterial equivalent to wallconstruction and eliminatecombustible projections


Install automatic deluge watercurtain over windows equippedwith wired glass or over 3/4-hourclosed openings and oncombustible projections


Install automatic deluge watercurtain over windows equippedwith ordinary glass and oncombustible projections




Table 5.6.1(e) Fire-Resistive Exposed Exterior Wall(Minimum 3-Hour Rating)


AdjustmentClose all openings with materialequivalent to wall or protect allwall openings with 3-hourprotection


Protect all openings with 11/2-hourprotection

Reduce by 75 percent[max. recommended =3 m (10 ft)]

Protect all wall openings with 3/4-hour protection

Reduce by 50 percent[max. recommended =6 m (20 ft)]

Install automatic deluge watercurtain on all wall openings withwired glass or with 3/4-hour or 11/2-hour protection

Reduce to 1.5 m (5ft)

Install automatic deluge watercurtain on all wall openingsequipped with ordinary glass




5.6.2 Combustible Eaves. Combustible eaves, cornices, and otherexterior ornamentation on exposed buildings should be treated asunprotected openings, in accordance with 5.6.1.

5.6.3* Protected Exposing Building. Where the exposing buildingor structure is protected throughout by an approved, properlymaintained system of automatic sprinklers of adequate design forthe hazard involved, no exposure hazard should be considered toexist.

5.6.4* Protected Exposed Building. Where the exposed building orstructure is protected throughout by an approved, properlymaintained system of automatic sprinklers of adequate design forthe hazard involved, the exposure hazard to the total exposedbuilding and its contents should be considered to be substantiallyreduced.


385

Annex A Explanatory Material

Annex A is not a part of the recommendations of this NFPA documentbut is included for informational purposes only. This annex containsexplanatory material, numbered to correspond with the applicable textparagraphs.

A.3.1.2 Exposure Severity . For the purposes of this document,exposure severity has been defined as the intensity of an exposingfire. Exposure severity is intended to be a measure of the radiationlevel developed per unit window area by the exposing fire. Itrepresents a combination of radiation emitted through the windowitself as well as that produced from the flames that project out thewindow and up the front of the building. Thus, because radianttransfer from the flames as well as from the interior room walls isinvolved, the flame emissivity, dependent on fuel character as wellas flame dimensions, could be of great importance. The emission of flames and hot gases from the window of a roomor building compartment during a fire could result from theestablishment of a thermal pump. The pump is created bybuoyancy differences between the hot combustion products andthe surrounding outside ambient air, and it provides a positivemeans for furnishing fresh air to the fire and discharging flamesand combustion products through the window. If the roominvolved is provided with only a single window and no internalsource of air, the window serves the dual purpose as a passage forthe entry of fresh air and the discharge of flames and other hotcombustion products. If, however, an internal duct or passage isavailable for the supply of fresh air to the fire room, a much largerfraction of the window can be used effectively for the discharge offlaming gases. Winds also could significantly influence theventilation behavior of a building fire and thus the exposureseverity. In addition to ventilation, a number of other system variablesinfluence exposure severity. The most important of these are asfollows:

(1) The combustible load, including both the occupancy andbuilding construction combustibles (2) The fuel dispersion or surface-to-volume ratio of the fuel (3) The size, geometry, and surface-to-volume ratio of the roominvolved (4) The thermal properties, conductivity, specific heat, anddensity of the interior finish

The current state of the art of fire protection engineering is suchthat it is not possible to define clearly how all or even a few of thesevariables interact to influence exposure severity. However, thisgeneral discussion provides a guide to trends.

A.3.1.4 Pilot Ignition. In practice, a glowing ember or a flash offlame could constitute a high-temperature ignition source, whichoften serves to ignite the flammable gases and volatiles. Thismechanism differs from spontaneous ignition by radiation in whichthere is no local high-temperature igniting source and for whichhigher intensities of radiation are necessary.

A.3.2.1 Approved. The National Fire Protection Association doesnot approve, inspect, or certify any installations, procedures,equipment, or materials; nor does it approve or evaluate testinglaboratories. In determining the acceptability of installations,procedures, equipment, or materials, the authority havingjurisdiction may base acceptance on compliance with NFPA orother appropriate standards. In the absence of such standards,said authority may require evidence of proper installation,procedure, or use. The authority having jurisdiction may also referto the listings or labeling practices of an organization concernedwith product evaluations that is in a position to determinecompliance with appropriate standards for the current productionof listed items.

A.3.2.2 Authority Having Jurisdiction. The phrase authority havingjurisdiction is used in NFPA documents in a broad manner, sincejurisdictions and approval agencies vary, as do theirresponsibilities. Where public safety is primary, the authorityhaving jurisdiction may be a federal, state, local, or other regionaldepartment or individual such as a fire chief; fire marshal; chief ofa fire prevention bureau, labor department, or health department;building official; electrical inspector; or others having statutoryauthority. For insurance purposes, an insurance inspectiondepartment, rating bureau, or other insurance companyrepresentative may be the authority having jurisdiction. In manycircumstances, the property owner or his or her designated agent

assumes the role of the authority having jurisdiction; at governmentinstallations, the commanding officer or departmental official maybe the authority having jurisdiction.

A.4.3.7 Separation Distances. Table 4.3.7.3 determines the separationdistance necessary between two buildings so that pilot ignition ofthe exposed building or its contents is unlikely, assuming no meansof protection are installed in connection with either building.Guide numbers are obtained from this table.

Table 4.3.7.3 is based on a maximum tolerable level of incidentradiation (I) at the facade of an unprotected exposed building of12.5 kW/m2 (0.3 cal/cm2sec or 66 Btu/ft2min), assuming thefacade is constructed of typical cellulosic materials.

(a) Derivation of Table 4.3.7.3. The principles underlying thederivation of the separations specified in Table 4.3.7.3 arediscussed in detail in Fire and the Spatial Separation ofBuildings.

The spread of fire from one building to another across a vacantspace can be caused by convective or radiative heat transfer orflying brands. The hazard created by large flying brands was not aconsideration in these recommendations. Convective heat transferis also disregarded where the source of hazard is associated withopenings in the faade of the exposing building, because ignitionby radiation can occur at distances substantially greater than thoseat which flame impingement and convective heat transfer usuallyconstitute a hazard. Therefore, ignition as a result of radiative heattransfer is the event that these recommendations are intended tocombat.

The applicable equation that expresses the relationship forradiant heat transfer is I = IO, or the intensity at an exposedbuilding is equal to the unit intensity at the exposing buildingmultiplied by the configuration factor (), based on radiator size,geometry, and spatial distance.

The maximum tolerable level of radiation (I) at the faade of anunprotected exposed building has been established as 12.5 kW/m2(0.3 cal/cm2sec or 66 Btu/ft2min). This value, originally derivedfrom work of the Joint Fire Research Organization in the UnitedKingdom, is now generally accepted as that below which the pilotignition of most cellulosic materials is unlikely to occur.Substantially higher levels of radiation are necessary to causespontaneous ignition. It is believed that a local high-temperatureignition source usually is present; thus the selection of pilotignition is indicated. Where materials are located in an enclosureirradiated through a small opening, appreciably lower levels cancause ignition. This factor has been ignored because irradiationtimes of more than 30 minutes usually are involved.

Since Table 4.3.7.3 was created, new building materials, otherthan cellulosic products (wood), having greater or lesser ability toresist ignition have been developed. Greater separation distancesare needed for materials with greater propensity to ignite. Thoseoffering greater resistance to ignition can be separated at lesserdistances.

Information on the radiation levels (IO) near burning buildingswas established by a number of case histories and by a series ofexperimental burns known as the St. Lawrence Burns. The mostimportant findings of the latter experiments were that radiationlevels were related to the percentage of openings in building wallsand that combustible interior walls or ceiling linings give rise toparticularly high levels of radiation outside the building.

Another notable conclusion of the St. Lawrence Burns was thatmaximum radiation levels were not greatly affected by the type ofexterior covering. In all the experiments, the exterior walls werenot close to penetration by the fire during times of maximumradiation.

The St. Lawrence Burns produced maximum levels of radiationso high that protection against them would involve unduly largedistances of separation. However, much lower levels prevailed forat least the first 20 minutes. It was decided to base separationdistance recommendations on these lower values. It was believedthat the likelihood of fire department attendance at an early stageof a fire justified this approach. Subsequently, a field incident hasconfirmed that the recommended separations cannot beconsidered universally adequate and that an unusual combination


386

of adverse conditions could allow fire spread even where therecommended separation distances are used.

In calculating the recommended separations, a uniformrectangular radiator has been assumed, the emissive power beingtaken as proportional to the percentage of window openings. The

expression for the configuration factor, F , of a rectangularradiator at an elemental receiving surface (i.e., the ratio of theradiant intensity at the receiver to that at the radiator) is as follows:

F =2p

xx2 +y2

arctanz

x2 +y2

+

zy2 +z2

arctanx

y2 +z2

where:

x = half-length of rectangular radiating surfacez = half-height of rectangular radiating surfacey = separation distance between radiator and receiving surface

Three levels of radiation hazard from a burning building wereconsidered: light, moderate, and severe. For light, moderate, andsevere hazard levels, configuration factors of 0.14, 0.07, and 0.035,respectively, were adopted.

An additional value of 1.5 m (5 ft) was added to the computedvalues of separation distance to account for the horizontalprojection of flames from windows and to guard against the risk ofignition by direct flame impingement where small separations areinvolved.

(b) Uniformity of Openings. The derivation of Table 4.3.7.3assumes that openings are uniformly distributed on the facade andthat the separation (blank wall) between openings is small (i.e., nomore than one-third of the separation between the buildings).Where this is not the case, insufficient spatial separations can bepredicted. The following measures remedy this deficiencysubstantially:

(1) Where an area of the facade includes a large number ofwindows, a separate calculation should be made with respect to thesmallest rectangle conveniently including all the windows in thisarea. In many cases, a single window constitutes this rectangle. Thespatial separation chosen for this area should be the largest valuedetermined by any of the calculations involving the windows for thearea.

(2) Where the separation (blank wall) between openings isappreciably more than one-third of the separation between thebuildings (as provisionally estimated), an additional calculation fora single window should be made. If a higher building spatialseparation results, this value should be used.

It is fundamental to the derivation of Table 4.3.7.3 that a row ofresults relating to a percentage of window openings of less than 20percent (severe hazard), 10 percent (moderate hazard), or 5percent (light hazard) is not valid for inclusion in the table.Separations less than those provided by the first row of the tablecan, however, often be derived by considering individual windowsor groups of windows. The radiation level opposite a particularpoint on a facade is hardly influenced by radiation from a region ofthe facade further removed from the point than twice the estimatedseparation between buildings recommended. If windows or groupsof windows are separated by more than this distance (which islikely if the percentage of openings is small), individualcalculations are considered to be valid. The resulting buildingseparations then can be used even though they need to be lowerthan those that would be predicted in association with a large areaof facade and the smallest percentage opening area provided by thetable.

A.4.3.8 Derivation of Table 4.3.7.2. NFPA searched its photographicrecords of building fires in which flames penetrated the roof. Ofthe thousands of photographs examined, 176 showed flames aboveroofs at what appeared to be maximum or near maximum heights.No significant correlation between flame height and occupancy wasapparent, and, in fact, the principal relationship was the number ofstories involved in the fire. Table A.4.3.8 provides the average of theflame heights illustrated in some of the records. This table isreproduced from the May 1968 issue of Fire Journal.

Table A.4.3.8 Average Heights of Flames Penetrating Roofs

No. of Stories BurningFlame Height (in

stories) Above Roof1 1.42 1.83 2.24 2.65 2.96 3.1

The relationships shown in Table A.4.3.8 do not agree with thosesuggested by British and Japanese work based on theory andexperiments, which, in general, would produce much highervalues. The NFPA study does indicate that flame heights can begreat under unusual circumstances, such as the heavy involvementof liquid fuels. The recommendations provided here are notintended to provide adequate protection under suchcircumstances.

In the event of a moderate wind, flames can be expected toextend horizontally for as great a distance as they might otherwiseextend upward. For this reason, protection is recommended wherethe separation between two buildings is no more than the height towhich the flames could otherwise extend.

Varying reductions in separation distance for blank fire-resistivewalls with less than 3-hour ratings have not been made, becausecurrent test data are insufficient to evaluate appropriate reductionsproperly. It is hoped that future studies and tests will producevarying reductions with varying resistance ratings. Three-hour fire-resistance-rated walls are assumed to be clad with noncombustiblematerial.

A.5.6.3 Where the exposing building is properly protected byautomatic sprinklers, a fire in that building is assumed to becontrolled, and exposure, therefore, is also assumed to becontrolled.

A.5.6.4 Where the exposed building is properly protected byautomatic sprinklers, ignition within the exposed building ispossible where separation distances are less than thoserecommended or where means of protection are not provided onexposed openings, walls, or projections with lesser separationdistances. Such an ignition, however, is assumed to be controlledby sprinklers in the exposed structures.

Where water curtain protection is provided for exposed openingsin sprinklered buildings, as recommended in 5.6.1, such sprinklerscould be located on the inside of the building, adjacent to theopening being protected and in a position where the sprinkler cansense the exposing fire. Under these conditions, such sprinklerscould be of the closed type supplied by the wet pipe system withinthe building. Their water demand, however, should be calculatedin addition to or separate from the demand of the remainder of thesystem.

Appendix B Example

This annex is not a part of the recommendations of this document but isincluded for informational purposes only.

Construction:Walls: North 4-hour openings as illustrated

South 4-hour openings as illustratedEast 4-hour openings as illustratedWest Nonrated wall

Floors: Reinforced concrete 3 hoursFloor openings: 2-hour enclosuresRoof: 2 hoursInterior finish: Noncombustible, except ceiling of office has a

flame spread rating of 100

Occupancy:Second floor: OfficeFirst floor: Receiving and shipping

Manufacturing electronic partsWarehouse palletized storage to 7.9 m (26 ft ) in

height

Analysis of Exposure:North: Width of exposing fire, w 22.9 m (75 ft) (The

blank wall casts no exposure, and the wall is ofsufficient fire resistance to contain the expected fire.)


387

Height of exposing fire, h 4.6 m (15 ft). [The floor is ofsufficient fire resistance to contain the expected fire,and openings are protected. If openings in the floorare unprotected, h is 9.1 m (30 ft).]

Severity (from Tables 4.3.7.3 and 4.3.8.2):Office fire loading lightAverage interior finish moderateShipping and receiving fire loading moderateInterior finishlightSeverity moderate

w/h or h/w 22.9 m/4.6 m (75 ft/15 ft) = 5Percentage of openings 30 percentGuide number (from Table 4.3.7.3) 1.85Separation distance [1.85 4.6 m (15 ft)] + 1.5 m (5 ft)

= 8.5 m (28 ft) + 1.5 m (5 ft) = 10 m (33 ft)South: Exposure hazard from the two-story section of the

building is the same as the north wall. The one-storysection then should be calculated.

Width of exposing fire, w 38 m (125 ft)Height of exposing fire, h 4.6 m (15 ft)Severity (from Tables 4.3.7.3 and 4.3.8.2):

Fire loading moderateInterior finish light

Severity moderatew/h or h/w 38 m/4.6 m (125 ft/15 ft) = 8.3Percentage of openings 20 percentGuide number (from Table 4.3.7.3) 1.32Separation distance [1.32 4.6 m (15 ft)] + 1.5 m (5 ft)

= 6 m (20 ft) + 1.5 m (5 ft) = 7.6 m (25 ft)Separation distance from south wall, therefore, should

be 10 m (33 ft) (the recommended separationdistance from the two-story section, which iscalculated as greater than that from the one-storysection).

East: Width, w 61 m (200 ft)Height, h 4.6 m (15 ft)Severity moderatew/h or h/w 61 m/4.6 m (200 ft/15 ft) = 13.3Percentage of openings 80 percentGuide number 5.04Separation distance [5.04 4.6 m (15 ft)] + 1.5 m (5 ft)

= 23 m (75.6 ft) + 1.5 m (5 ft) = 24.6 m (80.6 ft)West: Manufacturing area:

Width, w 30.5 m (100 ft)Height, h 4.6 m (15 ft)Severity moderatew/h or h/w 30.5 m/4.6 m (100 ft/15 ft) = 6.7Percentage of openings 100 percent (nonrated wall)Guide number 4.89Separation distance [4.89 4.6 m (15 ft)] + 1.5 m (5 ft)

= 22.4 m (73.4 ft) + 1.5 m (5 ft) = 23.9 m (78.4 ft)Warehouse:Width, w 30.5 m (100 ft)Height, h 9.1 m (30 ft)Severity (from Tables 4.3.7.3 and 4.3.8.2):

Fire loading severeInterior f inish lightSeverity severe

w/h or h/w 30.5 m/9.1 m (100 ft/30 ft) = 3.3Percentage of openings 100 percentGuide number 5.27Separation distance [5.27 9.1 m (30 ft)] + 1.5 m (5

ft) = 48.1 m (158.1 ft) + 1.5 m (5 ft) = 49.7 m (163.1ft)

38 m(125 ft)

22.9 m(75 ft)

4.6 m (15 ft)Blank masonry wall

61 m(200 ft)

Shipp

ing do

ck do

ors

Wind

ows

3(1

4.6 m(15 ft)

War

ehou

se

Man

ufac

turin

g

Warehouse

Manufacturing

1 story to 2 stories2 stories

1 story4-hr wall

4-hr

wall

2-hr

wallOffic

e, 2

d sto

ryRe

ceivi

ng an

d ship

ping,

1st s

tory

East

Wes

t

North

South

4.6 m (15 ft)

3(

Figure B.1 Illustration for example of application of NFPA 80A.

80A-A2001-rop

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