Air tightness of fire dampers for smoke exhaust systems in high-rise buildings

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Air tightness of fire dampers for smoke exhaust systems in high-rise

buildings

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AIR TIGHTNESS OF FIRE DAMPERS FOR SMOKE EXHAUST

SYSTEMS I N HIGH-RISE BUILDINGS

by

G.T. Tarnura and J.H. McGuire

Reprinted from

ASHRAE Transactions

Vol. 90, 1984, Part 1 B

p.

647

-

654

DBR Paper

No.

1254

Division of Building Research

L ' e x t r a c t i o n de l ' a i r d* l a zone e n f e u d ' u n biitiment r 6 d u i t n e t t e m e n t l e s p r o b l h e s r e l i B s B l a f u d e . En g g n g r a l , l ' e x t r a c t i o n de l a FumBe s e f a i t au w y e n d'une g a i n e comportant d e s r e g i s t r e s

a

chacun d e s s t a g e s du biitiment. En c a s d ' i n c e n d i e , les r e g i s t r e s du t o i t e t c e l u i de l ' 6 t a g e e n f e u s ' o u v r e n t pour Bvacuer l a fumBe.

L ' e f f i c a c i t i d e l a g a i n e d 1 6 v a c u a t i o n d e s fumBes diminue s i d e s F u i t e s s e p r o d u i s e n t aux r e g i s t r e s E e r d s d e s k t a g e s non a t t e i n t s p a r l e f e u . Des e s s a i s o n t i t 6 e f f e c t u i s a v a n t e t a p r s s un i n c e n d i e pour mesurer l e s f u i t e s d ' a i r de r e g i s t r e s c o u p e - f e u b r e v e t g s couramment u t i l i s i s s u r l e s g a i n e s d 1 6 v a c u a t i o n d e s fumBes. Avant l ' i n c e n d i e , l e r a p p o r t de l ' a i r e de f u i t e ii _{l ' a i r e du} r e g i s t r e G t a i t g6nEralement i n f 6 r i e u r B 2,5%. Aprss e x p o s i t i o n pendant un temps d6terminB

a

l a t e m p g r a t u r e d ' e s s a i , l e s r a p p o r t s 6 t a i e n t e n gBn6ral i n f g r i e u r s

a

4%. En r e d u i s a n t l a t e m p e r a t u r e maximale du g 6 n C r a t e u r d ' a i r chaud 2 _{1 000°F} (540°C), l ' a u g m e n t a t i o n d e l ' a i r e de E u i t e c o n s i c u t i v e 2 une e x p o s i t i o n au f e u 6 t a i t moins i m p o r t a n t e .

Air Tightness

of

Fire Dampers for Smoke

Exhaust Systems in High-Rise Buildings

G.T. Tamura

ASHRAE Member

J.H. McGuire

ABSTRACT

Venting t h e f i r e r e g i o n of a b u i l d i n g t o t h e e x t e r i o r s i g n i f i c a n t l y reduces smoke problems caused by a f i r e . T h i s i s of t e n a c h i e v e d by means of a smoke e x h a u s t s h a f t w i t h dampered openings on e a c h f l o o r . I n t h e e v e n t of f i r e , t h e dampers a t t h e t o p and on t h e f i r e f l o o r a r e opened t o e x h a u s t smoke t o t h e e x t e r i o r .

The performance of t h e smoke exhaust s h a f t is s e r i o u s l y a f f e c t e d by any e x t r a n e o u s a i r l e a k a g e through c l o s e d dampers l o c a t e d on t h e n o l r f i r e f l o o r s . T e s t s have b e e n conducted b e f o r e and a f t e r f i r e exposure t o measure t h e a i r l e a k a g e c h a r a c t e r i s t i c of p r o p r i e t o r y f i r e dampers c u r r e n t l y used f o r smoke s h a f t a p p l i c a t i o n .

The p r e - f i r e t e s t r a t i o s of l e a k a g e a r e a t o damper a r e a were g e n e r a l l y below 2f%. A f t e r exposure t o t h e s t a n d a r d time-temperature, t h e r a t i o s were g e n e r a l l y below 4%. R e s t r i c t i n g t h e maximum f u r n a c e temperature t o 1000°F (540°C) c o n s i d e r a b l y reduced t h e i n c r e a s e i n l e a k a g e a r e a r a t i o due t o f i r e exposure.

INTRODUCTION

Venting of smoke from t h e f i r e r e g i o n i n a b u i l d i n g t o t h e e x t e r i o r p l a y s a s i g n i f i c a n t r o l e i n r e d u c i n g smoke problems caused by f i r e . The p r e f e r r e d approach i s t o c r e a t e a steady- s t a t e c o n d i t i o n of lower p r e s s u r e i n t h e f i r e compartment r e l a t i v e t o t h a t i n a d j a c e n t compartments.

I n g e n e r a l , proper a p p l i c a t i o n of v e n t i n g of t h e f i r e r e g i o n can a c h i e v e t h i s

o b j e c t i v e , a l t h o u g h t e c h n i q u e s of v e n t i n g v a r y c o n s i d e r a b l y . The N a t i o n a l Building Code of Canada (1980), which r e q u i r e s p r o v i s i o n f o r v e n t i n g of e a c h f l o o r a r e a , p e r m i t s u s e of t h e b u i l d i n g a i r h a n d l i n g system t o a c h i e v e t h i s i f t h e f l o o r a r e a i s s p r i n k l e r e d . A r e c e n t survey of smoke c o n t r o l systems i n a Canadian c i t y * i n d i c a t e s t h a t b u i l d i n g s w i t h c e n t r a l

HVAC systems u s u a l l y make u s e of e i t h e r t h e r e t u r n a i r o r e x h a u s t systems, and t h a t

compartmented systems u s e t h e f r e s h air v e r t i c a l s h a f t . Only a few b u i l d i n g s u s e a s e p a r a t e smoke s h a f t a s a means of v e n t i n g a f i r e compartment.

I n s i n g l e - s t o r y b u i l d i n g s roof v e n t s o r powered roof e x h a u s t s may be used, b u t i n high- r i s e b u i l d i n g s a s e p a r a t e v e r t i c a l s h a f t o r d u c t i s o f t e n n e c e s s a r y . When f i r e i s d e t e c t e d , t h e s h a f t i s opened a t t h e t o p and a t t h e f i r e f l o o r and t h e e x h a u s t f a n ( l o c a t e d a t t h e t o p of t h e s h a f t ) i s a c t i v a t e d . The e x h a u s t dampers on non f i r e f l o o r s must b e closed.

. . . .

"Information t o be p u b l i s h e d s h o r t l y

G.T. Tamura i s a Research O f f i c e r , Energy and S e r v i c e s S e c t i o n , and J.H. McGuire f o r m e r l y a Research O f f i c e r , F i r e Research S e c t i o n , D i v i s i o n of B u i l d i n g Research, N a t i o n a l Research C o u n c i l Canada, Ottawa, Canada, K1A _OR6.

FIRE DAMPERS

Openings i n a f i r e - r a t e d e x h a u s t s h a f t must be p r o t e c t e d w i t h a f i r e damper a c c o r d i n g t o NFPA 90A, "Standard f o r t h e I n s t a l l a t i o n of A i r c o n d i t i o n i n g and V e n t i l a t i n g Systems

."

S p e c i f i c a t i o n f o r f i r e dampers i s g i v e n i n UL _{555, "Standard f o r F i r e Dampers and C e i l i n g} Assemblies." It i s t h e f u n c t i o n of a f i r e damper t o m a i n t a i n t h e i n t e g r i t y of f i r e

p a r t i t i o n s d u r i n g f i r e . The proposed "UL 5558, Standard f o r Leakage Rated Dampers f o r Use i n Smoke C o n t r o l Systems," i s b e i n g developed t o limit t h e amount of smoke m i g r a t i n g through a dampered opening.

The a i r l e a k a g e c h a r a c t e r i s t i c of dampers i s p a r t i c u l a r l y important when t h e y a r e used i n a smoke-exhaust s h a f t . Unless dampers on f l o o r s o t h e r t h a n t h e f i r e f l o o r a r e c l o s e d t i g h t l y t h e e f f e c t i v e n e s s of t h e smoke exhaust system w i l l be g r e a t l y impaired. T e s t s conducted on 7-story and 22-story b u i l d i n g s w i t h c e n t r a l a i r h a n d l i n g systems i n d i c a t e t h a t t h e r a t e s of a i r f l o w i n t o t h e smoke s h a f t through an open smoke damper a r e about one t h i r d t h e t o t a l flow r a t e a t t h e t o p of t h e smoke s h a f t ; a d d i t i o n a l a i r e n t e r s t h e s h a f t through c r a c k s i n t h e w a l l c o n s t r u c t i o n , around and between damper b l a d e s , and between damper frame and w a l l (Tamura and Shaw 1981). T e s t s conducted on a 3 0 s t o r y b u i l d i n g w i t h a smoke s h a f t c o n s t r u c t e d of s h e e t metal gave a v e n t i n g r a t e on t h e f o u r t h f l o o r of 1.4 a i r changes p e r hour; t h i s r e p r e s e n t e d 38% of t h e t o t a l e x h a u s t r a t e a t t h e t o p . When a l l c l o s e d smoke

dampers were s e a l e d w i t h p l a s t i c s h e e t , t h e v e n t i n g r a t e on t h e f o u r t h f l o o r i n c r e a s e d by 44% t o 2.0 a i r changes p e r hour. T h i s s u g g e s t s t h a t t h e performance of smoke e x h a u s t s h a f t s c a n be g r e a t l y improved by reducing l e a k a g e through c l o s e d smoke dampers.

C u r r e n t l y , t h e f i r e dampers used i n smoke e x h a u s t systems a r e t h e same a s t h o s e t h a t s e r v e a s f i r e c u t - o f f s i n a i r h a n d l i n g d u c t s , where t h e y a r e n o t expected t o b e p a r t i c u l a r l y t i g h t . The t e s t s now d e s c r i b e d were c a r r i e d o u t t o a s s e s s t h e i r a i r - l e a k a g e c h a r a c t e r i s t i c s f o r such a p p l i c a t i o n s .

TEST DAMPERS

Two each of n i n e d i f f e r e n t models of damper were purchased from f i v e manufacturers. A s noted i n T a b l e 1 , t h r e e were c u r t a i n t y p e , two were s i n g l e b l a d e , and f o u r were m u l t i b l a d e . A l l

were ULC approved, complying w i t h ULC S112 (comparable t o UL 5551, Standard Method of F i r e T e s t of Fire-Damper Assemblies.

P r i o r t o t e s t , v e r t i c a l and h o r i z o n t a l through-openings, a s d e f i n e d i n ULC S112, were measured on a l l dampers. There were no h o r i z o n t a l through-openings i n e i t h e r b l a d e o r c u r t a i n t y p e dampers, nor v e r t i c a l t h r o u g h w p e n i n g s i n c u r t a i n t y p e dampers; b u t t h o s e i n b l a d e t y p e dampers v a r i e d from 0 t o 0.32 i n . (8 mm). These through c l e a r a n c e s complied w i t h

being l e s s t h a n t h e maximum 0.031 i n . ( 1 ram) f o r h o r i z o n t a l through-openings and 0.375 i n . (10 mrn) f o r v e r t i c a l through-openings.

TESTS

A t o t a l of f i v e 2-hour f i r e t e s t s , f o l l o w i n g t h e ASTM E-119 s t a n d a r d time-temperature c u r v e

( F i g u r e l ) , were c a r r i e d o u t i n t h e l a r g e DBRINRCC w a l l f u r n a c e . Each t e s t i n v o l v e d between I t h r e e and f i v e dampers ( F i g u r e 2). The f i r s t was conducted w i t h n e g a t i v e f u r n a c e p r e s s u r e

I

r a n g i n g between 0.04 and 0.08 i n . of w a t e r (10 and 20 Pa), depending on t h e h e i g h t i n t h e

f u r n a c e of t h e damper under c o n s i d e r a t i o n . The remaining t e s t s were c a r r i e d o u t under a _i p o s i t i v e f u r n a c e p r e s s u r e of about 0.20 i n . of w a t e r ( 5 0 Pa). T h i s l a t t e r c o n d i t i o n i s more

s e v e r e t h a n would be encountered i n r e a l i t y , where t h e room a i r i n t h e non f i r e f l o o r s normally f l o w s through t h e c l o s e d dampers i n t o t h e smoke e x h a u s t s h a f t . A s i x t h 2-hour t e s t was c a r r i e d o u t w i t h a maximum f u r n a c e temperature of 1000°F (540°C).

A i r l e a k a g e t e s t s were conducted on each damper b e f o r e and a f t e r t h e f i r e exposure t e s t . F i g u r e 3 shows t h e t e s t arrangement f o r measuring t h e a i r t i g h t n e s s of t h e dampers. It

c o n s i s t e d of a s e a l e d plywood box 3 x 4 x 6 f t (0.91 x 1.22 x 1.83 m) w i t h a l a r g e opening on one s i d e f o r i n s t a l l i n g t e s t dampers. The o p p o s i t e s i d e of t h e box was connected t o a round

d u c t , i t s end connected t o t h e s u c t i o n s i d e of a fan. The d i s c h a r g e s i d e of t h e f a n was connected t o a s h o r t d u c t w i t h a damper t o c o n t r o l t h e r a t e of a i r f l o w through t h e t e s t damper. With t h i s arrangement t h e a i r was drawn from t h e room, through t h e t e s t damper, i n t o t h e l a r g e box, o u t through t h e d u c t and f a n , and back i n t o t h e room.

Three d i f f e r e n t duct-fan arrangements were used t o cover t h e expected range of l e a k a g e r a t e through t h e t e s t dampers:

Fan Duct Duct

C a p a c i t y Diameter Length Method of

cfm ( L / s ) i n . (m) i n . (m) Flow Measurement 350 (165) 4 (0.10) 96 (2.44) laminar flow element

800 (377) 8 (0.20) 108 (2.74) t o t a l p r e s s u r e a v e r a g i n g t u b e 3200 (1510) 12 (0.30) 120 (3.05) t o t a l p r e s s u r e a v e r a g i n g t u b e Flow r a t e measurements were made w i t h a s i n g l e p r e s s u r e r e a d i n g a f t e r each d u c t system had been c a l i b r a t e d u s i n g a l o - p o i n t l o g - l i n e a r p i t o t t r a v e r s e . A s t a t i c p r e s s u r e t a p was i n s e r t e d i n t o t h e w a l l of t h e l a r g e box t o measure t h e p r e s s u r e drop a c r o s s t h e t e s t damper w i t h a p r e s s u r e t r a n s d u c e r . P r e s s u r e r e a d i n g s were made w i t h a diaphragm t y p e p r e s s u r e t r a n s d u c e r ( s e n s i t i v i t y of 0.002 i n . of water (0.50 Pa)).

The l a r g e box was t e s t e d f o r a i r - t i g h t n e s s by o p e r a t i n g t h e f a n a f t e r t h e opening of t h e t e s t damper had been s e a l e d . The t e s t was t e r m i n a t e d a t 1 in. of w a t e r (249 Pa) 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 r e a d i n g s t i l l r i s i n g , i n d i c a t i n g t h a t t h e l a r g e box was v i r t u a l l y a i r t i g h t .

The t e s t f i r e dampers were i n s t a l l e d i n t h e l a r g e box w i t h t h e a x i s of t h e b l a d e s i n t h e h o r i z o n t a l p o s i t i o n . The dampers were c l o s e d by d i s c o n n e c t i n g t h e f u s i b l e l i n k s and a l l o w i n g them t o c l o s e by e i t h e r g r a v i t y o r s p r i n g a c t i o n . Even p r i o r t o f i r e t e s t i n g , t h e dampers d i d n o t , i n some c a s e s , c l o s e completely and had t o be c l o s e d manually.

I n i t i a l t e s t s were conducted t o determine whether r e p e a t e d opening and c l o s i n g o f

dampers a f f e c t e d t h e a i r l e a k a g e r a t e s . Fan flow was a d j u s t e d by means of t h e c o n t r o l damper t o m a i n t a i n a p r e s s u r e d i f f e r e n c e of 0.50 i n . of water (125 Pa) a c r o s s t h e t e s t damper and t h e corresponding l e a k a g e flow was measured. The t e s t damper was t h e n opened and c l o s e d and t h e a i r leakage flow was measured a t t h e same p r e s s u r e d i f f e r e n c e . This procedure was

r e p e a t e d s i x times. T h i s was followed by t e s t s t o d e t e r m i n e t h e a i r l e a k a g e c h a r a c t e r i s t i c s of t h e damper. Air-leakage flows were measured a t p r e s s u r e d i f f e r e n c e s of 0.10 t o 0.50 i n . of w a t e r (25 t o 125 Pa) i n increments of 0.10 in. of w a t e r (25 Pa).

E v a l u a t i o n of A i r T i g h t n e s s

The r e l a t i o n between a i r leakage flow and 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 t e s t damper c a n be e x p r e s s e d by

Q =

c

(AP)" ( 1 )

where

Q = leakage flow p e r u n i t damper a r e a , cmf / f t (L/s m2) C = flow c o e f f i c i e n t , c f m / f t 2 ( i n . of water)" (L/s m 2 ( p a l n ) I

AP = p r e s s u r e d i f f e r e n c e a c r o s s damper, i n . of w a t e r (Pa) I n = flow exponent

The flow c o e f f i c i e n t , C , and flow exponent, n, of t h e above e q u a t i o n d e f i n e t h e a i r - l e a k a g e c h a r a c t e r i s t i c s of t h e damper. During t h e t e s t s f i v e s e t s of v a l u e s f o r l e a k a g e flow, Q, and p r e s s u r e d i f f e r e n c e , AP, were obtained. The damper a r e a s , A , were a l s o

determined, based on t h e i n s i d e dimensions of t h e frame. The v a l u e s of flow c o e f f i c i e n t and exponent were c a l c u l a t e d u s i n g t h e l e a s t s q u a r e s method.

A i r t i g h t n e s s can be expressed i n terms of t h e percentage r a t i o of leakage opening a r e a t o damper a r e a by u s i n g t h e e q u a t i o n f o r flow of a i r through a sharp-edged o r i f i c e

where

-

A = l e a k a g e areaidamper a r e a p e r c e n t a g e r a t i o , % S u b s t i t u t i n g Q of Equation 2 i n Equation 1 g i v e s

Note: When S I u n i t s a r e used, c o n s t a n t 24 i n Equations 2 and 3

i s

r e p l a c e d by 0.72.

RESULTS

Table 1 g i v e s t h e r e s u l t s of t h e a i r leakage t e s t s b e f o r e and a f t e r each f i r e endurance t e s t . They a r e e x p r e s s e d i n terms of p e r c e n t a g e of damper a r e a ( i n s i d e dimensions of frame) and a r e based on Equation 3, w i t h a v a l u e of 0.30 i n . of w a t e r (75 Pa) f o r A€'. _{Values of t h e flow} exponent ranged from 0.47 t o 0.60, w i t h a mean v a l u e of 0.53 f o r a l l dampers b e f o r e and a f t e r t h e f i r e t e s t s , i n d i c a t i n g t h a t t h e l e a k a g e openings behaved much l i k e a s h a r p edged

o r i f ice.*

With r e p e a t e d c l o s u r e t h e v a r i a t i o n i n l e a k a g e f l o w r a t e a p p e a r s t o depend on t h e t y p e of s e a l between b l a d e s and s t o p s . The v a r i a t i o n s i n l e a k a g e flow r a t e f o r two c u r t a i n t y p e dampers from one manufacturer were 11 and 19%, and t h o s e from a n o t h e r manufscturer 4 and 6%. F o r b l a d e t y p e dampers t h e v a r i a t i o n s were 10 and 38% f o r dampers from o n e manufacturer, and 0 and 3% f o r t h o s e from a n o t h e r . I n t h e l a t t e r dampers t h e s p r i n g c l i p o r l a t c h c l o s u r e s provided i n a d d i t i o n t o t h e u s u a l b l a d e s t o p a t t h e bottom appeared t o e n s u r e c o n s i s t e n t a i r leakage r a t e s .

Table 1 g i v e s t h e l e a k a g e a r e a s f o r blade-type dampers t e s t e d w i t h t h e d i r e c t i o n o f a i r f l o w away from t h e s i d e of t h e damper c o n t r o l mechanism towards t h e o p p o s i t e s i d e . T h i s

i s t h e expected d i r e c t i o n of a i r f l o w f o r smoke s h a f t a p p l i c a t i o n . No such d i s t i n c t i o n could be made f o r c u r t a i n - t y p e dampers because b o t h s i d e s of t h e dampers were s i m i l a r i n

c o n s t r u c t i o n . Upstream s i d e s of t h e s e dampers were i d e n t i f i e d s o t h a t t h e y c o u l d be t e s t e d i n t h e same manner b e f o r e and a f t e r t h e f i r e t e s t .

Table 1 g i v e s an i n d i c a t i o n ( p r i o r t o f i r e t e s t i n g ) of t h e v a r i a t i o n i n l e a k a g e v a l u e s t h a t c a n b e e x p e c t e d w i t h t y p e of damper and manufacturer, even f o r two i d e n t i c a l dampers. The l e a k a g e a r e a s f o r a l l dampers t e s t e d were between 0.44 t o 2.85% of damper a r e a . Maximum l e a k a g e a r e a s were 1.42% f o r t h e c u r t a i n t y p e , 2.61% f o r t h e s i n g l e b l a d e t y p e , 2.43% f o r t h e m u l t i b l a d e t y p e , and 2.85% f o r t h e m u l t i b l a d e t y p e w i t h c e n t e r mullion. The maximum

d i f f e r e n c e between two i d e n t i c a l dampers was 0.72 p e r c e n t a g e p o i n t s , and t h e a v e r a g e d i f f e r e n c e was about 0.30 p e r c e n t a g e p o i n t s .

Following t h e i n i t i a l a i r - l e a k a g e t e s t s , t h e f i r e dampers were i n s t a l l e d i n t h e w a l l f u r n a c e w i t h t h e upstream f a c e , a s t e s t e d f o r a i r l e a k a g e , exposed t o t h e f i r e . T a b l e 1 , which a l s o g i v e s t h e r e s u l t s of t h e a i r - l e a k a g e t e s t s t h a t followed t h e f i r e t e s t s , i n d i c a t e s a n i n c r e a s e i n l e a k a g e a r e a s f o r c u r t a i n - t y p e dampers g r e a t e r by 0.5 t o 1.0 p e r c e n t a g e p o i n t when t h e f u r n a c e was under p o s i t i v e a s compared t o n e g a t i v e p r e s s u r e . With t h e f u r n a c e under n e g a t i v e p r e s s u r e t h e a i r i n t h e room induced through t h e f i r e damper, a s i s t h e c a s e f o r smoke-shaft a p p l i c a t i o n , would t e n d t o c o o l t h e damper, whereas an o p p o s i t e e f f e c t would t a k e p l a c e w i t h t h e f u r n a c e under p o s i t i v e p r e s s u r e .

A f t e r t h e p o s i t i v e p r e s s u r e f u r n a c e t e s t s , t h e i n c r e a s e i n l e a k a g e a r e a s of t h e c u r t a i n - t y p e dampers ranged from -0.06 t o 1.34 p e r c e n t a g e p o i n t s of t h e damper a r e a . The i n c r e a s e i n leakage a r e a s a f t e r a 2-hour f i r e endurance t e s t f o r t h e blade-type dampers ranged from -0.08 t o 5.1 p e r c e n t a g e p o i n t s of t h e damper a r e a . The g r e a t e s t i n c r e a s e s o c c u r r e d f o r t h e multi- blade t y p e dampers, followed by m u l t i b l a d e t y p e w i t h c e n t e r mullion. The l e a s t o c c u r r e d f o r t h e s i n g l e b l a d e dampers. The maxirmm through c l e a r a n c e s f o r a l l dampers were less t h a n t h e 0.375 i n . (10 mrn) s p e c i f i e d by ULC _{S112. The maximum gap between b l a d e s was a l s o l e s s t h a n} t h i s v a l u e , except f o r one m u l t i b l a d e damper t h a t had a 2111. (51-mm) gap caused by s e v e r e bowing of t h e t o p blade.

"-3

W o r e p r e c i s e l y , A, must be m u l t i p l i e d by

(-)

t o c o r r e c t f o r n

#

3

and .30

AP

#

0.30 in. of water. Because n-4 i s 0.09, t h i s c o r r e c t i o n i s n e g l i g i b l e i n t h i s case. 650

The i n c r e a s e i n a i r l e a k a g e v a l u e s f o r t h e dampers t e s t e d w i t h maxiaum f u r n a c e

t e m p e r a t u r e s of 1000°F (540°C), T e s t No. 6, were almost n e g l i g i b l e , i.e., -0.33 t o 0.14

p e r c e n t a g e p o i n t s of t h e damper a r e a .

DISCUSSION

P r e s s u r e l o s s e s can occur i n s i d e a smoke e x h a u s t s h a f t a s a r e s u l t of g a s f l o w through t h e open v e n t on t h e f i r e f l o o r and a r e u s u a l l y e x a c e r b a t e d by a i r f l o w through v a r i o u s l e a k a g e openings i n t h e w a l l s of t h e smoke s h a f t . These p r e s s u r e l o s s e s reduce 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 open smoke damper, w i t h c o r r e s p o n d i n g r e d u c t i o n i n t h e r a t e of smoke exhaust. A n a l y s i s of t h e performance of smoke s h a f t s i n d i c a t e s t h a t t h e a r e a of l e a k a g e

openings i s a n i m p o r t a n t parameter i n s i z i n g a smoke s h a f t . Because t h e number of r e q u i r e d

dampers i n c r e a s e s w i t h t h e h e i g h t of a b u i l d i n g , t h e w a l l s of t h e smoke s h a f t and t h e smoke dampers of h i g h b u i l d i n g s must be r e l a t i v e l y a i r t i g h t ; f f t h e y a r e n o t , t h e smoke s h a f t

cannot e f f e c t i v e l y vent t h e f i r e f l o o r . The desiga, of a mechanical smoke e x h a u s t system t h a t

t a k e s i n t o account damper l e a k a g e h a s been d e s c r i b e d (Tamura and Shaw 1978). L e a k a g e r a t e d

dampers, a s proposed i n UL _{5558 w i l l a s s i s t i n t h e d e s i g n of such systems.}

P a r t i a l l y c l o s e d dampers can r e s u l t i n e x c e s s i v e a i r l e a k a g e flow. S p e c i a l p r e c a u t i o n s s h o u l d be t a k e n f o r dampers i n v e n t i l a t i o n a i r d u c t s t h a t a r e open d u r i n g normal o p e r a t i o n but c a l l e d upon t o c l o s e on non f i r e f l o o r s d u r i n g a f i r e emergency. End s w i t c h e s on dampers c a n i n d i c a t e f u l l y c l o s e d o r f u l l y open damper p o s i t i o n s a t t h e c e n t r a l a l a r m and c o n t r o l f a c i l i t y d u r i n g a f i r e a s w e l l a s d u r i n g r o u t i n e maintenance of t h e smoke-control system. F i g u r e 1 i s a t y p i c a l r e c o r d of t h e t e m p e r a t u r e extremes t h a t p r e v a i l on t h e unexposed s u r f a c e s of dampers s u b j e c t e d t o t h e s t a n d a r d time-temperature curve and p o s i t i v e f u r n a c e p r e s s u r e . Unless, i n p r a c t i c e , a l l combustible m a t e r i a l s a r e k e p t w e l l away from t h e damper, r i s k of i g n i t i o n i s s u b s t a n t i a l .

CONCLUSIONS

I n t e s t i n g f i r e dampers f o r u s e i n smoke exhaust s h a f t s t h e f o l l o w i n g p o i n t s were observed. 1. The p r e - f i r e - t e s t r a t i o of l e a k a g e a r e a t o damper a r e a was g e n e r a l l y below 23%, e x c e p t

f o r two c a s e s i n which i t was 2.61 and 2.85%. I n some c a s e s t h e dampers d i d n o t c l o s e

completely u n t i l c l o s e d manually b e f o r e t e s t i n g .

2. The p o s t - f i r e - t e s t l e a k a g e a r e a was g e n e r a l l y below 4%, e x c e p t f o r two c a s e s i n which i t

was 5.53 and 7.29%.

3. Operating t h e f u r n a c e under p o s i t i v e ( f o r c u r t a i n - t y p e dampers o n l y ) r a t h e r t h a n n e g a t i v e p r e s s u r e gave s l i g h t l y b u t n o t s u b s t a n t i a l l y g r e a t e r p o s t - f i r e l e a k a g e a r e a r a t i o s .

4. R e s t r i c t i n g t h e maximum f u r n a c e temperature t o 1000°F (540°C) c o n s i d e r a b l y reduced t h e

i n c r e a s e i n l e a k a g e a r e a r a t i o .

5. C u r t a i n dampers g e n e r a l l y had s m a l l e r i n c r e a s e s i n l e a k a g e a r e a r a t i o t h a n d i d o t h e r t y p e s t e s t e d .

REFERENCES

N a t i o n a l B u i l d i n g Code of Canada. 1980. A s s o c i a t e Committee on t h e N a t i o n a l B u i l d i n g Code,

N a t i o n a l Research C o u n c i l of Canada, Ottawa, NRCC 17303, 547 p.

Tamura, G.T.; and Shaw, C.Y. 1978. "Experimental s t u d i e s of mechanical v e n t i n g f o r smoke

c o n t r o l i n t a l l o f f i c e b u i l d i n g s . " ASHRAE T r a n s a c t i o n s 84, P a r t 1, pp. 54-71.

Tamura, G.T.; and Shaw, C.Y. 1981. " F i e l d checks on b u i l d i n g p r e s s u r i z a t i o n f o r smoke

c o n t r o l i n h i g h - r i s e buildings." ASHRAE J o u r n a l 23, No. 2, (Feb. ), pp. 21-25.

ACKNOWLEDGEMENTS

The a u t h o r s a r e indebted t o R.G. Evans f o r conducting t h e a i r leakage t e s t s and t o

J.E. Berndt, P. Huot and R. Lamirande f o r c a r r y i n g o u t t h e f i r e tests. T h i s paper i s a

c o n t r i b u t i o n from t h e Division of Building Research, National Research Council Canada, and i s

TABLE 1

R e s u l t s of A i r Leakage T e s t s

Damper Leakage Area (% damper a r e a ) Dimensions

T e s t Furnace Type Width x Height Manuf ac- Before A f t e r I n c r e a s e No. P r e s s u r e in. (m) t u r e r T e s t T e s t 1 n e g a t i v e c u r t a i n 36 x 36 A 1.42 0.94 -0.4 8 (0.91 x 0.91) 30 x 40 B _{1.02 1.33 0.3 1} (0.76 x 1.01) C 0.64 0.67 0.03 2 p o s i t i v e c u r t a i n 36 x 36 A 0.80 1.10 0.30 (0.91 x 0.91) 30 x 40 B _{0.88 2.22 1.34} (0.76 x 1.01) C 0.60 1.10 0.50 3 p o s i t i v e c u r t a i n * 36 x 36 A 0.94** 0.88 -0.0 6 (0.91 x 0.91) 30 x 40 B 1.33** 1.51 0.18 (0.76 x 1.01) C 0.67** 0.75 0.08 4 p o s i t i v e m u l t i b l a d e 48 x 36 D 1.56 3.67 2.1 1 (with c e n t r e (1.22 x 0.91) mullion) r m l t i b l a d e 36 x 48 D 0.44 5.5 3 5.09 (0.91 x 1.22) 36 x 12 D 1.89 2.40 0.51 (0.91 x 0.30) s i n g l e b l a d e 36 x 14 E 2.06 1.98 -0.08 (0.91 x 0.35) 5 p o s i t i v e m u l t i b l a d e 36 x 48 D 0.77 3.66 2.89 (0.91 x 1.22) 36 x 36 E 2.22 7.29 5.07 (0.91 x 0.91) nu1 t i b l a d e 48 x 36 (with c e n t r e (1.22 x 0.91) E _{2.48 3.53 1.05} n u l l i o n ) 6*** p o s i t i v e s i n g l e blade 36 x 12 D 2.61 2.7 1 0.10 (0.91 x 0.30) nu1 t i b l a d e 36 x 36 E 2.43 2.2 2 -0.2 1 (0.91 x 0.91) n u l t i b l a d e 48 x 36 D 1.18 1.04 -0.14 (with c e n t r e (1.22 x 0.91) n u l l i o n ) 48 x 36 E 2.85 2.52 -0.3 3 (1.22 x 0.91)

*

Salvaged from t e s t No. 1

**

Before f i r e t e s t No. 3

F i g u r e 1 . TIME. MINUTES !Typical t e m p e r a t u r e s a t u n e x p o s e d f a c e o f damper s u b j e c t e d t o ASTM E - 1 19 t i m e - t e m p e r a t u r e c u r v e F i g u r e 2. A-I-thngement f o r f i r e e x p o s u r e t e s t S E A L I D P L Y W O O D BOX I P R E S S U R E T R A N S D U C E R f E S T D A M P E R I S T A T I C PRESSURE D A M P E R FOR TAP F L O W C O N T R O L

-

r r

A

-

f

F A N

-

/

/

\

T O T A L PRESSURE S T A T I C _{A V E R A G I N G TUBE} PRESSURE TAP

\

S T A T I C PRESSURE TAP T O R O O M A I R F i g u r e 3 . Arrangement f o r m e a s u r i n g a i r - t i g h t n e s s o f d a m p e r s

T h i s p a p e r , w h i l e b e i n g d i s t r i b u t e d i h r e p r i n t form by t h e D i v i s i o n of B u i l d i n g R e s e a r c h , remains t h e c o p y r i g h t of t h e o r i g i n a l p u b l i s h e r . It s h o u l d n o t be r e p r o d u c e d i n whole o r i n p a r t w i t h o u t t h e p e r m i s s i o n of t h e p u b l i s h e r . A l i s t of a l l p u b l i c a t i o n s a v a i l a b l e from t h e D i v i s i o n may be o b t a i n e d by w r i t i n g t o t h e P u b l i c a t i o n s S e c t i o n , D i v i s i o n of B u i l d i n g R e s e a r c h , N a t i o n a l R e s e a r c h C o u n c i l of C a n a d a , O t t a w a , O n t a r i o ,

KIA OR6.