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Principles of Fire Protection Applied in Part 3: Use and Occupancy,
National Building Code of Canada
TILL N21t2 n 6 . 2 7 2 , c . 2 i gLDc
NATIONAL RESEARCH COUNCIL OF CANADA DIVISION OT' BUILDING RBSEARCH
PRINCIPLES OF FIRE PROTECTION APPLIED IN PART 3 :
U S E A N D O C C U P A N C Y ,
NATIONAL BUILDING CODE OF CANADA b y R . S . F e r g u s o n n t t i i I \ r " . r l l l ' r I . - L ; ' " L I f , , r J T e c h n i c a l P a p e r D J o . 2 7 Z o f the D i v i s i o n o f B u i l d i n g R e s e a r c h O T T A W A M a r c h 1 9 7 0
T h i s technical paper was first prepared as notes for a l e c t u r e at the Ontario Fire College. T h e same lecture was i n c l u d e d in the program for the canadian Building officials c o n f e r e n c e i n Halifax in L964. It has also been used as a text f o r courses given by Professor J e a n L u c p o u l i n at the school of A r c h i t e c t u r e , U n i v e r s i t y o f Montreal.
T h e concepts discussed in this paper explain certain general a s p e c t s of the 1960 edition of the National Building Code. Atthough t h e c o d e was revised in 1965 and a new revised edition will appear i n 1970, this paper still reflects the basic concepts of part 3. It i s h o p e d t h a t i t m a y c o n t i n u e t o a s s i s t b u i l d i n g c o d e users by pro-v i d i n g a basis of understanding for a subject that is becoming i n c r e a s i n g l y c o m p l e x .
P R I N C I P L E S O I ' F I R E P R O T E C T I O N
APPLIED IN PART 3: U S E A N D O C C U P A N C Y ,
NATIONAL BUILDING CODE OF CANADA by R . S . F e r g u s o n R e d u c e d t o i t s s i r n p l e s t t e r r n s , f i r e p r o t e c t i o n i s r e q u i r e d f o r t h r e e p u r p o s e s : t h e p r o v i s i o n o f 1 . s a f e m e a n s o f e g r e s s , Z . s t r u c t u r a l s t a b i l i t y u n d e r f i r e c o n d i t i o n s , a n d 3 . p r o t e c t i o n a g a i n s t f i r e s p r e a d . F i r e p r o t e c t i o n i s c o r n p l e r n e n t a r y t o f i r e f i g h t i n g . T h e p r o t e c t i o n given to the building assists the Fire Departrnent in rnuch t h e s a r n e w a y a s r n i l i t a r y f o r t i f i c a t i o n s a s s i s t e d t h e a r r n i e s o f o l d . I n f i r e engineering parlance these two cornplernentary functions a r e k n o w n a s A c t i v e D e f e n c e ( t h e p a r t o f t h e F i r e D e p a r t r n e n t ) a n d P a s s i v e D e f e n c e ( t h e p a r t o f t h e B u i l d i n g D e p a r t r n e n t ) . T h i s
r e l a t i o n is shown in Figure I.
MEANING OF TERMS AND SCOPE AND A P P L I C A T I O N O F R E Q U I R E M E N T S
F o r the purposes of regulation the National Building Code e s t a b l i s h e s t h r e e c a t e g o r i e s o f s p a c e w i t h i n b u i l d i n g s . T h e f i r s t i s a space in a building that accornrnodates an occupancy. T h i s t y p e o f s p a c e c o u l d b e a n o f f i c e , a u d i t o r i u r n , b a t h r o o r n ' o r i t c o u l d b e g r o u p s o f s u c h r o o g l s s e r v e d b y a c o r r i d o r . S u c h a s p a c e i s c a l l e d a f l o o r a r e a ( F i g u r e 2 ) .
T h e s e c o n d c a t e g o r y i s a n e x i t . A n e x i t a l w a y s l e a d s f r o r n a f l o o r a r e a t o t h e o u t s i d e . T h u s an exit could be rnerely a doorway, b u t i t c o u l d a l s o b e a c o r n b i n a t i o n o f d o o r w a y s , s t a i r s a n d P a s s a g e -w a y s . A n e x i t i s d i f f e r e n t f r o r n a f l o o r a T e a b e c a u s e i t a l w a y s h a s t h e s a r n e p u r p o s e - r r e g r e s s r r ( F i g u r e 3 ) .
T h e third category is space that is norrnally unoccupied, s u c h a s an attic or crawl space. I t is different frorn the other two cate-g o r i e s b e c a u s e it is not intended for use by the buildincate-g occupants ( F i g u r e 4 ) .
T h e t h r e e c a t e g o r i e s o f s p a c e , f l o o r a r e a s ,
e x i t s , and
a t t i c , c r a w l a n d d u c t s p a c e s ,
a r e q u i t e d i s t i n c t , f r o r n t h e v i e w p o i n t o f intended purpose or function. A s rnany fire };.azards are related to function, these categories forrn l o g i c a l and convenient divisions for fire protection regulations. F o r e x a r n p l e , t h e l i r n i t s o n c o m b u s t i b l e f i n i s h e s a r e q u i t e d i f f e r e n t f o r t h e d i f f e r e n t c a t e g o r i e s t t h e p r e c a u t i o n s s u i t a b l e f o r o n e f l o o r a r e a
would not be suitable for rnany others, but those suitable for one exit would do for all. Again, an irnportant requirernent lirnits obstructions within the required width of an exit. It would be irnpractical to apply t h i s w i t h i n a floor area between pieces of furniture, b u t b e c a u s e o f t h e classification i t c a n b e a p p l i e d t o a l l e x i t s w i t h o u t d i f f i c u l t y o r f e a r of rnisinterpretation. I t rnight be supposed that there is no
} r a z a r d in attic duct and crawl spaces because these are never occupied, b u t this is not the case. T h e r e i s a different hazard. A f i r e c a n
o c c u r and develop without being seen.
T h e f i r e h a z a r d s a n d p r e c a u t i o n s r n o s t e a s i l y r e l a t e d t o t h e s p a c e s in buildings, a s d e f i n e d h e r e , are those that directly a f f e c t Iife. It is obvious that one cannot be in a building without being in o n e or other of these spaces. T h e l i f e s a f e t y p r o b l e r n f o r t h e o c c u p a n t s of any space where a fire occurs is related directly to t h e hazards within that one space and the rneasures, s u c h a s c o n t r o l o f flarne spread and rneans of egress, that are taken to neutralize t h e r n . T h e l i f e safety for occupants of other spaces depends on i s o l a t i o n b y f i r e separation frorn the burning space and access to e x i t s sirnilarly s h i e l d e d f r o m t h e f i r e .
A f i r e c a n c r e a t e h a z a r d s o t h e r t h a n d i r e c t l i f e h a z a r d s . P r o t e c t i o n r n u s t b e g i v e n to the firernen. T h i s is obtained through f i r e endurance of the structural p a r t s of the building. T h e n e e d i n c r e a s e s w i t h i n c r e a s e d b u i l d i n g s i z e b e c a u s e a l a r g e r b u i l d i n g c a n cause a fire of longer duration. T h e h a z a r d o f f i r e s p r e a d b e t w e e n buildings is also related to the building rather than the i n d i v i d u a l s p a c e s . B e c a u s e o f t h e s e h a z a r d s a n d o t h e r s i t i s n e c e s s a r y to recognize the building as a single entity as well as t h e individual interior s p a c e s .
3
-T h e classification o f space within buildings has been developed f o r the purposes of the National Building Code and is reflected in the
s p e c i a l arrangement o f P a r t 3, applied in the 1965 edition. T h e section h e a d i n g s are as follows:
3 . 1 I n t e r p r e t a t i o n
3 . 2 R e g u l a t i o n s applying to buildings
3 . 3 R e q u i r e r n e n t s f o r fire safety within floor areas 3 . 4 R e q u i r e r n e n t s f o r e x i t s
3 . 5 A t t i c , d u c t a n d c r a w l s p a c e s 3 . 6 H e a l t h r e q u i r e m e n t s
l l / i t h i n this basic grouping the regulations are gradually being r e f o r r n e d through periodic revisions. I t is probable therefore that t h e developrnent of Part 3, Use and Occupancy, will continue for at I e a s t a n o t h e r t e n y e a r s .
MEANS OF EGRESS
I n the National Building Code rneans of egress includes access t o an exit, and exits. T h e designation rraccesstt applies within floor areas a n d that of trexitrt applies only beyond the boundary of the floor area. A r y s P a c e within a floor area, including passages and corridors o r t h e space b e t w e e n d e s k s o r s t a i r s l e a d i n g t o a r n e z z a n i n e i s r r a c c e s s t o a n e x i t . t l
A door leading frorn a floor area to a street or a safe place of r e f u g e is an ltexitrr door. I t is a rule that an exit is a safe place; t h e r e f o r e i t l e a d s either directly to a street or indirectly, t h r o u g h a
s e r i e s o f s t a i r s a n d p a s s a g e w a y s , t o a s t r e e t . T o e n s u r e t h a t t h e s e e x i t s a r e s a f e p l a c e s o f r e f u g e , a l l e x i t f a c i l i t i e s - s t a i r s , p a s s a g e w a y s , e t c . - a r e s e p a r a t e d b y f i r e s e p a r a t i o n s f r o r n t h e f l o o r a r e a s . T h u s a f l e e i n g occupant who enters an exit should not have to re-enter a floor a r e a , b u t should be able to proceed through a clearly-rnarked a n d w e l l -p r o t e c t e d r o u t e t o a s t r e e t . I
I-
T h e N a t i o n a l Building Code follows usual practice t o t h i s r u l e in the rnain lobbies of large buildings. e x i t s are permitted to pass through a rnain lobby, a r e a .
and rnakes an exception One -half of the required t h u s r e - e n t e r i n g a f l o o r
T h e d e c i s i o n t o r n a k e a clear distinction b e t w e e n an exit and t h e p a r t o f t h e e g r e s s f a c i l i t i e s w i t h i n f l o o r a r e a s ( a n a c c e s s t o a n e x i t ) w a s a n o r i g i n a l d e c i s i o n r n a d e i n t h e N a t i o n a l B u i l d i n g C o d e ,
1 9 4 L . The staternent frorn that edition which expresses it best is -I t H a l l w a y s and corridors are not, in general, considered to be exits, b u t are regarded as providing access to exits frorn the storey or floor
a r e a i n w h i c h t h e y a r e l o c a t e d . H o w e v e r , a h a l l w a y o r c o r r i d o r r n a y f o r r n p a r t o f a n e x i t , e . g . a c o r r i d o r c o n n e c t i n g a s t a i r w a y t o t h e e x t e r i o r o f t h e b u i l d i n g ; and such a hallway or corridor i s c o n s i d e r e d a n interior p a s s a g e w a y and rnust cornply with the requirernents
d e s c r i b e d h e r e i n ( e x i t r e q u i r e r n e n t s ) f o r a n i n t e r i o r p a s s a g e w a y . t t T h i s i n f e r s t h a t u n l e s s a p a s s a g e w a y i s a n e x i t p a s s a g e w a y i t n e e d not cornply.
I n brief, r n e a n s o f e g r e s s e x t e n d f r o r n a n y p o s i t i o n i n a f l o o r a r e a t o t h e s t r e e t . T h e p a r t of these rneans that lies within a floor a r e a is an access to an exit. T h e p a r t that continues from the boundary o f a floor area is an exit.
M e a n s o f E g r e s s w i t h i n F l o o r A r e a s ( a c c e s s t o e x i t s )
I n the National Building Code rneasures for egress safety w i t h i n floor areas are found in Section 3. 3 'rRequirernents for Floor A r e a s . t r I t i s a g e n e r a l p r i n c i p l e o f e g r e s s s a f e t y f r o r n f l o o r a r e a s t h a t f r o r n any point within a floor area it should be possible to gain a c c e s s t o at least two exits rernote frorn each other so that the a c c e s s p a t h t o o n e i s d i f f e r e n t a n d g e n e r a l l y i n t h e o p p o s i t e d i r e c t i o n f r o r n t h a t o f t h e o t h e r . W h e r e i t i s n e c e s s a r y t o t r a v e l t h e s a m e p a t h over part of the distance to either exit, this cornrnon path is k n o w n as a dead end. There is only one way out.
I n p r a c t i c e , i t i s irnpossible to avoid dead ends cornpletely. T o do so would require, f o r e x a r n p l e , t h a t t h e r e b e t w o d o o r s t o e v e r y b e d r o o r n and bathroom. T h e i r n p r a c t i c a b i l i t y o f this leads q u i t e n a t u r a l l y t o c o r n p r o r n i s e and cornprornise leads to inconsistency.
This has been anticipated in the National Building Code and countered
w i t h a further ru1e. When a floor area is divided into roorns or
s u i t e s s e r v e d b y c o r r i d o r s , t h e t r a v e l d i s t a n c e i s r n e a s u r e d f r o r n t h e d o o r of the roorn or suite. R o o r n s or suites are private rather than p u b l i c places and egress arrangernents within thern are therefore o f l e s s p u b l i c c o n c e r n .
5
-A c c e p t i n g that there are dead ends within suites, the National B u i l d i n g Code does not tolerate a dead end beyond the threshhold of a n y one. T o do so would create a situation where the occupants of o n e suite have only one path of egress travel while those in another h a v e t w o . A s t h e c o d e e s t a b l i s h e s t w o m e a n s o f e g r e s s a s a safe m i n i r n u r n , t o p e r r n i t one for some rooms or suites would be to create a double safety standard that would quite arbitrarily afford less
s a f e t y to sorne occupants than to others. N o national reference document s h o u l d be so arbitrary o r d i s c r i r n i n a t o r y r e g a r d i n g the value of the
l i v e s of building occupants. T h e excuse of hardship is sornetirnes u s e d f o r p e r r n i t t i n g s o f i r e d e g r e e of relaxation, b u t this is one case w h e r e l r d e g r e e s r ! a r e v a l u e l e s s . T h e r e a l e r r o r i n s u c h a p o l i c y i s t h e failure to see that the dead endhazard is not one of degree. r t i s not a guestion of shades of grey but one of black and white. B o t h l i t e r a l l y a n d f i g u r a t i v e l y t h e r e are no two ways about itl
A century ago one exit was perrnitted frorn all roorns and s u i t e s . T h i s was, in effect, an unlirnited dead end. Now the practice is quite cornrnon in North America of perrnitting lir,nited dead ends. Z The intention is to rnitigate the hazard to a degree without creating t o o great a hardship, but instead, this policy elirninates the problern w i t h respect to sorne suites and leaves it completely unchanged with r e s p e c t t o o t h e r s .
r n b r i e f , the policy expressed in the National Building code i s to provide two means of egress for the occupants of any floor ar ea. T h e dernands of this purpose rnust be considered in con;unction with t h e needs of occupancy and there rnust be sorne give and take. Where r e l a x a t i o n is necessary an atternpt is rnade to apply it consistently a n d to avoid discrirnination. F i g u r e 5 illustrates t h e characteristics o f floor areas in relation to egress safety and how the requirernents r n a y b e r n e t w i t h d i f f e r e n t d e s i g n s ( s e e a l s o A r t i c l e 3 . 3 . 1 . l . N . B . c . ) .
2
- T h e
N F P A B u i l d i n g Exits Code 1966 perrnits dead ends of occupancies a s f o l l o w s : a s s e r n b l y , educational, i n s t i t u t i o n a l , r e s i d e n t i a l , m e r -c a n t i l e , offi-ce, industrial, s t o r a g e . T h i s paper was prepared for
I e c t u r e s in 1963. S i n c e that tirne the National Building Code has been r e l a x e d , a l l o w i n g a short dead-end in apartment buildings.
I t r n a y b e s e e n f r o m F i g u r e 5 t h a t t h e r e a r e r e a l l y o n l y t w o b a s i c d e s i g n s o f f l o o r a r e a s . O n e i s a n r r o p e n t t f l o o r a r e a w h e r e m o v e r r l e n t i s r e l a t i v e l y u n h i n d e r e d ; t h e o t h e r i s a r r c l o s e d t r floor a T e a w h e r e I n o v e r n e n t i s c h a n n e l l e d i n d e l i b e r a t e w a y s . T h e o p e n f l o o r a r e a p r e s e n t s n o s p e c i a l p r o b l e r n s b u t t h e c l o s e d o n e d o e s , a n d a p o l i c y r e g a r d i n g d e a d e n d s i s f o r r n u l a t e d . I t r n u s t n o w b e c o n f e s s e d t h a t a d e l i b e r a t e s i r n p l i f i c a t i o n h a s b e e n u s e d i n t h i s a r g u r n e n t f o r t h e s a k e o f c l a r i t y . O n e i r n p o r t a n t
variable has not been neentioned until nov/. The following rernarks
a p p l y t o w h a t r n i g h t b e d e s c r i b e d a s e x t r e r n e s i n s i z e a n d p e r t a i n t o b o t h f l o o r a r e a s a n d r o o r n s . W h e n a f l o o r a r e a i s l e s s t h a n 1 0 0 0 s q f t , c o n t a i n s n o h a z a r d o u s o c c u p a n c y , a n d i s i n t e n d e d f o r l e s s t h a n 6 0 p e r s o n s , i t c o r r e s p o n d s I n o r e o r l e s s t o a r o o l n a n d o n l y o n e e x i t i s r e q u i r e d . C o n v e r s e l y , w h e n a r o o r n e x c e e d s 1 0 0 0 s q f t i n a r e a o r i s i n t e n d e d f o r m o r e t h a n 6 0 Persons, it is required to have two d o o r s s e r v i n g a s e x i t s o r , w h e r e i t i s p a r t o f a c l o s e d f l o o r a r e a , t w o d o o r s g i v i n g a c c e s s t o e x i t s . I n s o r n e o c c u p a n c i e s s u c h a s
assernbly, the interior arfallgelrlents such as aisle and seating
a r r a n g e m e n t s a r e a l s o r e g u l a t e d .
T h u s , w h i l e t h e r u l e s d i f f e r a c c o r d i n g t o t h e v a r y i n g
h a z a r d s o f o c c u p a n c y a n d f l o o r a r e a s r n a y b e v e r y s r n a l l a n d r o o r n s v e r y l a r g e , 1 0 0 0 s q f t i s a s s u r n e d t o b e t h e c r i t i c a L a t e a , b e l o w w h i c h r u l e s are generally relaxed and above which they often becorne r n o r e s t r i n g e n t .
E x i t s
E x i t s are spaces outside the floor area intended only for e g r e s s . A s t h e s e s p a c e s a r e l i r n i t e d t o a s i n g l e p u r p o s e t h e y c a n b e s p e c i f i e d i n a p r e c i s e r n a n n e r . I n S e c t i o n 3 . 4 i n t h e
N a t i o n a l B u i l d i n g C o d e t h e d i r n e n s i o n a l r e q u i r e r n e n t s , c o n s t r u c t i o n , f i n i s h e s , e q u i p r n e n t a n d h a r d w a r e r e q u i r e r n e n t s f o r e x i t s a r e t o b e f o u n d .
T h e specifications f o r stairs and rarnPs and other types of e x i t f a c i l i t i e s f o r r n p a r t o f t h i s S e c t i o n . T h i s i s o f r e a l s i g n i f i c a n c e . I t c o n f i r r n s w h a t h a s n o t b e e n r n a d e c l e a r b e f o r e - t h a t t h e s e
dernanding specifications apply to exit facilities only and not to the
e g r e s s f a c i l i t i e s w i t h i n f l o o r a r e a s . T h e t r e a d a n d r i s e r r e q u i r e r n e n t s d o n o t a p p l y t o t h e s t e p s i n a s l o p i n g t h e a t r e b a l c o n y a n d t h e g u a r d
7
-r a i l -requi-re-rnents d o n o t apply to such balcony railings. A l s o , the 3-ft rninirnurn exit width does not prohibit a door as narrow a s l ft 8 in, provided it is not an exit door.
B e f o r e this arrangement was effected in the National Building C o d e , it was cornrnon practice to list exceptions to these rninirnurns, and while the list of exceptions grew it could never keep up with the situations that were continually arising. The exceptions proved. the n e e d to reconcile the sornetirnes conflicting dernands of occupancy a n d egress in floor areas. T h e new arrangernent accornplishes this c o n v e n i e n t l y . I t p r e s e r v e s t h e i d e n t i t y o f e x i t s , l i r n i t s the cornprornise o f e g r e s s f a c i l i t i e s t o f l o o r a r e a s , a n d c o n v e r t s w h a t used to be
e x c e p t i o n s for special occupancies to honest functional differences. H e n c e f o r w a r d , w h e n there are differences in the standards of egress f a c i l i t y between occupancies, it is hoped that these will be expressed p o s i t i v e l y i n the National Building Code in Section 3.3, Requirernents f o r Fire Safety within Floor Areas.
STABILITY UNDER FIRE CONDITIONS
F i r e p r o t e c t i o n i s a t e r m o f t e n u s e d l o o s e l y t o d e s c r i b e t h e q u a l i t y suggested by the title of this chapter. r n this paper fire p r o t e c t i o n is used in the general rather than the specific sense. F o r Example, t h e terrn fire protection ernbraces exit facilities a s well as the structural p r o t e c t i o n found in walls, columns and f l o o r s . T o distinguish the latter other more precisely descriptive w o r d s a r e u s e d
-F i r e r e s i s t a n c e i s t h e t e r r n c o r n m o n l y u s e d t o d e s c r i b e the a b i l i t y of construction to withstand the ravages of fire. T h e terrn i s , however, not very descriptive o f t h e test that rneasures this quality and the word rrendurancett is corning into rnore cornrnon use a s a replacernent for the word resistance.
T h e significance of fire endurance for building safety is i r n p l i c i t in the history of fire testing. T h e first attempt to rneasure f i r e resistance was rnade in London before 1900 by the fire officers comrnittee, and the beginning in North America carne afterward i n the early lgoots when the building departrnent of New york a p p r o a c h e d colurnbia university t o t e s t n e w rnaterials that had
b e e n s u b r n i t t e d a s s u b s t i t u t e s f o r t h o s e c o r n r n o n l y u s e d . 3 T h e s e w e r e
alrnost invariably rnanufactured rnaterials. The concept of fire
e n d u r a n c e i s , t h e n , l i k e s o m a n y o t h e r t h i n g s ' a n e x p r e s s i o n o f t h e n e w industrial a g e .
A t the University D r . I n g b e r g b u i l t a f u r n a c e , r o u g h l y a 1 0 - f t c u b e . A test specirnen could be substituted for one side or the top. A cord of wood was used for fuel and sufficient venting and air for c o r n b u s t i o n w a s p r o v i d e d . D u r i n g t h e t e s t t e r n p e r a t u r e r e a d i n g s i n s i d e t h e r o o r n w e r e t a k e n a n d t h e t e r n p e r a t u r e o n t h e u n e x p o s e d
s i d e o f t h e s a r n p l e w a s r n e a s u r e d . T h e tests were carefully watched f o r other phenornena and failure criteria w e r e e s t a b l i s h e d , b u t t h e s e d e t a i l s g o b e y o n d t h e p u r P o s e o f t h i s p a p e r .
The following description is a very general approxirnation of
t h e tests. T h e test sarnple was built or fixed in place, the therrno-c o u p l e s w e r e i n s t a l l e d a n d , w i t h t h e r o o r n e n therrno-c l o s e d a n d p r e p a r e d , t h e c o r d o f w o o d w a s i g n i t e d . T h e t e r n p e r a t u r e i n c r e a s e d t o a b o u t 1 ? 0 0 " F
andtlren dropped, total burnout being completed in about I hour. 1trhen
t w o c o r d s o f w o o d w e r e u s e d t h e f i r e w a s h o t t e r a n d a l s o l o n g e r . ' B u t c o r d w o o d i s n o t t h e r n o s t p r e d i c t a b l e f u e l , and eventually a standard t e s t p r o c e d u r e w a s d e v e l o p e d . T h e rise of ternperature w i t h t i m e
was rnade part of the standard, so that instead of the ternperature
i n s i d e t h e f u r n a c e b e i n g l n e a s u r e d i t w a s c o n t r o l l e d t o c o r r e s p o n d t o t h i s t i r n e t e r n p e r a t u r e r e l a t i o n . 4 I n t h i s w a y a l l s a r n p l e s w e r e s u b j e c t e d t o t h e s a r n e c o n d i t i o n s . T o d a y l r l a n y c o u n t r i e s h a v e s u c h a s t a n d a r d , a n d w h i l e t h e t i m e t e r n p e r a t u r e c u r v e s d i f f e r t h e s e d i f f e r e n c e s a r e n o t y e t i r n p o r t a n t t o b u i l d i n g r e g u l a t i o n s . F o r exarnple, t h e N a t i o n a l B u i l d i n g C o d e o f C a n a d a a c c e p t s b o t h t h e B r i t i s h a n d A m e r i c a n t e s t s w i t h o u t q u a l i f i c a t i o n . ?
" I t i" not unusual to find that new rnaterials are asked to rneet c e r t a i n p e r f o r r n a n c e c r i t e r i a b y r i g o r o u s t e s t t h a t t r a d i t i o n a l l y a c c e p t e d r n a t e r i a l s a n d c o n s t r u c t i o n f a i l e d t o p a s s .
4 T h .
c u r v e w h i c h r e s u l t s f r o r n p l o t t i n g f u r n a c e t e r n p e r a t u r e a g a i n s t
9
-T h i s test has been of real significance in the developrnent o f building technique. B e f o r e the test it had been necessary to rely cornpletely on experience, and change and irnprovernent was rnade b y cautious steps over long intervals. T h i s was quite intolerable i n a fast rnoving industrial age.
T h e reader will wonder perhaps at the irnportance placed o n this test, since it is really a relation between the burning of an a r b i t r a r y q u a n t i t y of wood and the ability of a construction to stand u p to it. W h a t is its relation to actual fires?
U n t i l 1940 this link was rnissing. I t was known that the i n t e n s i t y and duration of a fire were related to the arnount of fuel, b u t it was not until the late I930ts that authorities in Washington
m a d e any real surveys of cornbustibles in buildings. T h i s inforrnation w a s available after the war. T h e c o r n b u s t i b l e content of about 60 buildings o f different occupancies was rrreasured and the results were tabulated i n the forrn of weight per unit of floor area. T h i s new rneasure was t e r r n e d the fire load: the weight of combustible load per sq ft of floor a r e a .
T h e fire load of the cord of wood of the original test, or i t s equivalent fuel supply in later tests, could be deterrnined. T h i s w a s the link between the test fires and real fires. T h e figures that c a n b e g i v e n h e r e a r e v e r y r o u g h . T h e fire load in a l-hr fire test i s a b q r t l 0 l b p e r s q f t a n d i n a z - h r test about z0 lb per sq ft (l cord o f w o o d s p r e a d o u t e v e n l y o v e r I 0 0 sq ft is about l0 lb per sq ft). T h u s , c o n s t r u c t i o n w i t h a 1-hr fire resistance will withstand a b u r n o u t where the fire load of the space is lo Ib, and construction h a v i n g a 2-Jr.r fire resistance can withstand a burnout when the fire l o a d of the space is 20 lb. The relation between fire load and fire r e s i s t a n c e w a s e s t a b l i s h e d , a n d i t was possible then to predict the r n i n i r n u r n fire resistance for buildings of different occupancies. F I R E RESISTANCE - APPLICATIONS
r t is irnportant to recognize the distinction rnade in the N a t i o n a l Building Code between fire resistance and fire separation. F i r e r e s i s t a n c e o r f i r e e n d u r a n c e r e f e r s to a quality of the
c o n s t r u c t i o n o f a building cornponent. F i r e separation means a f i r e b a r r i e r a n d r e q u i r e s t h e c l o s u r e of openings as well as the f i r e r e s i s t a n c e o f t h e c o n s t r u c t i o n .
F i r e r e s i s t a n c e i s a terrn that has grown out of test p r o c e d u r e s , b u t t h e c o n c e p t o f f i r e r e s i s t a n c e i s v e r y r n u c h o l d e r . T h e terrn cornrnonly used in the past was Itfire proof. r t
It applied to construction that couldnlt burn and usually rneant stone
o r b r i c k . I n early congested cities one of the greatest public
dangers was conflagration, and it was thus cornrnon to find that the
e x t e r i o r w a l l s of buildings had to be rrfire proof .rr The objective w a s to provide a barrier, b u t the fire proof rnaterial was specified a s a n assurance that the walls would stand under fire conditions.
S o r n e o f this past experience has been overlooked in rnodern r e g u l a t i o n s . T h e t e r r n f i r e r e s i s t a n c e h a s b e e n s u b s t i t u t e d f o r f i r e p r o o f , b u t f i r e r e s i s t a n c e i s d e f i n e d i n t e r r n s o f a t e s t , w h i c h ( a t the tirne of writing) does not distinguish between those constructions
that collapse after surviving the testrs tirne period and those that
d o n r t . T h e arnount of stability that experience indicates is required u n d e r fire conditions varies. T h e r e are sorne circurnstances w h e r e
it would be advantageous to have the structure withstand any fire
a n d t h e r e a r e o t h e r s w h e r e l i t t l e s t r u c t u r a l s t a b i l i t y i s n e c e s s a r y . T h u s , while fire resistance at tirnes irnplies less stability than the e a r l i e r t e r r n f i r e p r o o f , l e s s s t a b i l i t y i s n o w r e c o g n i z e d a s a c c e p t a b l e i n r n a n y c i r c u r n s t a n c e s .
I n t h e p a s t t w o o r t h r e e d e c a d e s t h o s e r e s p o n s i b l e f o r
building regulations have corne to rely firore and rnore on fire
r e s i s t a n c e a s r n e a s u r e d b y t e s t , f , a n d i n t h e l a s t t e n y e a r s t h e r e h a s b e e n a rrrove to relate these requirernents t o t h e f i r e l o a d . T h e transition f r o r n t r a d i t i q n a l t o r n o d e r n a p p r o a c h h a s b e e n s l o w , h o w e v e r , a n d d u r i n g t h i s p e r i o d , w h i l e r e l i a n c e i s p l a c e d o n t h e
rnixture of the two, the student of building regulations is bound to
e n c o u n t e r sorne interesting a n o r n a l i e s .
5 T h "
N a t i o n a l B u i l d i n g C o d e 1 9 4 1 i n c l u d e d a s p a r t o f t h e t e x t a l i s t i n g o f c o n s t r u c t i o n c o r n p o n e n t s a n d t h e a r n o u n t o f f i r e r e s i s t a n c e w h i c h each afforded. M u c h of this was based on tests but much of i t w a s not. In the 1953 edition rnore test data were available and t h i s r e q u i r e r n e n t w a s rernoved frorn the text and placed as an ex-t e n s i v e l i s ex-t i n g i n a s u p p l e r n e n ex-t ex-t o ex-t h e C o d e . T h e supplernent included t e s t e d c o n s t r u c t i o n s a n d i n t e r p o l a t e d r e s u l t s f r o r n r e c o g n i z e d a u t h o r i t i e s a n d h a d a s o u n d e r b a s i s t h a n t h e l 9 4 I d o c u r n e n t . S i n c e 1 9 5 3 t h e b a s i s for sorne of the ratings included in the supplernent has been questioned. T h e r e is an evident trend away frorn ratings deterrnined on any basis o t h e r t h a n t e s t s .
1 I
-o n the basis -of experience, b u t in the language of fire s c i e n c e , i t c a n g e n e r a l l y b e assurned that a greater assurance of s t a b i l i t y under fire conditions is required for a larger than a s r n a l l e r building. T h i s is particularly t r u e f o r height. T h e larger s t r u c t u r e t a k e s longer to evacuate and presents lnore difficulties f o r the fire departrnent to control. T i r n e is the equalizer. T h r o u g h g r e a t e r fire resistance the fire department can have rnore tirne to o p e r a t e . s o r n e buildings, s u c h as very tall ones, w.,rld create i n t o l e r a b l e h a v o c if they were to colrapse, and this risk rnust be r e d u c e d to an infinitesirnal q u a n t i t y . F o r these buildings, t h e r e f o r e , a v e r y h i g h d e g r e e o f f i r e r e s i s t a n c e is,required, s o t h a t t h e
n o r r n a l relation to the fire load is lost. b
Those who are irnpatient for a change and question what a p p e a r to be abnorrnally high requirements f o r f i r e resistance r n u s t rernernber that present requirernents are based on some b a d past experiences. c o n d i t i o n s r r r a y have changed, but it takes t i r n e t o a s s e s s t h e s e c h a n g e s . T h e risks now are quite different f r o m what they were 50 years ago. The tirne has corne when we can r r r o v e cautiously towards eliminating precautions against risks that a r e n o l o n g e r a p p a r e n t ' b u t t h e r e h a s b e e n insufficient tirne to assess t h e nature and extent of the new risks involved in changes in occupancy a n d the shape and size of the buildings of today. During the last
c e n t u f y , N o r t h Arnerica was alarrned by conflagrations. T h e r e was one in alrnost every city. Yet in rrrany, a potential conflagration e x i s t e d for aknost a hundred years before accidental circurn"t"rr.u" r n a d e it a fact. o c c u p a n c i e s h a v e changed rapidly in the past 20 y e a r s , and it would be irnprudent to reduce the requirernents until t h e new hazards are fully cornprehended.
r t is interesting that the application of fire protection in
C a n a d a reflects the legal precept that the law rnust follow the expressed will of the citizens. The will of the chtizens of any cornrnunity appears 6- D e s p i t e
t h e higher factor of safety in larger buildings it is the p r a c t i c e in rnany building by-laws to take further precautions b y r e s t r i c t i n g t h e c o r n b u s t i b l e l o a d and requiring non-bearing p a r t i t i o n s , i n t e r i o r t r i r n and even furniture t o b e non-corrlUustiUte a n d sornetirnes sprinklers a r e r e q u i r e d on top of all this. T o the a u t h o r o f t h i s p a p e r t h i s a p p e a r s t o b e a marpractice. T h e c o r r e c t w a y to regulate is to assess the risk and apply regulations accordingly. r t should be unnecessary as a sequel to apply further requirernents to d i r n i n i s h t h e r i s k . t f i t i s n e c e s s a r y , t h e s e f u r t h e r r e g u l a t i o n s
s t i l l t o b e a f f e c t e d v e r y l a r g e l y b y l o c a l e x p e r i e n c e . T h i s w a s s h o w n r a t h e r strikingly d u r i n g t h e r e v i s i o n f o r t h e l g 6 5 e d i t i o n o f t h e N a t i o n a l B u i l d i n g C o d e . O l d e r c i t i e s , w h i c h h a d e x p e r i e n c e d b a d f i r e s , w i s h e d t o rnaintain fire resistance requirernents i n t h e i r p r e s e n t f o r r n a n d i n s o r n e r e s p e c t s t o i n c r e a s e t h e r n , b u t r e p r e s e n t a t i o n s c a r n e f r o r n f i l a n y s r n a l l e r c o r n m u n i t i e s a n d f r o r n F e d e r a l a n d P r o v i n c i a l a u t h o r i t i e s r e q u i r e d to adrninister r e g u l a t i o n s i n s r n a l l t o w n s t h a t g r e a t e r f r e e d o r n i n t h e u s e o f l e s s f i r e r e s i s t i v e t y p e s o f c o n s t r u c t i o n b e p e r r n i t t e d . O v e r t h e c e n t u r i e s i t h a s b e e n t h e e x p e r i e n c e t h a t n e w c o r n r n u n i t i e s b u i l d i n w o o d , l a t e r c h a n g i n g t o s t o n e . P u b l i c acceptance of fire
protection rnay be influenced by the technical inforrnation available,
b u t i t s t i l l r e s t s o n a s u b s t a n t i a l b a s e o f l o c a l e x p e r i e n c e .
In surnrnary, the ability of rnaterials and building cornponents
t o stand up to fire has been utilized for a long tirne. T r a d i t i o n a l p a t t e r n s of building and fire safety have evolved. R e c e n t l y , t h r o u g h t e s t p r o c e d u r e s a I n e a s u r a b l e r e l a t i o n b e t w e e n h a z a r d s a n d s a f e t y r n e a s u r e s h a s b e e n c r e a t e d . T h i s h a s l e d t o s o r n e a d j u s t r n e n t i n t h i n k i n g a n d h a s i n i t i a t e d a p e r i o d o f r e f o r r n i n b u i l d i n g r e g u l a t i o n s , a l t h o u g h t h e b a s i c p o l i c y r e g a r d i n g r e s i s t a n c e t o c o l l a p s e h a s r e r n a i n e d t h e sarne. I n g e n e r a l t e r r n s t h i s p o l i c y a c c e p t s t h a t t h e a p p r o p r i a t e p e r i o d o f f i r e e n d u r a n c e f o r a b u i l d i n g i s r e l a t e d t o s i z e a n d , i n p a r t i c u l a r , t o h e i g h t .
PREVENTION OF FIRE SPREAD
F i r e spread can be halted by the strategic placernent of b a r r i e r s i n a building or by extinguishrnent. A p a r t i a l b a r r i e r b y i t s e l f w i l l n o t p r e v e n t f i r e s p r e a d b u t i t c a n a i d e x t i n g u i s h r n e n t .
I t can provide a protective s h i e l d f o r t h e f i r e d e p a r t r n e n t . U n f o r t u n a t e l y , w h e n a fire barrier i s i n c o r n p l e t e t h e h o l e s a r e f r e q u e n t l y i n c o n c e a l e d
s p a c e s . T h e f i r e c a n b y p a s s t h e f i r e r n e n a n d t h e r e i s d a n g e r o f t h e i r b e i n g trapped. C o n s e q u e n t l y a p a r t i a l o r i n c o r n p l e t e b a r r i e r w i l l s e l d o r n p r e v e n t f i r e s p r e a d a n d i s o f q u e s t i o n a b l e v a l u e a s a n a i d i n f i r e f i g h t i n g . I t is safer and less costly in the long run to provide
c o r n p l e t e b a r r i e r s w h e n e v e r r n e a s u r e s t o p r e v e n t f i r e s p r e a d a r e r e q u i r e d . T h i s i s t h e p o l i c y a p p l i e d i n t h e N a t i o n a l B u i l d i n g C o d e . A n e x c e p t i o n i s r n a d e f o r b a r r i e r s b e t w e e n b u i l d i n g s w h e r e a l t e r n a t e s a f e t y r r l e a s u r e s a r e p r o v i d e d , b u t w i t h i n b u i l d i n g s a c o r n P l e t e b a r r i e r r n u s t b e p r o v i d e d a t a n y p o i n t w h e r e i t i s d e c i d e d t h a t f i r e s p r e a d
1 3
-r n u s t be halted. B y complete is rneant or hole through which flarne, srnoke or stopped. It rnust be fire tight as a ship t h e n that this purpose is different frorn e n s u r e s stability only.
t h a t every opening, crack h o t gases can pass rnust be
i s w a t e r tight. I t is evident the kind of fire protection that
With reference to the National Building Code it is important t o keep this difference upperrnost in mind. T h e term ttfire resistance', i s used where stability and support onry are required, and the terrn r r f i r e
s e p a r a t i o n t r where the ob;ect is to create fire cornpartrnents out o f which or into which a fire is restrained frorn spreading. p a r t i a l b a r r i e r s a r e n e v e r r n e n t i o n e d . T h e r e a r e n o c a s u a l r e f e r e n c e s t o f i r e doors or other closures. S u c h facilities a r e b y definition part o f a f i r e s e p a r a t i o n ( A r t i c l e 3 . I . 3 . 7 ) .
B y specifying a fire separation it is expected that a cornplete b a r r i e r i s ensured, but the intent is one thing and a satisfactory definition is sornething else. rt is the intent of the definition to i m p l y a c o r n p l e t e b a r r i e r , b u t i n r a w i t i s n e c e s s a r y t o b e p r e c i s e , s o that in addition to a general statement a particular staternent i s added setting forth all the kinds of openings to be protected. r t is doubtful whether such a particular s t a t e r n e n t could ever be
complete. There is always sorrre new purpose for making a hole t h a t isnrt covered by definition a n d f r e q u e n t l y because of this b a r r i e r s a r e n o t fire tight. o n e can irnagine the situation if the w a t e r tightness of a ship depended on a legal staternent. Fires will be stopped frorn spreading onry when we stop rooking for l o o p h o l e s in the code and start filing the real holes in walls.
F i r e separations are required by the National Building code t o separate the storeys of buildings, to separate exits from floor a r e a s , and to separate certain roorns or suites frorn the rernainder o f t h e building because of special hazards. F i r e separations are not required for roof s ot rr'ezzanines. A rne zzanirle is part of a f l o o r area that is required to be open. separation is therefore
i n a p p r o p r i a t e . M o s t roofs could not separate the building frorn any-t h i n g buany-t any-the sky and any-this is noany-t generaly necessary, buany-t while noany-t
c o v e r e d in the code there are solne instances where a roof could u s e f u l l y be built as a fire separation.
F i r e S e p a r a t i o n s B e t w e e n B u i l d i n g s
T h e p r e v e n t i o n o f f i r e s p r e a d b e t w e e n t w o a d j o i n i n g b u i l d i n g s is rnore cornplicated than that just described because t h e b o r d e r b e t w e e n t w o p r o p e r t i e s r n u s t s e r v e n o t o n l y f o r f i r e p r o t e c t i o n b u t also in several other capacities, a n d t h e d e r n a n d s o f sorne of these are in conflict with the needs for fire separation.
C o n f l i c t e x i s t s b e c a u s e o f t h e n e e d o r d e s i r e f o r w i n d o w s a n d d o o r s ( w h i c h i n r n a n y c a s e s a r e i r n p r a c t i c a b l e t o p r o t e c t ) and the need to perrnit exterior construction that does not rneet t h e s t a n d a r d o f f i r e e n d u r a n c e r e q u i r e d b y a f i r e s e p a r a t i o n .
T h e p r i n c i p a l a v e n u e o f f i r e s p r e a d b e t w e e n a d ; a c e n t b u i l d i n g s is radiation. A s r a d i a t i o n i s d i s s i p a t e d w i t h d i s t a n c e i n the same way that light is dissipated frorn a light source' t h e g r e a t e r the distance the weaker the effect of radiation will b e . I t i s p o s s i b l e t h e r e f o r e t o s u b s t i t u t e d i s t a n c e f o r a f i r e
s e p a r a t i o n a s a b a r r i e r t o f i r e s p r e a d . I t i s a c i r c u r n s t a n c e h i g h l y favourable to safety that the occasions which call for w i n d o w s or other breaks in the exterior f i r e s e p a r a t i o n a r e
u s u a l l y those which also call for sorne distance between buildings. T h e r e is hardly a developed rnunicipality i n t h e w o r l d w h e r e t h i s r e l a t i o n h a s n o t b e e n s p e l l e d o u t i n l a w . T h e p r i n c i p l e o f
p r o v i d i n g s p a c e i s u n i v e r s a l l y a c c e p t e d , b u t t h e r e i s l e s s c o n -v i c t i o n r e g a r d i n g t h e p a r t i c u l a r h a z a r d s t h a t t h e s p a c e i s s u p p o s e d t o rnitigate. F i r e s p r e a d i s a n i r n p o r t a n t h ; a z a r d , b u t t h e r e i s
s e l d o r n any correlation b e t w e e n the degree of }lrazard and arnount o f space provided. I t i s o n l y v e r y r e c e n t l y t h a t s t e p s h a v e b e e n t a k e n to calculate the safe separation distances for the varying r a d i a t i o n h a z a r d s .
T h e original work on radiation was done in Japan and G r e a t B r i t a i n . T h e requirernents i n t h e N a t i o n a l B u i l d i n g C o d e o f C a n a d a are based on the British work, s u p p l e r n e n t e d b y s p e c i a l i n v e s t i g a t i o n s t o o b t a i n r r r e a s u r e r n e n t s o f i n t e n s i t y o f f i r e s i n C a n a d a . I t was considered that because of clirnate conditions the intensity o f f i r e s i n C a n a d a , p a r t i c u l a r l y i n w i n t e r t i m e , r n i g h t b e d i f f e r e n t .
1 5
-M e a s u r e m ent of Radiation
T h e hazard of radiation depends on the ternperature of t h e fire, the size and shape of the radiating surface, and the d i s t a n c e between the burning building and that it threatens.
A srnall increase in the ternperature of the fire will c a u s e a large increase in radiation since the level of radiation i s p r o p o r t i o n a l t o t h e fourth power of the ternperature. T h u s a r i s e in ternperature f r o r n 1 8 0 0 to ?200 'F will slightly rnore t h a n double the radiation intensity. T h e ternperature o f r n o s t f u l l y developed fires lies within this range. A s the ternperature o f any single fire is unpredictable, i t i s unreasonable to corn-p l i c a t e the corn-problern by over-refinernent. D e p e n d i n g on the f i r e load, it is usual and practical to assurrle two categories -l o w and high hazard. r n general, the ternperatures o f l o w h a z a r d f i r e s would be in the vicinity of 1800 "F, and those of high lnazard f i r e s Z Z O O " F o r o v e r .
T h e intensity of radiation also depends on the size of t h e r a d i a t o r . E v e r y t h i n g e l s e b e i n g equal, an increase in the s i z e o f the radiator will result in an increase in radiation because o f the scatter effect of radiation. R a d i a t i o n resembles diagrarn A rather than diagrarn B in Figure 6. It will be seen from these f i g u r e s that the intensity of radiation is a variable.
S i r n i l a r l y b e c a u s e of this scatter effect the rnost cornpact s h a p e r o r a c i r c l e , w i l l p r o d u c e t h e g r e a t e s t r a d i a t i o n i n t e n s i t y . I n buildings the rnost cornpact forrn is a square (Figure 7). Again, b e c a u s e r a d i a t i o n i s s c a t t e r e d t h e i n t e n s i t y d e c r e a s e s w i t h d i s t a n c e . R a d i a t i o n at any point distant frorn the source is inversely proportional t o t h e s q u a r e o f t h e d i s t a n c e f r o r n t h a t s o u r c e ( F i g u r e 8 ) .
T h e s e are the factors that deterrnine the level of radiation i n t e n s i t y at any point. s e t against these factors, r n e a s u r e s r n u s t b e taken to ensure that the level of radiation on a building i n the p a t h of radiation does not exceed an intensity that will cause i g n i t i o n . T o effect this there rnust be sorne relation betwe€n the radiating building and its distance frorn the receiving building, b u t before such a relation can be established the rnaxirnurn t o l e r a b l e Ievel of radiation at the receiving building rnust be d e t e r r n i n e d .
The critical part of a building exposed to radiation is t h e w i n d o w . S o r n e o f the radiated heat penetrates windows, a n d a l t h o u g h t h e r e i s c o n s i d e r a b l e r e d u c t i o n i n i n t e n s i t y e x p e r i e n c e i n d i c a t e s t h a t f i r e s p r e a d s t h r o u g h w i n d o w s ; i t r n u s t b e a s s u r n e d , t h e r e f o r e , t h a t t h e c o n t e n t s o f t h e r o o r n s t i n c l u d i n g f a b r i c s a n d o t h e r c o r n b u s t i b l e s , a r e d i r e c t l y e x p o s e d . T h e u s e o f n o n - c o r n b u s t i b l e s o n t h e e x t e r i o r o f t h e b u i l d i n g w i l l n o t a l w a y s p r e v e n t f i r e s p r e a d u n l e s s t h e l e v e l of radiation is controlled to the point where cornbustibles on the interior as well will not be ignited. At this level of radiation cornbustibles on the exterior of the building are equally safe. It h a s t h e r e f o r e c o r n e t o b e g e n e r a l l y a c c e p t e d t h a t i f r a d i a t i o n i s t o b e c o n t r o l l e d i t r n u s t b e r e d u c e d t o a l e v e l t h a t w i l l p r e v e n t ignition of a building clad in cornbustible rnaterials that is d i r e c t l y i n i t s p a t h .
T h e s e are the rnain factors in the measurerrlent and c o n t r o l o f r a d i a t i o n t o p r e v e n t f i r e s p r e a d b e t w e e n b u i l d i n g s . With this inforrnation and ordinary text book physics one rnay
calculate the radiation frorn a burning building and find the rninirnurn safe distance between it and an adjacent edifice.
F o r the purpose of building regulation and enforcernent, h o w e v e r , i t i s o f t e n d e s i r a b l e t o u s e a r e g u l a t o r y c o n c e p t a n d w o r k e d - o u t e x a r n p l e s . E v e n w i t h s u c h a c o n c e p t r n a n y q u e s t i o n s a r i s e i n a d r n i n i s t r a t i o n . T h e s e w o u l d b e i n c r e a s e d b y r n a n y t i m e s w i t h o u t s o m e c l e a r r e g u l a t o r y c o n c e p t t h a t a c c o u n t s f o r a l l p o s s i b l e v a r i a t i o n s. T h e r e g u l a t o r y c o n c e p t s u s e d i n t h e N a t i o n a l B u i l d i n g C o d e are based on this theory but include sorne necessary rnodifications. One exarnple is the concept of the radiator.
It is obvious that it is the windows which ernit radiation, but is it n e c e s s a r y to calculate the radiation ernanating frorn each window o r u n p r o t e c t e d p a r t o f t h e w a l l ? T h i s w o u l d b e t e d i o u s , a n d different sizes and shapes of windows would dernand different d i s t a n c e s . F r o r n a practical v i e w p o i n t i t i s t h e w a l l s o f b u i l d i n g s a n d n o t t h e w i n d o w s t h a t a r e s e p a r a t e d f r o r n e a c h o t h e r .
W h a t e v e r calculations are rnade these rnust eventually deterrnine t h e d i s t a n c e o f a n , e x t e r i o r w a l l o f o n e b u i l d i n g f r o r n t h a t o f a n o t h e r b u i l d i n g , o r t o s o r n e a g r e e d s t a n d a r d l i n e o f r e f e r e n c e
L 7
-s u c h a-s a lot line. s i n c e one is positioning walls rather than w i n d o w s , a concept rnust be developed that accepts the wall a s a radiator. T h i s rnay appear to be contradictory s i n c e the s o l i d p a r t s of the exterior walls are considered as obstructing t h e radiation of the fire within the building. N e v e r t h e l e s s i t i s a useful fiction in the practicar application of radiation t h e o r y to the fire spread between buildings.
I t is further assurned that this wall is punctured by i n f i n i t e l y s r n a l l , uniforrnly s p a c e d openings through which fire r n a y radiate. T h e t o t a l area of such openings, as a percentage o f the wall area, is used in the calculation of distance. w h i l e w i n d o w s are never infinitely s r n a l l , the answers obtained in this way are a good approxirnation of the radiation frorn an e x t e r i o r w a l l punctured with uniforrnly s i z e d a n d uniforrnly
s p a c e d windows. A difficulty a r i s e s w h e n there is a concentration o f windows; and while it could be rnet, it was not rnet in the
I 9 6 0 edition of the National Building Code because it was considered t o be an unwarranted refinernent for such a new forrn of regulation.
T h e British work rnakes use of what is called the enclosing r e c t a n g l e . T h i s concept perrnits the regulating authority to elect t o use a rectangle, which fits a large window or a group of windows r a t h e r than the cornplete wall for purposes of rneasuring the
s e p a r a t i o n distance. I [ h e r e the shape of the group of windows is t h e same as the shape of the exterior wall, the distance will be t h e sarne whether the wall or enclosing rectangre is used. The u s u a l case, however, is that the group of windows has a shape quite different frorn that of the wall, and since it is the windows, n o t the wall, that are radiating, r n e a s u r e r n e n t of the size and shape o f t h e w i n d o w s g i v e s a b e t t e r r e s u l t . T h i s s e r v e s t o r e r n i n d u s t h a t it is really the windows, and not the wall, that are radiating. r n e v i t a b l y r ? n e n c l o s i n g rectangle or sorne sirnilar concept will h a v e t o b e u s e d .
rt will be apparent that the rnechanics of applying separation s t a n d a r d s in a building code lead one to diverge considerably frorn t h e o r y . T h e reader rnust now appreciate that the rnodifications a l r e a d y described are only the beginning. T h e n e x t irnportant
c o n c e s s i o n to building regulations is the rneasurernent of the distance frorn the lot line rather than frorn the adjoining building. In building r e g u l a t i o n s the distance is divided in two and taken to the lot line b e c a u s e an owner cannot lirnit the freedorn of the neighbour to use h i s p r o p e r t y . l f adlacent buitdings are identical, t h e d i s t a n c e b e t w e e n
t h e t w o b u i l d i n g s i s t h e c o r r e c t o n e , b u t i f t h e a d j a c e n t b u i L d i n g s differ greatly in size or in other aspects of design, then one building
will be safer than the other. A large building will have rnore than
the required safety from a fire in a srnaller one, but a srnall building w i l l h a v e l e s s t h a n t h e r e q u i r e d s a f e t y w h e n e x p o s e d t o a f i r e i n a l a r g e b u i l d i n g . I f there has to be a discrePancy, t h i s i s t h e w a y t h e f i r e d e p a r t r n e n t w o u l d p r e f e r t o h a v e i t ( F i g u r e 9 ) .
I n the use of these fire separation requirernents r n a n y r n i n o r p r o b l e r n s have arisen, but these are rnatters of detail that go beyond t h e p u r p o s e o f t h i s p a p e r . T h e r e i s o n e o t h e r r n a j o r r n o d i f i c a t i o n
that has been rnade to the theory and should be rnentioned. It has
been shown that the tolerable level of radiation should be that which
w i l l n o t c a u s e i g n i t i o n o f c o r n b u s t i b l e s i n a n e x p o s e d b u i l d i n g . F o r s a f e t y t h i s l e v e l o f r a d i a t i o n i n t e n s i t y s h o u l d n o t b e s u r p a s s e d a t a n y t i r n e d u r i n g t h e p e r i o d o f e n d u r a n c e o f t h e f i r e . I n fact, however, the d i s t a n c e s r e q u i r e d i n t h e N a t i o n a l B u i l d i n g C o d e a r e s u c h t h a t t h e
tolerable level of radiation would be reached within 20 rninutes of the
start of a fire or within its incipient stages and before the building h a s b e c o r n e f u l l y i n v o l v e d . W h e n the distances required for a fully i n v o l v e d b u i l d i n g w e r e c a l c u l a t e d i t w a s a g r e e d t h a t t h e s e w o u l d b e
unacceptable to rnost authorities in Canada and would have to be
r e d u c e d . I t was assurned, therefore, t h a t t h e p u r p o s e o f t h e d i s t a n c e s e p a r a t i o n w a s t o p r o t e c t a d l o i n i n g b u i l d i n g s u n t i l t h e f i r e d e p a r t r n e n t c o u l d a r r i v e a n d p r o v i d e a d d i t i o n a l p r o t e c t i o n a g a i n s t f i r e s p r e a d . I n u s i n g t h e N a t i o n a l B u i l d i n g C o d e t h e r e f o r e m u n i c i p a l i t i e s s h o u l d
b e aware that the distance separations tabled in the Code are no rnore than a rnethod of stalling a fire until the fire departrnent has had t i r n e t o g e t i n t o o p e r a t i o n .
A t the beginning of this paper the cornplernentary tasks of
the fire departrnent and building construction in providing fire
p r o t e c t i o r t w e r e d e s c r i b e d . I n d i s c u s s i n g f i r e s e p a r a t i o n s b e t w e e n
buildings the viewpoint has corne back to this initial policy of
c o o p e r a t i o n a n d h e n c e e c o n o r r l y t h r o u g h a c a r e f u l l y r n e a s u r e d p r o v i s i o n o f b o t h active and passive defence. T h e subSect of fire protection in b u i l d i n g r e g u l a t i o n s h a s b y n o r n e a n s b e e n e x h a u s t e d . T h i s p a p e r r n a y b e r e g a r d e d a s a n i n t r o d u c t i o n . W e rnay well leave the subject w i t h t h i s e x a m p l e o f c o - o p e r a t i o n u p p e r r n o s t i n r n i n d .
I \ \ (' \ t, G' q) L. a-v, c' €) ( t ) s -E F L & ta-o v r ta-o .NJ ( E t = o v' r-L v (10 L |J.J L! C) c'r
