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Analysis of smoke shafts for control of smoke movement in buildings
Tamura, G. T.
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NATIONAL RESEARCH COUNCIL OF CANADA -A b.!b,
I.,?{
Z
E
D
CONSEIL NATIONAL DE RECHERCHES D U CANADAS e r T H l N2lr2 no.
509
c . 2 IBLDG
Analysis of Smoke Shafts For Control Of
Smoke Movement In Buildings
by G. T. Tamura Reprinted from ASHRAE TRANSACTIONS Vol. 76, Part l I , 1970 p. 290-297
By permission of the American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.
of the
Division of Building Research
OTTAWA January 1972
L'ANALYSE DES CONDUITS DE FUMEE POUR CONTROLER LE MOUVEMENT DE L A FUMEE DANS LES EDIFICES
Cette communication traite du rendernent des conduits de fumee dans l a reduction de la concentration de furnCe a 1'Ctage du feu e t du transport de la furnee aux autres Ctages. En rCduisant l a pression
a
I'Qtage du feu par rapport aux autres etages, un conduit de furnCe peut provoquer un courant d'air au sein de I'enveloppe de I'etage en feu dans le reste de I'Ctage et I'Cvacuer par le conduit de furnCe. De cette f a ~ o n , I'evacuation de la furnCe dans les conduits verticaux et dans les etages supkrieurs est QvitCe. Cepen- dant, s i l e s fenetres a I'Ctage du feu sont brisees, la pression a cet Ctage atteint celle de I'exterieur et les conduits de fumCe ne sont plus utiles. Une tour I I'epreuve de la fumCe pour les puits d'escaliers intCrieurs peut &tre efficace dans l a plupart des cas pour prkvenir l a contamination des puits d'escaliers dans le casNo.
2163
G. T . TAMURAMember ASHRA E
Analysis of Smoke Shafts for
Control of Smoke Movement in Buildings
S m o k e m i g r a t i o n a s a r e s u l t of f i r e i n a b u i l d i n g i s p o t e n t i a l h a z a r d t o l i f e , p a r t i c u l a r l y for o c c u p a n t s in a t a l l b u i l d i n g w h e r e e v a c u a t i o n i s d i f f i c u l t .
-
C o m p u t e r s t u d i e s of s m o k e m o v e m e n t 1 ~ 2 ~ 3 . h a v e i n d i - c a t e d t h a t , w i t h a f i r e in a l o w e r s t o r y a n d w i t h o u t - s i d e t e m p e r a t u r e s l o w e r t h a n i n s i d e , s m o k e c a n , b y t h e m e c h a n i s m of s t a c k a c t i o n , q u i c k l y f i l l t h e e l e - v a t o r a n d s t a i r w e l l s h a f t s a n d u p p e r s t o r i e s . C o m - p u t e r a n d f i e l d s t u d i e s 4 w e r e c o n d u c t e d o n t h e a p - p l i c a t i o n of t o p a n d b o t t o m v e n t i n g t o v e r t i c a l s h a f t s s u c h a s e l e v a t o r s , s t a i r w e l l s a n d s e r v i c e s h a f t s t o p r e v e n t t h i s o c c u r r e n c e . T h i s p a p e r d e a l s w i t h t h e p e r f o r m a n c e of " s m o k e s h a f t s " t h a t a r e s o m e t i m e s p r o p o s e d a s a m e a n s of r e d u c i n g both t h e l e v e l of s m o k e c o n c e n t r a t i o n o n th-e fire-floor a n d s m o k e t r a n s f e r t o o t h e r s t o r i e s . T h e s m o k e s h a f t a s d e f i n e d in t h i s p a p e r is a v e r t i - c a l s h a f t of n o n c o m b u s t i b l e c o n s t r u c t i o n e x t e n d i n g from t h e b o t t o m t o t h e t o p of t h e b u i l d i n g w i t h o p e n - i n g s a t t h e t o p t o o u t s i d e a n d w i t h o p e n i n g s in t h e w a l l s of t h e s h a f t a t e a c h s t o r y . T h e s e o p e n i n g s a r e a s s u m e d t o b e s e a l e d w i t h d a m p e r s . In t h e e v e n t of f i r e , o n l y t h e d a m p e r s on t h e f i r e - f l o o r a n d t h e t o p o u t s i d e d a m p e r a r e o p e n e d t o e x h a u s t s m o k e from t h e fire-floor t o o u t s i d e . T h e m o v e m e n t of a i r a n d s m o k e t h r o u g h t h e s h a f c d e p e n d s s o l e l y o n s t a c k a c t i o n . T h e " s m o k e tower" is a s p e c i a l G. T . Tarnura i s R e s e a r c h O f f i c e r , B u i l d i n g S e r v i c e s Sec- tion, D i v . 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 , C a n a d a . T h i s p a p e r w a s pre- p a r e d for p r e s e n t a t i o n a t t h e A S H R A E A n n u a l M e e t i n g , K a n s a s C i t y , M i s s o u r i , J u n e 28 - J u l y 1, 1 9 7 0 . a p p l i c a t i o n o f t h e s m o k e s h a f t f o r t h e p u r p o s e of m a i n t a i n i n g i n t e r i o r s t a i r w e l l s s m o k e - f r e e a n d i s r e q u i r e d by s o m e b u i l d i n g c o d e s . >MATHEMATICAL MODEL
T h e m a t h e m a t i c a l m o d e l for t h i s s t u d y is e s s e n t i a l l y t h e s a m e a s t h e o n e d e s c r i b e d i n Ref 1. T h e b a s i c c o m p o n e n t s a r e i l l u s t r a t e d i n F i g . 1 for a 3 - s t o r y b u i l d i n g . Major s e p a r a t i o n s a r e e x t e r i o r w a l l s , w a l l s of v e r t i c a l s h a f t s , a n d f l o o r s . L e a k a g e a r e a s in t h e m a j o r s e p a r a t i o n s / s t o r y a r e l u m p e d a n d r e p r e s e n t e d by a r i f i c e a r e a s A,, As a n d Af. T h e v a l u e of A, r e p r e s e n t s t h e l e a k a g e a r e a s of t h e v a r i o u s s e r v i c e s h a f t s i n t h e b u i l d i n g . A 2 n d s h a f t w a s i n c l u d e d t o r e p r e s e n t a s m o k e s h a f t , w i t h v e n t o p e n i n g s i n t h e w a l l of t h e s h a f t a t e a c h s t o r y a n d a t t h e t o p of t h e s h a f t t o o u t s i d e , n o r m a l l y c l o s e d w i t h d a m p e r s a l - l o w i n g n o l e a k a g e . I n m o s t of t h e c a l c u l a t i o n s t h e o p e n i n g s t o e a c h s t o r y a n d a t t h e t o p w e r e a s s u m e d of e q u a l size for r e a s o n s of c o n v e n i e n c e . T h e v a l u e of o u t s i d e a b s o l u t e p r e s s u r e Po, ( F i g . 1) i s t a k e n a s n o r m a l a t m o s p h e r i c p r e s s u r e . O u t s i d e a i r p r e s s u r e s a t o t h e r l e v e l s d e p e n d o n t h e d e n s i t y of o u t s i d e a i r a s s u m i n g n o wind. I n s i d e p r e s s u r e s in t h e v a r i o u s s t o r i e s , Pf, a r e i n t e r r e l a t e d by t h e w e i g h t of t h e c o l u m n of i n s i d e a i r b e t w e e n l e v e l s a n d t h e p r e s s u r e d r o p a c r o s s t h e i n t e r v e n i n g f l o o r s . I n s i d e p r e s s u r e s a t v a r i o u s l e v e l s in t h e s h a f t , P, a n d Ps, a r e i n t e r r e l a t e d o n l y by t h e w e i g h t of t h e'
c o l u m n of s h a f c a i r , a s s u m i n g n o f r i c t i o n p r e s s u r e d r o p i n t h e v e r t i c a l s h a f t a n d i n t h e s m o k e s h a f t .V E N T fi
S M O K E /
VERTICAL
S H A F T
S H A F T S
Fig. 1 Mathematical Model.
T h e p r o b l e m e n t a i l s d e t e r m i n i n g t h e v a l u e s o f i n s i d e p r e s s u r e s w i t h w h i c h a m a s s f l o w b a l a n c e c a n b e o b t a i n e d f o r e a c h s t o r y a n d f o r t h e v e r t i c a l s h a f t s . A c o m p u t e r p r o g r a m w a s f o r m u l a t e d u s i n g a n i t e r a t i v e t e c h n i q u e t o s o l v e f o r a l l u n k n o w n i n - s i d e p r e s s u r e s . I t w a s d e s i g n e d t o p e r m i t v a r i a t i o n in t h e n u m b e r of s t o r i e s , i n t h e s i z e of v a r i o u s e q u i v a l e n t o r i f i c e a r e a s , a n d i n t h e v a l u e s of o u t - s i d e a n d i n s i d e a i r d e n s i t i e s . In t h e s t u d y of s m o k e m o v e m e n t i n t a l l b u i l d - i n g s , ' a 2 0 - s t o r y m o d e l b u i l d i n g ( p l a n d i m e n s i o n 1 2 0 f t s q ) w a s u s e d t o i n v e s t i g a t e t h e r e l a t i v e i n - f l u e n c e of a n u m b e r of f a c t o r s g o v e r n i n g s m o k e m o v e m e n t i n b u i l d i n g s . T h e e q u i v a l e n t o r i f i c e l e a k - a g e a r e a s f o r t h e 2 0 - s t o r y m o d e l b u i l d i n g w e r e b a s e d on a i r l e a k a g e m e a s u r e m e n t s in
4
t a l l o f f i c e b u i l d - i n g s . ' F o r t h i s s t u d y , s i m i l a r v a l u e s of e q u i v a l e n t o r i f i c e l e a k a g e a r e a s w e r e a s s u m e d a n d a r e a s f o l l o w s : A, : AS : Af = 2.5 : 5.0 : 3 . 7 5 s q f t T h e s e l e a k a g e a r e a s a r e f o r e a c h s t o r y a n d , for m o s t of t h e c a l c u l a t i o n s , a r e a s s u m e d t o b e t h e s a m e f o r a l l s t o r i e s .STACK ACTION
F i g . 2 s h o w s t h e p r e s s u r e d i f f e r e n c e p a t t e r n a c r o s s t h e m a j o r s e p a r a t i o n s of a 2 0 - s t o r y m o d e l b u i l d i n g c a u s e d b y s t a c k a c t i o n w i t h a n o u t s i d e t e m p e r a t u r e P R E S S U R E D I F F E R E N C E S C A L E A P - I N C H E S O F W A T E R A, A s A F ' 2 5 5 0 3 7 5 S Q FT C V E R T I C A L S H A F T P R E S S U R E S L N E U T R A L P L A N E 0 2 - 6 - A P A C R O S S-
4-
F L O O R S O U T S 1 O E W A L L A P A C R O S S-
A P A C R O S S 2 - W A L L S O F V E R T I C A L S H A F T S ' A B S O L U T E P R E S S U R E d Fig. 2 Pressure Pattern C a u s e d b y Stack Action.of 0 F. A l l d a m p e r s i n t h e s m o k e s h a f t a r e c l o ~ e d . B e c a u s e t h e c h a n g e s i n a b s o l u t e p r e s s u r e w i t h h e i g h t , b o t h i n s i d e a n d o u t s i d e t h e b u i l d i n g , a r e m u c h g r e a t e r t h a n t h e r e s u l t a n t p r e s s u r e d i f f e r e n c e s a c r o s s m a j o r s e p a r a t i o n s , i t is d i f f i c u l t t o i n d i c a t e t h e v a l u e s o f t h e s e d i f f e r e n c e s on a n a b s o l u t e p r e s - s u r e p l o t . F i g . 2 w a s c o n s t r u c t e d , t h e r e f o r e , w i t h t h e o u t s i d e p r e s s u r e l i n e d r a w n t o a n a r b i t r a r y , b u t c o n v e n i e n t , s l o p e . T h e i n s i d e p r e s s u r e l i n e s w e r e t h e n r e f e r e n c e d t o i t , u s i n g t h e c o m p u t e d p r e s s u r e d i f f e r e n c e s w i t h t h e p r e s s u r e d i f f e r e n c e s c a l e s h o w n o n t h e f i g u r e . F i g .
3
s h o w s t h e r e s u l t a n t a i r f l o w p a t t e r n c a u s e d by s t a c k a c t i o n a s i n d i c a t e d by t h e p r e s s u r e d i f f e r e n c e p a t t e r n g i v e n i n F i g . 2. Air f l o w s i n t o t h e b u i l d i n g t h r o u g h t h e o u t s i d e w a l l b e l o w t h e l e v e l o f t h e n e u t r a l p r e s s u r e p l a n e , u p t h r o u g h f l o o r s a n d v e r t i c a l s h a f t s , a n d o u t t h r o u g h t h e e x - t e r i o r w a l l a b o v e t h e l e v e l of t h e n e u t r a l p r e s s u r e p l a n e . T h e t o t a l I n f i l t r a t i o n r a t e i n t o t h e b u i l d i n g i s 1 9 , 7 3 0 c f m w i t h 1 9 , 0 7 0 c f m i n t o t h e v e r t i c a l s h a f t s a n d w i t h t h e r e m a i n d e r t h r o u g h o p e n i n g s in t h e f l o o r s . B e c a u s e of t h e s e r i e s f l o w r e s i s t a n c e rep- r e s e n t e d b y f l o o r o p e n i n g s , t h e a i r f l o w r a t e u p t h r o u g h f l o o r s is s m a l l a n d m o s t of i t o c c u r s i n t h e v e r t i c a l s h a f t s . If s m o k e i s a s s u m e d t o f o l l o w t h e a i r f l o w p a t t e r n s h o w n i n F i g . 3 , s m o k e m i g r a t e s from a n y f i r e - f l o o r b e l o w t h e n e u t r a l p l a n e i n t o s t o r i e s a b o v e t h r o u g h t h e v e r t i c a l s h a f t s .O P E R A T I O N O F SMOKE S H A F T
Under the conditions illustrated in Fig. 2, the pres- sure in the building i s higher than that outside a t the top. With a smoke s h a f t in the building, having an opening to outside a t the top and openings to the various s t o r i e s s e a l e d , the pressure in the shaft a t the top i s equalized with outside; at a l l lower levels in the s h a f t , which i s a t building temperature, pressures are l e s s than in the adjacent s p a c e s . If, in the event of fire the shaft i s opened to the fire- floor, air flow occurs from it into the smoke shaft, and the pressure on the fire-floor i s reduced. If the pressure on the fire-fIoor were reduced below that in the other vertical s h a f t s a t the same level and in the story above, a i r would flow from these regions to the fire-floor and smoke transfer to other parts of the building would not occur.
Fig.
4
illustrates the pressure pattern for this condition for the 20-story model building with a fire in the 2nd story. T h e air temperature in the smoke shaft and the fire-floor were assumed to be at 75 F . With the smoke shaft in operation, the floor and ver- tical shaft pressures are decreased at a l l levels. In the 2nd story, the pressure i s approximately equal to the vertical shaft pressure indicating negligible air flow into the fire-floor from the vertical shafts./ V E R T I C A L S H A F T S G O K E N E U T R A L P R E S S U R E P L A N E S O U T S I D E 0 F I N S I D E 7 5 F A,. 2 . 5 S Q FT A , . 5 . 0 A F = 3. 7 5 T O T A L L E A K A G E R A T E B U I L D I N G - 1 9 7 3 0 C F M S H A F T S - 1 9 0 7 0 C F M
Fig. 3 Airflow Pattern Caused b y Stack A c t i o n - Smoke Shaft not i n Operation.
I
A P A C R O S S T O P V E N T ( 7 . 5 0 S Q F T ) w----4 P R E S S U R E D I F F E R E N C E S C A L E 0 0. 10 0. 20 0 . 30 A P-
I N C H E S O F W A T E R A w : A S : A ~-
2.5:5.0:3.75 S Q F T I,:\;
O U T S I D E - 0 F Y I - Z-
-
V E R T I C A L'
4 S H A F T-
P R E S S U R E A B S O L U T E P R E S S U R EFig. 4 Pressure Pattern C a u s e d b y Stack A c t i o n With Smoke Shalt i n Operution.
The s i z e of opening required to achieve this condi- tion i s 7.50 s q f t based on openings of equal s i z e in the smoke shaft a t the 2nd story and top. The pressure in the fire-floor i s lower than in the s t o r i e s above and below, indicating that the direction of air flow i s into the fire-floor from these s t o r i e s . The resultant air flow pattern with the smoke shaft in operation i s illustrated in Fig. 5. It i s s e e n that the direction of air flow a c r o s s the fire-floor en- closure i s into the fire-floor and out through the smoke shaft; thus, in the event of fire, smoke migra- tion into upper s t o r i e s i s prevented.
With openings of equal s i z e in the smoke shaft at the 2nd story and a t the top, the total pressure difference available for venting smoke i s distri- buted equally a c r o s s the 2 openings. For the ex- ample in Fig.
4
the sum of these i s 0.27 in. of water and the calculated rate of air flow into the smoke shaft i s 6660 cfm. T h i s i s the rate of air exhaustfrom the 2nd story required to prevent air flow from it into vertical s h a f t s and into adjacent s t o r i e s ; a similar air flow pattern would be obtained with an exhaust fan of this capacity.
/ V E R T I C A L S H A F T S
KG"'0KE
S H A F T''
O U T S I D E 0 F I N S I D E 7 5 F N E U T R A L - P R E S S U R E P L A N E S 1 " VENT 7 . 5 S Q FT " FLOW R A T E I N S M O K E S H A F T F I R E O Nb
--
--
2 N D S T O R Y.
t
1 / * , I --
- NOI'L;: r \ l l l l V W S A I L E N O T T 0 S I : A L EFig. 5 Airllow Pattern Caused b y Stack Action With
Smoke Shalt in Operation.
If t h e o p e n i n g a t t h e t o p is l a r g e r t h a n t h a t i n t h e fire-floor, t h e s m o k e s h a f t p r e s s u r e is d e - c r e a s e d . C o n v e r s e l y , w i t h t h e t o p v e n t s m a l l e r t h a n t h e v e n t i n t h e fire-floor, t h e s m o k e s h a f t p r e s s u r e is i n c r e a s e d . I n t h e e x t r e m e , t h e s m o k e s h a f t p r e s - s u r e c o u l d e x c e e d t h a t i n u p p e r s t o r i e s , c a u s i n g s m o k e flow from t h e s h a f t i n t o t h e a d j a c e n t s p a c e s through l e a k a g e o p e n i n g s a r o u n d t h e d a m p e r s a n d i n t h e w a l l of t h e s m o k e s h a f t . T h e v e n t s i z e n e e d e d t o p r e v e n t s m o k e t r a n s f e r from t h e fire-floor t o o t h e r s t o r i e s d e c r e a s e s a s t h e h e i g h t of t h e fire-floor a b o v e g r o u n d i n c r e a s e s . S t o r i e s a t o r n e a r g r o u n d l e v e l t h e r e f o r e e s t a b l i s h minimum v e n t s i z e r e q u i r e m e n t s . N e g l e c t i n g f r i c t i o n p r e s s u r e l o s s i n t h e s h a f t , t h e minimum v e n t s i z e s w e r e f o u n d t o b e i n d e p e n d e n t of b u i l d i n g h e i g h t , a n d d e p e n d e n t o n t h e l e a k a g e a r e a s of t h e major s e p a r a t i o n s . With v e n t o p e n i n g s i n t h e s m o k e s h a f t of e q u a l s i z e a t t h e t o p a n d a t t h e fire-floor a n d w i t h r a t i o s of e q u i v a l e n t l e a k a g e a r e a s e q u a l t o t h o s e of t h e 2 0 - s tory b u i l d i n g (A, : As : Af = 1 . 0 : 2 . 0 : 1 . 5 ) t h e r e q u i r e d v e n t s i z e is a p p r o x i m a t e l y
3
t i m e s t h e l e a k a g e a r e a / s t o r y of t h e o u t s i d e w a l l . A s b u i l d i n g h e i g h t i n c r e a s e s t h e r e is a c o r r e s p o n d i n g i n c r e a s e i n t h e a m o u n t of a i r e x h a u s t e d t h r o u g h t h e s m o k e s h a f t from a fire-floor n e a r g r o u n d l e v e l . In t h e c a l - c u l a t i o n of v e n t s i z e s , p r e s s u r e d r o p i n t h e s m o k e s h a f t d u e t o f r i c t i o n w a s n e g l e c t e d . In p r a c t i c e , i t w o u l d b e n e c e s s a r y t o a c c o u n t for t h i s i n d e t e r m i n - ing t h e c r o s s - s e c t i o n a l a r e a of t h e s h a f t o r t h e mini- mum r e q u i r e d v e n t s i z e s , o r b o t h . T h e r e q u i r e d v e n t s i z e i s i n d e p e n d e n t of i n s i d e - o u t s i d e t e m p e r a t u r e d i f f e r e n c e . T h e s m o k e s h a f t c e a s e s t o f u n c t i o n w h e n o u t s i d e t e m p e r a t u r e is e q u a l t o o r g r e a t e r t h a n i n s i d e t e m p e r a t u r e , b u t u n d e r t h e s e i o n d i t i o n s t h e r e i s l e s s t e n d e n c y for s m o k e t r a n s f e r from s t o r y to s t o r y . I t is s o m e t i m e s s u g g e s t e d t h a t a n e x i s t i n g s h a f t , s u c h a s a n e l e v a t o r o r . s t a i r w e l 1 , might b e u s e d a s a s m o k e s h a f t . T h e p e r f o r m a n c e of a 1 - c a r e l e v a t o r s h a f t a s a s m o k e s h a f t w a s d e t e r m i n e d for t h e 20- s t o r y m o d e l b u i l d i n g . A l e a k a g e a r e a l s t o r y of 1 . 0 s q f t ( 0 . 5 f o r e l e v a t o r d o o r a n d 0.5 for w a l l ) w a s a s s u m e d for t h i s s h a f t . F i g .6
i l l u s t r a t e s t h e p r e s - s u r e d i s t r i b u t i o n s w i t h a v e n t o p e n i n g of 7 . 5 0 s q f t a t t h e t o p of t h e s h a f t a n d a t t h e 2 n d s t o r y . T h i s v e n t s i z e is i n a d e q u a t e b e c a u s e of t h e l a r g e l e a k - a g e a r e a of t h e s h a f t i n e a c h s t o r y . T h e 2 n d s t o r y p r e s s u r e is h i g h e r t h a n t h e p r e s s u r e i n t h e o t h e r v e r t i c a l s h a f t s a n d a l l o w s f l o w o f s m o k e i n t o them. S m o k e s h a f t p r e s s u r e i s a l s o h i g h e r t h a n i n a d j a c e n t ( A P A C R O S S T O P V E N T ( 7 . 5 0 S Q F T ) S M O K E S H A F T V E R T I C A L S H'
A B S O L U T E P R E S S U R E ---3Fig. 6 Pressure Pattern Caused b y Stack Actzon and
s p a c e s from the 1 5 t h t o 20th s t o r i e s , allowing trans- f e r of s m o k e from the s m o k e s h a f t into them. A larger vent s i z e would be required for a n e l e v a t o r s h a f t to perform a d e q u a t e l y a s a s m o k e s h a f t . T h e minimum s i z e of top v e n t required for t h e model building w a s computed t o be 1 3 . 0 s q ft, with a n opening of t h e s a m e s i z e t o t h e 2nd s t o r y .
In t h e e x a m p l e s i l l u s t r a t e d i n F i g s . 4 a n d 6 , i t w a s a s s u m e d that a i r t i g h t n e s s of the e x t e r i o r w a l l s w a s unaltered during the fire. It i s not u n u s u a l for breakage of windows to o c c u r on t h e fire-floor, e i t h e r a s a r e s u l t of e x p o s u r e to t h e f i r e or fire- fighting t a c t i c s . With a l a r g e opening in t h e exterior w a l l of a fire-floor, a i r p r e s s u r e in t h e fire-floor tends t o e q u a l i z e with that of t h e o u t s i d e a t t h e s a m e l e v e l . If t h i s h a p p e n s a t lower l e v e l s , the p r e s s u r e in t h e fire-floor r i s e s a n d the p o t e n t i a l for a i r flow from t h e fire-floor t o o t h e r p a r t s of the building i n c r e a s e s . ' A s s u m i n g an opening of 2 0 s q ft i n t h e o u t s i d e w a l l of t h e 2nd s t o r y (fire-floor) of the 20-story model building, a s m o k e s h a f t with vent a r e a of 7.50 s q ft h a s l i t t l e i n f l u e n c e on t h e fire- floor p r e s s u r e s and i s i n a d e q u a t e to prevent a i r flow from i t i n t o v e r t i c a l s h a f t s a n d i n t o s t o r i e s a b o v e and below. T h e r a t e of flow i n t o t h e s m o k e s h a f t i n c r e a s e s from 6660 to 8 4 5 0 cfm. T h e r a t e of a i r flow i n t o t h e v e r t i c a l s h a f t s a t t h e 2nd s t o r y , how- e v e r , i s only s l i g h t l y l e s s t h a n i t i s without t h e s m o k e s h a f t in operation. With a l a r g e opening in the o u t s i d e w a l l of a fire-floor, a s m o k e s h a f t i s not e f f e c t i v e in preventing the s p r e a d of s m o k e from the fire-floor to upper s t o r i e s . Smoke s h a f t s may, there- fore, h a v e s e r i o u s l i m i t a t i o n s in controlling t h e ver- t i c a l s p r e a d of s m o k e from interior s p a c e s t h a t have windows or s i m i l a r o p e n i n g s t o o u t s i d e .
T h e e f f e c t on s m o k e s h a f t operation of opening s t a i r w e l l doors w a s a l s o i n v e s t i g a t e d . T h e o u t s i d e w a l l s on t h e fire-floor w e r e a s s u m e d t o b e i n t a c t . With a l l o t h e r s t a i r w e l l doors c l o s e d , including t h a t to o u t s i d e , opening a door on t h e fire-floor h a s l i t t l e e f f e c t on t h e operation of t h e s m o k e s h a f t ; although s o m e s m o k e contamination of t h e s t a i r w e l l s h a f t can b e e x p e c t e d due to a i r i n t e r c h a n g e a c r o s s the open door a r i s i n g from t h e e l e v a t e d temperature in the fire-floor. Opening a s t a i r w e l l door a t an upper l e v e l r e s u l t s in a lowering of t h e s t a i r w e l l p r e s s u r e , which i n d u c e s a flow of a i r i n t o t h e s t a i r w e l l s h a f t from a fire-floor on a lower l e v e l . If a s t a i r w e l l door on t h e fire-floor were a l s o o p e n , t h e r a t e of air or s m o k e flow i n t o t h e s t a i r w e l l would b e g r e a t l y i n c r e a s e d . F R E I G H T S T A I R W E L L E A S T S T A I R W E L L \ A S S M O K E S H A F T
LSERVICE
E L E V A T O RFig. 7 Floor P l a n o/ T e s t Building.
FIELD MEASUREMENTS
T o c h e c k t h e performance of s m o k e s h a f t s a s indi- c a t e d by computer s t u d i e s , p r e s s u r e m e a s u r e m e n t s were made on a 17-story building u s i n g o n e of t h e 2 s t a i r w e l l s a s a s m o k e s h a f t . T h e floor plan of the building i s shown in F i g . 7 . T h e s t a i r w e l l s a r e pro- vided with 2 d o o r s a t e a c h s t o r y a n d with a roof hatch a t t h e top. T h e e a s t s t a i r w e l l w a s arranged to o p e r a t e a s a s m o k e s h a f t for fire on t h e 3rd s t o r y by opening t h e roof h a t c h (11.4 s q ft) a n d t h e 3rd s t o r y s t a i r w e l l door (20.0 s q ft). P r e s s u r e d i f f e r e n c e read- i n g s w e r e t a k e n b e t w e e n t h e 2nd a n d 3rd s t o r i e s , between t h e 4th a n d 3rd s t o r i e s and a c r o s s the ele- vator a n d w e s t s t a i r w e l l d o o r s on t h e 3rd story both before a n d during t h e s m o k e s h a f t s i m u l a t i o n . Mea- s u r e m e n t s were a l s o taken with 5 s m a l l exterior c a s e m e n t windows ( t o t a l a r e a of 1 2 . 8 s q ft) o p e n on the 3rd s t o r y . O u t s i d e temperature w a s 1 7 F. T h e r e s u l t s of p r e s s u r e m e a s u r e m e n t s a r e g i v e n in T a b l e I.
With a l l o u t s i d e windows c l o s e d , t h e normal air flow pattern a c r o s s the 3rd s t o r y e n c l o s u r e c a u s e d by s t a c k a c t i o n w a s from t h e 2nd to t h e 3rd s t o r y and from t h e 3rd to t h e 4th s t o r y through the floor c o n s t r u c t i o n , a n d from t h e 3rd s t o r y i n t o t h e e l e - vator a n d s t a i r w e l l s h a f t s . With t h e e a s t s t a i r w e l l a c t i n g a s a s m o k e s h a f t , t h e direction of flow through t h e floor c o n s t r u c t i o n b e t w e e n 3rd and 4th s t o r i e s a n d a c r o s s t h e w e s t s t a i r w e l l a n d e l e v a t o r doors on the 3rd s t o r y w a s r e v e r s e d . T h e direction of a i r flow w a s therefore i n t o t h e 3rd s t o r y from ad- j a c e n t s p a c e s a n d o u t through t h e s m o k e s h a f t .
With the e a s t s t a i r w e l l door a n d the roof h a t c h c l o s e d , opening the windows c a u s e d a n i n c r e a s e in
TABLE 1
PRESSURE DIFFERENCE MEASUREMENTS ON 3RD FLOOR O F A 17-STORY BUILDING WITH EAST
STAIRWELL AS SMOKE SHAFT
Notes: P r e s s u r e d i f f e r e n c e i n in. of water R e a d i n g s referenced to 3 r d floor
+ r e a d i n g : f l o w i n t o 3 r d floor
-
r e a d i n g : f l o w from 3 r d f l o o r O u t s i d e temperature : 1 7 Fthe 3rd story pressure resulting in a downward flow of air from the 3rd to the 2nd s t o r i e s and an increase in the flow rates from the 3rd to the 4th s t o r i e s and from the 3rd story into the elevator and stairwell shafts. T h e s e effects have already been n0ted.l With the e a s t stairwell arranged a s a smoke shaft, the flow pattern a c r o s s the 3rd story enclosure was unaltered, although a reduction in pressure differ- ence and, hence, flow rates occurred. T h i s con- firms that the smoke s h a f t i s not effective in pre- venting the spread of smoke in a building when there are large openings to outside on the fire-floor.
L O C A T I O N 0 F M E A S U R E M E N T S b e t w e e n 2 n d and 3rd floor between 4 t h and 3rd f l o o r w e s t s t a i r w e l l door on 3 r d floor w e s t e l e v a t o r door on 3 r d floor
SMOKE-PROOF TOWER
W I T H SMOKE S H A F TA smoke-proof tower i s specified in some building codes to prevent smoke contamination of stairwells. It c o n s i s t s of a vestibule between each story and the stairwell with an opening to outside in one of the walls of the vestibule. Where i t i s difficult to vent the vestibule to outside a s in the c a s e of a stairwell located in the core of a building, the vestibule i s vented to a vertical shaft extending from grade to top of the building. T h i s vertical s h a f t i s e s s e n t i a l l y a smoke s h a f t a s described previously.
T h e performance of a smoke tower for the protec- tion of interior stairwells was investigated with the computer model of the 20-story building. T h e com- puter model was modified to simulate a combination of stairwell, vestibule and smoke shaft a s shown in Fig. 8. Assuming a fire in a 2nd story and a vent
WINDOWS C L O S E D 0.017 0.011 0.004 0.005 W I T H O U T SMOKE S H A F T
area in the smoke s h a f t a t 2nd story and a t the top of 7.50 s q f t a s before, s e v e r a l c a s e s were investi- gated. T h e outside temperature was assumed to be 0 F .
With a l l vestibule and stairwell doors closed, the direction of air flow i s from the 2nd story and stair- well into the vestibule and thence to the smoke shaft, thus preventing spread of smoke into the stairwell. During the course of a fire, it might be expected that some of the doors would be open for fire fighting and evacuation. With the vestibule door open to the fire-floor the operation of a smoke tower i s e s s e n t i a l l y the same a s that of a smoke s h a f t a s described previously, and similar limitations there- fore apply; that i s , with a large opening in the ex- terior wall on the fire-floor or with open stairwell
WINDOWS O P E N
-
0.040 - 0.060-
0.070 - 0.075 WINDOWS C L O S E D 0.001-
0.009 -0.013-
0.009 V E S T l B U L EDOOR
WINDOWS O P E N-
0.090 - 0.115-
0.125 -0.130 V EN O P E S M O K E S H A F T7
I
V E S T l B U L Eand v e s t i b u l e doors on upper floors, s m o k e entry into t h e s t a i r w e l l c a n be e x p e c t e d . T h e amount of smoke entry into t h e s t a i r w e l l i s i n c r e a s e d if t h e 2nd s t o r y s t a i r w e l l door i s a l s o open.
With t h e s t a i r w e l l door a t the 2nd s t o r y l e v e l open a n d t h e other doors c l o s e d , t h e e f f e c t of t h e open s m o k e s h a f t v e n t i s t o lower t h e p r e s s u r e in t h e s t a i r w e l l below t h a t in upper s t o r i e s a n d t h u s to i n d u c e a i r flow from them into t h e s t a i r w e l l through t h e v a r i o u s v e s t i b u l e s . If t h e s e upper s t o r i e s were fouled with s m o k e a s a r e s u l t of flow in v e r t i c a l s h a f t s s o m e contamination of t h e s t a i r w e l l would r e s u l t . T o minimize s m o k e contamination of t h e s t a i r w e l l i t i s n e c e s s a r y t o minimize opening of v e s t i b u l e and s t a i r w e l l d o o r s of t h e s m o k e tower.
SUMMARY
T h e performance of s m o k e s h a f t s w a s i n v e s t i g a t e d for a building under t h e i n f l u e n c e of s t a c k a c t i o n , with o u t s i d e temperatures lower than i n s i d e . By reducing the p r e s s u r e in t h e fire-floor r e l a t i v e to a d j a c e n t s p a c e s the s m o k e s h a f t c a n i n d u c e a i r flow from t h e s e s p a c e s i n t o t h e fire-floor and out through t h e s m o k e s h a f t . In t h i s way, t h e s p r e a d of s m o k e into v e r t i c a l s h a f t s a n d upper s t o r i e s i s prevented. Neglecting friction p r e s s u r e l o s s in t h e s h a f t , t h e required v e n t s i z e i s i n d e p e n d e n t of building height and i s approximately3
t i m e s t h e l e a k a g e a r e a / s t o r y of t h e o u t s i d e wall. Where t h e exterior w a l l c a n be e x p e c t e d to remain i n t a c t , a s in t h e c a s e of a w i n d o w l e s s building, a s m o k e s h a f t c a n b e e f f e c t i v e in limiting s m o k e t r a n s f e r to upper s t o r i e s . If windows on a fire-floor a r e broken, how- e v e r , t h e p r e s s u r e in t h e fire-floor a p p r o a c h e s t h a t of the o u t s i d e a n d t h e s m o k e s h a f t i s no longer e f - f e c t i v e in preventing t h e s p r e a d of s m o k e . If a s t a i r - w e l l door on a n upper s t o r y i s open, t h e s t a i r w e l l p r e s s u r e i s r e d u c e d below that of t h e fire-floor a n d if a s t a i r w e l l door on the fire-floor i s a l s o open, smoke contamination of t h e s t a i r s h a f t c a n b e e x p e c t e d .T h e smoke-proof tower for interior s t a i r w e l l s c a n be e f f e c t i v e in preventing contamination of a s t a i r s h a f t in t h e e v e n t of fire provided t h a t t h e v e s t i - bule a n d the s t a i r w e l l doors on t h e fire-floor a n d upper s t o r i e s a r e c l o s e d .
ACKNOWLEDGEMENTS
T h e a u t h o r gratefully a c k n o w l e d g e s contributions from h i s c o l l e a g u e s : A . G. Wilson a n d J . H. McGuire during d i s c u s s i o n a n d review of t h i s s t u d y ; D. Templeton who a s s i s t e d in t h e running of t h e com- puter programs and R. G. E v a n s a n d L. P . Chabot who a s s i s t e d in t h e field m e a s u r e m e n t s . S p e c i a l t h a n k s a r e h e r e recorded to H . A . Smith a n d P . A .
Vincent of t h e NRC Computation C e n t r e who pre- pared t h e computer programs.
T h e author gratefully a c k n o w l e d g e s t h e contri- bution of t h e Department of P u b l i c Works for per- mission and a s s i s t a n c e in c a r r y i n g out t e s t s in their building.
. T h i s i s a contribution from t h e D i v i s i o n of Build- ing 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 and i s published with t h e approval of t h e Director of t h e Division.
REFERENCES
1. G. T . Tamura, Computer A n a l y s i s of Smoke Movement i n T a l l B u i l d i n g s , P r e s e n t e d a t ASHRAE Annual Meeting i n Denver, Colorado, J u n e 30 - J u l y 2 , 1969.
2. T . Wakamatsu, C a l c u l a t i o n of Smoke Movement in B u i l d i n g s , Building R e s e a r c h I n s t i t u t e , Ministry of C o n s t r u c t i o n , J a p a n , BRI R e s e a r c h P a p e r No. 34,
August 1968.
3. J . H . McGuire, Smoke Movement i n Buildings, F i r e Technology, Vol. 3, No. 3 , p. 163
-
174, A u g u s t 1967. 4. G. T. Tamura a n d A. G. Wilson, Natural Venting t oControl Smoke Movement i n Buildings via Vertical S h a f t s , T o b e p r e s e n t e d a t ASHRAE Annual Meeting, K a n s a s C i t y , J u n e 1970.
DISCUSSION
J .
B . S E M P L E , ( A i r B a l a n c e Inc., W e s t C o n s h o h o c k e n , P a . ) : H a v e y o u h a d a n y o p p o r t u n i t y t o d o a n y w o r k u n d e r s u m m e r c o n d i t i o n s on t h e o p e r a t i o n of t h e s e s h a f t s ? MR. TAMURA: T h e o p e r a t i o n of a s m o k e s h a f t d u r i n g t h e w i n t e r w a s d i s c u s s e d in t h e p a p e r . D u r i n g t h e s u m m e r , w i t h l i t t l e o r n o b u i l d i n g s t a c k a c t i o n , ther- m a l e x p a n s i o n a s a r e s u l t of t e m p e r a t u r e r i s e i n t h e fire-floor is a n i m p o r t a n t m e c h a n i s m by w h i c h s m o k e s p r e a d s from t h e fire-floor t o t h e v a r i o u s p a r t s o f t h e b u i l d i n g . T h e r a t e of s m o k e flow o u t of t h e fire-floor e n c l o s u r e by t h e r m a l e x p a n s i o n d e p e n d s o n t h e r a t e of t e m p e r a t u r e r i s e a n d on t h e l e a k a g e o p e n i n g s of t h e fire-floor e n c l o s u r e . T h e r a t e of flow c a n b e r e - d u c e d by v e n t i n g t h e fire-floor t o o u t s i d e w i t h a s m o k e s h a f t . I t c a n a l s o b e r e d u c e d b y v e n t i n g t h e fire-floor w i t h a l a r g e o p e n i n g i n t h e e x t e r i o r w a l l . With t h e m o d e l b u i l d i n g d e s c r i b e d i n t h e p a p e r , t h e e f f e c t i v e n e s s of s m o k e s h a f t i n v e n t i n g t h e f i r e - f l o o r w a s i n v e s t i g a t e d . I t w a s a s s u m e d t h a t a m e a n t e m p e r a t u r e i n t h e fire-floor of 1000 F w a s r e a c h e d in 30 min d u r i n g w h i c h t i m e t w o floor v o l u m e s of g a s l e f t t h e fire-floor. A m e a n t e m p e r a t u r e of 250 F in- s i d e t h e s m o k e s h a f t w a s a l s o a s s u m e d . U n d e r t h i s c o n d i t i o n , w i t h t h e s m o k e s h a f t i n o p e r a t i o n , t h e d i r e c t i o n of f l o w a c r o s s t h e fire-floor e n c l o s u r e is r e v e r s e d , w i t h a i r f l o w i n t o t h e fire-floor e n c l o s u r e from t h e a d j a c e n t a r e a s a n d i n t o t h e s m o k e s h a f t to o u t s i d e .This publication is being distributed by the Division of Building Research of the National Research Coun- cil of Canada. I t should not be reproduced in whole or in part without permission of the original pub- lisher. The Division would be glad to be of assistance in obtaining such permission.
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REPRINTED FROM ASHRAE TRANSACTIONS VOL. 76 PART 1 1 , 1970, BY PERMISSION OF THE AMERICAN SOCIETY OF HEATING, REFRIGERATING AND AIR- CONDITIONING ENGINEERS, INC. ASHRAE DOES NOT NECESSARILY AGREE WITH THE STATEMENTS OR OPINIONS HEREIN. THIS ARTICLE IS NOT TO BE RE- PRINTED OR USED FOR PROMOTION. A L L ARTICLES PUBLISHED I N ASHRAE TRANSACTIONS ARE ACCEPT- ED ON A N EXCLUSIVE BASIS AND ARE COPYRIGHTED BY THE SOCIETY.
