Smoke control and fire evacuation by elevators

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Smoke control and fire evacuation by elevators

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Smoke Control and Fire Evacuation

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Elevators

by

J.H. Klote and G.T. Tamura

Reprinted from

ASHRAE Transactions 1986

Vol. 92, Pt. 1A, p. 231

-245

(IRC Paper No. 1453)

Price $3.00

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No. 2949

SMOKE CONTROL AND FIRE

EVACUATION

BY

ELEVATORS

J.H.

Klote, P.E.

G.T. Tamura, P.E.

ASHRAE Member ASHRAE Member

ABSTRACT

I n r e c e n t y e a r s , t h e p o s s i b i l i t y of u s i n g e l e v a t o r s a s a means of f i r e escape has r e c e i v e d c o n s i d e r a b l e a t t e n t i o n . This i n t e r e s t has been sparked by an i n c r e a s e d awareness of l i f e s a f e t y problems of t h e handicapped and a l s o g e n e r a l f i r e e v a c u a t i o n problems of h i g h - r i s e b u i l d i n g s . The use of e l e v a t o r s a s a means of f i r e e v a c u a t i o n i s a p o t e n t i a l s o l u t i o n t o t h i s problem. The major t e c h n i c a l o b s t a c l e t o t h i s i s smoke contamination of e l e v a t o r l o b b i e s and s h a f t s . T h i s paper d i s c u s s e s e l e v a t o r smoke c o n t r o l systems i n c l u d i n g c r i t e r i a f o r e v a l u a t i o n and p r e s e n t s an a n a l y s i s of a i r f l o w due t o e l e v a t o r c a r motion. Computer a n a l y s i s of s e v e r a l e l e v a t o r smoke c o n t r o l systems a r e i n c l u d e d f o r s e v e r a l combinations of open and c l o s e d doors and f o r summer and w i n t e r c o n d i t i o n s .

INTRODUCTION

I n most e l e v a t o r l o b b i e s i n North America, t h e r e a r e s i g n s i n d i c a t i n g t h a t e l e v a t o r s should not be used i n f i r e s i t u a t i o n s , ; r a t h e r t h a t s t a i r s should be used. U n f o r t u n a t e l y , some people can- n o t u s e s t a i r s because of p h y s i c a l handicaps. The use of e l e v a t o r s is a p o t e n t i a l s o l u t i o n t o t h i s problem. L o g i s t i c s of e v a c u a t i o n , r e l i a b i l i t y of e l e c t r i c a l power, e l e v a t o r door jamming, and f i r e and smoke p r o t e c t i o n a r e long-standing o b s t a c l e s t o t h e use of e l e v a t o r s f o r f i r e e v a c u a t i o n . A l l of t h e s e o b s t a c l e s except smoke p r o t e c t i o n can be addressed by e x i s t i n g technology a s d i s c u s s e d by K l o t e (1984).

The N a t i o n a l Bureau of Standards (NBS) i n t h e United S t a t e s and t h e N a t i o n a l Research Council of Canada (NRCC) a r e engaged i n a j o i n t p r o j e c t t o develop smoke c o n t r o l technology f o r e l e v a t o r s . T h i s paper is t h e i n i t i a l r e p o r t of t h i s p r o j e c t and i t c o n t a i n s d i s c u s s i o n s of e l e v a t o r smoke c o n t r o l systems i n c l u d i n g e v a l u a t i o n c r i t e r i a . The t r a n s i e n t p r e s s u r e s due t o

" p i s t o n e f f e c t " when an e l e v a t o r c a r moves i n a s h a f t w i l l be addressed i n a f o l l o w i n g paper. PERFORMANCE CRITERIA

I d e a l l y , an e l e v a t o r smoke c o n t r o l system should p r o t e c t t h e e l e v a t o r s h a f t and t h e e l e v a t o r l o b b i e s such t h a t smoke contamination i n t h e s e a r e a s does not p r e s e n t a hazard. It is obvious f h a t a smoke c o n t r o l system can meet t h i s o b j e c t i v e , even i f a s m a l l amount of smoke i n f i l t r a t e s t h e p r o t e c t e d a r e a s . The f o l l o w i n g g e n e r a l d i s c u s s i o n of p r e s s u r e d i f f e r e n c e s and open doors i s p r e s e n t e d t o form a b a s i s f o r s e l e c t i o n of performance c r i t e r i a and i s i n c l u d e d i n t h i s paper f o r d i s c u s s i o n only.

P r e s s u r e D i f f e r e n c e s

When t h e lobby doors (doors between t h e e l e v a t o r lobby and t h e r e s t of t h e b u i l d i n g ) a r e c l o s e d , an o v e r p r e s s u r e of t h e e l e v a t o r lobby w i t h r e s p e c t t o t h e b u i l d i n g w i l l prevent smoke i n f i l t r a t i o n from t h e b u i l d i n g s p a c e s i n t o t h e lobby. The e x t e n t of t h i s lobby p r e s s u r i z a t i o n changes a s doors a t o t h e r l o c a t i o n s open and c l o s e , a s o u t s i d e a i r temperature changes, and. a s wind v e l o c i t y changes. T h e r e f o r e , e s t a b l i s h m e n t of only one o p e r a t i n g p r e s s u r e d i f f e r e n c e would be i n a d e q u a t e . More a p p r o p r i a t e would be t o e s t a b l i s h both minimum and maximum a l l o w a b l e

p r e s s u r e d i f f e r e n c e s , s o t h a t o p e r a t i o n w i t h i n t h e range would c o n s t i t u t e a c c e p t a b l e peformance.

John H. K l o t e , Center f o r F i r e Research, N a t i o n a l Bureau of S t a n d a r d s , G a i t h e r s b u r g , MD, and G.T. Tamura, 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 Council of Canada, Ottawa.

The maximum p r e s s u r e d i f f e r e n c e should be a v a l u e t h a t does not r e s u l t i n e x c e s s i v e door- opening f o r c e s . C l e a r l y , a p e r s o n ' s p h y s i c a l c o n d i t i o n is a major f a c t o r i n d e t e r m i n i n g a

r e a s o n a b l e door-opening f o r c e f o r t h a t person. S e c t i o n 5-2.1.1.4.3 of t h e N a t i o n a l F i r e

P r o t e c t i o n A s s o c i a t i o n (NFPA) L i f e S a f e t y Code (NFPA 1981) s t a t e s t h a t t h e f o r c e r e q u i r e d t o

open any door i n a means of e g r e s s s h a l l not exceed 50 l b (222 N). However, many smoke c o n t r o l

d e s i g n e r s f e e l t h a t a lower v a l u e should be used, e s p e c i a l l y i n occupancies i n v o l v i n g t h e e l d e r l y , c h i l d r e n , o r t h e handicapped. NFPA i s c u r r e n t l y e v a l u a t i n g p r o p o s a l s t o reduce i t s maximum door-opening f o r c e from 50 l b (222 N) t o 30 l b (133 N).

For t h e s a k e of d i s c u s s i o n , i f t h e maximum door-opening f o r c e i s considered t o be 30 l b

(133 N), and t h e f o r c e t o overcome t h e door c l o s e r i s 6 l b (27 N), a hinged door 36 x 84 i n

(0.91 x 2.13 m) would have a maximum a l l o w a b l e p r e s s u r e d i f f e r e n c e of 0.40 i n H20 (100 Pa). The c r i t e r i o n f o r s e l e c t i n g a minimum a l l o w a b l 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 is t h a t t h e r e s h a l l be no smoke i n f i l t r a t i o n i n t o t h e lobby. Of p a r t i c u l a r r e l e v a n c e is

whether t h e smoke c o n t r o l system has p r e s s u r e d i f f e r e n c e feedback c o n t r o l . A d i f f e r e n t i a l

p r e s s u r e s e n s o r l o c a t e d between t h e e l e v a t o r lobby and t h e b u i l d i n g on t h e f i r e f l o o r c o n t r o l s

t h e s u p p l y of a i r t o t h e smoke c o n t r o l system s o t h a t a c c e p t a b l e performance i s maintained. One

method t o a c h i e v e v a r i a b l e supply a i r is by means of a f a n bypass system a s used f o r s t a i r w e l l

smoke c o n t r o l (Klote and F o t h e r g i l l 1983). For such a system, when t h e p r e s s u r e on t h e f i r e

f l o o r i n c r e a s e s due t o wind, buoyancy, e t c . , t h e s e n s o r r e a c t s , causing i n c r e a s e d s u p p l y a i r f l o w and m a i n t a i n i n g t h e p r e s s u r e d i f f e r e n c e . These systems a l s o can prevent e x c e s s i v e p r e s s u r e

d i f f e r e n c e s by reducing supply a i r f l o w r a t e . I n o r d e r t o prevent smoke i n f i l t r a t i o n , such a

system need only m a i n t a i n a s m a l l p r e s s u r e d i f f e r e n c e of about 0.02 i n Hz0 ( 5 pa). I n c o r p o r a t i n g

a s a f e t y f a c t o r , a minimum p r e s s u r e d i f f e r e n c e v a l u e of 0.05 i n H20 (12 Pa) w i l l be used i n t h i s paper.

For systems without feedback c o n t r o l , t h e minimum p r e s s u r e d i f f e r e n c e must be s u f f i c i e n t t o avoid being overcome by t h e f o r c e s of wind, buoyancy of h o t smoke, o r s t a c k e f f e c t .

P i s t o n e f f e c t due t o e l e v a t o r c a r motion w i t h i n t h e s h a f t i s a l s o a concern, and a

c o n s e r v a t i v e approach is t o s e l e c t t h e minimum p r e s s u r e d i f f e r e n c e s o t h a t t h e system a l s o w i l l n o t be overcome by t h i s e f f e c t . * An a l t e r n a t e is t o d e s i g n f o r some i n f i l t r a t i o n of smoke d u r i n g t h e s h o r t p e r i o d s of time when t h e e l e v a t o r c a r i s t r a v e l i n g away from t h e f i r e f l o o r - Such a d e s i g n should be based upon an a n a l y s i s i n c l u d i n g t h e q u a n t i t y of smoke i n f i l t r a t e d , t h e

purging r a t e of t h e e l e v a t o r lobby, and t o x i c i t y d a t a about t h e smoke. Because of t h e c u r r e n t

l e v e l of u n d e r s t a n d i n g of f i r e t o x i c o l o g y , such an a n a l y s i s could a t b e s t only be an approxima- t i o n and i s beyond t h e scope of t h i s paper. For t h e p r e s e n t c a s e , d i s c u s s i o n w i l l be l i m i t e d t o systems where t h e p r e s s u r e d i f f e r e n c e due t o p i s t o n e f f e c t is s m a l l enough t h a t i t w i l l n o t overcome t h e smoke c o n t r o l system.

The p r e s s u r e d i f f e r e n c e between a f i r e compartment and i t s surroundings can be expressed a s

where:

AP = p r e s s u r e d i f f e r e n c e , i n H20 (Pa)

To = a b s o l u t e temperature of t h e s u r r o u n d i n g s , O R (OK)

TF = a b s o l u t e temperature of t h e f i r e compartment, O R (OK)

h = h e i g h t above t h e n e u t r a l plane between f i r e compartment and s u r r o u n d i n g s , f t (m)

Ks = c o n s t a n t , 7.64 (3460)

The n e u t r a l plane i s t h e plane of e q u a l h y d r o s t a t i c p r e s s u r e between t h e f i r e compartment

and i t s surroundings. For a f i r e w i t h a f i r e compartment temperature of 1470F (800°C), t h e

p r e s s u r e d i f f e r e n c e 5.0 f t (1.52 m) above t h e n e u t r a l plane is 0.052 i n Hz0 (13 Pa). Fang

- - - .

*The second paper of t h i s p r o j e c t w i l l p r e s e n t a method of a n a l y s i s of p i s t o n e f f e c t and w i l l demonstrate t h a t f o r slow moving e l e v a t o r c a r s i n m u l t i p l e c a r s h a f t s , p i s t o n e f f e c t i s not a concern.

(1980) has s t u d i e d p r e s s u r e s caused 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 f i r e t e s t s . During t h e s e t e s t s , t h e maximum p r e s s u r e d i f f e r e n c e reached was 0.064 i n H20 (16 Pa) a c r o s s t h e burn room w a l l a t t h e c e i l i n g . Water s p r a y from s p r i n k l e r s c o o l s smoke from a b u i l d i n g f i r e , reducing p r e s s u r e d i f f e r e n c e s due t o buoyancy. Thus t h e p r e s s u r e d i f f e r e n c e t h a t could r e s u l t from buoyancy is h i g h l y dependent upon t h e f i r e i n t e n s i t y and i t s proximity t o the e l e v a t o r lobby.

The p r e s s u r e d i f f e r e n c e due t o wind can become very l a r g e i n t h e event of a broken window i n a f i r e compartment. A wind of 50 mph (22 m/s) can r e s u l t i n a p r e s s u r e d i f f e r e n c e on t h e o r d e r of 1.2 i n Hz0 (300 Pa). Obviously i f a system were designed s o t h a t i t would not be overcome by such a wind p r e s s u r e , t h e door-opening f o r c e s would be unacceptably h i g h d u r i n g t i m e s of low wind v e l o c i t y . However, t h e occurance of such h i g h v e l o c i t y wind i s i n f r e q u e n t . A

15 mph (6.7 m/s) wind o c c u r s f a r more o f t e n and can r e s u l t i n p r e s s u r e d i f f e r e n c e s on t h e o r d e r of 0.10 i n H20 (25 Pa).

One p o t e n t i a l s o l u t i o n t o t h e wind problem is t o v e n t t h e f i r e f l o o r on a l l f o u r s i d e s t o r e l i e v e such p r e s s u r e s . For a b u i l d i n g t h a t is much l o n g e r t h a n i t is wide, i t may be appro- p r i a t e t o v e n t t h e f i r e f l o o r only on t h e two l o n g e r s i d e s . Another p o s s i b l e approach i s

r e l i a n c e upon f i r e s p r i n k l e r s . Even though l i t t l e r e s e a r c h has been done on t h e s u b j e c t , i t is

l i k e l y t h a t t h e o p e r a t i o n of f i r e s p r i n k l e r s would reduce t h e chances of a window breaking i n a f i r e compartment. A t h i r d approach might i n c l u d e t h e u s e of a v e s t i b u l e between t h e e l e v a t o r lobby and t h e b u i l d i n g i n an a t t e m p t t o provide a d d i t i o n a l p r o t e c t i o n a g a i n s t t h e f o r c e s of t h e wind. F u r t h e r r e s e a r c h is needed w i t h r e s p e c t t o wind and methods t o minimize wind e f f e c t s on p r e s s u r i z e d e l e v a t o r systems.

The s t a t e of smoke c o n t r o l technology has not progressed t o t h e p o i n t where p r e s s u r e d i f f e r e n c e c r i t e r i a can be based upon e n g i n e e r i n g d a t a a l o n e . However, f o r t h i s paper, a minimum p r e s s u r e d i f f e r e n c e of 0.10 i n H20 (25 Pa) w i l l be used f o r systems without feedback c o n t r o l .

Open Doors

When a door i n a boundary of a smoke c o n t r o l system i s open, smoke may flow through t h e open door i n t o t h e s p a c e t h a t i s i n t e n d e d t o be p r o t e c t e d . However, t h e door of an e l e v a t o r lobby i n t e n d e d f o r e v a c u a t i o n of t h e handicapped is a s p e c i a l case. Due t o t h e b a s i c i n s t i n c t f o r s e l f - p r e s e r v a t i o n , people i n s i d e t h e e l e v a t o r lobby w i l l not l e t smoke flow i n t o t h e lobby through an open doorway when they can c l o s e t h e door. Obviously, t h e lobby occupants w i l l s e e t o i t t h a t lobby doors a r e only open f o r t h e s h o r t p e r i o d s of time needed f o r o t h e r people t o t a k e r e f u g e i n s i d e t h e lobby. Thus smoke i n f i l t r a t i o n of t h e e l e v a t o r lobby w i l l be k e p t t o a minimum provided t h a t p o s i t i v e lobby p r e s s u r i z a t i o n is maintained. Small q u a n t i t i e s of smoke t h a t do i n f i l t r a t e when a door is momentarily opened w i l l be purged by t h e lobby p r e s s u r i z a t i o n a i r . This approach e l i m i n a t e s t h e need t o c o n s i d e r a d e s i g n a i r f l o w through open e l e v a t o r lobby doorways t o prevent smoke i n f i l t r a t i o n of t h e lobby.

SMOKE CONTROL SYSTEMS

To e v a l u a t e t h e performance of s p e c i f i c smoke c o n t r o l systems under c o n d i t i o n s of d i f f e r e n t outdoor temperature and w i t h v a r i o u s combinations of doors open and c l o s e d , t h e NBS computer program f o r a n a l y s i s of smoke c o n t r o l systems (Klote 1982) was used. A number of d i f f e r e n t systems were analyzed and e v a l u a t e d . A l l of t h e systems s t u d i e d succeeded i n m a i n t a i n i n g

adequate p r e s s u r i z a t i o n when a l l b u i l d i n g doors were c l o s e d ; however, many of t h e systems f a i l e d under p a r t i c u l a r c o n d i t i o n s of open doors. These systems a r e i n c l u d e d because they i l l u s t r a t e p i t f a l l s and form a l o g i c a l pathway t o a system w i t h feedback c o n t r o l , which can overcome many problems t h a t can develop when c e r t a i n b u i l d i n g d o o r s a r e open. However, it should not be i n f e r r e d t h a t t h i s is t h e only system t h a t can provide adequate e l e v a t o r smoke p r o t e c t i o n under a wide v a r i e t y of c o n d i t i o n s . The a n a l y s i s of t h e systems t h a t f o l l o w should be viewed a s examples of how t o e v a l u a t e a smoke c o n t r o l system based upon t h e p a r t i c u l a r c h a r a c t e r i s t i c s of t h e b u i l d i n g under c o n s i d e r a t i o n .

Example B u i l d i n g

An eleven-story b u i l d i n g with a t y p i c a l f l o o r plan shown i n Figure 1 was a r b i t r a r i l y s e l e c t e d f o r t h e a n a l y s i s . Because t h e b u i l d i n g i s symmetric, o n l y h a l f of each f l o o r was analyzed. A d i s c u s s i o n of symmetry is provided i n Chapter 2 of t h e ASHRAE smoke c o n t r o l manual ( K l o t e and F o t h e r g i l l 1983). The flow a r e a s p e r f l o o r f o r t h e example b u i l d i n g a r e l i s t e d i n Table 1. The flow a r e a s f o r open and c l o s e d e l e v a t o r doors a r e based upon f i e l d t e s t s done by Tamura and Shaw (1967). These v a l u e s a r e f o r center-opening double-panel doors b u t would be

much smaller for single sliding doors, which have smaller gaps. The leakage area of the first floor exterior wall with doors closed is 0.40 ft2 (0.037 m ) larger than other exterior wall leakage to reflect the presence of leakage around exterior doors. The flow area of open stair- well doors was selected as half the geometric area of the opening to reflect the reduced flow due to stationary vortices as described by Cresci (1973). *

Because smoke control is to be accomplished by maintaining the shaft and lobby at an over- pressure, it is counterproductive to top vent the shaft to the outside as is generally the custom. Accordingly, no shaft vent is incorporated in the model. This represents either an unvented shaft or a vent that is tightly dampered shut during smoke control operation. For this study, winter conditions and summer conditions have been arbitrarily chosen as SF (-15OC) and 90F (32'C), respectively, and will be simply referred to as winter and summer.

Shaft Pressurization

The system in this example consists of a roof-mounted fan supplying 4700 cfm (2220 L/s) into the top of the elevator shaft. The elevator lobbies are intended to be pressurized indirectly through the shaft, and the system has no automatic control beyond activation. This analysis and all others in this paper are based upon the idealization of a constant flow fan

-

a fan for which the flow rate is independant of pressure. This is an appropriate and slightly conservative approximation for centrifugal fans used in smoke control systems.

Table 4 lists pressure differences under three different conditions of open doors for both winter and summer. With all of the building doors closed during winter, the system will main- tain pressure differences across the elevator lobby doors of 0.13 in Hz0 (32 Pa) at the first floor, increasing to 0.17 in Hz0 (42 Pa) at the eleventh floor. This increasing pressure

difference with height is due to the greater density of the outside air compared to that inside. During summer, the pressure difference tends to decrease with height (Table 2) because of the lower density of air outside than inside.

A large path for airflow from the shaft to the outside exists on the first floor when the elevator doors are open, the elevator lobby doors are open, and the exterior doors are open. The resulting loss in pressurization is dramatic, especially in summer, as can be observed from the data in Table 2. This situation represents a real possibility, especially open elevator doors at the ground floor as required by many codes. When the elevator doors are closed but the exterior doors are open, the pressurization is higher but still not up to the minimum desired pressure difference

.

The computer runs summarized in Table 4 are representative of a larger number of runs. Although these other runs are not presented in tables in this paper, some interesting observa- tions are worth noting. Relocation of the supply fan to ground level had a negligible effect on the pressure differences produced across the elevator lobby doors. Another observation was that the large airf low path due to the first floor doors being open is not the only large path that can adversely affect the pressurization system. Another example involves flow through the stairwell due to an open exterior stairwell door and an open interior stairwell door. An open elevator vent to the outside is another path that significantly reduces shaft and lobby

pressurization.

If the stairwell were pressurized, the effect of open stairwell doors to the building would be such that they would raise the pressure of the floor spaces and thereby reduce lobby

pressurization only on the floor with the open stairwell door. Such a combination of systems would need to be analyzed to determine fully the effect of interactions.

Lobby Pressurization

The system in this example consists of a roof-mounted, constant-flow fan supplying 4700 cfm (2220 L/s) into the top of a supply shaft connected to all of the elevator lobbies. Air from this shaft pressurizes the lobbies directly and then indirectly pressurizes the shaft. Again, this system has no automatic control beyond activation.

Comparison of the pressure differences (Table 3) produced by this system with those

(Table 2) produced by elevator shaft pressurization shows that for the situation with all doors closed and the situation with the exterior door, first floor elevator, and elevator lobby doors open, the two systems produce essentially identical results. This is true for both winter and summer and can be accounted for by the fact that the flow area from the elevator shaft to the lobby is relatively large compared to that from the lobby to the building, even with the elevator doors closed (Table 1). Thus, in most cases, the shaft can be thought of as being at almost the

same p r e s s u r e a s t h e lobby. An exception i s when t h e e x t e r i o r door and f i r s t f l o o r e l e v a t o r lobby door a r e open but t h e e l e v a t o r doors a r e c l o s e d (Tables 2 and 3 ) , which r e s u l t s i n reduced lobby p r e s s u r i z a t i o n f o r both w i n t e r and summer. A d i r e c t p a t h e x i s t s from t h e lobby t o t h e o u t s i d e , which a l l o w s g r e a t e r l o s s of p r e s s u r i z a t i o n a i r . A s w i t h s h a f t p r e s s u r i z a t i o n , t h i s system cannot m a i n t a l n adequate p r e s s u r i z a t i o n w i t h c e r t a i n b u i l d i n g doors open.

Zoned Smoke C o n t r o l

Zoned smoke c o n t r o l most commonly used i n t h e United S t a t e s c o n s i s t s of usirlg t h e b u i l d i n g h e a t i n g , v e n t i l a t i n g , and a i r - c o n d i t i o n i n g (HVAC) f a n s t o exhaust t h e smoke zone (zone i n which a f i r e i s l o c a t e d ) and t o p r e s s u r i z e surrounding zones. When t h e smoke zone is one o r more f l o o r s of t h e b u i l d i n g , a r e s u l t i n g o v e r p r e s s u r e of t h e b u i l d i n g s h a f t s t o t h e smoke zone can e x i s t . Zoned smoke c o n t r o l was examined t o s e e t o what e x t e a t i t might be used

ts

a c h i e v e e l e v a t o r smoke c o n t r o l . However, t h e system d e s c r i b e d below f a i l e d t o produce adequate l e v e l s of p r e s s u r i z a t i o n .

For t h i s a n a l y s i s , t h e smoke zone c o n s i s t s of t h e f i r e f l o o r and t h e f l o o r abdve, which a r e exhausted a t a r a t e of 5000 cfm (2360 L / s ) p e r f l o o r . The f l o o r s d i r e c t l y above and below t h e smoke zone a r e s u p p l i e d ( p r e s s u r i z e d ) a t t h e same r a t e . This system was s e l e c t e d because of i t s a b i l i t y t o c o n t r o l smoke movement under a v a r i e t y of c o n d i t i o n s of open s t a i r w e l l doors. When s t a i r w e l l doors a r e open t o both t h e smoke zone and t o p r e s s u r i z e d nonsmoke zones, 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 c e i l i n g o f t h e smoke zone can drop t o a s low a s 0.01 i n Hz0 (2 Pa). Such a low l e v e l of p r e s s u r i z a t i o n may be s u f f i c i e n t t o c o n t r o l smoke from a f i r e i n a s p r i n k l e r e d b u i l d i n g o r from a smoldering f i r e , but i t would not c o n t r o l movement of h o t , buoyarit smoke. Smoke t h a t reaches t h e f l o o r above t h e f i r e f l o o r i s cooled due t o d i l b t i o n and h e a t t r a n s f e r . Thus, by i n c l u d i n g t h e f l o o r above t h e f i r e f l o o r i n t h e smoke zone, i t is much l e s s d i f f i c u l t t o c o n t r o l smoke movement.

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 lobby f o r t h r e e c o n d i t i o n s of open and c l o s e d s t a i r w e l l d o o r s , d u r i n g w i n t e r and summer, and when t h e second f l o o r is t h e f i r e f l o o r a r e l i s t e d i n Table 4. k i t h a l l doors c l o s e d , a s i g n i f i c a n t p r e s s u r e d i f f e r e n c e i s maintained f o r both f l o o r s of t h e smoke zone (0.29 i n Hz0 (72 Pa) d u r i n g w i n t e r and 0.37 i n H20 (92 Pa) d u r i n g summer). However i t can be observed from Table 3 t h a t p o s i t i v e p r e s s u r i z a t i o n of t h e e l e v a t o r l o b b i e s was not maintained on non-smoke-zone f l o o r s .

The perrormance c r i t e r i a f o r systems where t h e f i r e f l o o r i s i d e n t i f i e d should be extended. While i t is obvious t h a t t h e minimum p r e s s u r e d i f f e r e n c e of 0.10 i n H20 (25 Pa) s t i l l a p p l i e s t o t h e f i r e f l o o r , o t h e r f l o o r s a r e s u b j e c t e d t o lower t e m p e r a t u r e , l e s s buoyant smoke, o r no smoke a t a l l . T h e r e f o r e , much lower p r e s s u r e d i f f e r e n c e s would prevent smoke from e n t e r i n g t h e s h a f t . For d i s c u s s i o n , a minimum p r e s s u r e d i f f e r e n c e on nonf i r e f l o o r s of 0.02 i n Hz0 (5 Pa) w i l l be used u n l e s s t h e f l o o r i t s e l f is p r e s s u r i z e d . With a zoned smoke.contro1 system, a p r e s s u r i z e d f l o o r w i l l have a i r flowing through

i t s

e l e v a t o r l o b b i e s , i n t o and through t h e e l e v a t o r s h a f t , and from t h e r e i n t o t h e e l e v a t o r lobby on t h e smoke zone (which is an exhausted s p a c e ) . Thus t h e a i r f l o w r e s u l t i n g from t h i s zoned smoke c o n t r o l system, which i n d i r e c t l y p r e s s u r i z e s t h e e l e v a t o r lobby on t h e f i r e f l o o r , a l s o makes i t i m p o s s i b l e t o p r e s s u r i z e t h e e l e v a t o r l o b b i e s on some o t h e r f l o o r s .

I n t h e c a s e s with a l l t h e doors c l o s e d , t h e zoned smoke c o n t r o l system maintained

approximately 0.16 i n Hz0 (150 Pa) between t h e smoke zone and a d j a c e n t nonsmoke zones. Such a l a r g e p f e s s u r e d i f f e r e n c e would prevent smoke migration. However, on many n o n p r e s s u r i z e d ELoors, where smoke could m i g r a t e through b u i l d i n g s h a f t s , 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 e l e v a t o r lobby i s l e s s than 0.02 i n H20 ( 5 Pa). F u r t h e r , when s t a i r w e l l doors open, t h e

p r e s s u r i z a t i o n drops s i g n i f i c a n t l y , a s can be s e e n from Table 4 . T h i s p a r t i c u l a r form of zoned smoke c o n t r o l (sometimes r e f e r r e d t o a s t h e " p r e s s u r e sandwich" system) does not produce

adequate l e v e l s of p r e s s u r i z a t i o n . Zoned System P l u s S h a f t P r e s s u r i z a t i o n

This system c o n s i s t s of t h e preceeding system p l u s 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 a t t h e same flow r a t e of t h e f i r s t system d i s c u s s e d . This system m a i n t a i n s a c c e p t a b l e p r e s s u r e d i f f e r - ences a c r o s s t h e e l e v a t o r lobby w i t h s t a i r w e l l doors open on t h e f i r s t , second, t h i r d , and f o u r t h f l o o r s when t h e second f l o o r i s t h e f i r e f l o o r , a s shown i n Table 5. However, w i t h o n l y t h e second f l o o r s t a i r w e l l door open o r a l l doors c l o s e d , unacceptably h i g h l e v e l s of p r e s s u r i - z a t i o n r e s u l t a c r o s s t h e e l e v a t o r lobby a t t h e smoke zone.

Shaft Pressurization with Feedback Control

This system relies on feedback control to maintain a set pressure difference across the elevator lobby on the fire floor. The flow rate into the top of the elevator shaft is varied by modulating bypass dampers, which are controlled by a static pressure sensor that senses the pressure difference between the elevator lobby and the building. Obviously, these sensors would have to be reliable and be protected from heat or designed to withstand elevated temperatures.

As

with zoned smoke control, this system requires identification of the fire floor.

Pressure differences from computer analysis of this system with the second floor as the fire floor are listed in Table 6. The system maintains 0.05 in H20 (12 Pa) across the second floor elevator lobby in all cases, with all doors closed, and with a direct path to the outside during both winter and summer. It accomplishes this by varying the supply rate to the elevator shaft

from 2500 to 7750 cfm (1180 to 3650 L/s). Throughout all of this, the pressures at nonfire

floors are within the acceptable range. Selection of a fan for such a system should include some safety factor to allow for greater leakage areas in the actual building than those assumed in design analysis. For a 25% safety factor, the fan capacity would be approximately 10,000 cfm

(4720 L/s). Feedback control not only maintains the set pressure difference in situations of

open and closed doors, but also during conditions of pressure difference due to buoyancy of hot smoke.

SUMMARY

Computer analysis of several elevator smoke control systems was presented under a variety of conditions of open and closed doors. Of these systems, all but one failed to maintain adequate pressurization when some combination of doors were open. The successful one was a shaft

pressurization system with feedback control, which maintained a set pressure difference under any condition of open or closed doors. It should be noted that there are probably a large number of systems capable of providing adequate smoke control, and the proceedure followed in the paper can be viewed as an example of how to evaluate the performance of a system to meet the particular characteristics of a building under consideration.

REFERENCES

Cresci, R.J. 1973. "Smoke and fire control in high-rise office buildings

-

Part 11, Analysis

of stair pressurization systems." Symposium of Experience and Applications on Smoke and Fire Control. ASHRAE Annual Meeting, June 24-28, 1973, Atlanta, GA.

Fang, J.B. 1980. Static pressures produced by room fires. Nat. Bur. Stand. (U.S.),

NBSIR 80-1984. Feb.

Klote, J.H. 1982. A computer program for analysis of smoke control systems. Nat. Bur. Stand.

(U.S.), NBSIR 82-2512. June.

Klote, J.H. 1984. "Smoke control for elevators." ASHRAE Journal, Vol. 26, No. 4 (April)

pp. 23-33.

Klote, J.H., and Fothergill, J.W. 1983. Design of smoke control systems for buildings.

Atlanta: ASHRAE.

NFPA. 1981. Code for Safety to Life from Fire in Buildings and Structures, NFPA 101-1981.

Quincy,

MA:

National Fire Protection Association.

Tamura, G.T., and Shaw, C.Y. 1966. Air leakage data for the design of elevator and stair shaft

TABLE 1

Flow Areas Per Floor for the Example Building

Location Area ft 2

First floor exterior wall (exterior doors closed) First floor exterior wall (exterior doors open) Exterior walls (except 1st floor)

Stairwell to building (stairwell door closed) Stairwell to building (stairwell door open) Building floor

Building to elevator lobby (lobby doors closed) Building to elevator lobby (lobby doors open)

Elevator lobby to elevator shaft (elevator doors closed) Elevator lobby to elevator shaft (elevator doors open)

i g $

g = 3 g g o g Z

"

74 Z

"

"

- m

2

& : 8 c g 4 0 w a g O ; z

"

Z z

"

2 Id 0 u 0 0

"

d b. U a u c u u o a V) V)

:

r

2 8 p--

---

m a m m o a 3 3 B m m m

h n h h h " 7 O t . N N rl I I V V V V V d A N u m d 0 rl 9 9 3 3 ? n h h h n

2 1 -

N I O W V V V V d N U m d 0 rl 3 9 9 9 ? A n n n N V I V ) N 1 V V V V QI 0 0 d N N d ? ? ? ?

--

m o 0 0 0 m Y h h N 0 N rl I rm V V h 0 rl 0 0 0

g

rl 9 0

i=

w rl n rl "7 N a m I 1 V V

2

m 0 0 0 0 u N_? r _?l 0 u

---

2

--

h h h P O O N

3

rl d I V V V t4 "7 0 0 0 u u₃ u₉ r ₉l

5

V V V V V V w N W QI " 7 . 4 rl

y

?

?

!

;

?

n I 4 1 h h h h h m 0 m r . t . ~ m h U rn J J J J J C rl 0 c o o m m r l " i ? ? ? " i I 1 I m 4 9

L a , s

_{a d o 4} 2

--

C 0 u 4 0 N- 2 cu N. ~ l s 0 8 ~ E rl rl m a r n m o ~ 3 3 w

-

- - -- - --

,-.

,

TABLE 5

Pressure D i f f e r e n c e s from Computer Analysis of Elevator Smoke Control by Zoned Smoke Control and Shaft P r e s s u r i z a t i o n w i t h t h e Second Floor a s t h e F i r e Floor

E

Abbreviations: Elev.-EIwatar; WAode; S-Sumer; +Winter S e a s o n S t a i r - w e l l Doors Open on Floors

Pressure Difference in Inches F$D (pa) frcm Elevator Lobby t o the h i l d i n g m ~ l ~ o r s :

W N 3 .52 (129) . 4 6 ( 1 1 4 ) 4 -.07 (-17) - . 0 7 ( 1 7 ) 1 -.04 (-10) - . 0 6 ( - 1 5 ) id 2 .52 (129) . 3 0 ( 7 5 ) 2 5 .18 ( 45) . 2 0 ( 5 0 ) 11 .24 ( 60) . 2 9 ( 7 2 ) 6 .22 ( 55) . 2 5 ( 6 2 ) 1 0 .24 ( 60) . 2 8 ( 7 0 ) 7 8 9 .23 ( 57) . 2 8 ( 7 0 ) .23 ( 57) . 2 6 ( 6 5 ) .23 ( 57) . 2 7 ( 6 7 )

TABLE 6

Pressure Differences and Supply Airflow Rate from Computer Analysis of Elevator Smoke Control by Shaft P r e s s u r i z a t i o n with Feedback Control f o r t h e Second Floor a s t h e F i r e Floor

Abbreviations: E1ev.-Elevator; N-None; S-Summer; W-Winter *Flow Rate a t 70DF (21°C) and one atmosphere

I .

.

,.

I S e a s o 11 1 s t Floor E x t e r i o r Door Open I Elev. Doors Open on F l o o r s W Elev. Lobby Doors Open on F l o o r s Supply Air Flow Rate t o Shaft cfm* (L/S*) S Yes 3350 (1580)

Pressure Difference i n inches R20 (Pa) from Elevator Lobby t o t h e Building on Floors:

N No N 5 .08 (20) 1 .04 (10) 6 .08 (20) 7 .09 (22) 8 .09 (22) 4 .07 (20) 2 .05 (12) 10 .10 (25) 9 .10 (25) 3 .06 (15) ll .10 (25)

OFFICE SPACES

OFFICE SPACES

OFFICES SPACES

OFFICE SPACES

1

2

2

0

FT

SYMBOLS:

D DOORS

EL ELEVATOR LOBBY

Discussion

C. HEDSTEN, OPUS Corp., Minnetonka,

MN:

How do you correlate 10 story to 40-50 story? UBC

1

calls for 0.25" P on doors in stairwell; are these too high since you require 0.1 on fire I

floor or .02 on all others? Why the difference? Is UBC too high? I

KLOTE: The intent of the paper was to demonstrate the feasibility of smoke control systems for elevator evacuation of the handicapped. This was demonstrated for an eleven story building. The methods of computer analysis used in this paper can be applied to both taller and shorter buildings.

The pressure differences used for evaluation in the paper were values that we felt would provide protection from an intense fire during evacuation. There are many other values of pressure difference which could be used.

R.

MASTERS, Jaros, Baum & Bolles, New York, NY: In lieu of feedback control, why not use barometric damper control for simplicity and reliability?

KLOTE:

I

have made some computer runs of stairwell systems with barometric dampers for pressure relief. During this work, it became apparent to me that a very large number of computer runs would be required for my particular application. At that point

I

switched to analysis of a bypass fan system with feedback control, and it was very simple to find a system that met my objectives. I feel that feedback control systems are both easier to design and more likely to function as desired in a fire situation. For this reason, feedback control systems were included in the study that is described in this report.

It may be that barometric damper systems can perform well. Clearly, these systems should be studied in greater detail.

..

E.F. CHAPMAN, Deputy Chief, Fire Department, Brooklyn, NY: How would the system react to a fire located in the elevator lobby or elevator car?

KLOTE: This question can be stated more generally as how we should be prepared for a fire in any means of egress. I know that this has been a concern to fire protection

professionals, and that the concerns go beyond those of most ASHRAE members. Cost effective and reliable methods of detecting fires in egress routes and of going into appropriate smoke control modes are needed. The appropriate smoke mode may be just system shut down or

R.R.

HENRY, General Dynamics, Groton,

CT:

You stated that the same results/conclusion resulted from your study in the shaft pressurization and lobby pressurization. If the smoke were to migrate into the lobby or start in the lobby, wouldn't the lobby pressurization method be hazardous to other occupied spaces, including elevator occupants that were being evacuated? And wouldn't this condition be safer if the shaft pressurization method were used?

KLOTE: When

I

stated that the performance of the two systems was about the same,

I

meant with regard to the pressure differences produced between the elevator lobby and the building. Smoke movement is very complicated, and it is difficult to say what degree of hazards exists with either system in the case of fire in the elevator cab or shaft. However, in such a case, going into shutdown or a special smoke mode may be the most appropriate approach.

T h i s

paper

i s h i n g

d i s t r i b u t e d i n r e p r i n t

form by t h e I n s t i t u t e

f o r Research i n

C o n s t r u c t i o n . A

l i s t

of b u i l d i n g

practice

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from

the Institute may

be

obtained

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t h e ~ u b l i c a t { o n s Section, Institute for

Research i n

C o n s r r u c t i o n , N a t i o n a l

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of

C a n a d a , O t t a w a , O n t a r i o , K l A

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document e s t d i s t r i b u g s o u s

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I n s t i t u t de r e c h e r c h e e n c o n s t r u c t i o n . On p e u t o b t e n i r une

l i s t e

d e s p u b l i c a t i o n s d e 1 ' 1 n s t i t u t p o r t a n t s u r

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t e c h n i q u e s ou

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r e c h e r c h e s e n

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d e b t t i m e n t e n G c r i v a n t

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S e c t i o n d e s p u b l i c a t i o n s , f n s t i t u t d e r e c h e r c h e e n c o n s t r u c t i o n , C o n s e i l n a t i o n a l d e r e c h e r c h e s du Canada, Ottawa ( O n t a r i o ) , K I A

0R6.