Commentary on Part 3 (Use and Occupancy) of the National Building Code of Canada 1985

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National Research

Conseil national

**1*1**

Council Canada

de recherches Canada

Commentary on Part

3 (Use

and Occupancy) of

the

National Building

Code

of Canada

1985

Issued

by

the

Associate Committee on the National Building Code

National Research Council Canada

Ottawa

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Commentary on Part

3 (Use and Occupancy)

of the

National Building Code of Canada

1985

Issued by the

Associate Committee on the National Building Code

National Research Council Canada

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Table of Contents

Preface iii

Chapter 1 Appllcatlon and General Provlslons

Application of Part 3 1

Relationship between Part 3 and the National

Fire Code 2

General Provisions in Part 3 2

Chapter 2 Scope

The Arrangement of Part 3

General Requirements (NBC Section 3.1 ) Size and Occupancy Requirements for Fire Safety (NBC Section 3.2)

Safety Requirements within Floor Areas (NBC Section 3.3)

Requirements for Exits (NBC Section 3.4)

Sewice Spaces (NBC Section 3.5)

Health Requirements (NBC Section 3.6)

Barrier-Free Design (NBC Section 3.7)

Chapter 3 Concepts and Terrnlnology

General

What is a Building?

Classification of a Building by Major Occupancy Separation of Major Occupancies

Construction Types Fire-Resistance Ratings

Fire Separations versus Fire-Resistance Ratings Protection of Openings Firewalls Fire Stopping Flame-Spread Ratings Interior Finish Roof Asserrlblies Roof Coverings Occupant Load

Chapter 4 Requlrernents Affectlng the Bulldlng as a Whole

General 32

Building Size Determination 32

Structural Fire Protection 35

Spatial Separations 41

Exterior Wall Construction 52

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Commentary on Part 3

Equivalent Openings

Fire Exposure between Fire Compartments Vertical Fire Spread

Fire Alarm Systems

Fire and Smoke Detection Systems Fire Department Access

Fire Suppression Systems High Buildings

Interconnected Floor Space

Chapter 5 Safety wlthin Floor Areas

General Access to Exits Suites

Corridors

Capacity of Access to Exit Assembly Occupancies l nstitutional Occupancies Residential Occupancies

Business and Personal Services Occupancies Mercantile Occupancies

Industrial Occupancies

Chapter 6 Exl ts

General Width of Exits

Number of Exits and Travel Distance to Them Distance between Exits

Doorways

Separation of Exits Flame Spread in Exits Horizontal Exits Fire Escapes

Chapter 7 Servlce Facilltles

General Service Rooms

Vertical Service Spaces Horizontal Service Spaces

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Preface

This Commentary contains material to assist the Code user in applying the

requirements of Part 3 of the National Building Code of Canada 1985. It has

been prepared under the direction of the Standing Committees on Fire Protection and Occupancy of the Associate Committee on the National Building Code, who are also responsible for preparation of the requirements in Part 3 (except Section 3.7) of the National Building Code.

This Commentary describes the overall arrangement of Part 3 and its

interrelationship with the National Fire Code of Canada 1985. It discusses the

basic concepts and terminology used in Part 3 and provides examples to

illustrate and explain a number of the mare complicated requirements. Comments on this document are welcome and should be addressed to The Secretary, Associate Committee on the National Building Code, National

Research Council of Canada, Ottawa, Ontario K1 A OR6.

Ce document est publid en frawais. Les demandes doivent &re adresseds au Secdtaire, Comitd associd du Code national du batiment, Conseil national

de recherches Canada, Ottawa, Ontario K1 A OR6.

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COMMENTARY ON PART 3 - . - (USE AND OCCUPANCY)

OF THE

NATIONAL BUILDING CODE OF CANADA 1985

CHAPTER 1

APPLICATION AND GENERAL PROVISIONS

This commentary has been prepared as a guide for users of Part 3 of the National Building Code (NBC) because of the diversity and complexity of the conditions encompassed by that Part. Part 3 is concerned chiefly with the safety from exposure to fire and the health of the occupants of a building. In using this commentary it is helpful to understand the scope of Part 3 in relation to other Parts of the NBC and the relationship of Part 3 to the National Fire Code of Canada (NFC). The NFC is a separate code prepared under the auspices of the Associate Committee on the National Fire Code.

Appllcatlon of Part 3

Part 3 regulates all buildings classified by major occupancy as Group A, Division 1,2,3,or4, Group B, Division 1 or 2, or Group F, Division 1, regardless of size. It also regulates buildings of all other major occupancies which exceed 600 m2 in area or three storeys in height. Other buildings are regw lated by Part 9, Housing and Small Buildings. In buildings within the scope of Part 9 that contain rooms or spaces used for assembly, institutional, or high hazard industrial occupancy, those rooms or spaces must conform to the applicable requirements of Part 3.

Concerning the installation of building services and equipment, Part 3 regulates only those aspects which are not covered by other Parts of the Code. Part 6 contains the requirements for heating, ventilating and air conditioning installations, while Part 7, through reference to the Canadian Plumbing Code, specifies how the appropriate plumbing facilities are to be installed.

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Relations hip between Part 3 and the National Fire Code

A special relationship exists between Part 3 of the NBC and the NFC with respect to fire safety; the content of both Codes must be considered in building design, construction and maintenance. The role of each Code with respect to fire safety can be summarized as follows:

The NBC establishes the standard of fire safety for the construction of new buildings, for reconstruction of existing buildings, including alterations or extensions, and for buildings in which a change in occupancy occurs. The National Fire Code establishes standards for fire prevention, fire fighting and fire safety in buildings in use, including standards for the conduct of activities causing fire hazards, for maintenance of fire safety equipment and egress facilities, and for portable extinguishers. It limits building contents and requires fire safety plans, which include the organization of supervisory staff for emergency purposes. In addition, the NFC establishes standards for the prevention of fires outside of buildings, which could present a hazard to a community.

The two Codes have been developed as complementary and coordinated documents to reduce to a minimum any conflict in their contents. To ensure their effective application, building and fire officials must be fully conversant with the fire safety standards of both Codes.

General Provisions in Part 3

Part 3 regulates the building under consideration and does not in any way apply to adjacent buildings or properties. The spatial separation requirements in the Code, for instance, use the property line as a base line, rather than the distance between two buildings, if the buildings are located on different properties. In this way each building is regulated independently of buildings on neighbouring properties, but each of those buildings must in turn conform to the same requirements when any construction is undertaken on them. The requirements of Part 3 are intended to be interpreted and enforced by reasonable people using good judgment. This is especially important for users faced with situations which are not specifically covered in the Code, or in which alternative design solutions are proposed which were not envisaged by the Code committees. There is often insufficient factual knowledge to balance the safety of one set of conditions against another. In the design of any major complex or unusual building, situations arise in which such

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judgments must be made; the Code can never cover all possible situations, though it is revised as experience is gained from its use and additional knowledge obtained through research.

Fire fighting capabilities are assumed to be available in the event of a fire emergency. These capabilities may take the form of a paid or volunteer public fire department or, in some cases, a private fire brigade. Where fire fighting facilities are not available, additional fire safety measures may be required; again, good judgment must be exercised.

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CHAPTER 2 SCOPE

The Arrangement of Part 3

Part 3 contains seven major sections: 3.1 General

3.2 Size and Occupancy Requirements for Fire Safety 3.3 Safety Requirements within Floor Areas

3.4 Requirements for Exits 3.5 Service Spaces 3.6 Health Requirements 3.7 Barrier-Free Design

General Requirements (NBC Sectlon 3.1)

The requirements in Section 3.1 mainly define concepts that are used throughout the remainder of Part 3. To a large extent this Section is an extension to the definitions section of the NBC, except that some of these concepts or terms are complex. Many of the subjects relate to terms that are defined in an abbreviated form in the definitions Subsection (Subsection 1.3.2.).

Section 3.1 contains the scope of Part 3. It also contains the procedures for the classification of a building according to its use by a major occupancy. Classification is fundamental to the application of other requirements in Part 3. In addition, Section 3.1 contains requirements for combustible construction, heavy timber construction, noncombustible construction, tents and air-supported structures, fire separations, protection of openings, fire walls, fire stops in concealed spaces, flame-spread rating, interior finish, roof assemblies, roof covering, and occupant load. Most of these subjects are also defined terms in Subsection 1.3.2. and are used throughout Part 3, but in a context that includes the additional requirements of Section 3.1. It is from the foundation provided by this Section that many of the requirements of Part 3 have been developed. Copyright © NRC 1941 - 2019 World Rights Reserved © CNRC 1941-2019 Droits réservés pour tous pays

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Slze and Occupancy Requirements for Fire Safety (NBC Section 3.2) Section 3.2 includes requirements that affect the building as a whole structure. Approximately two-thirds of the Section contains requirements relating to storey-by-storey fire compartmentation and fire-resistance ratings for load- bearing structura,l asserrrblies and members. These requirements vary in relation to the use of the building, its size, the number of streets it faces, and whether it is sprinklered. Since many of the requirements in this Section depend on the size of the building, details are provided on how building size is determined.

Section 3.2 also specifies the minimum distances between buildings that may affect each other in the event of afire and sets limitson allowable openings and the construction of the building faces. These requirements for the face of a building that may be exposed to fire ot that may expose other buildings to fire are expressed in terms of fire-resistance rating and combustibility, but are not to be confused with the structural fire protection requirementsforthe loadbear- ing structural assemblies mentioned in the preceding paragraph. The structural fire protection requirements ensure that a building will remain structurally intact for agiven period of time after a fire breaks out within it, while the exposing building face requirements are intended to ensure that a fire in one building will not involve another building for a certain period of time. Requirements are included for public corridors, covered vehicular passage- ways and walkways between buildings. Fire alarm and detection systems are regulated in relation to building size, use and number of occupants. Require- ments relating to fire fighting include provisions for access, water supply, standpipe systems, and sprinkler systems. Other requirements cover emergency powerand lighting, and the lightingof exits and areasused by the public. Section 3.2 includes additional requirements for high buildings. These include smoke control and venting, elevator control, elevators for fire fighters, sprin- klering of certain spaces, central alarm and control facilities, voice communi- cation systems, and emergency power supply for essential equipment. Additional protection measures are incorporated in Section 3.2 for buildings with openings through the floor assemblies that are not protected by closures (buildings with mezzanines or interconnected floor space).

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Section 3.2 concerns requirements for the entire building. Section 3.3 regulates safety within individual storeys (floor areas), including all rooms and spaces other than service rooms and service spaces covered by Section 3.5. The requirements are grouped according to the occupancy of the floor area, room, or space. This occupancy is not necessarily the major occupancy for which the building is classified.

For example, an office building may be classified as a Group D major occupancy and the provisions for structural fire protection and fire protection equipment for Group D major occupancy buildings prescribed in Section 3.2 apply to the overall building. Within that building, a room or floor area, that is, a subsidiary occupancy, may be used as an assembly, institutional, business, residential, mercantile, or industrial occupancy; in such a case the special rules of Section 3.3 apply to the room or space containing that occupancy. An assembly room must therefore comply with the requirements .for assembly occupancy in Section 3.3, even if it is contained in an office building, hospital, hotel, theatre, industrial building or any other building which would be classified as a major occupancy other than Group A.

In the NBC, life safety for the occupants of any space or floor area depends on the use or occupancy of that space. The risk to these occupants occurs in the early stages of a fire. It is not the same for all occupancies, so each one must be regulated separately. Section 3.3 contains requirements for access to exit both from open floor areas and those floor areas divided into suites. Access to exit includes all portions of the floor area, exclusive of the exit portion. Section 3.3. also regulates the size of access to exits and limits the travel distance to the exitsfromwithin the floor area. Section 3.3 also contains restrictions on the design of guards around openings and in stairways and on the use of glass in doors or windows that may be mistaken for doors.

Requirements for Exlts (NBC Sectlon 3.4)

The requirements for exits are separate from the requirements that affect the building as a whole in Section 3.2 and from the requirements that affect the floor area in Section 3.3. The exit is that part of the escape route that leads from the floor area it serves to anotherbuilding, a public thoroughfare, or a safe open spaceoutside the building. In a typical building with exit stairs, it includes the stairway itself and the doors leading into and out of the stairway. Once in the exit system, a person is considered to be in a relatively safe place, thus

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exiting is generally accomplished without re-entering a floor area in the same building.

Section 3.4 defines what may be used as part of an exit system and the requirements for such facilities, their number and location, fire separation from the rest of the building, and exit signs and lighting.

Setvice Spaces (NBC Section 3.5)

Section 3.5 includes provisions applying to any space that accommodates building services such as chutes, ducts, pipes, or wiring. Also included are requirements affecting attics and crawl spaces, duct spaces, service shafts, service rooms, and concealed spaces in walls and floors. Requirements for these spaces are included in a separate Section because, unlike other parts of a floor area or exit system, they are not usually accessible either to the building occupants or the general public. They are not considered to have any appreciable occupant load and, in many cases, are unoccupied except for occasional inspection or servicing.

Health Requirements (NBC Section 3.6)

Section 3.6 comprises those requirements that affect the health of the occupants. It regulates the number of plumbing fixtures based on occupancy and occupant load and, through reference to other Parts of the Code, the height and area of rooms, natural lighting, and ventilation. Special reference is made to requirements for medical gas systems.

Barrier-Free Deslgn (N BC Sectlon 3.7)

The requirements in Section 3.7 affect the design of a building for accessibil- ity to persons in wheelchairs. The primary areas are the approach to a building, entry to and movement within a building, parking, washroom and bathroom layout and design, and special elevator requirements. Measures that address the special needs of persons with physical disabilities that do not restrict them to a wheelchair are included in other Sections of Part 3.

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CHAPTER 3

CONCEPTS AND TERMINOLOGY

General

In this chapter of the commentary, some of the terms and basic concepts that are defined in Subsection 1.3.2. are discussed in further detail. No attempt is made to coverall of the terms that are used; the chapter concentrates on those which give rise to the most misunderstandings.

What

Is

a Bulldlng?

Various attempts have been made to more precisely define the word building. These attempts have been relatively unsuccessful; the more precise the definition becomes, the more difficult it is to apply. What suits one authority may not suit another. Some common sense, therefore, is necessary in applying the present definition, which merely states that

a

building is any structure used or intended for supporting or sheltering any use or occupancy. An authorii adopting the Code may exclude certain specific structures from the provisions of the Code and also exclude structures covered by other legislation. In most cases there is no doubt that a structure is a building, but in a number of instances, a structure might not be classified as a building (e.g., a transmission tower). There is an advantage in maintaining the flexibility of the present definition for those instances where a structure presents a potential danger to the public but would not normally be considered a building. This occurs most often in industrial uses, particularly in manufacturing facilities and equipment that require specialized design. In structures such as steel mills, aluminum plants, refineries, power generating stations and liquid storage facilities, it may be impracticable to follow the specific requirements in Part 3. Awater tank or an oil refinery, for example, has no floor area as defined in the Code, so requirements for exiting from a floor area would not apply. Requirements for structural fire protection in large steel mills, and pulp and paper mills, particularly in certain sections, may not be practicable in terms of the construction normally used in those operations. In other portions of the same building, however, it may be quite reasonable to require that the provisions of Part 3 be applied (e.g., requirements for off ices).

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An area of an industrial occupancy such as an equipment penthouse, which may be occupied only periodically by service staff, would normally not need to have the same type of exit facility as a floor area occupied on a continuing basis. Thus good judgment must be exercised in determining whether to apply a requirement under extenuating circumstances, provided always that the safety of the occupants is not threatened.

One problem with many buildings designs concerns what constitutes part of a building and what does not. A courtyard that is open to the sky but is surrounded by walls, for example, is regulated by the egress requirements in Part 3, but is not normally considered to be part of a building. Where a floor or roof section is cantilevered over ground space and the space below is unenclosed, it is often aquestion of judgment whether the space below should be considered to be part of the building orto be outside the building. Numerous other examples could be cited on this subject, and each situation can present a different aspect of the problem. Since the degree to which certain factors of the building are regulated depends on the limits of the building, these boundaries become quite important in applying the appropriate requirements. There are obviously no simple answers to this complex problem; common sense and good judgment must be exercised in establishing the building limits.

Classification of a Bulldlng by Major Occupancy

The classification of a building by major occupancy is normally the starting point in establishing which Code requirements should apply to that building. This should not be confused with the term occupancy. Major occupancy is defined as the principal occupancy for which a building or part thereof is used or intended to be used, and includes the subsidiary occupancies which are an integral part of the principal occupancy.

For example, if the principal use of a building were educational, the building would be classified as a Group A, Division 2 major occupancy. In addition to the classrooms, the building could contain offices, laboratories, gymnasia, and workshops, which would be considered subsidiary occupancies. Neverthe- . less, the major occupancy of the building would be Group A, Division 2, and this classification would applywhereverthe requirements for majoroccupancy were specified.

Similarly, in a building whose principal use is manufacturing, the combustible content might require the building to be classified as a Group F, Division 3

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major occupancy. Within the building there could be subsidiary occupancies which are an integral part of the operation of the manufacturing plant, including offices and a cafeteria. These subsidiary occupancies would not normally be considered separate major occupancies; they are subsidiary to the principal occupancy, which is manufacturing.

If a building is used for more than one principal purpose, it must be classified for each major occupancy. For example, the main floor could be used primarily for mercantile operations and several upper storeys could contain offices not related to the mercantile operation. In this case the building would have to be classified for both types of occupancy and would be considered to have two major occupancies (Group D and Group E). Each major occupancy could include subsidiary occupancies.

These examples are relatively clear cut. In other cases the dividing line between a major occupancy and a subsidiary occupancy becomes obscure and judgment must be used to arrive at the appropriate classification. A hotel might have a number of shops on the main floor which might be leased to tenants. Although these shops would serve the clientele of the hotel, as well as other customers, they would not necessarily be subsidiary occupancies of the principal use of the building, which is a residential occupancy providing accommodation for the hotel guests, i.e. a Group C major occupancy. The shops might be considered a second major occupancy classified as Group E. If the hotel contained extensive convention meeting rooms, then there could be a further major occupancy classified as Group A, Division 2.

Except in the case of Group F, Division 1 or 2 major occupancies, if the aggregate area of a major occupancy does not exceed ten percent of the floor area of the storey in which it is located, the building does not have to be classified for that major occupancy for the purposes of determining structural fire protection. This does not exempt these major occupancies from the requirements in Section 3.1 that major occupancies must be separated from each other even though they occupy less than ten percent of the floor area. This provision also does not exempt these small major occupancies from the other requirements of Section 3.2, including spatial separation and fire alarm systems, nor from the requirements of Section 3.3 for specific occupancies. Sufficient information must be included on the plans and in the specifications for a building project to allow the building to be classified by major occupancy and the floor areas to be classified according to their intended use.

The classification of a building by major occupancy is based on the intended use of that building. Subsequent activities of an occasional nature, not

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foreseen in the original design, are not regulated under the specific requirements of Part 3. These activities may require additional safety measures to ensure that egress paths remain clear of obstructions, that combustible contents are controlled and that fire fighting begins promptly. The National

Fire Code includes requirements to address these situations.

Separation of Major Occupancies

Under certain conditions it is necessary to separate one major occupancy f rom another, to protect one from the hazards created by the other. In the case of a Group A major occupancy, where large numbers of persons may be involved, a Group B major occupancy, where persons may be under restraint or receiving medical care, or a Group C major occupancy, where persons may be asleep, it is considered necessary to protect one such occupancy from a hazard created in an adjacent one. The Code therefore requires that each of these major occupancies be protected with a fire separation, having a specified fire-resistance rating, from the other major occupancies. This is to provide sufficient time for evacuating one major occupancy in case of fire in an adjacent one.

In the case of a Group F, Division 1 major occupancy (high hazard industrial), there is a known hazard to be contained. Therefore this major occupancy is required to be isolated from all others by fire separations having specified fire- resistance ratings. In this case, the purpose is to contain the fire within the industrial occupancy and not to protect that occupancy from the effects of fire in another space; however, the fire separation will also control the spread of fire into the Group F, Division 1 major occupancy. Because of the extreme hazard involved, a Group F, Division 1 major occupancy may not be located in a building that contains a Group A, a Group B or a Group C majoroccupancy. Group E, Group D and Group F, Division 1 and 2 major occupancies do not present as serious a fire risk as a Group F, Division 1 major occupancy. It is not necessary, therefore, to contain these occupancies in the same way. Life safety is not as critical in these major occupancies as it is in Group A, Group B and Group C ma,jor occupancies. The occupants are awake and aware and there are no unusual evacuation problems. In these major occupancies, ,therefore, separation on the basis of major occupancy is not deemed necessary. There are of course requirements for separation other than those based solely on ma.jor occupancy. These separation requirements depend on the particular activities within afloor area and are not confined to a particular major

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Construction

Types

Many of the requirements throughout Part 3 depend on whether the building is of combustible or noncombustible construction. Buildings over a certain height or area are required to be of noncombustible construction. The building area and building height limits which allowa building to be of combustible construct ion depend on the major occupancy classification, the number of streets the building faces, and whether or not the building is sprinklered. Since combustible construction is defined as construction that does not conform to the requirements for noncombustible construction, it is important at this stage to appreciate what is meant by noncombustible construction, and to differentiate this from the term noncombustible as applied to a particular building material.

The terrn noncombustible, applied to a material, means that the material will pass the test for noncombustibility as defined in CAN4-S114, "Standard Method of Test for Determination of Non-Combustibility in Building Materials." This standard constitutes a severe test which a material either passes or fails,

. but is not the sole criterion for judging the acceptability of a building material. Because the terrn noncombustible applies to a specific product or material, the concept of noncombustible construction is used in the Code. In this type of construction the building asserrrblies are required to be Constructed of noncombustible materials, but the inclusion of certain combustible elements is permitted, specifically those that are listed in Article 3.1.4.5. Where combustible materials are permitted, there are in many cases restrictions on their flame spread properties: For some materials, such as interior finish, restrictions are also placed on the thickness. If an assembly constructed essentially of noncombustible material contains combustible elements not specifically permitted by the Code in noncombustible construction (e.g., combustible cladding), the assembly falls within the category of combustible construction.

Combustible construction is usually considered to be conventional wood frame or heavy timber construction. Conventional wood frame construction is described in detail in Section 9.23 of the NBC. Heavy timber construction is a special category of combustible construction and is acceptable where combustible construction would normally be required to have a h fire- resistance rating. This is achieved by placing minimum limits on the size of columns and beams, as well as on the thickness of floor and roof components. These limits on dimensions, given that this type of construction does not normally contain concealed spaces, provide this construction with a substan-

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tial degree of fire safety. Heavy timber construction is relatively difficult to ignite and, once ignited or subjected to an exposing fire, resists collapse reasonably well. I Under the standard fire test conditions wood will char at an average rate of about 0.64 mm per minute, so that after 40 minutes approximately 25 mm depth of the wood will have been burnt. Therefore, the larger the cross sectional area of the member, the longer the member will maintain its structural stability in a fire.

Tents and air-supported structures are another category of building construction that is regulated in Part 3. Air-s~~pported structures are those whose shapes are maintained through constant air pressure supplied by a blower. These structures must conform to the space separations required for any other structure (except when located on the same property) and to the requirements of Section3.3forfire safetywithinfloorareas andof Section3.4for exits. While these structures do not have to conform to the combustibility and structural fire protection requirements of Section 3.2, since this would obviously be impracticable, they do have to be constructed of a material that will meet ULC-S109, "Standard for Flame Tests of Flame-Resistant Fabrics and Films." This concession.is permitted on the basis that these structures do not contain interior walls, floors, mezzanines or similar construction.

Fire-Reslstance Ratlngs

A fire-resistance rating in Canada is based on Underwriters' Laboratories of Canada standard CAN441 01, "Standard Method of Fire Endurance Tests of Building Construction and Materials." Ina wall or floor furnace, assemblies are subjected on one side to standard conditions intended to simulate a rapidly developing fire. Tested wall assemblies must be not less than 9.3 m2 in area and tested floor assemblies, not less than 16.7 m2 in area. The standard temperature in the furnace reaches 538°C after five minutes, and increases to 904°C after ten minutes, 929°C after one hour, 1 01 0°C after two hours, and 1093OC at the end of four hours.

In this test, a specimen is normally rated on the basis of its ability to pass several criteria. The average temperature on the unexposed side of a wall or floor/ceiling assembly must be not more than 13g°C, but the rise in temperature of a single point can not be more than 181°C. Flames or hot gases that would ignite cotton batting must not pass through the wall or floor assembly, and the assembly must not collapse under a specified load. The period of time at which any one of these criteria is no longer satisfied determines the fire-

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resistance rating of the assembly. In the case of walls and partitions that are intended for a rating of one hour or more, a separate hose stream test is normally undertaken in addition, to determine the ability of the wall to withstand the effects of a hose stream. In the case of columns, all sides of the column are exposed to the temperature of the standard test.

There are a number of similar tests for fire-resistance rating in North America, and the authority having jurisdiction can review results from such tests to determine their acceptability by comparison with the procedures in CAN4- S101.

Chapter 2, "Fire-Performance Ratings," of the Supplement to the National Building Code of Canada 1985 provides methods for determining the fire- resistance rating of many common assemblies constructed with generic building materials. The ratings are largely based on past test results, although theoretical considerations have also been used to extend existing experimen- tal information.

In Canada, Underwriters' Laboratories of Canada and Warnock Hersey Professional Services Limited publish listings of proprietary products and assemblies which have been tested and rated. These listings are valuable sources of information on this subject.

In determining ratings, floorlceiling and rooflceiling assemblies are rated for fire exposure from the underside of the asserr~bly orrly. Interior walls and partitions are rated for fire exposure from each side (one side exposed at a time). Exterior walls, in contrast, are rated for fire exposure only from within the building. Fire-resistance ratings are assigned to combustible as well as noncombustible assemblies, and such ratings depend solely on the ability of the construction to meet the test criteria.

Fl re Separat Ions versus Fire-Resistance Ratlngs

It is important to keep in mind the difference between the terms fire separation and fire-resistance rating. A fire separation is defined as a construction assembly that acts as a bartier against the spread of fire. If an assembly is required to act as a fire separation, then all openings through it must be protected. A fire separation may or may not be required to have a fire- resistance rating. A fire-resistance rating measures the length of time a representative portion of the assembly is able to withstand the conditions of the

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If a fire separation is required to have a fire-resistance rating of one hour, the requirements are usually expressed in terms of "a fire separation having a fire- resistance rating of not less than 1 h." Slight differences in wording may occur, including the phrase "a 1 hfire separation," but these are all to be read with the same intent. Roofs and exterior walls are not normally required to be fire separations but in many cases are required to have a fire-resistance rating. Exterior walls that present an exposure hazard to adjacent buildings are required to be constn~cted as fire separations, even though they are permitted to have some unprotected openings (see next chapter on spatial separations). No limits are placed on the number of unprotected openings in an assembly that is only required to have a fire-resistance rating, however, openings in exterior walls will affect the required spatial separation between buildings on the same property or the distance between a building and a property line.

In general, floors must act as fire separations, but there are a number of exceptions to this requirement. Floor assemblies over crawl spaces, for example, need not be constructed as fire separations nor have a fire- resistance rating, provided they satisfy certain criteria. In these circumstances, no fire protection is required for any openings through the floor assembly, since no fire separation is required. In ot her situations openings are permitted through floors to create interconnected lloor space. This subject is considered in more detail under the heading "Interconnected Floor Space." However, in general, openings through floors that could allow fire to spread from one floor to another are required to be protected by shafts, fire dampers or fire stopping, depending on the size and function of the opening. A shaft wall that protects openings through floors is required to have a fire-resistance rating that is related tothefire-resistance rating of the floor assemblies through which it passes.

Protectlon of Openings

A closure is defined as "a device or assembly for closing an opening through a fire separation, such as a door, a shutter, wired glass or glass block, and includes all components, such as hardware, closing devices, frames and anchors." Aclosure may or may not be required to have a fire-protection rating. The term fire-protection rating is used instead of f ire-resistance rating because different criteria are used in determining the rating of a closure. Although the closure is subjected to the same exposure to heat as required in the standard wall and floor tests, the criteria for rating closures are less severe. For example, closures generally do not have to meet the criterion of

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temperature rise on the unexposed face. Exit doors in buildings more than three storeys high, including fire doors in exit shafts, are an exception to this rule. Fire doors opening onto a separated dead end conidorthat provides the only access to exit are also an exception. Temperature rise limits are imposed on these types of doors to ensure that the occupants of a building will be able to pass the fire door without being unduly affected by the heat from a fire. If an exit door is protected by an unoccupied vestibule or corridor, these limits are waived on the assumption that the potential for direct fire exposure is substantially reduced. Doors ,through fire walls have temperature rise limits because of the critical nature of this type of fire separation.

Closures are permitted to have a rating that is less than that required for the wall or floor assembly in which they are located. They normally occupy only a portion of the fire separation and do not have a stnrctural function, so a lower rating can be tolerated without undue overall reduction in fire safety. It is assumed that combustible items will not be stored adjacent to closures. An exit stair enclosure penetrating a floor required to be a fire separation with a two-hour fire-resistance rating would have to have walls with a two-hourfire- resistance rating; the exit door into the exit stairway would be required to have a 1112 h fire-protection rating and be equipped with appropriate hardware and latches. Exit doors to the exteriir do not need a fire-protection rating unless required for exposure protection.

There are special cases in which 20-minute door assemblies are permitted in fire separations required to provide up to a one-hour fire-resistance rating. A 20-minute fire-protection rating would normally be achieved by a well constructed 45-mm-thick solid core wood door with a frame and hardware designed to withstand a 20-minute fire test exposure. In general these doors are permitted only in fire separations that do not require a fire-resistance rating of more than h in buildings not more than three storeys in building height, and for suite entrance doors or doors serving classrooms or patients' bed- rooms, provided the fire-resistance rating of the corridor wall is not required to be more than one hour.

If the fire-resistance rating of a floor or roof assembly has been determined on the basis of Chapter 2, "Fire Performance Ratings" of the Supplement to the National Building Code of Canada 1985, and part or all of the required fire- resistance rating is achieved by a protective membrane, such as gypsum board or lath and plaster, openings to ducts through the ceiling membrane may be protected with fire stop flaps. A fire stop flap is a device for maintaining the integrity of the membrane fire protection, whereas afire damper is a device that

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is separately tested and rated to ensure that it will provide a specific fire- protection rating. Fire stop flaps are permitted only when openings are less than 930 cm2 and lead directly into a noncombustible duct. If an opening is less than 130 cm2, the fire stop flap may be omitted, provided the opening leads directly into a noncombustible duct. There are restrictions on the spacing and percentage of openings in the ceiling membrane in any fire compartment. If actual tests conducted on an asserr~bly have demonstrated that other sizes and quantities of openings will not reduce the fire-resistance rating below the required rating, then of course these other openings can be substituted. Figures C-1 , C-2, and C-3 show typical assemblies where fire stop flaps and fire dampers are required.

REQUIRED FlRE SEPARATIONS

FlRE DAMPERS HEL OPEN BY FUSIBLE LINKS

RESTRICTED A N D NEED N O T VERTICAL FIRE SEPARATION HAVE FIRE STOP FLAPS

Figure C-1

REQUIRED

FIRE

{

DUCT

SEPARATION

FIRE STOP FLAP BY FUSIBLE LINK

VERTICAL FlRE SEPARATION

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When membrane ceilings form part of an assembly which is rated by one of the testing laboratories mentioned previously, openings in such ceilings must be protected by those means specifically accepted by the laboratory for that assembly. The generic acceptance of protection for openings in assemblies assigned a rating on the basis of Chapter 2 of the Supplement to the National Building Codeof Canada 1985 does not apply to these proprietary assemblies. For example, recessed fluorescent lighting fixtures must be protected by the methods specified by the testing laboratory.

STRUCTURAL MEMBERS

/ VERTICAL FIRE SEPARATION

FlRE STOP FLAP

CElLING WITH FlRE RESISTANCE RATING AT LEAST EQUAL TO VERTICAL

I

FlRE SEPARATION REQUIRED FlRE SEPARATION L I Figure C-3

Portions of a protective membrane which have a lesser rating than that required for the assembly being considered must also be protected to ensure that the membrane continues to perform for the required time. A number of proprietary means have been developed, including the 'tents' for protecting recessed fluorescent lighting fixtures. The purpose of this additional protection is to prevent excessive radiated heat from enteringthe concealed space and causing premature failure of the structural members. The Code does permit minor penetrations for wiring, piping, conduit and electrical boxes without additional protection, but within certain limits.

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Firewalls are special fire separations that divide a building into two or more entities that may be considered individual buildings for the purposes of fire protection. If a building extends across a property line, a dividing wall on the property line must be constructed as a firewall. A firewall may also be constructed within a building on one property and underone ownership for the purpose of applying less stringent fire protection requirements. The building area of each portion is less than that for the whole building, since by definition the building area can be bounded by a firewall. The firewall effectively divides the building into smaller buildings, and the fire safety requirements for the individual portions can be less than for the building as a whole. One exception to this generalized requirement concerns fire alarm systems when there are doorways through a firewall. In this case the fire alarm system must be designed as though the structure were one building.

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FOOTINGS OR FOLINDATIONS

AS REQUIRED _{Figure C-5}

A firewall is defined as having "stmctural ability to remain intact under fire conditions for the required fire-rated time." This means that if a portion of the building on either side of the firewall is exposed to a fire as intense as that simulated under standard fire test temperatures, a collapse of a portion of the building during that period would not cause the firewall to collapse. If a designer chooses to use two walls that together provide the required fire- resistance rating, the collapse of one of the walls must not damage the other wall and thereby reduce its ability to remain intact for the necessary period of time. See Figures C-4 and C-5 for typical firewall details.

If a firewall is required to have a two-hour fire-resistance rating and supports a one-hour roof assembly, the roof details must be designed so that the roof can collapse without damaging the structural stability of the firewall. On the other hand, if the entire structural assembly has a two-hour fire-resistance rating, there is little to be gained by having special design features to permit the roof assembly to collapse without damage to the firewall, since by that time the firewall would no longer be expected to perform as a fire separation.

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Commentary on Part 3

Firewalls are required to be constructed so that the required fire-resistance rating is provided by concrete or masonry. Any additional material, such as a protection membrane, does not contribute to the required rating. If a firewall is supported on the structural frame of a building, such as in an offset, the supporting frame must have at least the same fire-resistance rating as the firewall. This does not, however, waive the general rule that firewalls must extend continuously from the footing through all the storeys. If a one-storey portion of a building is adjacent to a three-storey portion, the firewall must extend up the entire three storeys to complete the separation. The only exception to this rule is where the firewall is located above a basement storage garage. In this instance, the firewall may terminate at the floor assembly immediately above the storage garage, provided that floor assembly is constructed as a two-hour reinforced concrete fire separation.

Since firewalls are expected to withstand a complete burnout of any portion of a divided building, the degree of fire resistance required for the firewall depends on the fire load of the adjacent occupancies. In those occupancies with higher fire loads, such as mercantile, or high or medium hazard industrial occupancies, the firewall is required to have a fire-resistance rating not less than four hours. For the occupancies that have lesser fire loads, the fire- resistance rating has to be not less than two hours.

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Figure C-7 . . . . . . _. _. _. . .

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-Since Tirewalls are intended to prevent the spread of fire across the firewall for the duration of the rating, they are required to extend through the roof and form a parapet above the roof. This parapet must be 150 mm high for a firewall which has a fire-resistance rating of two hours and 900 mm high for a firewall which has a fire-resistance rating of four hours. If the firewall terminates at the underside of a concrete roof slab, a parapet is not required, provided the roof slab has a two-hour fire-resistance rating in the case of a firewall with a rating of four hours and the roof s!ab has a fire-resistance rating of one hour-in the case of a firewall with a fire-resistance rating of two hours (Figures C-6 and C- 7). If the difference in roof elevations on the two sides of the firewall is more than 'three metres, parapets are not necessary.

SMOKE TIGHT JOINT

Fire Stopping

Fire stops are elements of building assemblies that are installed at strategic places to resist the passage of fire from one space to another. Typically, fire stops perform two functions. One is to maintain the integrity of a fire separation, such as filling around pipe or duct penetrations. The second function is to limit the size of concealed spaces such as stud or crawl spaces, attics or ceiling spaces.

J

In typical platform type wood frame construction, fire stopping is normally provided by the top and bottom wall plates (Figure C-8). If balloon frame type construction is used, however, fire stops must be placed between the studs to prevent the passage of fire from one storey to another (Figure C-9).

. \ 2

Spaces between ceiling furring strips in buildings required to be of noncombustible construction must be fire stopped to close off any spaces that would allow the spread of fire, if the surface of the ceiling finish material that is

. . 1 . 2 h ROOF SLAB h FIREWALL 4 h FIREWALL/ 1 h ROOF SLAB TIGHT JOINT 4 . . . .' .

*'

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Figure C-10

exposed within the concealed space has a flame-spread rating of more than 25. The maximum area of the concealed space is 2

m2.

The materials used for this fire-stopping must conform to the requirements of Article 3.1.9.4. To restrict the spread of fire in an unsprinklered crawl space, the crawl space must be separated into compartments having a maximum area of 600

m2

and a maximum dimension of 30 m. The materials used for this fire-stopping must conform to the requirements of Article 3.1.9.4.

Large concealed spaces, such as attic spaces, must be fire stopped so that the area of individual compartments is not more than 300 m2 for standard combustible construction and not more than 600 m2 if the flame-spread rating of the materials within the space is not more than 25. In concealed spaces within soffits, or gambrel or mansard style roofs, the fire stopping must extend

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into the concealed space beyond the end of any required fire separation. In the case of a fire separation that is required to be noncombustible, no combustible material is permitted to extend around the end of the fire separation. The space between the upper and lower levels of a gambrel or mansard style roof must also be firestopped (Figure C-10).

A variety of materials can be used for fire stopping. The basic requirement is that the material remain in place and prevent the passage of flames when installed in a typical assembly and subjected to the exposure conditions of Underwriters' Laboratories of Canada standard CAN4-S101, "Standard Met hod of Fire Endurance Testsof Building Construction and Materials." The duration of the test is 15 minutes for fire stopping for concealed spaces, but for fire stopping around penetrations of afire separation, the duration depends on the fire-protection rating that would be required for closures. If a building is of noncombustible construction, the fire stopping must be noncombustible unless it conformsto the performance requirementsof the standardorconsists of gypsum board or wood furring strips used to attach finish materials. Typically in combustible construction, combustible materials are used. In the case of fire stopping of small concealed spaces, such as between furring strips or floor sleepers, or at floor levels, 38-rnm-thick lumber is commonly used, particularly with wood frame construction (Figure C-1 1 ). In larger spaces, such as attic spaces or spaces within gambrel or mansard roofs, sheet materials such as plywood, waferboard or gypsum board are used.

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Flamespread Ratlngs

Flame-spread ratings are specified in various articles in Part 3 to control the surface burning characteristics of building materials. The flame-spread rating of a building material is determined by standard tests (CAN4-S102 and CAN4- S102.2) in which the specimen is mounted in a test chamber with a gas burner at one end directing a flame at the specimen; a draft is induced at the opposite end. In the case of CAN4-S102, the underside of the specimen is exposed to the flame. For materials intended to be installed horizontally with the top surface exposed to air (such as carpets or attic insulation), materials that are not self supporting in the test apparatus (such as loose fill insulation), and materials that are thermoplastic, the top surface is exposed to the flame. Carpet material intended for application on floors is tested to CAN4-S102.2, whilecarpet material intended for application on walls is tested to CAN4-S102. A flame-spread rating is calculated according to the speed at which flame travels along the test specimen or the maximum distance that a flame travels in a given period of time. The rating system is complex, but essentially it attempts to compare the rate of flame travel along the surface of a material against two standard materials: red oak is 100 and asbestos cement board is 0. For example, ordinary gypsum board on this scale would have a flame- spread rating of 10 to 30, and 19-mm-thick untreated, unfinished softwood lumber would have a flame-spread rating of 65 to 150, depending on the species of wood. The standard flame-spread test equipment can also provide comparative values for smoke developed and fuel contributed ratings, again using red oak as 100 and asbestos cement board as 0. Fuel contributed ratings are not used to determine requirements for materials regulated by the NBC.

Flame-spread requirements are employed in several areas of the Code to control the characteristics of building materials. In noncombustible construction, for example,flame-spread limits are specified for many of the combustible elements permitted in these buildings. Any fire retardant treatment process for certain corr~bustible materials used in noncombustible construction is required to penetrate the material rather than be merely a surface application, and the flame spread limit is applies to "any exposed surface or any surface that would be exposed by cutting through the material in any direction." Fire-retardant- treated wood roof systems, which are permitted in lieu of unrated noncombustible construction, also have flame spread requirements to limit the propensrty of the material to propagate flame. Fire retardant treatment processes do not significantly improve the fire-resistance rating of an assem-

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bly, nor do they reduce the fire load that is contributed by the combustible material. The treatment process normally only changes the surface burning characteristics of the material.

lnterlor Flnlsh

In general, flame-spread rating requirements apply to interior finish materials and are more restrictive in the critical areas of a building, such as public corridors and exits. Ratings are generally more restrictive for ceilings than for walls. Flame-spread requirementsfor surfaces also depend on the occupancy of the room or space, with more restrictive requirements for institutional and assembly occupancies.

In high buildings (Subsection 3.2.6.), there are additional restrictionson flame- spread rating of interior finish materials. The restrictions apply only if the building is not sprinklered. Where additional flame-spread rating requirements are specified for high buildings, restrictions on smoke developed classiqfication are also specified. These additional limits on flame-spread rating and smoke developed classification apply only to the more critical areas of these buildings, including public corridors, service rooms, elevator cars, elevator and exit lobbies, and exit stairs and adjacent vestibules. The flame- spread rating for -floor surfaces in these specific areas is also regulated. All carpeting material must meet a ''flame resistance test" whereby a small combustible pellet of standard chemical composition is ignited on the surface to be tested. This is regulated under the Hazardous Products Act. If the fire or charring produced by the pellet is confined to certain specified limits of the test specimen, the carpet has passed the test. This test determines ignitability from a small ignition source rather than flame resistance and does not measure smoke production.

For certain building materials, including some foamed plastic insulations, the standard flame-spread test may not measure the relative hazard of the material in an actual fire. These materials must be protected by other less hazardous materials; the manner depends on the flame-spread rating of the material and the size of the building.

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Roof Assem bl les

Specific requirements are included for two different types of roof deck assemblies. One assembly is a fire retardant treated wood roof system that is permitted in smaller buildings of combustible construction in place of a combustible mof system having a fire-resistance rating. Limits are placed on the type of supporting structure that can be used. The other assembly that has specific requirements is a metal roof deck system which is overlaid by a material that could lead to a propagating fire under the deck. Both of these systems have to be tested in accordance with Undennrriters' Laboratories of Canada standard ULC S-126M, "Standard Method of Test for Fire Spread under Roof Deck Assemblies." The test is not required on a metal roof deck assembly that has a fire-resistance rating of 3/4 h, or where a thermal barrier protects combustible material above the roof deck from effects of fire in the space below the deck.

Roof Coverlngs

In general, Part 3 requires that all roof surfaces meet the requirements for Class A, B, or C roofs. If a rating is required, the Code does not differentiate between Class A, B, or C ratings; any one is acceptable. Class C is the lowest rating, about equivalent to the spread of flame over the surface of asphalt shingles. Untreated wood shingles would not meet the requirements of Class C. One exception is included in the Code but it applies only to Group A, Division 2 assembly occupancy buildings not more than 1000 m2 in building area and not more than two storeys in building height.

The standard Canadian test and rating procedure for mof surfaces is ULC- S107, Test Method for Fire Resistance of Roof Covering Materials." In this test, the upper surfaces of roof coverings are subjected to aflame. In addition, other samples are subjected to a 'burning brand' test to measure their ability to withstand the effect of flying brands. A Class A roof covering provides more resistance to the spread of flame and burning brands than does a Class B or Class C roof covering.

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Occupant Load

The concept of occupant load in Part 3 sometimes leads to misunderstandings. Occupant load is the number of persons for which a building or part of a building is designed. The principal application of occupant load is to determine the number and width of exit facilities that must be provided, as well as the width of access routes leading to exits from within floor areas. Occupant load is also used to determine the number of sanitary fixtures required in washrooms and whether a fire alarm system or.emergency lighting must be installed. It is also one of the parameters used in establishing whether a building is subject to the additional requirementsfor high buildings in Subsec- tion 3.2.6.

Occupant load must be determined on the basis of the total numberof persons that the building or part of the building will accommodate. Occupants of sewice spaces, such as furnace rooms and electrical equipment rooms, and transitory occupants of areas such as access corridors and washrooms, would not normally be counted in determining the occupant load, since any occupants of these areas would have already been included in the occupant load in the regularly occupied parts of the building.

As a general rule the occupant load must be wt less than that determined from Table 3.1.14.A. This table shows the area assumed to be occupied per person, so that the total occupant load can be calculated. However, due to the large potential variation in population densities in most of the categories listed, it is very difficult to establish hard and fast rules for each category. For this reason, some deviation from these values may be justified if the area is to be occupied by fewer persons. In manufacturing and process rooms, for example, a value of 4.6 m2 per person is shown. Depending on the type of manufacturing operation and the degree of automation, this value can vary widely and could be excessively restrictive. In cases such as this, the occupant load estimates may be relaxed from those calculated from the table, provided there is reasonable assurance that the occupant load will not be exceeded in the future. On the other hand, if the occupant load exceeds the values determined from the table, the higher values must be used.

Table 3.1.14.A. is not intended to limit the number of persons that can occupy an area, although it is sometimes interpreted this way. For example, even though the table lists 9.3 m2 per person for offices, it is quite permissable to have offices that provide less space per person. In this caselathe occupant load of the offices would be higher than that normally anticipated and the higher value would be used for Code purposes. However, other legislation may

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govern the maximum number of persons permitted in certain occupancies, and this legislation would be outside the jurisdiction of a building inspector, unless the inspector has been given enforcement powers under the other legislation.

In general the values listed in Table 3.1.14.A. apply to those areas intended for occupancy, including 'the space occupied by fixtures. In the case of mercantile occupancies, for example, the area per person shown in the table includes the areas occupied by the products and display counters, as well as the aisle space.

A storage area for a mercantile operation that is separate from the area accessible to the public would have to be treated separately and would nbrmal~y be considered warehouse space. In certain cases, however, the occupant load of certain non-occupied rooms must be considered in relation to the egress requirements from that room. For example, in industrial occupancies, where washrooms and osther spaces can be extensive and able to accommodate one or even two entire shifts of employees, the egress requirements from these special spaces would have to be adequate for the number of persons who could be expected to use the space at any one time. A lunch room or a cafeteria in a factory would have to have egress facilities to accommodate the anticipated occupant load from that room. However, the occupant load of the cafeteria wou Id not have to be added to the occupant load of the general factory area, in determining the total occupant load of the building since this would in effect be counting the same people twice. The same situation could arise in a school auditorium. The occupant load of the auditorium, if it is to be used exclusively for the students of the school, would not have to be added to the occupant load of the classrooms in determining the total occupant load of the school. Common sense has to be exercised as to how the occupants use a building in order to calculate the egress requirements throughout the building. If a cafeteria, gymnasium, or similar facility is available for use by persons other than the usual occupants of the building, then the occupant load of that space would have to be added to the occupant load of other parts of the building.

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Coninientary on Part 3

CHAPTER 4

REQUIREMENTS AFFECTING THE BUILDING AS A WHOLE

General

Previous chapters of this commentary have dealt with the general arrangement of Part 3 and with concepts and terminology used to develop its requirements. There would have been some advantage in having all the concepts and terminology explained in the same chapter. However, following the general arrangement of Part 3, some of the terminology and concepts are included in this chapter as well. Chapter 4 applies to the requirements in Section 3.2 of the Code that are concerned with structural fire protection by fire-resistance rating for structural members and by fire compartmentation.

Buildlng Slze Determinatlon

Since the structural fire protection requirements, as well as the scope of Part 3, depend on the building size, the Code user must be familiar with how the building size is determined. Throughout Part 3, many requirements are dependent on building height and on building area as defined in the Code. Building area is the greatest horizontal area of a building above grade within the outside surface of exterior walls or within the outside surface of exterior walls and the centre line of firewalls (Figure D-1). Asdescribed previously, the building area may be altered by the judicious use of firewalls.

BUILDING AREA WOULD BE AREA OF 3rd STOREY

Figure D-1

Building height is the number of storeys contained between the roof and the floor of the first storey. The first storey in turn is the uppermost storey having its floor level not more than 2 m above grade (Figure D-2). Thus, a building

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Commentary on Part 3 (Use and Occupancy) of the National Building Code of Canada 1985

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