Canadian Consulting Engineer

Objectives in Sight

May 1, 2000
By John C. Haysom

As Canada's first objective-based national model codes evolve towards a 2003 publication deadline, we are approaching an important step in the consultations. Committees and the staff at the Canadian C...

As Canada’s first objective-based national model codes evolve towards a 2003 publication deadline, we are approaching an important step in the consultations. Committees and the staff at the Canadian Codes Centre of the National Research Council’s Institute for Research in Construction have been carrying out a “bottom-up analysis” of all the requirements in the National Building Code, the National Fire Code and the National Plumbing Code. The results are nearly ready for public review. But it won’t be the traditional review about possible technical changes to the code requirements. Rather, it will be about the objectives of the codes.

In the past some indication of objectives was contained in the code prefaces, but these goals have never been clearly articulated. The bottom-up analysis was undertaken to rectify this situation.

Although, for example, the National Building Code is widely acknowledged to be concerned with issues of safety, health and accessibility, requirements related to several other issues have been incorporated over the years. An example: Part 9 now has two minimum widths for doors; the original was there for fire safety reasons, namely for ease of evacuation. It appears the second minimum width was introduced to make it easier to move furniture, thus addressing the issue of convenience.

During the consultation process scheduled for this fall, code users and other interested parties will be asked whether the codes should continue to address objectives that are beyond the original ones of safety, health and accessibility. Alternatively, they will be asked if the code should be contracted by dropping parts not concerned with those basic issues.

New format

The development of prototypes for the objective-based codes is also under way. The proposed format will be part of this fall’s public consultation.

It is being proposed that each new code be divided into two parts. Division A will contain the statement of the code’s objectives and functional requirements. This division will seldom need to be revised since a code’s objectives do not change frequently.

Division B will be the part for everyday use. It will set out the quantitative performance criteria with which solutions must comply to satisfy the code’s objectives. It will also provide “deemed-to-comply” solutions drawn from the current editions of the codes. This division will be revised on a regular schedule as with the present codes.

It is envisioned that Division A will have a tree-like structure of increasingly specific objectives, sub-objectives, sub-sub-objectives and functional requirements, whereas Division B will follow the discipline-based structure of the present codes.

Of course, the two divisions will be linked so that a user wishing to propose an innovative alternative to one of the acceptable solutions in Division B can quickly find the appropriate objectives and functional requirements in Division A that the alternative must satisfy.

As a by-product of the bottom-up analysis, the national model codes will also include the detailed intent statements for each code requirement. These statements will be published in a separate document, probably on CD-ROM.

Working example

Division B, the part of the code that will be used most of the time, will look much like the present code and will include all the present prescriptive and performance requirements. Users content simply to follow the current requirements need never look beyond Division B.

But if you want to try something different, the rest of the code kicks into action. In one sense, the situation will not differ from that of the present codes with their provisions for “equivalents.” However, there will be much more information available to help designers and enforcement officials evaluate proposed alternative solutions.

Consider, for example: Article (1) of the National Fire Code: Foundations and Supports:

1) Storage tanks shall rest on the ground or on foundations, supports or piling made of concrete, masonry or steel in conformance with:

a) Appendix B of API 650, “Welded Steel Tanks for Oil Storage,” and

b) Appendices C and D of API 620, “Design and Construction of Large, Welded, Low-Pressure Storage Tanks.”

Suppose you wanted to propose the use of a preservative-treated wood foundation for a storage tank. There is no indication in the above requirement as to why the support must be concrete, masonry or steel. However, once the objective-based codes are available, you could consult the intent statement for this sentence and find something like the following:

Intent: To reduce the probability that combustible supports will contribute to a fire under the tank, leading to failure of the tank from exposure to fire.

Thus, since preservative-treated wood supports are defined as combustible, they would not be acceptable.

For more information on the new codes structure, visit ccbfc/tgs/obc/index.

To take part in the upcoming public review, E-mail

John Haysom is with the Canadian Codes Centre of the NRC/IRC, Ottawa. E-mail john.haysom

Prototypes of the objective-based codes are under way.


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