Experimental fire tower studies on mechanical pressurization to control smoke movement caused by fire pressures

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Experimental fire tower studies on mechanical pressurization to control

smoke movement caused by fire pressures

Tamura, G. T.; Klote, J. H.

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Experimental Fire Tower

Studies on Mechanical

Pressurization to Control

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Fire Pressures

by G.T. Tamura and J.H. Klote

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Fire Safety Science

Proceedings of the Second International Symposium

Tokyo, Japan, June 13- 17,1988

p. 761-769

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Experimental Fire Tower Studies

on Mechanical Pressurization to Control

Smoke Movement Caused

by

Fire Pressures

G. T. TAMURA

Institute for Research in Construction National Research Council of Canada Ottawa, Canada

J. H. KLOTE

Center for Fire Research National Bureau of Standards Gaithersburg, Maryland 20899, USA ABSTRACT

I n d e s i g n i n g a m e c h a n i c a l smoke c o n t r o l s y s t e m t o p r o t e c t e s c a p e r o u t e s , i t i s n e c e s s a r y t o have i n f o r m a t i o n o n t h e a d v e r s e p r e s s u r e d i f f e r e n c e s c a u s e d by t h e v a r i o u s mechanisms and on t h e l e v e l of m e c h a n i c a l p r e s s u r i z a t i o n needed t o overcome them. T h i s p a p e r d e a l s w i t h p r e s s u r e d i f f e r e n c e s c a u s e d by b o t h t h e buoyancy f o r c e and t h e r m a l e x p a n s i o n due t o f i r e . The t e s t s were c o n d u c t e d i n t h e t e n - s t o r e y e x p e r i m e n t a l f i r e tower i n c o n j u n c t i o n w i t h a p r o j e c t on smoke c o n t r o l t e c h n o l o g y f o r a f i r e s a f e e l e v a t o r . The c a l c u l a t e d v a l u e s o f a d v e r s e 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 t h e e l e v a t o r s h a f t w a l l s c a u s e d by t h e buoyancy f o r c e a g r e e d w e l l w i t h t h e measured v a l u e s , f o r f i r e

t e m p e r a t u r e s from 450 t o 850°C. Also, t h e minimum amounts of m e c h a n i c a l p r e s s u r i z a t i o n r e q u i r e d f o r n e u t r a l i z a t i o n were e q u a l t o t h e a d v e r s e p r e s s u r e s c a u s e d by t h e buoyancy f o r c e . Those c a u s e d b y t h e r m a l e x p a n s i o n d u e t o t h e r a p i d t e m p e r a t u r e r i s e were d e t e r m i n e d w i t h t h e o u t s i d e w a l l v e n t s c l o s e d and w i t h them opened. The t e s t r e s u l t s v e r i f i e d t h a t a d v e r s e p r e s s u r e s c a u s e d by f i r e c a n b e c o n t r o l l e d by m e c h a n i c a l p r e s s u r i z a t i o n t o p r e v e n t smoke c o n t a m i n a t i o n of p r o t e c t e d s p a c e s . The m e c h a n i c a l p r e s s u r i z a t i o n s y s t e m s h o u l d b e o p e r a t e d a s s o o n a s p o s s i h l e a s t h e p u r g i n g t i m e f o r a c o n t a m i n a t e d e l e v a t o r s h a f t o r l o b b y c a n b e long. INTRODUCTION

The performance r e q u i r e m e n t f o r most m e c h a n i c a l smoke c o n t r o l s y s t e m s i s t o c o n t r o l p r e s s u r e s i n a b u i l d i n g s o t h a t smoke i s p r e v e n t e d from e n t e r i n g e s c a p e r o u t e s , s u c h a s a n e l e v a t o r s h a f t o r s t a i r s h a f t . I n d e s i g n i n g s u c h s y s t e m s , a knowledge of t h e a d v e r s e p r e s s u r e d i f f e r e n c e s c a u s e d by t h e f i r e and o t h e r mechanisms i s needed t o d e t e r m i n e t h e amount o f p r e s s u r i z a t i o n o r e x h a u s t r e q u i r e d t o overcome them. The mechanisms t h a t s h o u l d b e c o n s i d e r e d a r e t h e t e m p e r a t u r e e f f e c t of f i r e , s t a c k a c t i o n due t o t h e d i f f e r e n c e i n a i r t e m p e r a t u r e i n s i d e and o u t s i d e a b u i l d i n g , wind a c t i o n , and t h e o p e r a t i o n of m e c h a n i c a l v e n t i l a t i o n systems. The maximum a d v e r s e p r e s s u r e d i f f e r e n c e d u e t o a c o m b i n a t i o n o f t h e s e mechanisms c a n t h e n s e r v e a s a c r i t e r i o n f o r d e s i g n i n g a smoke c o n t r o l s y s t e m and f o r t e s t i n g i t s p e r f o r m a n c e i n a b u i l d i n g .

The a d v e r s e p r e s s u r e s c a u s e d by t h e s e mechanisms were i n v e s t i g a t e d i n t h e t e n - s t o r e y e x p e r i m e n t a l f i r e t o w e r , a s p a r t of a j o i n t p r o j e c t

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b e i n g c o n d u c t e d b y t h e N a t i o n a l R e s e a r c h C o u n c i l o f Canada and t h e N a t i o n a l Bureau o f S t a n d a r d s (USA) on d e v e l o p i n g smoke c o n t r o l t e c h n o l o g y f o r a f i r e s a f e e l e v a t o r (1). T h i s p a p e r r e p o r t s on t h e r e s u l t s o f t e s t s

,

c o n d u c t e d t o d e t e r m i n e t h e a d v e r s e p r e s s u r e s c a u s e d by buoyancy a n d

t h e r m a l e x p a n s i o n d u e t o f i r e , and t h e amount o f m e c h a n i c a l

p r e s s u r i z a t i o n r e q u i r e d t o p r e v e n t smoke from e n t e r i n g t h e e l e v a t o r s h a f t and e l e v a t o r l o b b i e s .

TEMPERATURE EFFECT OF FIRE

Heat g e n e r a t e d by f i r e r e s u l t s i n i n c r e a s e d g a s t e m p e r a t u r e . Assriming t h a t a f i r e compartment l e a k s s u f f i c i e n t l y t o p r e c l u d e a n a p p r e c i a b l e b u i l d u p of p r e s s u r e , i t f o l l o w s from t h e g a s l a w , t h a t t h e g a s volume i n c r e a s e s a p p r o x i m a t e l y i n p r o p o r t i o n t o i t s a b s o l u t e

t e m p e r a t u r e . The p r e s s u r e d e v e l o p e d by t h e o u t f l o w i n g g a s d e p e n d s o n t h e l e a k a g e a r e a and volume o f t h e f i r e compartment and on t h e r a t e o f t e m p e r a t u r e r i s e . When t h e f i r e t e m p e r a t u r e r e a c h e s a s t e a d y v a l u e , t h e g a s i s no l o n g e r e x p a n d i n g and t h e smoke moves o u t o f t h e compartment by buoyancy f o r c e a l o n e . With f i r e i n one f l o o r of a b u i l d i n g , a i r f l o w s i n t h r o u g h l e a k a g e o p e n i n g s i n t h e w a l l s of t h e f i r e compartment a t low l e v e l s and smoke f l o w s o u t of t h e compartment a t u p p e r l e v e l s t o a d j a c e n t a r e a s . T h i s p a p e r d e a l s w i t h a f i r e i n a compartment o f o n e - s t o r e y h e i g h t , n o t i n a l a r g e s p a c e s u c h a s a n a t r i u m . The p r e s s u r e d i f f e r e n c e d u e t o buoyancy between a f i r e compartment and i t s s u r r o u n d i n g s c a n b e e x p r e s s e d by t h e f o l l o w i n g e q u a t i o n : where AP = p r e s s u r e d i f f e r e n c e , Pa g = g r a v i t a t i o n a l c o n s t a n t , m / s 2 h = d i s t a n c e from t h e n e u t r a l p r e s s u r e l e v e l , m p = g a s d e n s i t y , kg/m3 T = t e m p e r a t u r e , K S u b s c r i p t s i = o u t s i d e t h e f i r e compartment f = f i r e .

The l e v e l where t h e p r e s s u r e s of t h e f i r e compartment and t h e s u r r o u n d i n g a r e a s a r e e q u a l i s c a l l e d t h e n e u t r a l p r e s s u r e l e v e l (NPL).

Above t h i s l e v e l t h e p r e s s u r e s i n t h e f i r e compartment a r e g r e a t e r t h a n t h o s e o u t s i d e t h e compartment, r e s u l t i n g i n g a s f l o w o u t o f t h e f i r e compartment; c o n v e r s e l y , below t h i s l e v e l a i r f l o w s i n t o t h e f i r e compartment. The l o c a t i o n o f t h e n e u t r a l p r e s s u r e l e v e l depends on t h e v e r t i c a l d i s t r i b u t i o n and s i z e of l e a k a g e o p e n i n g s and on t h e t e m p e r a t u r e o f g a s e s i n t h e f i r e compartment and t h e s u r r o u n d i n g a r e a . It o c c u r s on a l e v e l which r e s u l t s i n a b a l a n c e of mass f l o w i n t o and o u t o f t h e f i r e compartment.

DESCRIPTION OF THE EXPERIMENTAL FIRE TOWER

The f i r e tower (1) i s p a r t of t h e e x p e r i m e n t a l f a c i l i t i e s of t h e N a t i o n a l F i r e L a b o r a t o r y of t h e N a t i o n a l R e s e a r c h C o u n c i l o f Canada, and

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i s l o c a t e d a b o u t 60 km w e s t o f Ottawa. The p l a n v i e w o f a t y p i c a l f l o o r i s shown i n F i g u r e 1. The e x p e r i m e n t a l tower c o n t a i n s a l l t h e s h a f t s and

,

o t h e r f e a t u r e s n e c e s s a r y t o s i m u l a t e t h e a i r a n d smoke movement p a t t e r n s of a t y p i c a l m u l t i - s t o r e y b u i l d i n g , i n c l u d i n g t h e e l e v a t o r , s t a i r , smoke e x h a u s t , s e r v i c e , s u p p l y , and r e t u r n a i r s h a f t s . The e x t e r i o r w a l l s and t h e w a l l s o f v e r t i c a l s h a f t s a r e p r o v i d e d w i t h v a r i a b l e o p e n i n g s t h a t c a n b e s e t t o s i m u l a t e t h e l e a k a g e a r e a s o f t y p i c a l b u i l d i n g s . 'Itro p r o p a n e g a s b u r n e r s e t s , e a c h c a p a b l e o f p r o d u c i n g h e a t a t a r a t e o f 2.5 MW, a r e l o c a t e d on t h e second f l o o r b u r n a r e a . A s e p a r a t e s t r u c t u r e a d j a c e n t t o t h e t o w e r h o u s e s t h e a i r moving and h e a t i n g p l a n t of t h e e x p e r i m e n t a l tower; t h e a i r d u c t s r u n underground t h r o u g h a s h o r t t u n n e l t o t h e b o t t o m of t h e e x p e r i m e n t a l f i r e tower. One s y s t e m h a n d l e s t h e main a i r s u p p l y and h e a t i n g l o a d and t h e o t h e r

s u p p l i e s o u t s i d e a i r , e i t h e r t o t h e e x p e r i m e n t a l s t a i r and e l e v a t o r s h a f t s , o r t o v e s t i b u l e s i n t e r p o s e d between t h e e n t r a n c e s t o t h e s e s h a f t s and t h e b u r n a r e a . T e m p e r a t u r e s a r e measured i n t e n d i f f e r e n t l o c a t i o n s o n e a c h f l o o r u s i n g chrome-alumel t h e r m o c o u p l e s . 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 t h e v a r i o u s w a l l s a r e measured u s i n g e i g h t e e n s t a t i c p r e s s u r e t a p s mounted f l u s h t o t h e w a l l s o n e a c h f l o o r . A l l p r e s s u r e l i n e s a r e c o n n e c t e d t o a 24-port p r e s s u r e s w i t c h e q u i p p e d w i t h a diaphragm-type m a g n e t i c r s l u c t a n c e p r e s s u r e t r a n s d u c e r a n d l o c a t e d o n t h e same f l o o r i n t h e o b s e r v a t i o n a r e a . Carbon d i o x i d e c o n c e n t r a t i o n s a r e measured a t s i x l o c a t i o n s o n e a c h f l o o r i n t h e s h a f t s , l o b b i e s , c o r r i d o r s , and b u r n a r e a by c o p p e r s a m p l i n g t u b e s c o n n e c t e d t o a 12-port s a m p l i n g s w i t c h u n i t w i t h a n o n d i s p e r s i v e i n f r a r e d g a s a n a l y z e r . A l l d e v i c e s of t h e t h r e e s y s t e m s a r e c o n t r o l l e d and m o n i t o r e d by a computer-based d a t a a c q u i s i t i o n and c o n t r o l s y s t e m i n t h e a t t a c h e d s e r v i c e s u n i t .

S E R V I C E TOWER

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The l e a k a g e a r e a s of t h e e x p e r i m e n t a l f i r e tower were s e t f o r a b u i l d i n g w i t h a v e r a g e a i r t i g h t n e s s and a n a r e a p e r f l o o r o f 900 m2 o r # s e v e n t i m e s t h a t o f t h e f l o o r a r e a of t h e e x p e r i m e n t a l tower ( I ) . They were b a s e d on measurements i n s e v e r a l m u l t i - s t o r e y b u i l d i n g s ( 2 , 3 ) . The f i r e t e s t s were c o n d u c t e d u s i n g t h e p r o p a n e g a s b u r n e r o n t h e s e c o n d f l o o r n e a r e s t t h e e l e v a t o r s h a f t ( F i g u r e 1 ) w i t h t h e t e m p e r a t u r e n e a r t h e c e i l i n g above t h e b u r n e r s t o f o l l o w c l o s e t o t h e ASTM-El19 s t a n d a r d t i m e - t e m p e r a t u r e c u r v e u p t o t h e maximum t e s t t e m p e r a t u r e s and h e l d c o n s t a n t t h e r e a f t e r . I n a d d i t i o n t o t h e p r e s s u r e s r e c o r d e d t h r o u g h o u t t h e tower w i t h t h e d a t a a c q u i s i t i o n s y s t e m , 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 t h e e l e v a t o r l o b b y w a l l o n t h e d o o r s i d e a t t h e 0.40, 1.93 and 3.08 m l e v e l s o f t h e s e c o n d f l o o r were r e c o r d e d c o n t i n u o u s l y w i t h a pen r e c o r d e r . F i v e m i n u t e s a f t e r i g n i t i o n , t h e e a s t and w e s t w a l l v e n t s on t h e second f l o o r , e a c h w i t h a n a r e a of 0.46 m 2 , were opened t o s i m u l a t e b r o k e n windows. T h i r t y m i n u t e s a f t e r i g n i t i o n , t h e p r e s s u r i z a t i o n f a n f o r t h e e l e v a t o r s h a f t was a c t i v a t e d and t h e s u p p l y a i r r a t e a d j u s t e d t o n e u t r a l i z e t h e a d v e r s e p r e s s u r e d i f f e r e n c e a c r o s s t h e e l e v a t o r l o b b y w a l l measured a t t h e 3.08 m l e v e l o n t h e f i r e f l o o r ( s e c o n d f l o o r ) . A f t e r t h e t e s t , w i t h t h e tower b a c k t o normal t e m p e r a t u r e , t h e e l e v a t o r s h a f t was p r e s s u r i z e d a t t h e same s u p p l y a i r r a t e t o r e c o r d t h e p r e s s u r e d i f f e r e n c e a c r o s s t h e l o b b y w a l l a t t h e same l e v e l . S i x s u c h b u r n t e s t s were c o n d u c t e d a t f i r e t e m p e r a t u r e s o f 450, 550, 660, 750, and 840°C. They were c o n d u c t e d w i t h t e m p e r a t u r e d i f f e r e n c e s between i n s i d e and o u t s i d e t h e tower of l e s s t h a n 6'K and wind s p e e d o f l e s s t h a n 16 krnlh.

To i n v e s t i g a t e t h e a d v e r s e p r e s s u r e s c a u s e d by t h e r m a l e x p a n s i o n , b o t h t h e e l e v a t o r l o b b y p r e s s u r e d i f f e r e n c e a t t h e 3.08 m l e v e l a n d t h e b u r n t e m p e r a t u r e were r e c o r d e d on a c o n t i n u o u s pen r e c o r d e r d u r i n g t h e t e m p e r a t u r e r i s e from t h e t i m e of i g n i t i o n o f t h e g a s b u r n e r . The measurements were r e p e a t e d w i t h two o u t s i d e w a l l v e n t s ( t o t a l a r e a o f 0.93 m2) opened p r i o r t o i g n i t i n g t h e b u r n e r . Two f i r e t e s t s were c o n d u c t e d a t 750°C w i t h t h e e l e v a t o r s h a f t p r e s s u r i z e d ; i n t h e f i r s t , t h e e l e v a t o r s h a f t was p r e s s u r i z e d b e f o r e i g n i t i o n and i n t h e s e c o n d , i t was p r e s s u r i z e d 5 0 m i n u t e s i n t o t h e b u r n p e r i o d . For b o t h t e s t s t h e e l e v a t o r s h a f t was p r e s s u r i z e d t o o b t a i n a p r e s s u r e d i f f e r e n c e a c r o s s t h e e l e v a t o r l o b b y w a l l o f 25 Pa u n d e r n o n - f i r e c o n d i t i o n . The v a l u e o f 25 Pa i s o f t e n u s e d i n d e s i g n i n g smoke c o n t r o l s y s t e m s t o combat f i r e p r e s s u r e s i n b u i l d i n g s . P r e s s u r e

d i f f e r e n c e s , t e m p e r a t u r e s , and Cog c o n c e n t r a t i o n s were measured t h r o u g h o u t t h e tower d u r i n g t h e t e s t s .

RESULTS AND DISCUSSION Buoyancy F o r c e

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 t h e w a l l s of t h e e l e v a t o r l o b b y and t h e e l e v a t o r s h a f t a t t h e 3.08 m l e v e l o n t h e f i r e f l o o r ( s e c o n d f l o o r ) b o t h r e f e r e n c e d t o t h e b u r n a r e a p r e s s u r e f o r f i r e t e m p e r a t u r e s from 450 t o 840°C a r e shown i n F i g u r e 2. They v a r i e d from 9 t o 14 Pa f o r t h e e l e v a t o r s h a f t w a l l and from 5 t o 7 Pa f o r t h e e l e v a t o r l o b b y w a l l . The d i f f e r e n c e s were s m a l l e r f o r t h e l o b b y w a l l b e c a u s e t h e e l e v a t o r w a l l

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0 ELEVATOR SHAFT WALL ELEVATOR LOBBY WALL

CL REFERENCE PRESSURE

-

BURN AREA Y L CALCULATED BY EQ. 1

-

a _*-.-*-- Y D: p. 0 200 400 600 800 1009 F I R E TEMPERATURE, OC FIGURE 2. P r e s s u r e d i f f e r e n c e a c r o s s e l e v a t o r s h a f t w a l l and e l e v a t o r l o b b y w a l l f o r v a r i o u s f i r e t e m p e r a t u r e s ( p r e s s u r e d i f f e r e n c e s measured 3.08 m above 2nd f l o o r l e v e l ) . c o n t a i n i n g t h e e l e v a t o r d o o r p r o v i d e d a d d i t i o n a l r e s i s t a n c e t o g a s f l o w from t h e b u r n a r e a t o t h e e l e v a t o r s h a f t , and b e c a u s e t h e t e m p e r a t u r e was h i g h e r (54OC) i n t h e l o b b y t h a n i n t h e s h a f t (23OC). The n e u t r a l

p r e s s u r e l e v e l s were l o c a t e d a t a b o u t 1.7 m above f l o o r l e v e l b a s e d o n t h e p r e s s u r e d i f f e r e n c e measurements on t h e d o o r s i d e o f t h e e l e v a t o r l o b b y wall. Using t h i s v a l u e , 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 t h e e l e v a t o r s h a f t w a l l were c a l c u l a t e d u s i n g E q u a t i o n 1 ; t h e y a g r e e d r e a s o n a b l y w e l l w i t h t h e measured v a l u e s , a s shown i n F i g u r e 2.

The maximum measured v a l u e was 14 Pa. Fang ( 4 ) h a s measured p r e s s u r e s c a u s e d by room f i r e s d u r i n g a s e r i e s of f u l l - s c a l e t e s t s i n a

room w i t h an open doorway and a c e i l i n g h e i g h t o f 2.4 rn. The maximurn p r e s s u r e d i f f e r e n c e r e a c h e d was 1 5 Pa, a c r o s s t h e b u r n room w a l l a t t h e c e i l i n g , measured s h o r t l y a f t e r f l a s h o v e r . DeCicco ( 5 ) r e p o r t e d a d v e r s e

p r e s s u r e d i f f e r e n c e s i n t h e o r d e r o f 10 t o 15 Pa and a s h a r p peak o f 35 Pa f o u r m i n u t e s a l t e r i g n i t i o n Prom a f u l l a c a l e f i r e t e f l t i n a room with a f l o o r h e i g h t of 3.5 m i n a m u l t i - s t o r e y b u i l d i n g . B u t c h e r e t a l . (6)

r e p o r t e d a n a d v e r s e p r e s s u r e d i f f e r e n c e o f 5 Pa a t t h e t o p o f a s t a i r d o o r w i t h a wood c r i b f i r e a t 1000°C. About 1 5 Pa a p p e a r s t o be t h e e x p e c t e d f i r e p r e s s u r e due t o buoyancy f o r c e i l l n g heights up t o 3.5 rn.

As t h e f i r e p r e a s u r e v a r i e s d i r e c t l y with t h e d i s t a n c e from t h e n e u t r a l p r e s s u r e l e v e l (Eq. I ) , h i g h e r p r e s s u r e s c a n h e e x p e c t e d f o r f l o o r s of g r e a t e r c e i l i n g h e i g h t . During e a c h f t r e t e s t t h e e l e v a t o r s h a f t was p r e a a u r i z e d t o n e u t r a l i z e t h e a d v e r s e p r e s s u r e d i f f e r e n c e a c r o s s t h e e l e v a t o r lobby w a l l a t t h e 3.08 m l e v e l . F i g u r e 3 show^ t h e v e r t i c a l p r e s s u r e d i f f e r e n c e p r o f i l e w i t h , the f i r e t e m p e r a t u r e a t 750°C. Without p r e s s u r i z a t i o n t h e n e u t r a l p r e s s u r e l e v e l was l o c a t e d at t h e 1.7 m l e v e l ; w i t h p r e s s u r i z a t i o n i t was r a i s e d t o t h e 3.08 m l e v e l , w i t h a n accompanying shift i n the p r e s s u r e p r o f i l e t o t h e r i g h t Ln t h e a r e a o f p o s i t i v e p r e s s u r e s . The s u p p l y a i r r a t e s f o r p r e s s u r i z a t i o n r e q u i r e d t o n e u t r a l i z e t h e a d v e r s e p r e s s u r e s f o r t h e r a n g e of f i r e t e m p e r a t u r e s t e s t e d were from 8 0 0 t o 900 L / s f o r t h e t e s t e l e v a t o r s h a f t . When t h e e l e v a t o r s h a f t was

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F I R E T E M P E R A T U R E , 7 5 0 ° C 2.5

-

E

.

2.0

-

C I

!?

1.5 Y I B U R N A N D 1.0

-

P R E S S U R I Z A T I O N ( 7 PO ) 0 - 4 0 - 2 0 0 2 0 4 0 P R E S S U R E D I F F E R E N C E , P a FIGURE 3. P r e s s u r e d i f f e r e n c e a c r o s s t h e w a l l s of t h e second f l o o r e l e v a t o r l o b b y d u r i n g f i r e t e s t w i t h e l e v a t o r s h a f t p r e s s u r i z a t i o n .

p r e s s u r i z e d w i t h t h e s e s u p p l y a i r r a t e s and w i t h t h e t o w e r back t o normal t e m p e r a t u r e , t h e amounts o f p r e s s u r i z a t i o n were f o u n d t o be a b o u t e q u a l t o t h e p r e s s u r e d i f f e r e n c e s c a u s e d by t h e f i r e . The p r e s s u r i z a t i o n r e q u i r e d t o p r e v e n t smoke i n f i l t r a t i o n , t h e r e f o r e , would b e e q u a l t o t h e a d v e r s e p r e s s u r e c a u s e d by t h e f i r e . The t e s t s d e m o n s t r a t e d t h a t i t i s a p p r o p r i a t e t o u s e t h e a d v e r s e p r e s s u r e d i f f e r e n c e due t o f i r e a s a component of t h e maximum r e q u i r e d p r e s s u r e d i f f e r e n c e a s recommended i n t h e ASHRAE D e s i g n Manual ( 7 ) .

Thermal Expansion

The p r e s s u r e d i f f e r e n c e s shown i n F i g u r e s 2 and 3 a r e t h o s e f o r f i r e t e m p e r a t u r e a t a q u a s i - s t e a d y s t a t e . A t i g n i t i o n o f t h e g a s b u r n e r , a s shown i n F i g u r e 4, t h e p r e s s u r e d i f f e r e n c e i n c r e a s e d i n s t a n t a n e o u s l y t o a peak of 31 Pa. I m m e d i a t e l y t h e r e a f t e r , i t dropped s h a r p l y t o 16 Pa and g r a d u a l l y d e c r e a s e d t o 6 Pa when t h e t e m p e r a t u r e s t a b i l i z e d a t 600°C. The c r o s s - h a t c h e d a r e a i n F i g u r e 4, which was o b t a i n e d by s u b t r a c t i n g t h e p r e s s u r e d i f f e r e n c e s d u e t o buoyancy f o r c e from t h e measured p r e s s u r e d i f f e r e n c e s , r e p r e s e n t s t h e p r e s s u r e d i f f e r e n c e s d u e t o t h e r m a l e x p a n s i o n . The t e s t was r e p e a t e d w i t h t h e two o u t s i d e w a l l v e n t s ( a t o t a l a r e a of 0.93 m2) opened b e f o r e i g n i t i o n o f t h e b u r n e r . As s e e n i n F i g u r e 5 , a s h a r p peak of 8 Pa o c c u r r e d a t i g n i t i o n , f o l l o w e d by a p r e s s u r e i n c r e a s e t o a maximum p r e s s u r e d i f f e r e n c e o f 9 Pa a t 0.9 min a f t e r i g n i t i o n ; a f t e r t h a t i t d e c r e a s e d g r a d u a l l y t o 7 Pa when t h e t e m p e r a t u r e r e a c h e d 52O0C. The a r e a of o p e n i n g i n t h e f i r e f l o o r e n c l o s u r e h a s a s i g n i f i c a n t i n f l u e n c e on t h e e f f e c t o f t h e r m a l e x p a n s i o n . The o p e n i n g s i n t h e f i r e compartment a f f e c t t h e amount o f p r e s s u r e d e v e l o p e d i n t h e f i r e f l o o r and t h e r a t e o f t e m p e r a t u r e r i s e which, i n t u r n , a f f e c t s t h e r a t e of g a s expansion. For b u i l d i n g s o f t y p i c a l c o n s t r u c t i o n , i t i s u n l i k e l y t h a t t h e peak p r e s s u r e d i f f e r e n c e c a u s e d by t h e r m a l e x p a n s i o n , b e c a u s e o f i t s s h o r t d u r a t i o n , c a n s e r i o u s l y a f f e c t t h e performance of a smoke c o n t r o l system. However, i t c a n b e s u b s t a n t i a l f o r a r e l a t i v e l y a i r t i g h t

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1 S

'1

' ' I M E , i n l n

2 0 2 5

PRESSURE DIFFERENCE DUE TO BUOYANCY -PRESSURE DIFFERENCE DUE TO THERMAL

EXPANSION (CROSS-HATCHED AREA )

t

I

N 0 T E : REFERENCE PRESSURE - ELEVATOR LOBBY I G N I T I O N AT TlME ZERO

FIGURE 4 . Pressure difference across elevator lobby wall and fire

temperature vs time

-

outside wall vents closed.

FIRE TEMPERATURE

LOBBY WALL AT THE 3.08 m LEVEL

-

I -

-

V) I I I I W = 0 .I-

5

5 10 15 20 25 ! 3 C I 0 t

/

L T I M E , m i n

5

!- C PRESSURE DIFFERENCE DUE TO BUOYANCY

t

_I

-PRESSURE DIFFERENCE DUE TO THERMAL EXPANSION ( CROSS-HATCHED AREA 3

I

NOTE: REFERENCE PRESSURE - ELEVATOR LOBBY IGNITION AT TlME ZERO

FIGURE 5. Pressure difference across elevator lobby wall and fire

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compartment such as a bank vault or a ship compartment; pressure relief vents should be provided for such cases.

Elevator Shaft Pressurization and Smoke Concentrations

The vertical profile of pressure difference across the elevator lobby wall during the burn period with pressurization is shown in Figure 3. The required outside supply air rate for pressurization was 1880 L/s. m e concentrations of C02 as surrogate indicator of smoke can be expressed as percentage of concentration in the fire floor (second floor) measured 0.3 m below the ceiling in the burn area. Although a detailed hazard analysis is beyond the scope of this paper, a simplified approach to the smoke obscuration problem assumes that particulate concentrations from a solid fuel fire would be proportional to the C02 concentrations measured from these tests. From a consideration of smoke obscuration, an area is assumed to be reasonably safe if i: is not contaminated to an extent greater than 1% of that in the vicinity of a fire area (8). This assumption is probably conservative, in that smoke deposition reduces particulate concentration.

The C02 concentration in the burn area was 5.2%. Without mechanical pressurization, the C02 concentrations (expressed in percent

concentration of that in the burn area) were well above the 1% level in all spaces except the ground floor elevator lobby. Examination of the flow pattern as inferred from the pressure difference readings indicated that the combustion products spread from the burn area into the leakage openings in the walls of all vertical shafts and the ceiling of the second floor. When the elevator shaft pressurization system was activated prior to ignition, the elevator shaft and lobbies were maintained smoke free during the burn period. Then it was activated during the burn period, the elevator shaft was cleared of C02 in a short time but the levels of CO in the elevator lobbies, though much reduced, were still above the critfcal level. This indicated that the

pressurization system should be activated before the elevator shaft and lobbies are heavily contaminated with smoke.

Although the tests were conducted in the ten-storey tower, the results are generally applicable to multi-storey buildings with typical leakage characteristics, as far as smoke movement due to fire pressures are concerned. Smoke movement due to wind and stack action was minimized by conducting tests under conditions of low wind and low

inside-to-outside temperature difference.

CONCLUSION

1. The equation for calculating pressure differences due to the buoyancy force agreed reasonably well with the measured values at steady-state for the range of fire temperature from 450 to 840°C. The maximum adverse pressure difference was about 14 Pa for the elevator shaft wall and

7

Pa for the elevator lobby wall. The pressure difference due to thermal expansion can be substantial, hut because of its short duration, it is unlikely to seriously affect the performance of smoke control systems in buildings of average air tightness. During this short period a substantial amount of smoke and hot gas will flow into surrounding spaces if there is no pressurization to prevent it. With a large outside wall opening such as that caused by broken windows, the peak pressure difference due to thermal expansion is considerably

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less than without such openings. It should be cautioned that pressures due to thermal expansion can be substantial for relatively air-tight compartments.

m

2. The tests demonstrated that it is appropriate to use the adverse pressure difference due to the buoyancy force as a component of the minimum design pressure difference for designing smoke control systems for buildings.

3. The tests verified that adverse pressures caused by fire can be controlled by mechanical pressurization to prevent smoke

contamination of elevators, so long as the required pressurization is maintained. The pressurization system should be operated as soon as possible, before the elevator shaft and lobbies are heavily

contaminated with smoke, as the purging time can be long. The authors gratefully acknowledge the contribution of

R.A. MacDonald in setting up and conducting the tests in the experimental fire tower and processing the test results; of J.E. Rerndt in running the data acquisttion and control system and the gas burner system; and of other staff members of the National Fire Laboratory in assisting during the preparation and conduct of the tests. This paper is a contribution of the Institute for Research in Construction, National Research Council of Canada.

REFERENCES

1. Tamura, G.T. and Klote, J.H., "Experimental Fire Tower Studies on Elevator Pressurization Systems for Smoke Control". ASHRAE Transactions, V. 93, Part 2, 1987.

2. Tamura, G.T., and Shaw, C.Y., "Air Leakage Data for the Design of Elevator and Stair Shaft Pressurization Systems". ASHRAE

Transactions, Vol. 82, Part 2,,,pp. 179-180, 1976.

3. Tamura, G.T., and Shaw, C.Y., Experimental Studies of Mechanical Venting for Smoke Control in Tall Office Buildings". ASHRAE Transactions, Vol. 84, Part 1, pp. 54-71, 1978.

4. Fang, .J. B., "Static Pressures Produced by Room Fires". National Bureau of Standards, NBSIR 80-1984, February 1980.

,

5. DeCicco, P.R., "Smoke and Fire Control in High-Rise Office

Buildings

-

Part I: Full Scale Tests for Establishing Standards". Proceedings, Symposium on Experience and Applications on Smoke and Fire Control, ASHRAE, pp. 9-16, 1973.

6. Butcher, E.G., Fardell, P.J., and Clarke, J., "Pressurization as a Means of Controlling the Movememnt of Smoke and Toxic Gases on Escape Routes". Proceedings, JFRO Symposium No. 4, Movement of Smoke on Escape Routes in Buildings, Paper 5, Watford, 1969.

7. Klote, J.H., and Fothergill, J.W., "Design of Smoke Control Systems Eor Buildings". American Society of Heating, Refrigerating and Air Conditioning Engineers, Inc., Atlanta, September 1983.

8. McGuire, J.H., Tamura, G.T., and Wilson, A.G., "Factors in

Controlling Smoke in High Buildings". Proceedings, Symposium on Fire Hazards in Buildings, ASHRAE, pp. 8-13, 1970.