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Attenuation of smoke detector alarm signals in residential buildings
Halliwell, R. E.; Sultan, M. A.
- - .-
Ser
,
National Research
Conseil national
TH1
Council
Canada
de
recherches
Canada
N21d
Institute for
lnstitut de
no,
1372
Research in
recherche en
c.
2
Construction
construction
BLDG
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Attenuation of Smoke Detector
Alarm Signals in Residential
Bulldings
Reprinted from
Fire Safety Science
-
Proceedings
of
the
First International Symposium
Gaithersburg, MD, 4 1
1 October 1985
p. 689
-
697
(IRC Paper No. 1372)
b
NRC-
CISTIBLDG.
RES.
Price $2.00
NRCC 25897
L I B R A R Y
86-
07-
1
5
I
B I S L ~ O T H ~ Q U E
Rcch.
Bbtirn.
On
a 6tudiB la, propagation, dans des imrneubles rgsidentiels, du
son provenant de detecteurs de fumee en considgrant l'effet de
l'ameublement, du type d'installation de chauffage et du nombre
de portes ferdes.
Cedocument decrit
un
modele simple
representant
la
voie de propagatton c o m e une sgrie de pieces
attenantes, chacune d'elles modifiant l'intensits du son les
attenuations calcul6es ont St6 comparees
B
celles mesurges dans
11 habitations. Ce modsle peut servir
B determiner le nombre
et l'emplacement ideals des ddtecteurs de fum6e.
Attenuation of Smoke Detector Alarm
gignals in Residential Buildings
,R. E. HALLIWELL and M.
A.
SULTAN Division of Building Research National Research Council of Canada Ottawa, Canada K I A OR6ABSTRACT
The p r o p a g a t i o n of sound from smoke d e t e c t o r alarms through r e s i d e n t i a l b u i l d i n g s h a s been i n v e s t i g a t e d w i t h r e s p e c t t o t h e e f f e c t of f u r n i s h i n g s , t y p e of h e a t i n g system, and number of c l o s e d doors. A simple model r e p r e s e n t i n g t h e p r o p a g a t i o n p a t h a s a s e r i e s of l i n k e d rooms, each modifying t h e sound l e v e l , is d e s c r i b e d and compared w i t h measured a t t e n u a t i o n s i n 11 houses. The model c a n be used t o determine t h e optimum number and l o c a t i o n of smoke d e t e c t o r alarms. INTRODUCTION
It i s e s t i m a t e d 1 t h a t 40 t o 50% of t h e p e o p l e k i l l e d i n f i r e s e a c h y e a r could be saved i f adequate e a r l y - w a r n i n g f i r e d e t e c t i o n d e v i c e s were i n s t a l l e d .
A s t u d y by
e ones^
of m u l t i p l e d e a t h f i r e s i n t h e U.S. i n d i c a t e s t h a t 81.4% of f i r e s occur between 8:00 p.m. and 8:00 a.m., w i t h t h e l a r g e s t number (40.5%) between midnight and 4:00 a.m.Smoke d e t e c t o r s a r e g e n e r a l l y c o n s i d e r e d t o be more e f f e c t i v e t h a n p e o p l e i n d e t e c t i n g f i r e a e r o s o l s , and because t h e y can be used t o monitor unfrequented a r e a s t h e y a r e e f f e c t i v e e a r l y - w a r n i n g d e v i c e s f o r f i r e . It i s i m p o r t a n t t o remember t h a t i n many c a s e s t h e sound of t h e smoke d e t e c t o r i s t h e only means of a l e r t i n g a s l e e p i n g p e r s o n t o t h e e x i s t e n c e of f i r e . D e t e c t o r s c a n s a v e l i v e s only i f people h e a r them.
The f i r e d e t e c t o r h a s two main components: a combustion a e r o s o l d e t e c t o r t h a t determines t h e e x i s t e n c e of f i r e , and an alarm d e v i c e t o a l e r t t h e occupants. A breakdown i n e i t h e r component w i l l prevent a f i r e warning.
r
I n t h e l a s t two decades a e r o s o l d e t e c t i o n h a s r e c e i v e d world-wide a t t e n t i o n and i s now reasonably w e l l understood, But t h e problem of producing a
s u f f i c i e n t l y loud a l a r m s i g n a l h a s r e c e i v e d s c a n t c o n s i d e r a t i o n . Defining t h e a l a r m l e v e l d i s t r i b u t i o n throughout a r e s i d e n t i a l home i s i m p o r t a n t , however, i f t h e s e l f - c o n t a i n e d d e t e c t o r a l a r m i s t o be a n e f f e c t i v e warning device.
The sound power o u t p u t of a smoke d e t e c t o r u u s t be such t h a t a f t e r a t t e n u a t i o n a s i t p r o p a g a t e s through a b u i l d i n g t h e sound l e v e l i s s t i l l
s u f f i c i e n t l y h i g h t o waken a s l e e p i n g occupant. The Underwriters L a b o r a t o r i e s s t a n d a r d ~ ~ 2 1 7 ~ r e q u i r e s t h a t such a d e v i c e must provide an A-weighted sound p r e s s u r e l e v e l of a t l e a s t 85 dB a t 3.05 m when mounted n e a r t o two r e f l e c t i n g s u r f a c e s . Nober e t a ~ concluded t h a t an a l a r m l e v e l of 55 dBA a t t h e e a r . ~ p o s i t i o n i n a q u i e t background i s a d e q u a t e t o waken a college-age p e r s o n w i t h
normal h e a r i n g , b u t t h a t 70 dB i s r e q u i r e d i f a window a i r c o n d i t i o n e r i s
o p e r a t i n g i n t h e bedroom. I n a n o t h e r s t u d y , ~ a h n ~ s u g g e s t e d t h a t 70 dB i s t h e minimum l e v e l r e q u i r e d a t t h e e a r i n a q u i e t background t o waken college-age
4
p e r s o n s w i t h normal h e a r i n g . C l e a r l y , t h e minimum l e v e l t o waken p e o p l e i s n o t w e l l d e f i n e d and r e q u i r e s f u r t h e r s t u d y . Although i t is beyond t h e scope of the$ p r e s e n t i n v e s t i g a t i o n , t h e q u e s t i o n r e q u i r e s a t t e n t i o n i f t h e r e s u l t s of t h i s b s t u d y a r e t o be used e f f e c t i v e l y .Once t h e a l a r m sound l e v e l h a s been e s t a b l i s h e d , t h e r e i s s t i l l t h e q u e s t i o n of where t o l o c a t e an a l a r m s o a s t o p r o v i d e maximum b e n e f i t . The answer t o t h i s q u e s t i o n r e q u i r e s a model t h a t can be used t o c a l c u l a t e t h e a t t e n u a t i o n of t h e a l a r m s i g n a l a s i t p r o p a g a t e s through a b u i l d i n g . The model would p e r m i t one t o determine t h e optimum l o c a t i o n f o r a n a l a r m t o a c h i e v e t h e r e q u i r e d s i g n a l l e v e l a t any l o c a t i o n i n t h e b u i l d i n g . It i s t h e purpose of t h e p r e s e n t s t u d y t o develop such a model.
To a s s e s s t h e a t t e n u a t i o n of t h e a l a r m s i g n a l from smoke d e t e c t o r s i n r e s i d e n t i a l b u i l d i n g s i t was n e c e s s a r y t o make measurements i n a number of b u i l d i n g s and from t h e d a t a t o develop a g e n e r a l model t o be a p p l i e d f o r any r e s i d e n t i a l b u i l d i n g . Eleven b u i l d i n g s were s t u d i e d , c o n s t i t u t i n g a r e a s o n a b l e c r o s s - s e c t i o n of t h e common t y p e s of dwelling: bungalows, s p l i t - l e v e l , and two-story houses. I n c l u d e d i n t h e s t u d y were both f u r n i s h e d and u n f u r n i s h e d homes
.
MEASUREMENT PROCEDURE
Measurements were made u s i n g a smoke d e t e c t o r (modified t o o p e r a t e c o n t i n u o u s l y ) a s a s o u r c e of a l a r m s i g n a l . It was mounted on a s t a n d 2.1 m i n h e i g h t s o a s t o s i m u l a t e a c e i l i n g - m o u n t e d d e t e c t o r and p l a c e d i n a number of l o c a t i o n s i n each d w e l l i n g : i n t h e basement n e a r t h e f u r n a c e room, i n t h e main hallway n e a r t h e k i t c h e n , and i n t h e hallway n e a r t h e bedrooms. From e a c h s o u r c e l o c a t i o n t h e a t t e n u a t i o n of n o i s e was measured t o e v e r y o t h e r room. T h i s was done f i r s t w i t h a l l doors i n t h e p r o p a g a t i o n p a t h open, t h e n w i t h them c l o s e d s u c c e s s i v e l y u n t i l a l l doors i n t h e p a t h were c l o s e d .
To determine t h e a t t e n u a t i o n a l o n g e a c h p a t h , t h e sound l e v e l was measured s i m u l t a n e o u s l y n e a r t h e s o u r c e and i n t h e r e c e i v i n g room. The s o u r c e microphone was i n a f i x e d p o s i t i o n 1 m from t h e smoke d e t e c t o r , w h i l e t h e r e c e i v i n g room microphone was moved about t h e room t o p r o v i d e an average sound l e v e l f o r t h e room. A two-channel FFT a n a l y s e r c o l l e c t e d d a t a from t h e two microphones s i m u l t a n e o u s l y . S i x t y - f o u r s p e c t r a were averaged and t h e r e s u l t a n t s p e c t r a f o r each microphone were s t o r e d f o r subsequent a n a l y s i s . A c a l i b r a t i o n s i g n a l was recorded on each microphone a t t h e beginning and end of e a c h measurement p e r i o d .
A s a c o u s t i c a l d a t a a r e u s u a l l y p r o v i d e d i n t h i r d - o c t a v e bands, t h e
narrow-band s p e c t r a provided by t h e FFT a n a l y s e r were c o n v e r t e d t o t h i r d - o c t a v e s p e c t r a by summing t h e energy w i t h i n t h e s t a n d a r d t h i r d - o c t a v e bands. T h i s was done by assuming a r e a l i s t i c f i l t e r shape and c o r r e c t e d u s i n g t h e c a l i b r a t i o n s i g n a l t o o b t a i n t h e a b s o l u t e sound l e v e l s i n t h i r d - o c t a v e bands. The a t t e n u a t i o n was t h e n c a l c u l a t e d a s t h e d i f f e r e n c e between s o u r c e and r e c e i v e r l e v e l s f o r each t h i r d - o c t a v e .
Sound power measurements were made f o r two smoke d e t e c t o r s of e a c h of s e v e n models i n accordance w i t h ANSI ~ 1 . 3 1 - 1 9 8 0 ~ i n t h e r e v e r b e r a t i o n chamber a t t h e 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.
DISCUSSION OF RESULTS
1.
The r e d u c t i o n i n sound l e v e l t h a t i s p r o v i d e d by w a l l s , d o o r s , e t c . , w i t h i n \ a b u i l d i n g and t h e sound a b s o r p t i o n p r o v i d e d by f u r n i s h i n g s i n c r e a s e w i t h t i n c r e a s i n g f r e q u e n c y . To be most e f f e c t i v e i t would t h u s be r e a s o n a b l e f o r a &smoke d e t e c t o r t o have most of i t s a c o u s t i c a l o u t p u t a t low f r e q u e n c i e s , s a ybelow 500 Hz. The human e a r , on t h e o t h e r hand, i s most a c u t e i n t h e 2000- t o 5000-Hz range. It i s a l s o more economical t o produce a n i n e x p e n s i v e a l a r m o p e r a t i n g i n a h i g h e r f r e q u e n c y r a n g e , b u t t h i s means t h a t s u c h a l a r m s mst
o p e r a t e a t a h i g h e r sound power i f t h e y a r e t o be a d e q u a t e a s warning d e v i c e s . Sound power measurements on a number of smoke d e t e c t o r s a r e l i s t e d i n T a b l e 1, which shows t h a t most smoke d e t e c t o r s o n l y p r o v i d e n o i s e o u t p u t i n a few bands, t h e two dominant o n e s b e i n g t h e 3150- and 4000-Hz bands. F o r t h e p u r p o s e of t h i s s t u d y o n l y t h e 3150-Hz band h a s been u s e d t o d e v e l o p a p r o p a g a t i o n model. The h i g h e r f r e q u e n c y band, which was n o t p r e s e n t f o r a l l smoke d e t e c t o r s , w i l l t e n d t o be a t t e n u a t e d more and t h u s w i l l be l e s s u s e f u l i n a l e r t i n g occupants. Where t h e r e i s e n e r g y i n l o w e r f r e q u e n c y bands, t h e model w i l l p r e d i c t t o o l i t t l e a t t e n u a t i o n and t h u s p r o v i d e a n e x t r a margin of s a f e t y .
Two d i f f e r e n t models were c o n s i d e r e d f o r p r e d i c t i n g t h e a t t e n u a t i o n of n o i s e from t h e alarms. The f i r s t was based on a model proposed by
err^.^
I t smost a t t r a c t i v e f e a t u r e i s i t s s i m p l i c i t y , t h e b a s i c a t t e n u a t i o n b e i n g assumed t o be a f u n c t i o n of t h e s t r a i g h t - l i n e h o r i z o n t a l d i s t a n c e between s o u r c e and t h e m i d - p o i n t of t h e r e c e i v i n g room, w i t h o u t r e g a r d f o r changes i n e l e v a t i o n . Added t o t h i s b a s i c a t t e n u a t i o n a r e t h r e e c o r r e c t i o n s , one f o r t h e number of f l o o r changes i n e l e v a t i o n , a n o t h e r f o r e a c h c l o s e d d o o r a l o n g t h e p r o p a g a t i o n p a t h , and a t h i r d f o r e a c h open doorway a l o n g t h e p r o p a g a t i o n path.
TABLE 1. Maximum sound power output of smoke d e t e c t o r s
113 Octave Frequency Band, Hz
A1 0.203 38 39 39 39 63 57 73 96 84 63 50 A2 0.230 37 38 38 38 44 56 70 98 92 67 56 B1 0.877 82 82 60 71 74 81 79 95 95 95 88 B2 0.870 79 81 66 72 76 81 77 93 94 96 92 C 1 0.986 44 44 44 45 45 50 61 79 102 90 69 C2 0.989 44 44 44 45 45 50 62 79 102 91 70 D 1 0.844 46 46 46 46 47 52 63 80 103 93 71 D2 0.845 44 44 44 45 45 50 62 80 102 88 68 E 1 1 .O 84 70 69 85 76 92 88 96 92 91 80 I E 2 1.0 76 83 63 69 80 87 85 97 100 91 89 k F1 1.0 61 60 72 70 70 74 86 75 83 90 82 F2 1.0 58 61 69 70 72 77 90 81 82 89 82 / .
I
G1 G2 0.667 0.643 37 38 37 38 37 38 38 38 39 39 50 48 63 61 88 84 95 95 69 71 55 56 ' ~ e t e c t o r s with t h e same l e t t e r d e s i g n a t i o n a r e i d e n t i c a l models.2 ~ h e duty c y c l e i s t h e f r a c t i o n of time during which t h e alarm i s operating. 10 l o g ( l / r ) was added t o t h e measured mean sound power l e v e l t o g i v e t h e maximum sound power l e v e l .
I 1 1 1 I ! I 1 I
-
-
-
1 I I I I I I I I I I0
10
20
A T T E N U A T I O N .
d B
Figure
1.Histogram of sound attenuation due to closure of single door in
propagation path.
Figure 1 shows a histogram of the increase in attenuation provided by
closing a single door in a propagation path. The wide range in attenuation is a
result of the wide variation in fit among doors, from doors with large gaps
beneath to those carefully weather-stripped. The mean value is
10dB, and this
was used in the model as the correction for closed doors.
Atfirst glance this
result appears to be in conflict with NFPA* work, which suggests
15dB, and with
that of Bradley and wheeler9 and of ~ o b e r , ~
who found 16.4 dB and 15 dB,
respectively. This is, however, the change in attenuation with a door closure
rather than an overall~transmission
loss of the wall-door system.
The best fit to the data was found with the following corrections:
10dB
for each floor between the source and receiver, 3 dB for each open doorway along
the path, and
10dB more for each closed door along the path. Figure
2shows
the measured attenuation minus the three corrections plotted as a function of
distance from the source for the best fit values for these corrections. The
slope of the least squares fit line drawn through the points gives the
dependence on distance for this model. There is a very large range in the
scatter, making this a less than satisfactory model for sound attenuation. Some
of the scatter is a result of the range in measured attenuation of doors, but it
is insufficient to explain all of the scatter. The major weakness of the model
is its inability to make allowances for differing sound absorption in different
rooms.
0
5
10
15
2
0
D I S T A N C E F R O M S O U R C E ,
m
Figure 2. Measured a t t e n u a t i o n minus c o r r e c t i o n s f o r open d o o r s , c l o s e d doors, and number of f l o o r s between alarm and r e c e i v e r .
The second model considered t a k e s a s l i g h t l y d i f f e r e n t approach. I n i t ,
t h e propagstion p a t h i s viewed a s a s e r i e s of l i n k e d rooms, each of which modifies t h e sound l e v e l . The p a t h t o be used i s t h e most d i r e c t p a t h a s would be t r a v e r s e d by a person walking from t h e source t o t h e r e c e i v e r . Each space enclosed by w a l l s o r p a r t i t i o n s , i n c l u d i n g hallways, i s counted a s a room provided t h a t t h e opening l e a d i n g from t h e previous room i s a doorway o r e q u i v a l e n t . For t h e purpose of t h i s model, i t i s assumed t h a t l i t t l e , i f any, sound i s t r a n s m i t t e d through t h e p a r t i t i o n s o r f l o o r s . From r e v e r b e r a t i o n room theory, t h e sound l e v e l i n a room due t o t r a n s m i s s i o n of sound through a n opening o r p a r t i t i o n i n t o t h e room i s given by1'
S T6'
C
(1.086) LR =L
-
R+
10 l o g[
60 vRI
where R = t r a n s m i s s i o n l o s s of p a r t i t i o n , LS = sound p r e s s u r e l e v e l i n s o u r c e room, LR = sound p r e s s u r e l e v e l i n r e c e i v i n g room, S = a r e a of p a r t i t i o n (m2), TsO = r e v e r b e r a t i o n time, C = speed of sound (m/s), VR = volume of r e c e i v i n g room (m3).I
T60
LR
= Ls-
+l o log
"RI
(2)
'
I
It may be further simplified by assuming that sound enters the room only via an
open doorway of area 2 m2 with zero transmission loss, and that rooms are always
2.4 m high. A normally furnished room of average size, that is one with carpet
and furniture, has a reverberation time of about 0.4 s at 3150 Hz.*
The result
is that the receiving room level is given by
area
L
R
=L
s
-
[lo
log
(m)
+ corr]
( 3 )where 'area' is the floor area of the receiving room and 'corr' provides a
means of adjusting this correction for instances in which reverberation time
differs substantially from 0.4 s, as happens in a "hard," unfurnished room or in
*an extremely "soft" room. This would have a value of -2 dB for hard rooms such
as bathrooms or kitchens, zero for normal rooms, and
+2dB for very soft rooms
such as a bedroom with carpet, heavy drapes, and bedspread. Thus, the term
10 log
+ corr
(4)
may be viewed as a correction to the sound level due to absorption within the
room or, alternatively, as the room attenuation. Attenuation due to absorption
can thus be calculated for each room in the house, independent of where source
and receiver are located. The overall attenuation of the detector alarm is thus
the sum of the attenuations for all rooms in the propagation path plus 10 dB for
each closed door.
The derivation of Eq. (1) is based on the assumption that there is a
diffuse sound field in both source and receiving rooms, a condition very
unlikely to occur in a residential building. Similarly, the assumption of zero
transmission loss through the open doorway is an over-simplification because it
ignores any edge or interference effects of the doorway.
A comparison of the
sound attenuation predicted by this model with the measured attenuation
indicates that an additional
5 dB attenuation needs to be added for each room in
the propagation path. This may be viewed as the transmission loss associated
with an open doorway. Note that the addition of transmission loss for the open
doorway to the 10 dB insertion loss of the closed door gives a total attenuation
of 15 dB, which compares favourably with values quoted by other workers.
1It is well established from field studies of transmission loss of walls and
floors that heating ducts can provide a flanking path that will short-circuit a
partition and result in lower noise reductions than would otherwise be obtained.
This was borne out in the present study; it was found that buildings that do not
*J.S. Bradley. Unpublished data.
have forced-air h e a t i n g provide an a d d i t i o n a l
6
dB a t t e n u a t i o n f o r each room i n9 t h e propagation path.
These c o r r e c t i o n s can a l l be summarized i n t h e following expression:
n a r e a
Atten = [
1
{ l o l o g(d)
+
5+
c o r r r+
K}]+
10 (door) r = lwhere a r e a = f l o o r a r e a of room 'r
'
(m2), door = number of c l o s e d doors i n p a t h , c o r r = -2 f o r hard rooms ( k i t c h e n , b a t h ) ,= 0
f o r normal rooms,= 2 f o r s o f t rooms ( r u g s , d r a p e r i e s ) ,
K = 0 f o r f o r c e d a i r h e a t i n g ,
= 6 f o r e l e c t r i c o r h o t water h e a t ,
n = number of rooms i n p a t h from smoke d e t e c t o r t o p o i n t of i n t e r e s t , n o t counting room c o n t a i n i n g smoke d e t e c t o r .
Figure 3 shows t h e a t t e n u a t i o n c a l c u l a t e d u s i n g t h i s model p l o t t e d a g a i n s t measured a t t e n u a t i o n s f o r a l l source-receiver c o n f i g u r a t i o n s i n t h e 11 houses s t u d i e d . The s o l i d l i n e i s t h e l e a s t - s q u a r e s f i t t o t h e d a t a , w i t h a s t a n d a r d d e v i a t i o n of 7.5 dB. Although some of t h i s s c a t t e r w i l l be due t o v a r i a t i o n i n t h e a t t e n u a t i o n f o r c l o s e d doors (shown i n Fig. l ) , much of i t appears t o be a s s o c i a t e d with measurement of t h e source room sound l e v e l . The source room sound p r e s s u r e l e v e l was measured a t a s i n g l e p o s i t i o n r a t h e r t h a n w i t h a moving microphone, a s was done i n t h e r e c e i v i n g room. The measured sound l e v e l w i l l be
- 1 0 0
10 20 30 40 5 0 6 0 70 80 9 0 1 0 0
MEASURED A T T E N U A T I O N , d B
more r e p r e s e n t a t i v e of t h e n e a r f i e l d of t h e alarm, a s modified by a d j a c e n t r e f l e c t i n g s u r f a c e s , r a t h e r t h a n t h e mean sound l e v e l i n t h e room. c
Obviously t h e r e a r e many o t h e r t r a n s m i s s i o n p a t h s i n r e a l b u i l d i n g s which could be included i n a more d e t a i l e d c a l c u l a t i o n . The i n c l u s i o n of such e x t r a
1
d e t a i l s would r e q u i r e extremely complicated c a l c u l a t i o n s and i s u n l i k e l y t o*
provide a b e t t e r f i t t o t h e measured d a t a t h a n t h e semi-empirical methodd e s c r i b e d above.
The a t t e n u a t i o n c a l c u l a t e d by Eq. ( 5 ) , when s u b t r a c t e d from t h e i n i t i a l sound l e v e l provided by t h e alarm s i g n a l , g i v e s t h e alarm s i g n a l l e v e l a t t h e p o i n t of i n t e r e s t . The i n i t i a l sound l e v e l provided by t h e a l a r m s i g n a l can be obtained i n one of two ways. The most d i r e c t i s t o measure t h e mean sound l e v e l i n t h e room c o n t a i n i n g t h e smoke d e t e c t o r alarm. This i s n o t always p r a c t i c a l , however, e s p e c i a l l y i f one i s t r y i n g t o a s c e r t a i n t h e b e s t room i n which t o l o c a t e t h e alarm. Thus, t h e second method i s t o c a l c u l a t e t h e i n i t i a l sound l e v e l from t h e sound power output of t h e alarm,6 using t h e e x p r e s s i o n
"s Ss
A
L
= P-
10
l o g [(F)(l+
-)]
+
14
6 0 "s
where Ls = mean sound p r e s s u r e l e v e l i n source room, P = sound power output of alarm (dB),
V,
= volume of source room (m3), T60 = r e v e r b e r a t i o n time,Ss = s u r f a c e a r e a of source room (m2),
X = wave l e n g t h of sound (m).
For a n alarm o p e r a t i n g p r i m a r i l y a t
3150
Hz i n a n approximately s q u a r e room w i t h 2.4- c e i l i n g and a r e v e r b e r a t i o n time of0.4
s, t h i s can be reduced t oLS = P
+
14
-
10
l o g[6.06~
+
.3a]
-
c o r r ( 7 ) whereA
= a r e a of room, c o r r = -2 f o r hard rooms ( k i t c h e n , b a t h ) , =0
f o r normal rooms, = 2 f o r s o f t rooms ( r u g s , d r a p e s , e t c . ) . RECOMMENDATIONSOf t h e seven smoke d e t e c t o r s considered d u r i n g t h e s t u d y , n o t one provided any information about t h e sound power output of t h e alarm. It would seem t o be
d e s i r a b l e t h a t e i t h e r a minimum sound power o u t p u t should be e s t a b l i s h e d f o r smoke d e t e c t o r s o r t h a t manufacturers should be r e q u i r e d t o i n d i c a t e c l e a r l y t h e sound power o u t p u t and t h e dominant frequency band.
One of t h e problems a s s o c i a t e d w i t h t h e s e s e l f - c o n t a i n e d smoke d e t e c t o r s i s t h a t t h e optiaum l o c a t i o n f o r e a r l y d e t e c t i o n of f i r e s is n o t t h e same a s t h e optimum l o c a t i o n t o e n s u r e t h a t t h e alarm i s heard. This problem can be
overcome i n s e v e r a l ways, one being t o make t h e alarms louder. It may i n c r e a s e
:
t h e c o s t of t h e u n i t , and may a l s o r i s k h e a r i n g damage f o r people c l o s e t o t h e1
alarm when i t i s a c t i v a t e d . Another i s t o have a number of smoke d e t e c t o r s i n t e r c o n n e c t e d s o t h a t d e t e c t i o n of a f i r e by any one would t r i g g e r a l l t h e alarms. A t h i r d method would be t o s e p a r a t e t h e d e t e c t o r and t h e a l a r m s o t h a t each could be p l a c e d i n i t s optimum l o c a t i o n . It i s recommended t h a t t h e l a s t two o p t i o n s be i n c o r p o r a t e d i n b u i l d i n g r e g u l a t i o n s and p r a c t i c e s f o r f i r e s a f e t y design.CONCLUSION
A simple e x p r e s s i o n h a s been developed t o c a l c u l a t e t h e a t t e n u a t i o n of t h e a l a r m s i g n a l from a smoke d e t e c t o r a s i t propagates through a r e s i d e n t i a l b u i l d i n g , w i t h t h e p a t h viewed a s a s e r i e s of connected rooms. A t t e n u a t i o n depends on f l o o r a r e a and t y p e of f u r n i s h i n g s i n each room. C o r r e c t i o n s a r e a p p l i e d i f t h e house does n o t have f o r c e d a i r h e a t i n g o r i f a number of d o o r s
-
a r e closed. The e x p r e s s i o n can be used t o determine t h e optimum l o c a t i o n f o r alarms. A s t h e b e s t l o c a t i o n f o r an a l a r m is n o t n e c e s s a r i l y t h e b e s t l o c a t i o n,
f o r a smoke d e t e c t o r , i t i s recommended t h a t i n t e r c o n n e c t e d m u l t i p l e d e t e c t o r / a l a r m systems be used o r t h a t d e t e c t o r and a l a r m be s e p a r a t e d .I
REFERENCES
1. B r i g h t , R.G.: "Recent Advances i n R e s i d e n t i a l Smoke D e t e c t o r s , "
Fire
J o u r n a l , 68:6, 69-77, 1974.2. Jones, J.C.: "1982 Multiple-Death F i r e s i n t h e United S t a t e s , "
Fire
J o u r n a l , 77:4, 10-25, 1983.3. Underwriters L a b o r a t o r i e s Inc. Standard f o r S a f e t y UL217: "Single and M u l t i p l e S t a t i o n Smoke Detectors."
4. Nober, E.H., P e i r c e , H., Well, A., and Johnson, C.C.: "Waking E f f e c t i v e n e s s of Household Smoke and F i r e D e t e c t i o n Devices," NBS-GCR-80-284, Washington, DC, 20234, 1980.
5. Kahn, M.J.: "Detection Times t o Fire-Related S t i m u l i by S l e e p i n g Subjects." NBS-GCR-83-435, Washington, DC, 20234, 1983.
6. ANSI S1.31-1980.: "American N a t i o n a l Standard P r e c i s i o n Method f o r t h e Determination of Sound Power Levels of Broad-Band Noise Sources i n Reverberation Rooms." American I n s t i t u t e of Physics, New York. 7. Berry, C.H.: " W i l l Your Smoke D e t e c t o r Wake You?"
F i r e
72:4,105-108, 1978. w
8. American N a t i o n a l Fire Codes, 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 74, Batterymarch Park, Quincy, MA, 02269, 1974.
9. Bradley, H.L. and Wheeler, W.P.: "The A n a l y s i s of t h e Audible S i g n a l From S i n g l e - S t a t i o n Heat and Smoke Detectors." Unpublished paper f o r ENFP 416, F i r e P r o t e c t i o n Engineering Department, U n i v e r s i t y of Maryland, College Park,
MD,
1977.10. ASTM E90-81: "Standard Method f o r Laboratory Measurement of Airborne Sound Transmission Loss of B u i l d i n g P a r t i t i o n s . "
T h i s p a p e r
