FMDS0120 Protection Against Exterior Fire Exposure

7/25/2019 FMDS0120 Protection Against Exterior Fire Exposure

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January 2007

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PROTECTION AGAINST EXTERIOR FIRE EXPOSURE

Table of Contents Page1.0 SCOPE ................................................................................................................................................... 3

1.1 Changes .......................................................................................................................................... 3

2.0 LOSS PREVENTION RECOMMENDATIONS ....................................................................................... 3

2.1 For Fire Exposure from Buildings .................................................................................................... 3

2.1.1 Construction and Location .................................................................................................... 3

2.2 For Fire Exposure from Yard Storage ........................................................................................... 10

2.2.1 Construction and Location .................................................................................................. 10

3.0 EXPOSURE FIRES (GENERAL) ......................................................................................................... 12

3.1 Exposing Building .......................................................................................................................... 12

3.1.1 Construction ........................................................................................................................ 12

3.1.2 Ventilation ............................................................................................................................ 13

3.1.3 Wind .................................................................................................................................... 133.1.4 Effect of Fire Department .................................................................................................... 13

3.1.5 Length of Wall Creating the Fire Exposure ......................................................................... 13

3.2 Exposed Building ........................................................................................................................... 13

3.2.1 When Not Sprinklered ......................................................................................................... 13

3.2.2 Construction ........................................................................................................................ 13

3.2.3 Protection of Openings ........................................................................................................ 13

3.2.4 Protection Beyond Ends of Exposing Building ................................................................... 14

3.2.5 Protection of Side Walls ...................................................................................................... 15

3.2.6 Protection when Walls at an Angle with Exposing Building ................................................ 16

3.2.7 Protection for Roof When Lower Than Exposing Building ................................................. 18

3.2.8 Protection of Walls Above Lower Exposing Building .......................................................... 18

3.3 Fire Exposure From Yard Storage ................................................................................................ 20

3.4 Yard Housekeeping ....................................................................................................................... 20

4.0 REFERENCES ..................................................................................................................................... 23

4.1 FM Global ...................................................................................................................................... 23

4.2 National Institute of Standards and Technology ............................................................................ 23

APPENDIX A GLOSSARY OF TERMS ...................................................................................................... 23

APPENDIX B DOCUMENT REVISION HISTORY ..................................................................................... 24

List of FiguresJob Aid No. 1 for Using Tables 1 and 2. ........................................................................................................ 4

Job Aid No. 2 for Yard Storage. .................................................................................................................. 10

Fig. 1. Exposed building walls are longer than exposing walls. .................................................................. 14

Fig. 2. Protection for side walls of exposed building. .................................................................................. 17

Fig. 3. Protection for exposed building when walls are at an angle () with exposing building. ............... 18

Fig. 4a. Protection for exposed buildings higher than the exposing building. ........................................... 20

Fig. 4b. Protection of walls above the exposure (English units). ................................................................ 21Fig. 4c. Protection of walls above the exposure (SI Units). ........................................................................ 22

List of TablesTable 1a. Determination of Separation Distance, or Exposure Category for Use in Table 2When Exposed

Wall is 1, 2 or 3 hour ..................................................................................................................... 5

Table 1b. Determination of Separation Distance, or Exposure Category for Use in Table 2 When Exposed

Wall is Category C ......................................................................................................................... 6

FM GlobalProperty Loss Prevention Data Sheets 1-20

2007 Factory Mutual I nsurance Company. All rights reserved. No part of this document may be reproduced,stored in a retrieval system, or transmitted, in whole or in part, in any form or by any means, electronic, mechanical,photocopying, recording, or otherwise, without written permission of Factory Mutual Insurance Company.


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Table 1c. Determination of Separation Distance, or Exposure Category for Use in Table 2

When Exposed Wall is Category D ................................................................................................ 7

Table 2. Multipliers for Space Separation ...................................................................................................... 8

Table 3. Levels of Passive Protection, P .................................................................................................... 15

Table 4. Protection for Longer Exposed Walls ............................................................................................ 15

Table 5. Multipliers for Non-Parallel Exposures .......................................................................................... 16

1-20 Protection Against Exterior Fire ExposurePage 2 FM Global Property Loss Prevention Data Sheets

2007 Factory Mutual Insurance Company. All rights reserved.


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1.0 SCOPE

This data sheet provides guidelines for recognizing and dealing with a potential fire exposure from one or

more existing buildings or yard storage. Another objective is to enable designers and architects to avoid

exposure problems when laying out new buildings.

This data sheet does not discuss fire exposure from flammable liquid transmission pipelines. For discussionon that subject, refer to Data Sheet 7-32, Flammable Liquid Operations.

This data sheet generally considers the fire exposure to be on adjacent property, where control of the exposure

may be outside the influence of the owner of the exposed building. The data sheet may also be used, if

applicable, when the fire exposure and the exposed building are on the same insured property and the

exposing building is not adequately sprinklered. The latter case is infrequent. Provision of automatic sprinklers

in the exposing buildings would greatly reduce the hazard. This data sheet assumes that unimpaired sprinkler

protection is available in the exposed building. Refer to section 2.2.2 of Data Sheet 1-22, Maximum

Foreseeable Loss Limiting Factorswhen using this data sheet to calculate space separation for maximum

foreseeable loss.

This document should not be used for exposing flammable liquids storage buildings that are unsprinklered.

Refer to Data Sheet 7-29, Flammable Liquid Storage in Portable Containers for separation of flammable

liquid yard storage pads, and separation and protection of detached, sprinklered flammable liquid storage

buildings.

For the recommended separation from storage tanks in the yard, refer to Data Sheet 1-57, Rigid Plastic

Building Materialsor Data Sheet 7-88, Storage Tanks for Flammable and Combustible Liquids.

This document is not intended to be used for exposure protection from another tenant within the same

multi-tenanted building. For such situations refer to Data Sheet 1-19, Fire Walls, Subdivisions and Draft

Curtainsor Data Sheet 1-22.

For a description of storage commodities, see Data Sheet 8-1, Commodity Classification.

1.1 Changes

January 2007. Minor editorial changes were made.

2.0 LOSS PREVENTION RECOMMENDATIONS

2.1 For Fire Exposure from Buildings

2.1.1 Construction and Location

2.1.1.1 When the exposing building is sprinklered, and it can be established that the sprinkler protection in

the exposing building is adequate and reliable, no fire exposure is considered to exist.

2.1.1.2 Exposed buildings should be separated from exposures according to Tables 1 and 2. Job Aid No. 1

should be used to facilitate the use of these tables.

If an existing building is nearer to the exposure than the recommended separation distances determined

from Tables 1 and 2, passive protection such as the provision of a fire-rated wall over the outside face, or

active protection such as the provision of automatic outside sprinklers will provide the needed protection. For

example, the provision of two layers of 58 in. (15 mm)-thick Type X gypsum board faced with steel panels,

applied to the wall exterior will provide 1-hour fire resistance. For various combinations of protection usingmasonry, see Data Sheet 1-21, Fire Resistance of Building Assemblies.

The categories of construction materials used for Table 1 are not based on the combustibility of a material

only. Consideration is also given to the ease of ignition, and the potential for burn through or melting as it

relates to an exposing building giving off radiant heat and an exposing building resisting it.

CAT. A. Category A materials include steel faced panels or cementitious panels, with or without

noncombustible insulation (as defined in Section 1.1). It also includes FM Approved (see Appendix A for

definition), steel faced class 1 insulated panels on steel framing; and EIFS assemblies using noncombustible

insulation or Approved class 1 insulation over gypsum board on steel framing.

CAT. B. Category B materials include painted, unpainted or asphalt shingled wood; rigid plastic panels such

as fiberglass reinforced plastic (FRP) or polyvinyl chloride (PVC); any aluminum panels; EIFS assemblies

Protection Against Exterior Fire Exposure 1-20FM Global Property Loss Prevention Data Sheets Page 3



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using EPS insulation or a combustible sheathing board; non-Approved insulated steel panels; or other

assemblies supported by wood framing that is unprotected on the interior.

CAT. C. Category C materials include Approved Class 1 insulated, steel or aluminum faced sandwich panels

with thermoset plastic insulation; EIFS assemblies having noncombustible insulation and gypsum board

sheathing; and aluminum or steel panels that are uninsulated or insulated with noncombustible insulationsuch as glass fiber, mineral wool, or expanded glass. It also includes cementitious panels or shingles over

steel or wood.

CAT D. Category D materials include painted or unpainted wood, metal faced wall assemblies with

thermoplastic insulation such as expanded or extruded polystyrene, or polyethylene; metal faced panels with

thermoset insulation, such as polyurethane or polyisocyanurate foam, which are not Approved; all rigid plastic

panels such as FRP or PVC; and EIFS assemblies having EPS insulation or a combustible sheathing board.

1. For additional details on exposing construction, refer to Appendix A and 3.1.1.

2. For additional details on the exposing occupancy, refer to Appendix A.

3. For additional details on the exposed wall construction, refer to Appendix A and 3.2.2.

Job Aid No. 1 for Using Tables 1 and 2.

1. Details include wall and roof construction type, percent window openings (include door openings if doorconstruction has a lesser fire rating than the wall), exposing wall height and width.

2. Details include exposed wall construction type, details of unprotected openings and roof construction type.




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Table 1a. Determination of Separation Distance, or Exposure Category for Use in Table 2When Exposed Wall is 1, 2 or 3 hour

ExposedWall Exposing Building Percent Unprotected Openings in Exposing Wall

Construction Wall Roof Occupancy Category for Use in Table 2 or Minimum Separation Required

3 hr SFR NC, Class 1orCombustible

Light,Ordinaryor High

DNANo minimum separation required

3 hr Cat. A NC, Class 1or

Combustible

Light orOrdinary

DNA

No minimum separation required

3 hr Cat. A NC, Class 1or

Combustible

High 70% 70%


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Table 1b. Determination of Separation Distance, or Exposure Category for Use in Table 2When Exposed Wall is Category C

CAT. C.: Category C materials include FM Approved Class 1 insulated, steel or aluminum faced sandwich panels withthermoset plastic insulation; EIFS assemblies having noncombustible insulation and gypsum board sheathing;

and aluminum or steel panels that are uninsulated or insulated with noncombustible insulation such as glass fiber,mineral wool, or expanded glass. It also includes cementitious panels or shingles over steel or wood.

ExposedWall Exposing Building Percent Unprotected Openings in ExposingWall


Cat. C SFR NC orClass 1

Light 0%, 40% 60% 80% 100%

1 2 3 4

Cat. C SFR NC orClass 1

Ordinary 0%, 30% 50% 80% 100%

1 2 3 4

Cat. C SFR NC, Class 1or

Combustible

High 0%, 25% 50% 80% 100%

6 7 8 9

Cat. C SFR Combustible Light 0%, 30% 50% 80% 100%

1 2 3 4

Cat. C SFR Combusti ble Ordi nary 20% 40% 60% 80% 100%

1 2 3 4 5

Cat. C Cat. A NC orClass 1 Light 0%, 25% 50% 70% 100%1 2 3 4

Cat. C Cat. A NC orClass 1

Ordinary 0%, 10% 30% 60% 100%

1 2 3 4

Cat. C Cat. A NC, Class 1or

Combustible

High 0%, 5% 30% 60% 100%

6 7 8 9

Cat. C Cat. A Combustible Light 0%, 10% 30% 60% 100%

1 2 3 4

Cat. C Cat. A Combustible Ordinary 0% 20% 40% 60% 100%

1 2 3 4 5

Cat. C Cat. B NC orClass 1

Light DNA

6

Cat. C Cat. B NC orClass 1

Ordinary DNA

7

Cat. C Cat. B NC, Class 1or

Combustible

High DNA

9

Cat. C Cat. B Combustible Light orOrdinary

DNA

7

For explanation of Combustible, Stable Fire Resistive (SFR), Noncombustible (NC), or Class 1, see Appendix A.




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Table 1c. Determination of Separation Distance, or Exposure Category for Use in Table 2When Exposed Wall is Category D

CAT. D: Category D materials include painted or unpainted wood, metal faced wall assemblies with thermoplastic insulationsuch as expanded or extruded polystyrene, or polyethylene; metal faced panels with thermoset insulation, such

as polyurethane or polyisocyanurate foam, which are not FM Approved; all rigid plastic such as FRP or PVC;and EIFS assemblies having EPS insulation or a combustible sheathing board.

ExposedWall Exposing Building Percent Unprotected Openings in ExposingWall


Cat. D SFR NC orClass 1

Light 0% 25% 40% 50% 60% 80% 100%

1 2 3 4 5 6 7

Cat. D SFR NC orClass 1

Ordinary 0% 10% 20% 30% 50% 60% 80% 100%

3 4 5 6 7 8 9 10

Cat. D SFR NC, Class 1or

Combustible

High 0%,15% 40% 60% 80% 100%

9 10 11 12 13

Cat. D SFR Combusti ble Light orOrdinary

0% 10% 20% 30% 50% 60% 80% 100%

3 4 5 6 7 8 9 10

Cat. D Cat. A NC orClass 1

Light 0% 20% 30% 40% 60% 100%

2 3 4 5 6 7

Cat. D Cat. A NC, Class 1 orCombustible

Combustible

Ordinary

Light

0% 10% 30% 40% 60% 100%

5 6 7 8 9 10

Cat. D Cat. A NC, Class 1or

Combustible

High 0% 40% 60% 100%

10 11 12 13

Cat. D Cat. B NC or Class1

Light DNA

10

Cat. D Cat. B NC or Class1

Ordinary DNA

11

Cat. D Cat. B NC, Class 1or

Combustible

High DNA

13

Cat. D Cat. B Combustible Light DNA

11

Cat. D Cat. B Combustible Ordinary DNA12

For explanation of Combustible, Stable Fire Resistive (SFR), Noncombustible (NC), or Class 1, see Appendix A.




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Table 2. Multipliers for Space Separation

Category

Number

L/H or H/L of Exposing Wall (whichever is greater than 1.0)

L = length in ft (m), H = height in ft (m)

1.0 1.3 1.6 2.0 2.5 3.2 4. 5. 6. 8. 10. 13. 16. 20. 25. 32. 40

or

higherSeparation Multiplier

(multiply by lesser dimension, add 5 feet, (1.5 m) to obtain building-to-building separation)

1 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

2 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

3 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

4 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

5 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

6 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

7 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

8 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

9 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

10 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

11 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

12 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 10.05 10.50 10.84

13 2.96 3.32 3.72 4.16 4.65 5.19 5.78 6.43 7.13 7.88 8.67 9.50 10.33 11.15 11.91 12.59 13.15

Additional comments regarding the use of Table 2 are as follows:

1. If the wall and roof of the exposing building are stable fire resistive (SFR) and there are no wall openings

or roof openings (such as skylights or heat and smoke vents), no minimum separation is needed.

2. If the wall of the exposed building is asphalt shingle over wood or asphalt coated metal (ACM), increase

the space separation recommended for Category D exposed walls by 25%.

3. If adequate horizontal or vertical fire cutoffs exist in the exposing building, they may be used to reduce

the L/H (length/height) ratio and lesser exposure dimension as applicable.

4. It is reasonably accurate to interpolate between aspect ratios.

5. If the exposed construction is of a type noted in Category D, asphalt shingle or ACM, the space separation

need not exceed 300 ft (91 m), regardless of other parameters in Table 1 and Table 2. For all other types

of exposed construction, the space separation need not exceed 200 ft (61 m).

6. Where the occupancy is light or ordinary and the walls, roof and interior finish are all noncombustible,

the height of the storage can be used to determine the L/H ratio.

7. For light occupancy classifications with combustible interior finish, increase the occupancy classification

by one level. This applies to buildings that have combustible ceilings, combustible interior walls or wood

floors.

8. For exposing buildings that are multistory with wood floors, use high hazard exposure.

9. For existing buildings where the exposing building is considerably longer than the exposed building,L

may be effectively taken to be four times the actual separation distance if that distance is less than the actual

length of the exposing building.

While this method may be used for proposed installations, it may involve several iterations if the originally

proposed space is less than needed. In each successive iteration the effective length must be increased until

the proposed space is at least equal to the needed space. A more simplified approach is to use the entire

length of the exposing building which may yield a more conservative answer.




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2.1.1.3 Where the exposure and space separation is such that a 2- or 3-hour fire rated exposed wall is needed,

window openings need to be filled in with masonry or protected by automatic closing, shutters comparable

in fire rating to that of the wall. Approved minimum 112-hour fire rated doors that are normally closed (equipped

with a door closure) or automatic closing and latched should be provided in door openings (blank steel doors

suitable for a class D opening). If the space separation provided is at least 5 ft (1.5 m), an alternative is to

provide listed (tested by a nationally recognized laboratory) fire rated glass (such as ceramic glass, glass blockor wired glass that has passed a hose stream test, see Data Sheet 1-21) and automatic window sprinklers.

2.1.1.4 Where the exposure and space separation is such that a 1-hour fire rated exposed wall is needed,

listed minimum 34 hour fire rated glass should be installed in window openings in accordance with area

limitations of the listing. Combustibles should be kept away from the inside of the exposed windows by a

distance at least equal to the largest dimension of the window.

Door openings should be protected by Approved, minimum34-hour fire rated fire doors (suitable for a Class E

exterior opening). The doors should be normally closed (self-closing) or automatic closing, and latched.

2.1.1.5 Where the exposed wall needs to be of a type outlined in Category C of Table 1, windows should

be tempered glass.

Where the exposure and space separation is such that a Category C exposed wall is needed, doors on the

exposed wall should be normally closed (self-closing) or automatic closing, and latched steel doors that are

either blank or have vision panels made of fire rated or tempered glass.

2.1.1.6 Where window or outside sprinklers are needed, they should be installed according to Data Sheet

2-8N,NFPA 13 Standard for the Installation of Sprinkler Systems 1996 Edition. They should be arranged for

automatic operation.

Window sprinklers can be considered an alternative to upgrading the type of glass, except where 2-or-3 hour

fire rated exposed walls are needed and listed fire rated glass and sprinklers must be provided.

2.1.1.7 Combustible materials should not be stored or used within the separation space. When combustibles

are stored within a space between buildings, adequate space separation should be provided between the

yard storage and the buildings on both sides (see Section 3.0). The storage of fuels or chemicals near the

interior side of an exposed wall should be avoided.

2.1.1.8 Exposed roof coverings, or portions thereof, should have a Class A roof system, based on the

American Society for Testing and Materials (ASTM) test standard E 108, in the following areas:a) Where they are within a distance of 150 ft (46 m) from a building constructed with a wood roof, walls

or floors, or combustible yard storage.

b) On the entire roof of buildings subdivided by Maximum Foreseeable Loss (MFL) fire walls. See Data

Sheet 1-22 for an explanation and details of additional protection that may be needed for the roof.

c) Where the occupancy below the roof is susceptible to water, smoke or other nonthermal damage.

When the roof of the exposed building is lower than the exposing building, protection for the roof should

be provided within 50 ft (15 m) from the exposure as outlined below:

a) For built-up roof coverings (BUR), place a minimum of 4 lb/ft 2 (20 kg/m2) of pea gravel in a flood coat

of hot asphalt or coal tar.

b) For single-ply roof coverings, large stone ballast or concrete paver blocks should be provided as outlined

in Data Sheet1-29, Roof Deck Securement and Above-Deck Roof Components.

2.1.1.9 When any significant exterior fire exposure exists, the fire department should conduct prefire planning

taking into consideration protection of the exposed property.

2.1.1.10 Exposing buildings that are of noncombustible or fire resistive construction and that are vacant or

contain only noncombustible contents do not necessitate space separation or other protection for adjacent

buildings.

2.1.1.11 When the exposed wall is longer than the exposing wall, protection beyond the end(s) of the exposing

building should be provided according to Section 3.2.4.

2.1.1.12 When the exposed wall is shorter than the exposing wall, protection for the end walls of the exposed

building should be provided according to Section 3.2.5.




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2.1.1.13 When the exposed building is not parallel to the exposing wall, protection for the exposed walls

should be provided according to Section 3.2.6.

2.1.1.14 When the exposed wall is higher than the exposing wall, and the separation distance between the

two buildings is less than needed according to Recommendation 2.1.1.2, protection for the higher portions

of the exposed wall should be provided according to Section 3.2.8.2.1.1.15 If a combustible (see Appendix A) canopy or overhanging eave is provided on the exposed building,

the separation distance between the exposing building and the outer edge of the canopy or overhang should

be based on Category D exposed construction, regardless of the type of wall construction. Alternatively,

separation which is adequate for the wall construction is acceptable provided the combustible canopy or

overhang is sheathed with a material having fire resistance at least equal to that of the wall.

2.1.1.16 In some cases the potential for non-thermal damage to the contents of an exposed building will

be significant. If so, automatic closing dampers should be provided on outside air intakes. For new

construction, outside air intakes should be located as close to grade level as practical.

2.1.1.17 The most likely time for a major exposure fire to occur is during the demolition of adjacent property.

Precautions for such demolition operations are outlined in Data Sheet 1-0, Safeguards During Construction,

Alteration and Demolitionand should be followed.

2.2 For Fire Exposure from Yard Storage

Use Job Aid No. 2 to facilitate the application of recommendations in this section.

2.2.1 Construction and Location

2.2.1.1 Refer to Section 3.3 for a list of various outdoor storages that are covered by other data sheets. Use

this document to supplement those or where no other specific data sheet exists. For the exterior protection

of the roof systems, see Section 2.2.1.8.

Job Aid No. 2 for Yard Storage.




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2.2.1.2 When large quantities of high-value products are stored in the yard, consideration should be given

to a sprinklered enclosure over them. This will a) protect the products themselves from fire, and b) reduce the

hazard of exposure to nearby buildings.

2.2.1.3 Yard hydrants should be provided when combustible materials are stored outside the plant buildings

(Data Sheet 3-10, Installation and Maintenance of Private Fire Service Mains and their Appurtenances).Hydrants should be provided just outside the ends of spaces between buildings and at intervals in between

not exceeding 300 ft (90 m).

2.2.1.4 Relocating the yard storage so that separation distances are adequate is preferable to special

exposure protection.

For ordinary or light hazard yard storage with all types of exposed walls, and for high hazard yard storage

with all types of exposed walls except Category D (Appendix A), use Tables 1 and 2 to determine needed

space separation. Treat the yard storage as an exposing building, assuming the wall and roof of the exposing

building are a Category A type and noncombustible, respectively, with 100% openings in the exposing wall and

using the applicable details of the occupancy and exposed walls.

Tables 1 and 2 should not be used to determine space separation between yard storage classified as high

hazard and exposed Category D walls. For such situations the following formula should be used:

(Equation 1)

S = 3.07LH

or

(Equation 2)

S = 16 H

where: S = minimum recommended space separation, ft (m)

L = Length of the yard storage in the direction parallel to the exposure, ft (m)

H = Height of the yard storage, ft (m)

Use Equation 1 when L 24 H

Use Equation 2 when L > 24 H

Use Equation 1 and 2 only for yard storage of high hazard materials exposing combustible walls.

When storage is in a yard, it is reasonable to assume that the maximum length (parallel to the exposed wall)across which a fire in any commodity will burn at its maximum rate of heat release is about 400 ft (122 m).

In other words, the maximum length (L) used in determining the needed separation distance is 400 ft

(122 m).

Because of other factors such as re-radiation, more rapid fire spread could be expected throughout the entire

fire cutoff area of a building.

Consequently, this maximum length should not be used to determine building-to-building separation.

Where adequate space separation is not available, and provision of a protected enclosure for the yard storage

is not practical, provide water spray protection for the exposed building as outlined in Data Sheet 2-8N.

2.2.1.5 Unpaved yards should be mowed so that the height of grass and weeds does not exceed 4 in.

(100 mm). All combustible trash should be removed from the premises.

2.2.1.6 Dumpsters (rubbish skips) should be located at least 35 ft (11 m) from exposed buildings, unlessthe exposed walls are of blank masonry or concrete construction.

2.2.1.7 Loaded trailers stored in the yard should be treated as a building separation would, taking into

consideration the contents and construction of the trailer.

2.2.1.8 Metal chain link fencing should be provided around the yard, with an adjacent aisle space between

it and yard storage to prevent direct access by vandals. (See Data Sheet 9-17, Protection Against Arson

and Other Incendiary Fires.)




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3.0 EXPOSURE FIRES (GENERAL)

When evaluating the magnitude of the exposure fire, the type of construction; area, percent wall openings

and occupancy of the exposure should be considered. Consideration should also be given to the type of wall

and roof exposed to the radiant heat.

Recommended separations are based on estimated portions of the exposing flame height that is unobscuredby smoke. For applications simplicity, exposing wall or storage heights are used for input.

A fire that results in ignition of or radiant heat damage to nearby buildings or other property is an exposure

fire. In many large exposure fires, the origin of the fire has been on neighboring or adjoining property. Plant

buildings also have been exposed and damaged by exposure fires starting in yard storages such as lumber,

roll paper, tires, plastics, etc., or in separate, unsprinklered structures. Automatic sprinklers and firefighters

usually control the fire and keep it from spreading throughout the exposed building, although heat, water and

smoke damage may be considerable.

1. It is necessary to consider fire exposure protection (to buildings) from a fire in adjacent buildings or yard

storage when:

a) Separation distances are close enough so that a hazard to the exposed building is judged to exist,

and

b) Any one of the exposing properties is unsprinklered, or has sprinkler protection that is inadequate or

is not considered reliable.

Once a fire exposure hazard is judged to exist, guidelines in this data sheet can be used to determine if

separation distances between the exposing and exposed buildings are safe for the degree of protection

afforded by the construction and sprinklers in the exposed building, or if protection for the exposed building

is needed.

Protection may be active,in which case water is applied directly to the exposed building during a fire, or

passive, in which the exposed building is coated or shielded with a noncombustible or fire resistive material,

or a large space separation is provided.

Protection needed for the exposed buildings depends on the size and intensity of the exposure fire, the

horizontal distance from the fire, and the position of the exposed portion in relation to the fire. The growth

of a building fire will depend on a) the nature and quantity of combustibles in the building construction and

occupancy, b) the amount of ventilation air, c) external factors such as wind velocity, promptness of detection,proximity of the local fire department, and available water supplies. In the vast majority of cases, it is

reasonable to assume that there will be sufficient ventilation air to feed the fire.

Table 1 combines construction and occupancy to give various degrees of fire exposure classification, and

assumes that conditions are favorable for a free-burning fire.

3.1 Exposing Building

3.1.1 Construction

If the exposing building is fire resistive such that the floor and/or roof deck, the framing and the exposing

exterior wall (must be blank) are at least adequate for the expected exposure fire duration (so as to contain

the exposure fire), no separation is needed for the exposed building.

Exposing walls are categorized as either stable fire resistive, Category A or Category B.

If a wall is fire resistive but tied to unprotected steel framing, for example, it may partially collapse as the

steel fails early in a fire and is not considered stable. Such an assembly should be treated as Category A.

Category A groups exposing materials that have some fire resistance or a high melting temperature that

will not burn through. Consideration is given to the fact that some breakage or opening of panel joints may

occur during the fire.

Category B groups exposing materials that may burn through with a significant fire exposure, or may melt

at fire temperatures, eventually allowing the exposed wall to feel the full effect of radiation.

Masonry walls may be brick, concrete block or stone. Noncombustible (NC) walls have less fire resistance

and are curtain walls constructed of panels such as protected metal, corrugated iron or cementitious panels




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on steel frame. Combustible walls may consist of wood or rigid plastic building materials. Wood walls with

an exterior veneer of stucco, brick, masonry, etc., are considered to be Category B (Table 1) when considered

as the exposing building (fire exposure from its interior), but is fire resistive when exposed from the exterior.

The presence of cementitious shingles over exposed wood walls lessens space separation needed, while

the presence of asphalt shingles over exposed wood walls increases the space separation needed.

3.1.2 Ventilation

The exposure classifications given in Table 1 are based on well ventilated fires in the exposing buildings

with adequate air supply to support the fire growth. Openings or spaces in the building wall are necessary

to admit combustion air, while openings in the roof (vents, skylights, etc.) will discharge hot gases and allow

entry of additional air to aid in the fire development. There is normally enough air within a building to feed

a fire in the early stages. Typically openings are present or will develop in the early stages of a fire (windows

or skylights break, heat and smoke vents open, combustible construction burns, steel panels buckle,

aluminum panels melt, etc.). Consequently it is safe to assume there will be adequate ventilation for an

exposure fire in the vast majority of cases.

3.1.3 Wind

When the exposed building walls are combustible, it is assumed that wind will carry a spark or ember to

the exposed wall and pilot-ignite the surface.

3.1.4 Effect of Fire Department

The exposure categories (as determined by using Table 1) are based on full flame front at the exposure

fire, however, long exposures to combustible materials could still cause ignition. It is assumed that the fire

department and site conditions are adequate for the fire conditions, and that only a brief delay between ignition

and fire department set up will be experienced.

3.1.5 Length of Wall Creating the Fire Exposure

The relative exposure categories given in Table 1 are determined from the nature of the construction and

occupancy in the exposing building, and the construction in the exposed building. An additional factor,

however, is the aspect ratio of the potential flame front or the length/height or height/length ratio of the

exposing wall. When two buildings are exposed by a rectangular building, the building exposed by the longer

wall will experience the greater fire exposure, provided both walls are the same height and are fully aflame.

Table 2 reflects the effect of the relative size of the flame front.

3.2 Exposed Building

3.2.1 When Not Sprinklered

The exposed building will usually be sprinklered. If unsprinklered, but in need of sprinklers, sprinklers should

be recommended. When not in need of sprinklers, the separation distances determined from Tables 1 and

2 still apply.

3.2.2 Construction

Construction types and categories are described in Sections 1.0 and 2.0.

3.2.3 Protection of Openings

Category D Walls. Exposed walls having a combustible exterior surface are about as vulnerable to fire

exposure as ordinary doors and windows. Installation of fire doors and fire rated glass windows would serve

little purpose. When the separation distance is adequate for Category D exposed walls, ordinary doors and

windows can be tolerated.

Category C Walls. Where separation distances are adequate for noncombustible construction, self-closing

or automatic closing steel doors that are blank or have fire rated or tempered glass vision panels may be

considered equivalent to the wall in fire resistance.




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Levels of exposed wall passive protection are ranked from best to worst as outlined in Table 3.

Table 3. Levels of Passive Protection, P

3 Hour Fire Rated

2 Hour Fire Rated1 Hour Fire Rated

Category C*

Category D*

* see footnotes to Table 1

For example, Category C is one level down from 1 hour fire rated. The protection of openings should be

as outlined in Section 2.0 and 3.2.3 for the respective level of passive wall protection.

Table 4. Protection for Longer Exposed Walls

Location of Exposed Wall with

Respect to Exposing Wall Directly across 15 15 < 30 30 < 45

Designation on Fig. 1 x 1 x 2 x 3 x 4Distance Protection is Needed For L 0.25S 0.25S 0.5S

Level of Protection* P P P-1 P-2

S = Separation distance needed per Tables 1 and 2. If the actual separation distance dis greater than

Sfor the type of exposed wall construction provided, the distance (X1, X2 or X3) that passive or active

protection is needed for openings should be based onS and notd. IfS is less than 40 ft (12.2 m) provide

a level of protection P, P-1 and P-2, of at least 10 ft (3.0 m), 10 ft (3.0 m) and 20 ft (6.1 m), respectively,

beyond the end of the exposing wall.

P = Level of passive protection needed per Tables 1 and 2. For details on protection of openings or alternative

sprinkler protection, see Section 2.0 and 3.2.3.

P-1 = One level of passive protection less than needed per Tables 1 and 2 for the separation provided.

P-2 = Two levels of passive protection less than needed per Tables 1 and 2 for the separation provided.

L = Length of the exposing building.

3.2.5 Protection of Side Walls

When the separation between buildings is adequate for the type of construction available, no additional

protection is needed for the exposed wall or adjacent sidewall (exterior wall perpendicular to the exposed

wall, see Fig. 2). When separation is inadequate for the exposed construction and passive protection or

outside sprinklers are recommended for the exposed wall, and the exposure is longer than the exposed wall,

protection will also be needed for some portion of the side wall of the exposed building. In such cases:

a) Determine (using Tables 1 and 2) the safe separation distance (S) needed for that construction.

b) Multiply that figure by 0.5. The result is the distance out from the face of the exposing building that

protection is needed for the exposed building side walls.

c) Subtract from this the actual separation distance (d) to arrive at (X), the length of the side wall that

needs outside sprinkler protection (Fig. 2), or passive protection including the protection of openings, as

outlined in Section 2.0.

Outside sprinklers will protect the front wall, if it is at least 5 ft (1.5 m) away from the exposure. If the actual

separation distance (d) is at least equal to 0.5 S, no side wall protection is needed.

When the exposed building is fire resistive (such as masonry), having adequate separation for the wall, but

having openings, openings need to be filled in with material of sufficient fire resistance along the front wall

(or comparably protected) and possibly for some distance along the side wall. To determine this distance:

a) Using Tables 1 and 2, determine the needed separation distance (S).




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b) Multiply that figure by 0.5. The result is the distance out from the face of the exposing building to where

filling in or other protection of the openings in the exposed side wall is needed.

c) Subtract d from this to determine X (See Fig. 2).

The same procedure can be used for determining how far beyond that more fire resistant glass alone is

needed (See Section 3.2.3), by multiplying 0.5 times S needed for combustible exposed walls (point beyondwhich plain glass windows are acceptable).

3.2.6 Protection when Walls at an Angle with Exposing Building

The safe separation distances determined from Table 1 and 2 are for cases in which the exposed and exposing

walls are nearly parallel. In that situation the exposed wall feels the most radiation. When heat radiation falls

on a wall whose angle is greater than 15 with the exposing wall, the reduced intensity of radiation may

be taken into account. This may be done by use of the multiplier (M) shown in Table 5.

Table 5. Multipliers for Non-Parallel Exposures

(This is the angle between the exposing wall and the exposed wall.) M

015 1.00

1530 0.92

3045 0.84

4560 0.75

6075 0.66

7590 0.58

90 0.50

Example 3.2.6.1:

In Figure 3, the distance out from the exposing wall to the point where protection is needed may be determined

as follows (assumeis between 15D and 30D for the west exposed wall and between 60-75for the south

exposed wall): Assume the exposure is such that the masonry walls are adequate. But if the exposed walls

were parallel to the exposing wall, the separation distance within which openings (currently tempered glass)

need bricking in or fire rated glass and window sprinklers is 30 ft (9.1 m). From Table 5, the multiplier (M)

is 0.92 for the longer west wall and 0.66 for the shorter south wall. It is necessary only to adjust the separationby using the multiplier, which varies with the angle .

The same procedure may be used to determine how far out from the exposing wall that fire rated glass alone

should be installed by calculating the needed separation from this exposure for Category C exposed walls,

where tempered glass would be acceptable. For a given situation, assume that figure is 60 ft (18 m) if the

walls are parallel. Since the west wall is between 15and 30of being parallel to the exposure, the multiplier

per Table 5 is 0.92. Similarly the south wall is between 60 and 75 of being parallel to the exposure, so

the multiplier is 0.66. Multiplying 60 ft (18 m) by 0.92 and 0.66 will yield the distance out from (as measured

perpendicular to) the exposing wall in which fire rated glass is needed along the west (55 ft, 17 m) and south

wall (40 ft, 12 m), respectively.




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Fig. 2. Protection for side walls of exposed building.




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West Wall

60 ft 0.92 = 55 ft, 18 m 0.92 = 17 m

South Wall

60 ft 0.66 = 40 ft, 18 m 0.66 = 12 m

3.2.7 Protection for Roof When Lower Than Exposing Building

When the roof of the exposed building is below the top of the exposing building, the exposed roof may receive

sufficient radiant heat to be ignited. A burning brand, large enough to cause pilot ignition, may also fall on

the roof. For built-up roof coverings (BUR), placing a minimum of 4 lb/ft 2 (20 kg/m2) of pea gravel on the roof

in a flood coat of coal tar or asphalt is recommended. For single-ply membranes, large stone ballast or paver

blocks may be used. (See Data Sheet 1-29.) It would only be necessary to provide this protection within

50 ft (15 m) of the exposure; however, the remaining portion of the roof should have a Class A rating, for

the distance defined in recommendation 2.8.

3.2.8 Protection of Walls Above Lower Exposing Building

When the height of the exposed building does not exceed the height of the exposing building, use Tables 1

and 2 to determine the safe separation distance or needed protection for the entire exposed wall. When

the height of the exposed building exceeds the height of the exposing building (Fig. 4a), and the separation

between buildings is not adequate according to Tables 1 and 2, protection for the portion of the exposed

wall that is above the height of the exposing wall should be provided as outlined in Figures 4b and 4c. The

type of protection needed should be based on the severity of the exposure (Tables 1 and 2) and the horizontal

separation distance between buildings.

When there is considerable height difference between a significant exposure and the higher exposed building,

the level of protection of openings may be decreased one level for each story height above the distance

of needed protection according to Figures 4b or 4c. As in example 3.2.8.1 below, windows on floors one

Fig. 3. Protection for exposed building when walls are at an angle () with exposing building.




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through seven need to be bricked in (or have sprinklers and fire rated glass), those on the eight floor should

have fire rated glass, those on the ninth floor should be tempered (or fire rated).

Example 3.2.8.1

In Figure 4a, a nine-story sprinklered building with 12 in. (300 mm)-thick brick exterior walls and plain glass

windows is exposed by a three-story unsprinklered building. Separation distance is only 30 ft (9.1 m).

The exposing building is a plank-on-timber fully occupied furniture warehouse having wood walls and a fire

area of 15,000 ft2 (1,400 m2) per floor. The length of the exposing wall is 112 ft (34 m). The story height

in both buildings is 15 ft (4.6 m). What protection is required for the openings in the exposed building?

Solution:The exposing building is multi-story, with wood walls and plank-on-timber floors, so the occupancy

should be treated ashighregardless of the exposure. Since the length of the exposing wall is 112 ft (34 m)

and the height of the exposure is 45 ft (13.7 m), the aspect ratio of the exposure (for use in Table 2) is 2.5.

The fire resistance of the exposed brick wall is in excess of 3 hours (see Data Sheet 1-21); however,

separation would need to be adequate for exposed wall Category D for plain glass windows to be acceptable.

The corresponding multiplier from Table 2 for category 1 and 13 is 0.48 and 4.65, respectively (for exposed

3-hour fire-rated walls and exposed Category D walls). The respective recommended separation distances

are 27 ft (8.1 m) for 3 hour walls and 215 ft (66 m) for wood walls. The separation distance of 30 ft (9.1 m)

provided is adequate for the brick walls, but not the plain glass. According to Figure 4b, the height above theexposure needing protection is at least 36 ft (11 m). Consequently, since the story heights are 15 ft (4.6 m),

protection comparable to a 3 hr wall rating is needed for the first six floors, three up to the top of the exposing

wall and three above it. The seventh floor and the eighth floor should have protection comparable to a 2 hr

(blank wall or fire rated glass plus sprinklers) and 1 hr (fire rated glass) exposed wall, respectively. The ninth

floor should have tempered or fire-rated glass to provide protection comparable to Category C.




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3.3 Fire Exposure From Yard Storage

Combustibles stored outdoors may create an exposure hazard to nearby buildings.

There are a number of data sheets that consider this problem and discuss protection for yard storage. These

include 7-10, Wood Processing and Wood Working Facilities; 7-28N,Explosive Materials; 7-29, Flammable

Liquid Storage in Portable Containers; 7-85, Metals and Alloys; 7-88, Storage Tanks for Flammable and

Combustible Liquids; 8-3,Rubber Tire Storage; 8-7, Baled Fiber Storage; 8-10, Coal and Charcoal Storage;

8-21,Roll Paper Storage; 8-22, Storage of Baled Waste Paper; 8-24, Idle Pallet Storage; 8-27, Storage of

Wood Chips; 8-28,Pulpwood and Outdoor Log Storage; 7-52,Oxygen. For outdoor storage that is not covered

by any of the above data sheets, use this document to determine the separation and protection.

When using this document, yard storage should be categorized as outlined in Appendix A.

3.4 Yard Housekeeping

Unpaved yards with grass, weeds and bushes are hazardous, especially to buildings with combustible walls.

Piles of combustibles, stored either in the yard or on nearby property, add to the hazard. Combustible yard

storage may be vulnerable both to incendiarism and to fire spread from adjoining properties. These hazards

may be reduced by yard paving, metal fencing, and the maintaining of an aisle space along the fence.

Fig. 4a. Protection for exposed buildings higher than the exposing building.




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Fig. 4b. Protection of walls above the exposure (English units).




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Fig. 4c. Protection of walls above the exposure (SI Units).




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4.0 REFERENCES

4.1 FM Global

Data Sheet 1-0, Safeguards During Construction, Alteration and Demolition

Data Sheet 1-19, Fire Walls, Subdivisions and Draft CurtainsData Sheet 1-21, Fire Resistance of Building Assemblies

Data Sheet 1-22, Maximum Foreseeable Loss Limiting Factors

Data Sheet 1-29, Roof Deck Securement and Above-Deck Roof Components

Data Sheet 1-57, Rigid Plastic Building Materials

Data Sheet 2-8N, NFPA 13 Standard for the Installation of Sprinkler Systems 1996 Edition

Data Sheet 3-10, Installation and Maintenance of Private Fire Service Mains and their Appurtenances

Data Sheet 7-28N, Explosive Materials

Data Sheet 7-29, Flammable Liquid Storage in Portable Containers

Data Sheet 7-32, Flammable Liquid Operations

Data Sheet 7-52, Oxygen

Data Sheet 7-85, Metals and Alloys

Data Sheet 7-88, Storage Tanks for Flammable and Combustible Liquids

Data Sheet 8-1, Commodity Classification

Data Sheet 8-3, Rubber Tire StorageData Sheet 8-7, Baled Fiber Storage

Data Sheet 8-10, Coal and Charcoal Storage

Data Sheet 8-21, Roll Paper Storage

Data Sheet 8-22, Storage of Baled Waste Paper

Data Sheet 8-24, Idle Pallet Storage

Data Sheet 8-27, Storage of Wood Chips

Data Sheet 8-28, Pulpwood and Outdoor Log Storage

Data Sheet 9-17, Protection Against Arson and Other Incendiary Fires

4.2 National Institute of Standards and Technology

NIST-GCR-98-751, Window Breakage Induced by Exterior Fires, Mowrer, FW.

APPENDIX A GLOSSARY OF TERMS

Actual Separation Distance (d): The existing or proposed separation distance between adjacent buildings

or between yard storage and a building.

Class 1:Class 1 includes Approved plastic panelsand plastic building panels. Approved Foam Insulated

wall/ceiling constructions which utilize a polyurethane or polyisocyanurate foam core and steel or aluminum-

faced panels are considered Class 1. Approved insulated steel deck roofassemblies are also considered

Class 1.

Combustible: Combustible includes painted or unpainted wood, rigid plastic building materials that are not

Approved, and Class 2 insulated steel decks.

Concrete Block on Exposed (From the Exterior Side) Steel Frame:When any portion of the steel framing

is on the exterior side of concrete block, expansion of the steel frame under heat exposure may open up the

mortar joints. This tends to weaken the wall as well as permit the passage of heat and flame to the unexposed

side. Some credit, however, can be given to this type of wall to act as a fire barrier under reduced exposure.If an exterior grade fire resistant coating (such as an intumescent mastic) is applied to the exterior side of the

exposed steel to provide a comparable rating to that of the wall, that rating may be used to determine the

separation. Otherwise, using the separation distances for noncombustible construction will provide a very

conservative estimate of the needed separation.

Exterior Insulation and Finish System (EIFS). EIFS often use expanded or extruded polystyrene insulation

(EPS). The exterior coating for the EPS is a thin (about 18 in., 3 mm) layer of proprietary plaster-like material

which may be only 50% cement and 50% polymers. It offers considerably less thermal resistance than stucco

(lath and plaster) which is typically 12 in. to 34 in. thick (13 to 19 mm).

Fire Rated Glass:Glass such as wired glass, glass block or ceramic glass that has passed a minimum 34hour

fire endurance test and hose stream test.




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Fire Resistive:For more information including specific hourly fire ratings, refer to Data Sheet 1-21, Fire

Resistance of Building Assemblies. This category includes concrete (tilt-up, precast, poured-in-place),

concrete block, brick (but not quarter brickwhich is only about 12in. (13 mm) thick when used as a veneer

in EIFS systems), metal sandwich panels with a gypsum board core, and plaster/stucco (not EIFS). Well

maintained concrete or masonry walls without openings generally need little or no separation or protection

against fire exposure.

High Hazard Occupancy:Storage of Class 3 or 4 or greater hazard commodities, storage of flammable liquids,

plastics, roll paper, rubber tires and storage of any material judged to have a comparable or higher hazard.

When palletized storage of Class 3 commodities are no more than one tier or 6 ft (1.8 m) high, the hazard

may be reduced to Ordinary.

Light Hazard Occupancy: Manufacture of noncombustible products in which small amounts of cutting oils,

flammable liquids, or other combustibles are used. Assume a light hazard occupancy for use in Table 1 when

the exposing building is a hospital, office (with minimal combustible furniture and limited books and papers

in the open), school, or other building having a comparable occupancy hazard, or when any portion of the

exposing building is combustible and the building is vacant. This classification can also be used for the

palletized storage of Class 1 or 2 commodities to one tier high or 6 ft (1.8 m).

Noncombustible (NC):Noncombustible walls usually consist of panels over steel framing. Panels may be

painted or galvanized steel, corrugated iron, or corrugated cementitious supported on a steel frame. Thepanels are light in weight, and unless protected or adequately separated, they may buckle and open at their

joints, or crack under fire exposure. Since heat will easily conduct through thin steel and ignite combustible

insulation, insulations acceptable for use in this category include glass fiber, mineral wool and expanded

glass. For other types of insulation, see Class 1 or combustible categories.

Noncombustible panels also includeprotected metal panelsandfiber-reinforced cement panels Approved

and listed under Exterior Roofing and Siding.

Ordinary Hazard Occupancy:Manufacture of Class 3 and Class 4 commodities. Storage of Class 1 or 2

commodities, and storages of Class 3 palletized commodities to one tier high or a maximum of 6 ft (1.8 m)

high; metal-working in which significant amounts of cutting oils are present; or when the exposing building

is occupied as a hotel, dwelling, retail store, garage, or any occupancy where there is a moderate amount of

combustible material.

Safe Separation Distance (S):The distance recommended per this document to prevent ignition of a building

or its contents due to an exposure fire in an adjacent building or yard storage.

Stable Fire Resistive (SFR):SFR walls are constructed of materials having a fire resistance rating at least

adequate for the exposing occupancy. The exposing wall must be constructed so that it will not collapse in an

uncontrolled fire. This includes freestanding fire walls. It does not include fire walls that are laterally supported

by structural framework that does not have adequate fire resistance.

APPENDIX B DOCUMENT REVISION HISTORY


September 2006. Minor editorial changes were made.


May 2003. This revision of the document has been reorganized to provide a consistent format.

In September 1999, the March 1979 version was completely revised.


Documents

FMDS0120 Protection Against Exterior Fire Exposure