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National building code update to stress design flexibility
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National Research
Conseil national
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NATIONAL BUILDING CODE UPDATE TO STRESS DESIGN FLEXIBILITY
by J.F. Berndt and G.C. Gosselin
Reprinted from
Canadian Consulting Engineer Vol. 26, No. 8, August 1984 p. 28,29
DBR Paper No. 1249
Division of Building Research
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ABSTRACT
F i r e p r o t e c t i o n r e g u l a t i o n s i n t h e N a t i o n a l B u i l d i n g Code were t r a d i t i o n a l l y developed i n r e s p o n s e t o f i r e l o s s e s and r e p r e s e n t a t i o n s from i n d u s t r y . More r e c e n t l y , advances i n t e c h n o l o g y , i n c r e a s e d knowledge, changing p h i l o s o p h i e s and u s e r n e e d s have become t h e i m p e t u s f o r Code changes. The c o n t i n u e d s u c c e s s of t h e Code i n m e e t i n g f i r e p r o t e c t i o n needs w i l l depend on d e s i g n e r s ' i n c r e a s e d knowledge of f i r e p r o t e c t i o n e n g i n e e r i n g p r i n c i p l e s .
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Les rPglements du Code n a t i o n a l du b a t i m e n t c o n c e r n a n t l a s G c u r i t 5 i n c e n d i e o n t g6nl5ralement l5t6 l5laborGs 5 l a s u i t e de
p e r t e s caus'ees p a r l e f e u ?i l a requGte d e s r e p r g s e n t a n t s de l ' i n d u s t r i e . P l u s r G c e m m e n t , c e s o n t l e s p e r c C e s t e c h n o l o g i q u e s , 11am151ioration d e s c o n n a i s s a n c e s , d e n o u v e l l e s o p t i q u e s e t l e s b e s o i n s d e s u t i l i s a t e u r s q u i o n t entra2nl5 d e s m o d i f i c a t i o n s a u Code. Le succGs du Code e n matisre de p r o t e c t i o n i n c e n d i e dgpendra dans une l a r g e mesure d'une m e i l l e u r e compr6hension d e s p r i n c i p e s d e p r o t e c t i o n i n c e n d i e d e l a p a r t d e s c o n c e p t e u r s . - -
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Fire & Security
National Building Code update
to stress design flexibility
By John F. Berndt, P. Eng. and Guy C. Gosselin, P. Eng.*
v
oluntary fire protection is probably as old as fire itself. Over the years, however, the ravages of fire made it evident that this voluntary approach was ineffec- tive in preventing conflagrations or large losses of life. The major obstacle in developing adequate protection was a lack of understanding of the growth and spread of fire. Thus, it is not surprising that early attempts to legislate fire-safe or fire-resistant building construction methods were very conservative.Also characteristic of early build- ing regulations was the tendency to adopt band-aid solutions to prevent the recurrence of fire caused by specific hazards. Although helpful, these specific rules were inflexible and also inconsistent in treating
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comparable fire risks.The National Building Code (NBC), first published in 1941, reflects the minimum levels of fire safety deemed acceptable to Canadi- an society. Society's changing norms and the shortcomings of early fire- regulations are the main justifications for revising the NBC. This article discusses some of the more recent code revisions, the factors that ini- tiated them and the approaches followed in their review.
Stimuli for code changes
In the early years, changes to the NBC often resulted from social pres- sure following a major fire or from industry representations. Although no longer predominant, these still influence the code change process. For example, a dramatic fire that
'John Berndt, P.Eng., and Guy Gosselin, P.Eng., are with the Codes and Standards Group of the Division of Building Research. National Research Council of Canada, Ottawa.
Berndt
spread quickly through a row-hous- ing complex in Winnipeg in 1980 led to code changes intended to prevent similar disasters in new construc- tion.
In another case, manufacturers of sheet-steel/foamed-plastic sandwich panels demonstrated that a generic assembly, by meeting a specified performance level, could provide protection equivalent to that of foamed-plastics covered with a heavy thermal barrier. Permission to use these wall panels in buildings of noncombustible construction was eventually included in the NBC.
Although these traditional reasons for change still emerge sporadically, fortunately they are now overshad- owed by other catalysts of a less urgent character. As a result code committees can devote more atten- tion to the many proposals for change. They now have a better opportunity to carefully review per- ceived hazards, develop appropriate
Gosselin
provisions to counteract those haz- ards and apply new fire protection knowledge. This more in-depth response results in consistent require- ments that are in keeping with the overall level of safety contemplated by the NBC.
Occupant needs
For instance, accommodating oc- cupant needs is rapidly growing in importance as a reason for code change. In the past, flexibility and efficiency were often ignored in favor of safety, resulting in regulations that conflicted with the functional goals of the building. One example is hospi- tals and nursing homes where fire compartmentation rules calling for doors with closers contradicted the access needs of the staff in perform- ing their duties.
In the last five years, through collaboration with the health care community, an alternate means of ensuring patient safety from fire has Canadian Consulting Engineer - August, 1984
evolved. By analyzing the hazards inherent in hospitals and nursing homes, and by acknowledging train- ing of health care staff and other available means of fire protection, an interactive approach to fire safety was developed.
Another example of accommodat- ing user needs through code changes is the permission to use electromag- netic locking devices on exit doors. These devices are required to have certain features that reconcile the need for improved security in build- ings with that for unrestricted eva- cuation in the event of a fire.
Many arbitrary provisions of past codes, now considered overly conser- vative, are gradually being relaxed as more information becomes available. Recently, for instance, researchers demonstrated that penetration of a fire separation by a combustible drain, waste or vent (DWV) pipe could be effectively protected to
changes of philosophy. For instance, experience has established that a well designed and supervised automatic sprinkler system not only minimizes property loss but provides a high level of life safety. A change in code philosophy has thus placed greater dependence on sprinklers as a reliable fire protection measure. This is demonstrated by the increasing relax- ation of other protection measures in fully sprinklered buildings, including the recent waiving of all roof ratings and the deletion of redundant provi- sions for atrium spaces.
With the expansion of barrier-free access for physically disabled persons in buildings, the code committees recognized the need to provide for the safety of these people. Special meas- ures were thus developed and incor- porated in the NBC, a move which departs from the previous phlosophy of not distinguishing physically dis- abled persons from other occu-
approach for covered malls with an oversized corridor concept. This accommodated both the safety needs of the public and the commercial needs of the owner. However. in the development of this approach, many related issues arose. For example, it was recognized that an occupant load should be stipulated for the pedestri- an mace itself. Also taken into consideration were the merits of interconnecting two levels with a large opening and the most cost effective method of providing safe egress for the occupants.
The egress problem was resolved by adapting a new fire protection concept originating in Great Britain wluch calls for a large unobstructed space at the top of the mall to collect and dilute smoke. To ensure that smoke production does not over- whelm t h s reservoir, provision was also made for automatic suppression by sprinklers.
prevent the passage of-flames, even pants.
when subjected to a pressure differen- Looking ahead
The ultimate success of the Nation- tial. This led to a relaxation of the rule Code responses a1 Building Code in responding to that prohbited this piping from Whatever the initial reason for a need for change is measured by the penetrating rated fire separations. code response, i.e. a change in tech- practicality and effectiveness of the Experiments also demonstrated that nology, philosophy, research infor- requirements whle in use. Success fire does not spread in a cavity wall mation or user needs, most cannot be hinges on a systematic evaluation of filled with insulation. The NBC considered in isolation; many factors the problem and the impact potential requirement to fire-stop such cavities need to be considered. Past code solutions have on building design and was thus eliminated. responses were often subjective and cost; it also depends on the available
Similarly, studies of stairs showed limited because of insufficient knowl- knowiege on which to base the that the rise/run product rule regulat- edge in fire matters. Now, more evaluation,
ing stair treads and risers prohibited information allows the committees to AS more is learned, prescriptive many geometries of equivalent safety. recognize the many Parameters code requirements will be replaced by The product rule was therefore del- involved and to apply the principles the performance type - a transition eted in favor of specific limits on of fire protection engineering in similar to that which took place in tread and riser dimensions. formulating a response. A ComPre- ~tructural design after World War 11. hensive evaluation can be made only Among the direct benefits of such a Technological advance after identifying the hazards and transition are greater economies and Advances in technology represent considering the impact of control flexibility in building design and another stimulus that must also be measures on design flexibility and construction. BY increasing their accommodated through code revi- construction costs. knowledge of the principles of fire sions. A typical example is the T h s multifaceted code response is protection engineering, designers development, in the past decade, of illustrated by the recent redirection in could contribute significantly to the sensitive, reliable and inexpensive regulations for covered malls. Origi- process of changng the code. They smoke detectors. More recently, fire nally intended solely as sheltered would also gain more freedom in alarm systems with a multiplex fea- pedestrian concourses between exist- determining how to design a "fire- ture have been developed that are ing buildings, the covered mall con- safe" building withn the code param- considerably less expensive to install cept rapidly became popular in the eters.
and maintain. In both cases, code new construction of major retail changes were necessary to acknowl- complexes. Also, a trend developed to edge t h s new technology. conduct commercial activities in the
The examples mentioned so far are pedestrian concourses themselves. responses to external influences. Fre- The committees responded to quently, discussions within the code those changes in user needs by committees themselves lead to replacing the traditional regulatory
Reprinted from
T h i s p a p e r , w h i l e b e i n g d i s t r i b u t e d i n r e p r i n t form by t h e D i v i s i o n of B u i l d i n g R e s e a r c h , remains t h e c o p y r i g h t of t h e o r i g i n a l p u b l i s h e r . It s h o u l d n o t be reproduced i n whole o r i n p a r t w i t h o u t t h e p e r m i s s i o n of t h e p u b l i s h e r . A l i s t of a l l p u b l i c a t i o n s a v a i l a b l e from t h e D i v i s i o n may be o b t a i n e d by w r i t i n g t o t h e P u b l i c a t i o n s S e c t i o n , D i v i s i o n of B u i l d i n g R e s e a r c h , N a t i o n a l R e s e a r c h C o u n c i l of C a n a d a , O t t a w a , O n t a r i o , K l A OR6.
