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September 1981

Revised January 2000

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FIRE PROTECTION FOR BUILDING OVER HIGHWAYS

Table of ContentsPage

1.0 SCOPE ................................................................................................................................................... 2

1.1 Changes .......................................................................................................................................... 2

2.0 LOSS PREVENTION RECOMMENDATIONS ....................................................................................... 2

2.1 Construction and Location ............................................................................................................... 2

2.2 Protection ......................................................................................................................................... 4

2.3 Human Element ............................................................................................................................... 4

3.0 SUPPORT FOR RECOMMENDATIONS ............................................................................................... 5

3.1 General ............................................................................................................................................ 5

4.0 REFERENCES ....................................................................................................................................... 8

4.1 FM Global ........................................................................................................................................ 8

4.2 Others .............................................................................................................................................. 8APPENDIX A GLOSSARY OF TERMS ....................................................................................................... 8

APPENDIX B DOCUMENT REVISION HISTORY ....................................................................................... 8

List of FiguresFig. 1. Four 32-story apartment buildings and a bus terminal built over the Trans-Manhattan

Expressway. ........................................................................................................................................ 2

Fig. 2. Building slab extending 50 ft (15 m) beyond the building line. (Plan view). ...................................... 3

Fig. 3. Fire resistive walls of building over highway. (Plan view). ................................................................. 4

Fig. 4. Wall hydrants in the space under Detroits Cobo Hall. ...................................................................... 5

Fig. 5. The Post Office Building in Chicago is built over the Eisenhower Expressway. ............................... 6

Fig. 6. Cobo Hall in Detroit is built over the John C. Lodge Expressway. .................................................... 6

Fig. 7. This supermarket in Newton, Massachusetts was built over the Massachusetts Turnpike............... 7

FM GlobalProperty Loss Prevention Data Sheets 1-16

2002 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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1.0 SCOPE

This standard outlines fire protection guidelines for buildings over highways with respect to the hazards

created by vehicles using the highways.

1.1 ChangesJanuary 2000. This revision of the document has been reorganized to provide a consistent format.

2.0 LOSS PREVENTION RECOMMENDATIONS

2.1 Construction and Location

2.1.1 Floors, beams, and columns of a building over a highway that are exposed to the space below should

have a minimum fire resistance of four hours as established by Data Sheet 1-1, Firesafe Building Construction

and Materials, and Data Sheet 1-21, Fire Resistance of Building Assemblies.

2.1.2 Exposure protection against fires at the entrances or exits of the space under a building should be

provided by the more practical of the recommendations below:

a) Buildings over highways should be built on unpierced fire resistive slabs, as specified by Recommen-

dation 2.1.1 or 2.2.1, that extend 50 ft (15 m) beyond the building line (Figs. 1 and 2); or

Fig. 1. Four 32-story apartment buildings and a bus terminal built over the Trans-Manhattan Expressway.

1-16 Fire Protection for Building Over HighwaysPage 2 FM Global Property Loss Prevention Data Sheets

2002 Factory Mutual Insurance Company. All rights reserved.

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b) For 20 ft (6 m) above the top of the building slab or for at least one story, building walls facing the high-way should beblankand have fire resistance of at least two hours. The walls parallel to the highway for

at least 20 ft (6 m) should also be blank for the same height from either entrance and have fire resis-

tance of at least two hours (Fig. 3).

2.1.3 When a new building is to be located over a highway, an increased level of protection may be warranted,

depending on the length of the building, etc.

a) A complete drainage system should be provided for the highway space under the building. Sumps

with automatic pumps should be provided where necessary. The design of the drainage system should

be equipped with protected collection areas so that the spills of hazardous materials, such as flammable

liquids, cannot create a fire hazard in another area.

b) Roadways under buildings in excess of 200 ft (60 m) long should be equipped with an emergency

exhaust ventilation system designed for the removal of smoke and other toxic fumes from the roadway dur-

ing fires. The design of the system should also prevent or minimize adverse effects on the buildings andtheir occupants from the fire products such as heat, smoke, and toxic gases. The system should be

designed to provide at least ten air changes per hour.

2.1.4 Where possible, walkways, elevated 6 in. (152.4 mm) and about 4 ft (1.23 m) wide, should be provided

on both sides of the roadway to facilitate manual fire fighting.

Fig. 2. Building slab extending 50 ft (15 m) beyond the building line. (Plan view).

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2.2 Protection

2.2.1 As an alternative to recommendation 2.1.1, the floors, beams, and columns of the building should have

a minimum fire resistance of at least two hours and the space under the building should be protected with

automatic sprinklers. The sprinklers should be on an extra-hazard pipe schedule (see Data Sheet 2-8N,Instal-

lation of Sprinkler Systems[NFPA]), with spacing not to exceed 100 ft2 (9.30 m2) per sprinkler. Either dry

or preaction systems are suitable in cold climates. An adequate water supply of two-hour duration for sprin-

kler and hydrant protection of at least 500 gpm hose demand should be provided in accordance with Data

Sheet 3-26, Fire Protection Water Demand for Nonstorage Sprinklered Properties. The sprinkler system

should also be protected against corrosion.

2.2.2 The sprinkler system fire alarm should be at least Class V as specified by Data Sheet 9-1, Supervi-

sion of Property.

2.2.3 If hydrants are not readily accessible, they should be installed immediately outside the space under

the building entrances and exits. Additionally, for buildings over 200 ft (60 m) long, wall hydrants should be

spaced every 150 ft (45 m) in accordance with Data Sheet 4-4N, Standpipe and Hose Systems (Fig. 4).

2.2.4 Manually-activated emergency alarms should be provided which transmit to a constantly attended

location, preferably the local fire department.

2.3 Human Element

2.3.1 An emergency preplanning traffic control system should be provided to prevent the involvement of addi-

tional vehicles in an accident, to slow traffic during inclement weather conditions, and to assist in fire depart-

ment vehicle access.

2.3.2 Dangerous cargo, as defined by the Department of Transportation, should be prohibited from passing

under buildings over highways.

Fig. 3. Fire resistive walls of building over highway. (Plan view).



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3.0 SUPPORT FOR RECOMMENDATIONS

3.1 GeneralBuildings that span highways in and around metropolitan areas are becoming more common. Fire emergen-

cies that may be anticipated range from fires in passenger vehicles to major accidents involving loaded trucks

carrying flammable liquids or other hazardous cargoes. Heavy traffic and adverse weather conditions may

contribute to the seriousness of the accident by involving approaching vehicles and obstructing fire depart-

ment access. (See Figs. 5, 6, 7, and 1.)

The structural members supporting a building over a highway could be subjected to very high tempera-

tures during a flammable liquid fire or explosion, even though of short duration. Damage to these members

could have a serious effect on the building. Most fires of these types may substantially exceed the ASTM

Standard Time-Temperature Curve during the early stages and would drop below the curve after two or three

hours. The structural elements that support the building may also be subjected to physical damage during

impact from motor vehicle accidents.

Flammable liquids or vapors can flow by gravity or via drainage systems and spread the fire well beyond

the area of the original emergency. During a fire, smoke can also spread in all directions as result of den-

sity and pressure differentials, thus impeding efficient manual fire fighting. Consequently, a drainage sys-

tem and emergency ventilation are needed in the space under the building to help fire fighting and control the

spread of the fire.

Many highway spaces under buildings are not equipped with manual fire fighting equipment, such as hydrants

and fire extinguishers. This equipment is especially needed when the space is not protected with sprinklers.

Limited access to highways under buildings and backed-up traffic frequently hinder the public fire depart-

ment response. Problems are further complicated by the lack of adequate communication facilities for report-

ing emergency conditions and for warning approaching vehicle operators of fire emergencies, hazardous

conditions, or visibility limitations.

Fig. 4. Wall hydrants in the space under Detroits Cobo Hall.



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Fig. 5. The Post Office Building in Chicago is built over the Eisenhower Expressway.

Fig. 6. Cobo Hall in Detroit is built over the John C. Lodge Expressway.



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Fig. 7. This supermarket in Newton, Massachusetts was built over the Massachusetts Turnpike.



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