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Photometric and psychophysical measurements of exit signs through
smoke
Rea, M. S.; Clark, F. R. S.; Ouellette, M. J.
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PHOTOMETRIC AND PSYCHOPHYSICAL MEASUREMENTS OF EXIT SIGNS THROUGH SMOKE ANALYZED by M.S. Rea B u i l d i n g S e r v i c e s S e c t i o n F.R.S. C l a r k F i r e R e s e a r c h S e c t i o n M . J . O u e l l e t t e B u i l d i n g S e r v i c e 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 DBR P a p e r No. 1 2 9 1 J u n e 1985 ISSN 0381-4319 NRCC 24627 P r i c e $6.00 O N a t i o n a l R e s e a r c h C o u n c i l of Canada 1985
Table of Contents
Page I. Introduction
11. Experimentation A. Apparatus
1. The smoke chamber and viewing booth 2. The exit signs
3. Smoke generation 4. Smoke measurement
5. Smoke chamber lighting fixtures B. Photometric measurements
1. Illuminance measurements
2. hminance measurements of the exit signs 3. Chromaticity measurements of the exit signs C. Psychophysical Observations
1. Observers
2. Experimental design 3. Procedures
111. Results and Discussion
A. The results of the analysis of variance (ANOVA) B. The brightness of the exit signs
C. The ambient illumination D. The threshold criteria
1. Scattered light created by the signs 2. Very dim exit signs
E. The spectral sensitivity of the subjects F. The age of the subjects
IV. Conclusions and recommendations A. Sign brightness
B. Sign colour
C. Spatial characteristics of the signs D. Recommendations for 'static' exit signs E. 'Smart' signs Acknowledgements References Appendix A Appendix B Appendix C
I. INTRODUCTION
Exit signs are important components of modern fire protection systems in buildings. They are supposed to be visible through smoke and, thus, to guide occupant evacuation. Nevertheless, the design of exit signs is not generally based upon experimental research nor upon principles of good visibility.
Several kinds of investigations have been performed on the subject of exit sign visibility through smoke. One kind of ~ t u d ~ l ' ~ has followed the methodology recommended b the General Services Administration (GSA) of the United States government.' In these studies, determinations are made of the maximum distances from which particular signs can be seen in a smoke-filled corridor. However, an important visual parameter, the apparent size of the sign, varies with viewing distance, and, therefore its influence cannot be unambiguously evaluated. Consequently, it is more difficult to use the results of these studies as bases for recommendations of exit sign visibility.
Collins and ~erner, in a second kind of study, used a combination of absorbing filters and 'veiling' luminous sources to simulate the optical properties of smoke. Whereas this approach is convenient for assessing sign visibility under controlled conditions of luminance and contrast, it does not characterize the visual conditions found in smoke, because it does not properly simulate the scattering of light, particularly scatter originating from the sign itself.
in^
has developed an empirical model for predicting sign visibility through smoke. He expressed visibility as the minimum viewing distance at which the sign becomes completely obscured. Considered in the model are theluminance and the threshold contrast of the sign, ambient illumination, smoke density, and the scattering and absorbing properties of the smoke. However, this model is based upon data obtained with the GSA methodology,5 and therefore presents the same difficulties. Further, the empirical relations established by Jin between visibility, luminance and contrast threshold are not in complete agreement with known principles of human
isi ion.^'^^
Finally, the signs used in Jin's study were not thoroughlydescribed so it is difficult to translate the results into design
guidelines. It should be pointed out, however, that the model could be useful for making comparisons of visibility in various smokes.
Visibility-related recommendations for exit signs have been made by various sanctioning bodies throughout the world. Sign brightness, one of the most important factors determining visibility in smoke, is not specified by some of these bodies. Others do provide some guidance, but the
foundations of the specifications are not adequately documented. In the United Kingdom, l L luminance levels between 2 and 80 cd m" are recommended for trans-illuminated signs (with internal lamps behind translucent letters or backgrounds). A note in this specification suggests, however, that the "most suitable level" is between 17 to 34 cd m-2. In the corresponding United States standardL2, a distinction is made between signs with (a) trans-illuminated letters and opaque backgrounds, (b) trans-illuminated backgrounds and opaque letters, and (c) trans-illuminated letters and backgrounds. For type (a) the letters must have an average luminance not less than 2 fL (6.85 cd me') and not more than 3 fL (10.28 cd m-2); for type
S M O K E C H A M B E R
V I E W I N G B O O T H
Figure 1. F l o o r p l a n of t h e smoke chamber and viewing booth. A l l dimensions i n mm.
1 8 2 9 2 0 5 1 2 9 0 1 0 0 0 5 0 0
_
6 1 0 -!- 1 7 0 0 - ,\ *-I--L--,
7 7 0
C H A M B E R
Figure 2. S i d e view of t h e smoke chamber and viewing booth. A l l dimensions i n mm.
(b), the background must have a minimum average luminance of 3 fL, but no maximum luminance is set; for type (c), the average luminance of the brighter portion (letters or background) must be at least 6 fL.
Standards from both the United Kingdom and the United States make exceptions for "approved self-illuminated" signs. These signs are made luminous in the dark by beta radiation-induced chemiluminescence of the coating from a chamber filled with tritium ( 1 ~ 3 ) gas. In the United
States, l2 these signs are permitted to have a minimum luminance of 0.06 fL (0.21 cd m-2). In the United Kingdom13 the minimum permitted initial luminance is 0.51 cd m-2, and the manufacturer must specify how long the sign luminance is expected to be above 0.14 cd md2.
No specification of sign luminance appears in the National Buildin Code of Canada (NBC), l4 but the Canadian General Standards Board (CGSB) f 5
requires that "the intensity of the light emitted by the sign shall not be less than that from a 25 W incandescent filament lamp when activated by a regular circuit". The NBC and the CGSB also differ in particulars related to visibility of exit signs, including letter size, colour, and the use of glyphs
The differences between exit sign specifications in Canada (and elsewhere) and the lack of definitive information that might allow such specifications to be written led the CGSB and the Associate Committee of the NBC to ask the Division of Building Research, National Research Council of Canada (DBRINRCC) to examine the visual effectiveness of some exit signs in smoke.
The purpose of the study reported here was to provide information on the visibility of selected exit signs through smoke to these Canadian sanctioning bodies. Based upon the results, which were largely consistent with well-established principles of vision and optics, some design
recommendations for exit signs and emergency lighting have been proposed. A few design considerations and topics for further research have also been formulated from the data. It is hoped that the information reported here will lead to improved fire safety in Canada and elsewhere.
11. EXPERIMENTATION
Two classes of measurements were made of thirteen exit signs selected for testing: 1) broad-band photometric measurements16 were made of the signs under clear conditions and through smoke of different types and densities; 2) sixteen observers made threshold psychophysical observations of each sign through cosmetic oil smoke.
A. Apparatus
1. The smoke chamber and viewing booth
The smoke chamber and viewing booth (Figures 1 and 2) were constructed of lumber framing covered with black polyethylene film. A 1.2 m x 2.4 m clear plastic window (transmittance, t = 0.92) of high optical fidelity separated the smoke chamber from the viewing booth. The smoke chamber contained (a) the exit signs, mounted on a stationary vertical rack, (b)
exhaust pipes from the two types of smoke-generating apparatus (just outside the smoke chamber), (c) a smoke density measuring apparatus, and (d) two fluorescent luminaires mounted near the smoke chamber ceiling. The viewing booth housed (a) on-off controls for each exit sign and the fluorescent luminaires, (b) a smoke density monitor, (c) on-off controls for smoke generation, (d) the experimenter(s), and, either, (e) the photometer and time averaging equipment or (f) a human observer.
2. The exit signs
Samples of nine exit sign designs, including some recommended for use in Canada, were chosen for the study. Appendix A describes these signs in detail. All signs were affixed to a stationary rack in the centre of the smoke chamber, 4.9 m from the window dividing the smoke chamber and the viewing booth. Colour photographs of the exit sign array in the dark and in room lighting are shown in Appendix B.
Thirteen exit signs were actually tested in this experiment. Seven electric, trans-illuminated signs and two chemiluminescent, self-illuminated signs were employed, but four of the seven trans-illuminated signs housed both incandescent and fluorescent lamps. Because the kind of lamp within a trans-illuminated sign affects the luminous quality and brightness of that sign, the seven different trans-illuminated sign designs were treated as eleven completely different signs for experimental testing.
Each trans-illuminated sign (and, where relevant, lamp type within a sign) could be turned 'on' and 'off' with switches in the viewing booth operated by the experimenter. Each self-illuminated sign could be covered and uncovered with a mechanical flap attached to a fine string manipulated from the viewing booth.
3. Smoke generation
Except for preliminary photometric testing (Appendix C), smoke was generated using a Model 3020 oil smoke generator (Les Enterprises MDG Inc., Quebec City, Quebec, Canada). This device sprayed cosmetic oil onto a hot plate; smoke was produced as the oil evaporated. The smoke was blown into the smoke chamber at floor level by compressed carbon dioxide gas. Smoke could be removed with an exhaust fan installed in the ceiling. Two 18 cm diameter fans located on the floor dispersed the smoke evenly throughout the chamber. The density and uniformity of the smoke was accurately
controlled.
4. Smoke measurement
A helium-neon laser (1.0 mW) and a silicon diode photodetector were located in the smoke chamber (Figures 1 and 2) and operated continuously during testing. This monitoring device has been described in detail
elsewhere. l Briefly
,
however, obscuration of the 632.8 nm wavelength laserbeam was measured across a 3 m or a 1 m path. All estimates of smoke
density are based upon recordings from this device and are reported in terms of optical density per meter (OD m-I
1,
where OD = loglO(Ic/Is)
I, is the recorded value without smoke (a constant value) and Is is the recorded value in smoke (variable values)
5. Smoke chamber lighting fixtures
Ambient illumination in the smoke chamber was provided by two lighting fixtures mounted near the ceiling (Figure 2). Each commercially available luminaire (0.3 m x 1.3 m) had a pair of F40-CW fluorescent lamps within a clear, acrylic, wrap-around prismatic lens. As with the exit signs, the ambient illumination could be turned 'on' and 'off' from within the viewing booth.
8 . Photometric measurements
1. Illuminance measurements
With both ceiling luminaires 'on', horizontal plane illuminances along the centre line of the smoke chamber were obtained under smoke-free
conditions, at a height of 1.7 m (Table I). At the plane of the exit sign rack, a vertical illuminance of 75 lx was obtained 1.5 m above the smoke chamber floor.
In a darkened laboratory, illuminance measurements were obtained from each exit sign at a distance of 30.5 cm normal to the centre of the face of the sign and, where applicable, 30.5 cm below the sign, normal to the centre of the downlight aperture. These values are included in Appendix A as
'general illuminances', front and below, respectively. 2. Luminance measurements of the exit signs
Photometry was performed with a Spectra Pritchard, Model 1980A,
photometer fitted with a 3 mm diameter aperture on the objective lens. Some measurements under low luminances (through smoke in the dark) were achieved by time averaging 1000 readings over a 12 s interval with a 12 bit
analog-todigital converter and a microcomputer. Table I
Smoke Chamber Illuminance at Height of 1.7 m with Room Lights 'on' Distance from Horizontal exit signs, m Illuminance, lx
The photometer was p o s i t i o n e d on a t r i p o d 7.2 m from t h e e x i t s i g n rack. Except where n o t e d , t h e ' g e n e r a l luminance' of e a c h s i g n was measured through t h e window s e p a r a t i n g t h e darkened viewing booth and ( a ) t h e
darkened o r ( b ) t h e i l l u m i n a t e d smoke chamber by p i v o t i n g t h e photometer on t h e s t a t i o n a r y t r i p o d (Appendix A). The window was c l e a n e d r o u t i n e l y . The ' g e n e r a l luminance' was measured u s i n g a c i r c u l a r f i e l d a p e r t u r e j u s t l a r g e enough t o c o v e r t h e f a c e of t h e e x i t s i g n ; t h e measured l o c a t i o n s and a r e a s a r e i n d i c a t e d by dashed c i r c l e s i n Appendix A.
I n a s e p a r a t e s e r i e s of measurements, t h e luminances of s e v e r a l small
p o i n t s on t h e f a c e of e a c h e x i t s i g n were measured i n a d a r k room u s i n g a 6 minute d i a m e t e r f i e l d a p e r t u r e . I n Appendix A, t h e s e l o c a t i o n s a r e
i d e n t i f i e d by s o l i d c i r c l e s . The photometric d a t a a r e a l s o given. 3. Chromaticity measurements of t h e e x i t s i g n s
The Model 1980A P r i t c h a r d photometer a l s o c o n t a i n s , nominally, ' b l u e ' , ' r e d ' and 'green ( o r VA)' broad band c o l o r f i l t e r s . These f i l t e r s were used t o e s t i m a t e t h e c h r o m a t i c i t y c o o r d i n a t e s 1 6 of t h e t e x t and, where
a p p r o p r i a t e , t h e background, of e v e r y s i g n under smoke-free c o n d i t i o n s . S e v e r a l small a r e a s of t h e t e x t and of t h e background were measured. Chromaticity c o o r d i n a t e s w i t h i n t h e two sets of measurements ( t e x t and background) d i f f e r e d very l i t t l e f o r any g i v e n s i g n . Appendix A p r o v i d e s t y p i c a l v a l u e s f o r each s i g n .
The c h r o m a t i c i t y c o o r d i n a t e s of a w h i t e r e g i o n of Sign 1 were a l s o measured under d i f f e r e n t d e n s i t i e s of t h e c o s m e t i c o i l smoke. A s shown i n F i g u r e 3, t h e c h r o m a t i c i t y c o o r d i n a t e s s h i f t e d toward l a r g e r v a l u e s of x and
F i g u r e 3. C.I.E. c h r o m a t i c i t y c o o r d i n a t e s f o r a w h i t e luminous r e g i o n of Sign 1 a t d i f f e r e n t smoke d e n s i t i e s . The p o i n t s a r e l a b e l e d i n u n i t s of OD m-l.
s m a l l e r values of y ( t h e redder region of t h e c h r o m a t i c i t y space) w i t h i n c r e a s i n g smoke d e n s i t y . Though n o t p a r t i c u l a r l y l a r g e , t h i s s h i f t d i d demonstrate t h e p r e f e r e n t i a l s c a t t e r i n g of s h o r t e r wavelengths i n t h e
cosmetic o i l smoke. It should be noted t h a t such p r e f e r e n t i a l s c a t t e r i n g i s
not n e c e s s a r i l y a c h a r a c t e r i s t i c of a l l smoke.7 C. Psychophysical o b s e r v a t i o n s
1. Observers
S i x t e e n v o l u n t e e r s (Table 1 1 ) from DBRINRCC made t h r e s h o l d v i s i b i l i t y e v a l u a t i o n s of each e x i t sign. P r i o r t o t h e experiment, t h e e y e s i g h t of each o b s e r v e r was a s s e s s e d w i t h a b a t t e r y of v i s u a l tests from a Keystone Ophthalmic Telebinocular and, i f found c o l o u r d e f i c i e n t by one of t h e t e s t s , w i t h a Schmidt and Haensch anomalasope. S u b j e c t s r e q u i r i n g c o r r e c t i v e
l e n s e s wore them d u r i n g both t h e assessment and t h e experiment, s o t h a t a l l s u b j e c t s had normal o r b e t t e r a c u i t y i n one o r both eyes. S i x s u b j e c t s were c l a s s e d a s colour d e f i c i e n t ; some d e t a i l s about t h e d i f f e r e n t c l a s s e s of colour v i s i o n a r e given i n Table 11.
2. Experimental Design
Data c o l l e c t i o n was organized f o r subsequent a n a l y s i s of v a r i a n c e (ANOVA) i n t o a t h r e e - f a c t o r , r e p e a t e d measures experimental d e s i g n l a .
C r i t i c a l smoke d e n s i t y ( S e c t i o n II.C.3) was used a s t h e dependent v a r i a b l e . Factor 1: E x i t s i g n (13 d i f f e r e n t s i g n s )
F a c t o r 2: Threshold v i s i b i l i t y c r i t e r i o n
adopted by t h e o b s e r v e r s : ' d e t e c t a b i l i t y ' (can j u s t s e e t h e s i g n ) o r ' r e a d a b i l i t y ' (can j u s t r e a d t h e s i g n )
F a c t o r 3: Ambient smoke chamber i l l u m i n a t i o n ( l i g h t i n g f i x t u r e s 'on' o r ' o f f ' )
Each o b s e r v e r was exposed t o a l l of t h e 52 (13 s i g n s x 2 c r i t e r i a x 2 l e v e l s of ambient i l l u m i n a t i o n ) c o n d i t i o n s once.
3. Procedures
One o b s e r v e r and one experimenter s a t i n t h e viewing booth d u r i n g a n experimental s e s s i o n . Each observer faced t h e window and was approximately
5.2 m from t h e d i s p l a y e d s i g n i n t h e smoke chamber. When t h e ambient i l l u m i n a t i o n was ' o f f ' , o b s e r v e r s had adapted t o t h e darkness f o r a t l e a s t 10 minutes before any o b s e r v a t i o n s were recorded.
During a n experimental t r i a l , s u b j e c t s were i n s t r u c t e d t o adopt one of t h e two t h r e s h o l d c r i t e r i a ( d e t e c t a b i l i t y o r r e a d a b i l i t y ) . One e x i t s i g n was d i s p l a y e d i n t h e smoke chamber, and a f t e r a uniform smoke d i s t r i b u t i o n was e s t a b l i s h e d , t h e s u b j e c t r e p o r t e d whether t h e e x i t s i g n was above o r below t h e adopted t h r e s h o l d c r i t e r i o n . I f i t was s t i l l above t h r e s h o l d , more smoke was added and t h e experimenter asked f o r a n o t h e r judgement. When t h e e x i t s i g n was j u s t below t h r e s h o l d , t h e d e n s i t y of t h e smoke a c r o s s a 1 m p a t h ( S e c t i o n II.A.4) was taken a s t h e c r i t i c a l smoke d e n s i t y . These t r i a l s continued u n t i l t h e c r i t i c a l smoke d e n s i t i e s had been o b t a i n e d f o r a l l c o n d i t i o n s o r u n t i l t h e s u b j e c t wanted t o s t o p .
Table I1
Characteristics of Observers
- --
Subject no. Sex Age Colour vision1
l~richromats (T), or colour normals, are people having all three types of cone photopigments ; short (blue), middle (green), and long (red) wavelength sensitive cone types present in the retina. The spectral sensitivity of the long wavelength cone is shifted toward the centre of the visible
spectrum relative to colour normals for protanomolus trichromats (Tp). The spectral sensitivity of the middle wavelength cone is shifted toward the long end of the visible spectrum relative to colour normals for
deuteranomalous trichromats (Td).
Dichromats (D), or colour blinds, are people with only two of the three types of cone photopigments. Protanopes (Dp) are dichromats effectively missing the long wavelength sensitive cone.
In this docuxent, all observers with reduced sensitivity to the long
wavelengths f a the visible region of the spectrum (Tp and Dp observers) are labeled as 'p'otans'. Besides abnormal colour perception, protans have reduced overall luminous efficiency. Thus luminous stimuli emitting energy in the long wavelength region of the visible spectrum will be less
efficacious in evoking brightness perceptions in protans than in colour normals.
Deuteranomalous trichromats are also called deutans in this report.
For a more detailed explanation of the various types of colour vision and its influence on colour and brightness perception, see references 16
Several t r i a l s were conducted d u r i n g a n e x p e r i m e n t a l s e s s i o n . These s e s s i o n s v a r i e d i n d u r a t i o n , depending upon t h e m o t i v a t i o n of t h e o b s e r v e r ; h e o r s h e c o u l d s t o p a t any time. Between 4 and 8 h o u r s o v e r one o r two days were r e q u i r e d t o o b t a i n a l l t h e d a t a f o r a s i n g l e s u b j e c t . Signs were t y p i c a l l y p r e s e n t e d i n i n c r e a s i n g o r d e r of b r i g h t n e s s t o s h o r t e n s e s s i o n l e n g t h . Sometimes i t was n e c e s s a r y , however, f o r t h e experimenter t o exhaust some smoke from t h e chamber s o t h a t s u b j e c t s c o u l d make t h r e s h o l d judgements of dimmer e x i t s i g n s .
111. RESULTS AND DISCUSSION
A. The r e s u l t s of t h e a n a l y s i s of v a r i a n c e (ANOVA)
Table I11 p r e s e n t s t h e r e s u l t s of t h e t h r e e - f a c t o r , r e p e a t e d measures
ANOVA u s i n g c r i t i c a l smoke d e n s i t y a s t h e dependent v a r i a b l e . A l l of t h e main e f f e c t s ( s i g n ( S ) , t h r e s h o l d c r i t e r i o n (C), and ambient i l l u m i n a t i o n
( R ) ) and a l l of t h e two-way i n t e r a c t i o n s (SxC, SxR, and CxR) were
s i g n i f i c a n t a t a c o n f i d e n c e l e v e l of p
<
0.003; t h e t h r e e w a y i n t e r a c t i o n (SxCxR) was n o t s i g n i f i c a n t .B. The b r i g h t n e s s of t h e e x i t s i g n s
The ANOVA shows t h a t t h e t h i r t e e n e x i t s i g n s were s i g n i f i c a n t l y d i f f e r e n t i n t h e i r v i s i b i l i t y through smoke (Table 111). F i g u r e 4
g r a p h i c a l l y c h a r a c t e r i z e s t h i s s i g n i f i c a n t main e f f e c t ; i t shows t h e
r e l a t i o n between ' g e n e r a l luminance' measured w i t h o u t room l i g h t s ( S e c t i o n II.B.2) f o r t h e t h i r t e e n s i g n s and c r i t i c a l smoke d e n s i t y (II.C.3), averaged o v e r t h e two o t h e r experimental f a c t o r s , t h r e s h o l d c r i t e r i o n and ambient i l l u m i n a t i o n . Table I11 A n a l y s i s of Variance .- - Source of Sum of V a r i a t i o n Squares df Mean Square F P S 20.700 12 R 16.000 1 C 1.340 1 S x R 1.540 12 S x C 0.182 12 R x C 0.085 1 S x R x C 0.076 12 S: e x i t s i g n R: room l i g h t s ( ' o n ' o r ' o f f ' ) C: t h r e s h o l d c r i t e r i o n ( ' d e t e c t a b i l i t y ' o r ' r e a d a b i l i t y ' ) Dependent v a r i a b l e : c r i t i c a l smoke d e n s i t y
D > C - 0 6 - Ln Z u n ", 0 """"' """'" """"' """"' 0 1 1 10 1 0 0 1000 G E N E R A L L U M I N A N C E , c d m
Figure 4 . Critical smoke densities for the 13 exit signs as a function of general luminance (sign numbers at top).
-
YI I . Or
,!
..,, , , , . , , , AMBIENT ILLUMINATION-
LIGHTS OFF ( M = 0 6 2 1 E - 0 L!GHTs-?N--I--!-E-o:?P.-~ n 0 > C 0 6 - Z LL, a Y - 0 4 0 1 1 10 1 0 0 1 0 0 0 G E N E R A L L U M I N A N C E , c d m - 2Figure 5. Critical smoke densities for the 13 exit signs as a function of general luminance at both levels of ambient illumination (sign numbers at top). Mean values of critical smoke density for the two levels of ambient illumination are inset. Columns at bottom show, for each sign, the difference in critical smoke density
General luminance i s only one of many ways t o c h a r a c t e r i z e t h e s e
s i g n s ; t h e ANOVA i s performed w i t h o u t r e g a r d f o r t h e luminances of t h e
s i g n s . However, g e n e r a l luminance i s a r e a s o n a b l e and convenient way t o
c h a r a c t e r i z e t h e s e s i g n s because t h e r e i s a s t r o n g , p o s i t i v e l i n e a r
r e l a t i o n s h i p ( r = 0.86) between t h e l o g a r i t h m of g e n e r a l luminance and
c r i t i c a l smoke d e n s i t y (dashed l i n e i n F i g u r e 4). This s t r o n g p o s i t i v e
c o r r e l a t i o n l e a d s one t o conclude, t h e n , t h a t b r i g h t e r e x i t s i g n s w i l l be more v i s i b l e i n smoke.
N e v e r t h e l e s s , o t h e r f a c t o r s a s s o c i a t e d w i t h t h e s i g n s , t h e environment and t h e o b s e r v e r s c o n t r i b u t e d t o t h e v a r i a t i o n (shaded a r e a i n F i g u r e 4) about an i d e a l i z e d l i n e a r model r e l a t i n g l o g g e n e r a l luminance and c r i t i c a l
smoke d e n s i t y . Some of t h e f a c t o r s are d e s c r i b e d below.
C. The ambient i l l u m i n a t i o n
L i g h t from ambient i l l u m i n a t i o n i n t h e smoke chamber s i g n i f i c a n t l y
reduced t h e v i s i b i l i t y of a l l e x i t s i g n s (Table 111). Figure 5 documents
t h e s t a t i s t i c a l l y d i f f e r e n t average (fl) c r i t i c a l smoke d e n s i t i e s f o r t h e two
l e v e l s of ambient i l l u m i n a t i o n , 'on' and 'off
'.
F i g u r e 5 a l s o i l l u s t r a t e s t h e s i g n i f i c a n t i n t e r a c t i o n between t h e
f a c t o r s e x i t s i g n (S) and ambient i l l u m i n a t i o n (R) (SxR t e r m i n T a b l e 111). Ambient i l l u m i n a t i o n a f f e c t e d t h e v i s i b i l i t y of some e x i t s i g n s more t h a n
t h a t of o t h e r s . T h i s i s i l l u s t r a t e d by t h e h e i g h t s of t h e columns at t h e
bottom of F i g u r e 5; t h e h i g h e r t h e column, t h e more t h e s i g n s were a f f e c t e d
by ambient i l l u m i n a t i o n . The columns f o r S i g n s 4 and 5 were n o t i n c l u d e d i n
t h i s f i g u r e because t h e g e n e r a l luminances of t h e s e two s i g n s (Appendix A)
changed s u b s t a n t i a l l y under ambient i l l u m i n a t i o n . It should be noted t h a t
d e l e t i n g t h e d a t a f o r t h e s e two s i g n s d i d n o t a f f e c t t h e s i g n i f i c a n c e of t h e
SxR i n t e r a c t i o n n o r any o t h e r term i n t h e ANOVA. Adequate i n t e r p r e t a t i o n of
t h i s i n t e r a c t i o n r e q u i r e s a more s o p h i s t i c a t e d p a r a m e t r i c s t u d y t h a n was performed here.
Ambient i l l u m i n a t i o n was a l s o important t o t h e c r i t i c a l smoke d e n s i t y r e q u i r e d t o r e a c h t h e two v i s i b i l i t y t h r e s h o l d c r i t e r i a , ' d e t e c t a b i l i t y ' and
' r e a d a b i l i t y ' . The s i g n i f i c a n t i n t e r a c t i o n (CxR i n Table 1 1 1 ) between t h e
f a c t o r s ambient i l l u m i n a t i o n (R) and v i s i b i l i t y t h r e s h o l d c r i t , e r i o n (C) i s
shown i n F i g u r e 6. The b e t t e r o p t i c a l q u a l i t y c r e a t e d when t h e room l i g h t s
a r e ' o f f ' ( i . e . when t h e r e i s less s c a t t e r e d l i g h t ) n o t o n l y e n a b l e s
s u b j e c t s t o s e e t h e s i g n s b e t t e r , b u t i t a l s o enhances t h e d i f f e r e n c e s between t h e c r i t i c a l smoke d e n s i t i e s r e q u i r e d f o r d e t e c t a b i l i t y and
r e a d a b i l i t y (0.10 OD m-l v e r s u s 0.06 OD m-l).
D. The t h r e s h o l d c r i t e r i a
S i g n i f i c a n t l y h i g h e r smoke d e n s i t i e s were r e q u i r e d t o r e a c h t h e ' d e t e c t a b i l i t y ' c r i t e r i o n t h a n t h e ' r e a d a b i l i t y ' c r i t e r i o n (Table 111).
F i g u r e 7 documents t h e s t a t i s t i c a l l y d i f f e r e n t average
(R)
c r i t i c a l smoked e n s i t i e s f o r t h e two t h r e s h o l d c r i t e r i a .
There w a s a s i g n i f i c a n t i n t e r a c t i o n (SxC) between t h e f a c t o r s e x i t s i g n
(S) and t h r e s h o l d c r i t e r i o n (C), a l s o d e p i c t e d i n F i g u r e 7. The columns at
t h e bottom of t h e f i g u r e r e p r e s e n t t h e d i f f e r e n c e s i n mean c r i t i c a l smoke d e n s i t i e s f o r each s i g n a t t h e s e two c r i t e r i a ; i f t h e r e had n o t been a
LQ READABILITY ES DETECTABILITY
1
0 FF O N A M B I E N T I L L U M I N A T I O N
Figure 6. C r i t i c a l smoke d e n s i t i e s f o r t h e 13 e x i t s i g n s f o r both t h r e s h o l d c r i t e r i a a t t h e two l e v e l s of ambient i l l u m i n a t i o n .
YI
4,
.
,4,
* *, , , , , 7 ,.,THRESHOLD CRITERION
Figure 7. C r i t i c a l smoke d e n s i t i e s f o r t h e 13 e x i t s i g n s a s a f u n c t i o n of general luminance a t both t h r e s h o l d c r i t e r a ( s i g n numbers a t top). Mean v a l u e s of c r i t i c a l smoke d e n s i t y f o r t h e two
t h r e s h o l d c r i t e r i a a r e i n s e t . Columns a t bottom show, f o r each s i g n , t h e d i f f e r e n c e i n c r i t i c a l smoke d e n s i t y (Ad) between t h e two t h r e s h o l d c r i t e r i a .
s i g n i f i c a n t i n t e r a c t i o n between t h e f a c t o r s e x i t s i g n and t h r e s h o l d c r i t e r i o n , t h e h e i g h t s of t h e s e columns would b e s t a t i s t i c a l l y i n d i s t i n g u i s h a b l e . 1 . S c a t t e r e d l i g h t c r e a t e d by t h e s i g n s A s d e s c r i b e d i n t h e p r e v i o u s s e c t i o n , s c a t t e r e d l i g h t from ambient i l l u m i n a t i o n reduced t h e v i s i b i l i t y of t h e e x i t s i g n s . Although n o t s t u d i e d p a r a m e t r i c a l l y i n t h i s experiment, t h e r e was a n i n d i c a t i o n t h a t s c a t t e r e d
l i g h t from luminous, b u t u n l e t t e r e d , a r e a s of a s i g n reduce i t s r e a d a b i l i t y
r e l a t i v e t o i t s d e t e c t a b i l i t y .
Any a p e r t u r e i n an e x i t s i g n (e.g. a downlight) w i l l i n c r e a s e t h e
amount of l i g h t s c a t t e r e d i n smoke through which a s i g n must be d e t e c t e d o r
a l e t t e r must be r e a d ( S e c t i o n 1II.C). However, s c a t t e r e d l i g h t i n smoke
w i l l l i k e l y reduce t h e r e a d a b i l i t y of a l e t t e r more t h a n t h e d e t e c t a b i l i t y
of t h e s i g n . D e t e c t i o n of a s i g n through smoke i s determined l a r g e l y by t h e
t o t a l amount of l i g h t e m i t t e d from t h e s i g n i n any d i r e c t i o n , whereas
r e a d a b i l i t y of a l e t t e r through smoke depends more upon t h e o p t i c a l f i d e l i t y
of t h e atmosphere. I n o t h e r words, one may s t i l l be a b l e t o d i s c e r n t h e
l o c a t i o n of a luminous s i g n i n smoke even i f s p a t i a l d e t a i l s , l i k e t h e
l e t t e r i n g , a r e obscured. Thus, luminous f e a t u r e s of s i g n s unimportant f o r
r e a d i n g w i l l a d v e r s e l y a f f e c t r e a d a b i l i t y more t h a n d e t e c t a b i l i t y .
Text s i z e and t h e luminous c o n t r a s t between t e x t and background a r e i m p o r t a n t f o r e x i t s i g n r e a d a b i l i t y b u t unimportant f o r e x i t s i g n
d e t e c t a b i l i t y . S c a t t e r e d l i g h t w i l l reduce t h e r e a d a b i l i t y of low c o n t r a s t
l e t t e r s (e.g. S i g n s 8 and 13) more t h a n h i g h c o n t r a s t l e t t e r s (e.g. S i g n s 2
and lo).* Thus t h e columns a t t h e bottom of F i g u r e 7 a r e g e n e r a l l y h i g h e r
f o r t h e low c o n t r a s t l e t t e r e d s i g n s t h a n t h e h i g h c o n t r a s t ones. Smaller
t e x t i s a l s o more s u s c e p t i b l e t o r e a d a b i l i t y l o s s e s from s c a t t e r e d l i g h t .
T h i s i s e v i d e n t from t h e h i g h e r columns i n F i g u r e 7 f o r t h o s e S i g n s (5, 8 ,
and 1 3 ) which have s m a l l e r l e t t e r i n g .
2. Very dim e x i t s i g n s
The g e n e r a l luminances of t h e t r a n s - i l l u m i n a t e d s i g n s were
approximately t h e same w i t h and w i t h o u t ambient i l l u m i n a t i o n , b u t , a s n o t e d
i n S e c t i o n I I I . C , t h e luminances of t h e self-luminous s i g n s (Signs 4 and 5)
were q u i t e d i f f e r e n t under t h e s e two c o n d i t i o n s (Appendix A ) . The r e s u l t s
i n F i g u r e 8 s u p p o r t t h e h y p o t h e s i s t h a t a d i f f e r e n t c l a s s of p h o t o r e c e p t o r was used by s u b j e c t s t o d e t e c t t h e s e v e r y dim s i g n s when t h e smoke chamber
l i g h t s were 'off
'.
There a r e two c l a s s e s of p h o t o r e c e p t o r s , r o d s and c o n e s , i n t h e human
eye t h a t o p e r a t e a t d i f f e r e n t b r i g h t n e s s l e v e l s . 1 6 The more s e n s i t i v e r o d s
a r e used under dim c o n d i t i o n s (below approximately 0.001 c d m-') and cones
a r e used under b r i g h t c o n d i t i o n s (above approximately 3 cd m"). I n t h e
mesopic r e g i o n (between 0.001 and 3 cd me') b o t h r o d s and c o n e s o p e r a t e .
These p h o t o r e c e p t o r s d i f f e r n o t only i n terms of t h e b r i g h t n e s s l e v e l s a t
which t h e y o p e r a t e , b u t a l s o i n terms of t h e amount of s p a t i a l d e t a i l t h a t *For t h e s e purposes, c o n t r a s t may be c o n s i d e r e d a s t h e r a t i o of t e x t t o
background luminances on t h e s i g n f a c e . Appendix A p r o v i d e s t e x t and
-RODS & CONES CONES ONLY-+ THRESHOLD CRITERION 0 DETECTABILITY O
r?E_nonelc!T_v
-
I
LIGHTS OFF Q\/
LIGHTS ONFigure 8. C r i t i c a l smoke d e n s i t i e s f o r t h e two self-luminous s i g n s a t t h e two t h r e s h o l d c r i t e r i a a s a f u n c t i o n of g e n e r a l luminance ( s i g n numbers a t t o p ) . Columns a t bottom show, f o r each s i g n , t h e d i f f e r e n c e i n c r i t i c a l smoke d e n s i t y (Ad) between t h e two t h r e s h o l d c r i t e r i a .
W A V E L E N G T H , nrn
Figure 9. The r e l a t i v e s p e c t r a l s e n s i t i v i t y of c o l o u r normals and
they can resolve. Only cones can be used to see fine detail or to read letters of the size encountered in this experiment.
With the ambient illumination 'on', the brightnesses of the
chemiluminescent signs were above 3 cd m'2, so cones were used both to
detect and to read these two signs (and all of the trans-illuminated signs). With room lights 'off', however, their brightnesses were below this level. Under these dim, mesopic conditions, cones were needed to read the signs but rods could be used to detect them. The sensitivity range of the eye was
thus extended at the lower luminances (left side of Figure 8) relative to
that at higher luminances (right side of Figure 8).
E. The spectral sensitivity of the subjects
Observers with different cone spectral sensitivities were intentionally included in this study; colour normals, protans and deutans were tested (see
Table 11). It is reasonable to suppose that the spectral sensitivity (or
colour vision) of subjects would be important to the outcome of this experiment. Protans, for example, should be less sensitive (give lower
critical smoke densities) to red signs (e.g. Signs 6, 7, 9, and 12), because
these subjects have attenuated cone (photopic) luminous efficiencies at long
wavelengths (Figure 9). In fact, protans should be less sensitive to any
sign at photopic (high) brightnesses.
Unlike the other variables discussed before, however, colour vision cannot be randomly assigned to subjects, and other personal factors that could affect visibility can be easily confounded with the subject's spectral sensitivity. For example, the small group of subjects categorized as
protans in this experiment could, by chance, also have been more cautious or conservative in their psychophysical judgements. These psychological
factors would also contribute to lower critical smoke densities, and it is impossible, just with this test, to know whether the differences between protans and the other subjects were due to colour vision alone.
Fortunately, there is a good understanding of colour vision and its consequences to visibility.
Despite potential confounding, colour vision was included in another ANOVA with the original three experimental factors (exit sign, threshold
criterion and ambient illumination). The sixteen observers were categorized
according to colour vision as (a) colour normals (n = lo), (b) deutans
(n = 2), or (c) protans (n = 4). The new ANOVA showed that colour vision
was a significant factor, and a subsequent statistical test (the Tukey test of paired comparisons18) showed that the protan group was significantly worse than the colour normal and deutan groups with respect to the average
critical smoke density required to reach threshold (p
<
0.001). There wasalso a significant interaction between the factors colour vision and exit
sign (p G 0.03). Both results are illustrated in Figure 10.
The critical smoke densities were consistently lower for the protans than the colour normal and the deutan groups. The inconsistent heights of the columns at the bottom of the figure illustrate the significant
interaction between the factors colour vision and exit sign; the higher columns tend to be associated with red signs, showing that protans were systematically penalized by signs having proportionally more energy in the long wavelengths.
* YI I.O
r
,..!
,,,, COLOUR VISION-
OTHERS ( 2 = 0 . 5 0 1 ' E O. - 0 PROTANS--~~M~~0.4?-1. 0 0 > C,
0 . 6 - Z w 0 W x 0 2 0 . 4 - V) A 4 U - t - a U 0 . 1 I 1 0 1 0 0 1 0 0 0Figure 10. Critical smoke densities for the 13 exit signs for the group of protans and for the group of colour normals and deutans (others)
tested in this experiment (sign numbers at top). Mean values of
critical smoke density for the two groups of subjects are inset. Columns at bottom show, for each sign, the difference in
critical smoke density (Ad) between the two groups of subjects.
The ANOVA also showed a significant interaction between the factors
colour vision and ambient illumination (p < 0.01). The differences between
critical smoke densities for the protan group and the other two groups were smaller with ambient illumination than without. Long wavelengths will be preferentially transmitted through the cosmetic oil smoke employed in this
experiment as indicated by the shift in chromaticity values with increasing
smoke density (Figure 3). Proportionally more energy at long wavelengths
will, therefore, be available to all subjects without ambient illumination than with ambient illumination. This fact and the reduced sensitivity of protans to the proportionally higher energy at long wavelengths when ambient illumination was 'off' likely produced this significant interaction.
No other factor interacted with colour vision to a significant degree in the ANOVA (p 2 0.05).
,
It is possible to make some coarse quantitative comparisons between these data and predictions from the literature. From documented spectral power distributions for appropriate lamps and from typical spectral
sensitivity functions for different classes of observers, it is possible to predict the luminous efficiency of a given light source for protans or deutans relative to colour normal observers. In making the quantitative comparisons, it was assumed that the spectral power distributions of cool-white fluorescent16 and incandescent16 lamps could be used to
they all had coloured, translucent fronts. The two deuteranomalous subjects used in this experiment are not expected to have luminous efficiencies
substantially different from colour normals. l9 Because the data from these
two subjects were not significantly different from those of the colour normal group, the data from the protan group were compared to all other
subjects (colour normals and deutans). It was also assumed that a spectral
sensitivity function for protanopes l6 (Figure 9) could characterize the
spectral response of the group called protans, which in fact also included protanomolus individuals who are more sensitive than protanopes to long
wavelengths (Table 11). These two assumptions introduce errors that tend to
cancel each other. The relative spectral power distributions of the red exit signs were actually higher in the long wavelength region than
characterized by the light sources alone, but, to partially compensate, the spectral sensitivity of the protan group was knowingly underestimated in this region of the spectrum.
The reduction in luminous efficiency for protans relative to colour normals is 13% for a cool-white fluorescent source, and 17% for an
incandescent source operating at 2856 K. These estimates agree favourably
with the differences in critical smoke densities observed between the protans and the other subjects, indicated by the heights of the columns at the bottom of Figure 10. For those signs with red lettering on dark
backgrounds, the overall difference between protans and colour normals in terms of observed critical smoke densities was about 20%.
There are also some finer points that support the hypothesis that colour vision contributed to the differences shown in Figure 10. It was argued in the previous section that subjects used rods to detect Signs 4 and
5 in the absence of ambient illumination. Rod vision is the same for protans, deutans and colour normals. As can be seen in Figure 10, both groups have nearly the same detection threshold for these signs, as
expected. Further, the brighter green signs (2 and lo), seen with cones,
produced shorter columns than the red signs in Figure 10. This is also expected; to protans, compared to other people, red signs would be relatively less efficient than green signs.
F. The age of subjects
Age, like colour vision, cannot be selectively assigned to subjects. Other physiological and psychological factors affecting vision can be
confounded with the age of the observers. Nevertheless, age was included in yet another ANOVA along with the original three experimental variables (exit
sign, threshold criterion, and ambient illumination). The 16 observers were
arbitrarily divided into six age groups (a) under 21, (b) 21-30, (c) 31-40, (d) 41-50, (e) 51-60, and (f) over 60 years. Age groups were significantly
different (p
<
0.001) in the ANOVA, but none of the other factors interactedsignificantly with the factor age (p 2 0.05).
Figure 11 shows the average critical smoke densities for the six age groups. The significant decrease in visibility observed by the middle age
groups is not consistent with the l i t e r a t ~ r e ~ O - ~ ~ and is likely due to a
confounding of age group with colour vision. Two of the three observers in the 31-40 age group were protans with reduced visual efficiency (Table 11). Further, all protan observers were confined to the three age groups
0 I I 1
1 0 2 0 30 40 5 0 6 0 70
A G E G R O U P
F i g u r e 11. Critical smoke d e n s i t i e s f o r t h e s i x age groups of s u b j e c t s t e s t e d i n t h i s experiment a s a f u n c t i o n of g e n e r a l luminance.
A wide body of p u b l i s h e d d a t a i n d i c a t e s t h a t t h e human v i s u a l s y s t e m d e t e r i o r a t e s s t e a d i l y , w i t h i n c r e a s i n g r a t e , from about t h e age of 20. Although t h e r e i s a good d e a l of v a r i a t i o n w i t h i n a g e groups, r e t i n a l i l l u m i n a n c e i s reduced approximately t h r e e f o l d between t h e ages of 20 and
60. Such d e t r i m e n t a l a g e e f f e c t s were n o t e v i d e n t i n t h i s experiment,
perhaps because t h e s m a l l sample was n o t r e p r e s e n t a t i v e of t h e p o p u l a t i o n a t l a r g e . N e v e r t h e l e s s , t h e s e i n e v i t a b l e and i r r e v e r s i b l e d e p r e c i a t i o n s i n v i s u a l c a p a c i t y w i t h age a r e worthy of c o n s i d e r a t i o n and f u t u r e
experimentation.
I V . CONCLUSIONS AND RECOMMENDATIONS
S e v e r a l f a c t o r s were found t o b e important t o e x i t s i g n v i s i b i l i t y through smoke. Some of t h e s e f a c t o r s were d i r e c t l y a s s o c i a t e d w i t h t h e c h a r a c t e r i s t i c s of s i g n s , and i t a p p e a r s t h a t d e s i g n recommendations f o r t r a d i t i o n a l , ' s t a t i c ' e x i t s i g n s c a n be improved. Other f a c t o r s a s s o c i a t e d w i t h t h e b u i l d i n g and t h e o b s e r v e r a l s o i n f l u e n c e e x i t s i g n v i s i b i l i t y . Recognizing a l l of t h e s e f a c t o r s and developing new s t r a t e g i e s f o r improving e x i t s i g n v i s i b i l i t y c o u l d make b u i l d i n g s s a f e r .
Of c o u r s e , s a f e t y i s o n l y one f e a t u r e t o c o n s i d e r i n t h e d e s i g n and t h e o p e r a t i o n of a b u i l d i n g . Energy usage, a e s t h e t i c s , r e l i a b i l i t y , and c o s t a r e a l s o i m p o r t a n t c o n s t r a i n t s on t h e f i n a l b u i l d i n g c h a r a c t e r . They c a n n o t b e i g n o r e d , and f i n a l recommendations and s o l u t i o n s should r e f l e c t t h e s e c o n s t r a i n t s a s w e l l .
A. Sign B r i g h t n e s s
An o b j e c t cannot b e s e e n w i t h o u t h a v i n g some luminous c o n t r a s t w i t h i t s
s i g n s w i l l be d e t e c t a b l e through much h i g h e r smoke d e n s i t i e s . Equipping t r a n s - i l l u m i n a t e d s i g n s w i t h compact, f l u o r e s c e n t lamps would l i k e l y improve t h e b r i g h t n e s s , and t h u s enhance t h e v i s i b i l i t y , of t h e s e s i g n s through smoke. J u s t a s t h e s i g n must have luminous c o n t r a s t w i t h i t s background, t h e l e t t e r i n g on a s i g n must a l s o have luminous c o n t r a s t w i t h i t s background ( i . e . t h e s i g n f a c e ) f o r i t t o be readable. Signs w i t h , f o r example,
t r a n s - i l l u m i n a t e d l e t t e r s and opaque f a c e s (i.e. c u t o u t o r s t e n c i l l e d s i g n s ) w i l l have high c o n t r a s t l e t t e r i n g . P r e s e n t l y , no Canadian n a t i o n a l
s a n c t i o n i n g body provides adequate s p e c i f i c a t i o n s f o r e x i t s i g n b r i g h t n e s s o r l e t t e r c o n t r a s t .
It has been argued t h a t t h e r e a d a b i l i t y of e x i t s i g n s i n c l e a r
c o n d i t i o n s can be reduced i f they a r e t o o bright.2'3 This argument can be somewhat misleading. Unlike r e a d a b i l i t y , t h e d e t e c t a b i l i t y of t h e s i g n may n o t be reduced i f i t i s b r i g h t e r . Although a person may not be a b l e t o read an e x i t s i g n , he o r s h e may s t i l l know t h a t a r e l a t i v e l y b r i g h t and coloured l i g h t p o s i t i o n e d over a doorway i s an e x i t sign. This knowledge would a l s o a i d s a f e e g r e s s . More i m p o r t a n t l y , however, a dim s i g n cannot be r e a d n o r can i t be d e t e c t e d i n smoke, and t h e r e f o r e w i l l not provide a s s i s t a n c e f o r s a f e e g r e s s . B r i g h t e r s i g n s w i l l be more d e t e c t a b l e , even i n c l e a r
c o n d i t i o n s , a t d i s t a n c e s beyond t h e person's r e a d a b i l i t y l i m i t
.*
9 2 4Knowing t h a t t h e b r i g h t ( b u t perhaps unreadable) l i g h t i n t h e d i s t a n c e i s a n e x i t s i g n w i l l a l s o i n c r e a s e t h e occupants' chances f o r s a f e egress.
A r c h i t e c t s and i n t e r i o r d e s i g n e r s may, however, f i n d b r i g h t e x i t s i g n s unacceptable f o r a e s t h e t i c reasons. They a r e concerned p r i m a r i l y w i t h t h e appearances of t h e b u i l d i n g and i t s i n t e r i o r ; any implanted and h i g h l y
v i s i b l e s a f e t y f e a t u r e t h a t d e t r a c t s from t h e a e s t h e t i c s of t h e i r design may be d i f f i c u l t f o r them t o accept. An attempt should be made t o work w i t h a r c h i t e c t s and i n t e r i o r d e s i g n e r s b e f o r e l e g a l requirements a r e made f o r e x i t s i g n b r i g h t n e s s .
B. Sign Colour
North America has t r a d i t i o n a l l y , b u t n o t e x c l u s i v e l y , employed t h e c o l o u r red i n e x i t s i g n design, o f t e n i n c o n c e r t w i t h o t h e r , red f i r e
p r o t e c t i o n equipment. Green, on t h e o t h e r hand, h a s been used most o f t e n i n Europe and now is being used i n c r e a s i n g l y i n t h e United S t a t e s . Without knowing t h e s p e c t r a l power d i s t r i b u t i o n of t h e l i g h t s o u r c e and t h e s p e c t r a l t r a n s m i s s i o n o r r e f l e c t a n c e of t h e coloured f i l t e r o r s u r f a c e , i t i s
impossible t o a c c u r a t e l y determine whether r e d o r g r e e n s i g n s w i l l be more luminous and, t h u s , more v i s i b l e . In p r i n c i p l e , however, green
t r a n s - i l l n m i n a t e d s i g n s should be b r i g h t e r . C e r t a i n l y t h e dominant v i s i b l e wavelengths t r a n s m i t t e d by t h e s e s i g n s should be more e f f i c a c i o u s t o p r o t a n ( r e d i n s e n s i t i v e ) observers. Nevertheless, one has no a s s u r a n c e s about t h e apparent b r i g h t n e s s of t h e s i g n from a q u a l i t a t i v e d e s c r i p t i o n of i t s
c o l o u r , and u s e f u l recommendations mst account f o r t h e p h y s i c s of t h e l i g h t , t h e s p e c t r a l s e n s i t i v i t y of t h e i n d i v i d u a l , a s well a s t h e s p e c t r a l t r a n s m i s s i o n and s c a t t e r c h a r a c t e r i s t i c s of t h e smoke.
Any coloured s i g n w i l l t r a n s m i t l e s s l i g h t and t h e r e f o r e w i l l be less
b r i g h t than a white one w i t h t h e same broad-band wavelength l i g h t source. Based only upon a c r i t e r i o n of photometric luminance, e x i t s i g n s should n o t be coloured. However, c o l o u r can h e l p people d i s c r i m i n a t e between an e x i t s i g n and a n o t h e r white, luminous s o u r c e , l i k e a c e i l i n g f i x t u r e . It may b e
more important, then, to have a coloured sign with somewhat lower luminance than a white sign of higher luminance that might be confused with other light sources in the building. An experiment exploring this hypothesis should be conducted.
The psychological effects of green versus red for exit signs have not been properly studied here or elsewhere. These effects might influence the likelihood that a person will find an exit. For example, a person's
expectations about the meaning of green or red may have some impact on his or her chances for safe egress. The importance of these psychological effects, however, should not be over emphasized in making exit sign recommendations until credible data are available.
C. Spatial characteristics of the sign
Although the size of the sign and the letters on the sign were not
specifically studied here, larger signs will typically be more d e t e ~ t a b l e , ~ ~ and larger letters on signs will be more readable in smoke and over greater
distances.
Unevenly lit lettering will probably be more difficult to read in smoke than uniformly lit letters. Luminous surrounds and downlights will also reduce one's ability to read the exit sign lettering in smoke because of the scatter they produce. Detectability, and perhaps the information content conveyed by the sign, might not be limited, but this is not known for certain. The significance of all these spatial factors in limiting the information conveyed by the exit sign should be studied more carefully in situations similar to those encountered in real buildings.
D. Recommendations for 'static' exit signs
This study has only considered 'static' signs that do not change their luminous characteristics in response to environmental changes. It is
possible to make some preliminary recommendations for static signs from the data collected in this study and the arguments presented before in this section:
1) In order to be visible in smoke the sign should be as bright as possible. Under these conditions electric, trans-illuminated signs are clearly better than self-luminous signs and those signs relying on reflection. However, practical and aesthetic constraints can
(and should) influence the final luminance recommendations.
2) The s i m should be coloured. Although this has not been clearly -.
established, the colour of the sign should help a person
discriminate between other luminous sources in smoke. Green seems a logical colour choice due to its (likely) higher luminous efficacy.
3 ) The sign and its lettering should be large. Large displays are easier to see.
4 ) Signs should be designed to enhance the luminous contrast of the text and to minimize sources of scattered light outside the area
required to read the lettering. Luminous sign faces and down-lights
will limit the contrast of the exit sign letters in smoke and thus reduce their readability.
I n s h o r t ( i f a c o n v e n t i o n a l , s t a t i c e x i t s i g n uust b e recommended) a
b r i g h t , green, l a r g e , c u t o u t e x i t s i g n w i l l l i k e l y be t h e most v i s i b l e
( d e t e c t a b l e and r e a d a b l e ) i n a s m o k e l i l l e d environment.
E. 'Smart' s i g n s
B r i g h t s i g n s a r e n o t needed under a l l c o n d i t i o n s . I n non-emergency
s i t u a t i o n s , people s t i l l want t o f i n d an e x i t , and r e l a t i v e l y dim e x i t s i g n s
w i l l s e r v e t h i s purpose. Also, i n t o t a l l y d a r k i n t e r i o r s (e.
.
a f t e r apower f a i l u r e ) a v e r y b r i g h t s i g n may c r e a t e d i r e c t g l a r e 20-2' and a c t u a l l y a
l i m i t o n e ' s a b i l i t y t o t r a v e r s e a c l u t t e r e d space.26 A s mentioned b e f o r e , very b r i g h t s i g n s may a l s o d e t r a c t from t h e a e s t h e t i c q u a l i t i e s of t h e
b u i l d i n g i n t e r i o r . T h e r e f o r e , s i g n s t h a t a r e b r i g h t i n smoke b u t dim a t
o t h e r times would be advantageous. P h o t o e l e c t r i c o r i o n i z a t i o n d e t e c t i o n of
smoke c o u l d , f o r example, s i g n a l a n i n c r e a s e i n e x i t s i g n b r i g h t n e s s . S i m i l a r l y , a f l a s h i n g e x i t s i g n would be i m p r a c t i c a l f o r e v e r y day
o p e r a t i o n , b u t , i f a c t i v a t e d a f t e r smoke d e t e c t i o n , t h e d e t e c t a b i l i t y and t h e d i s c r i m i n a b i l i t y of t h e e x i t s i g n might b e enhanced i n a smoke f i l l e d i n t e r i o r .
The v i s i b i l i t y of e x i t s i g n s i n smoke i s reduced by s c a t t e r e d ambient
i l l u m i n a t i o n . T h e r e f o r e , i t i s advantageous t o e x t i n g u i s h o r lower t h e
l e v e l of ambient i l l u m i n a t i o n n e a r a n e x i t s i g n i n smoke. F i r e s a f e t y h a s
been a n e g l e c t e d a s p e c t of a u t o m a t i c , c e n t r a l i z e d l i g h t i n g c o n t r o l systems. Such systems c a n be d e s i g n e d t o e x t i n g u i s h o r dim l i g h t s t h a t would
o t h e r w i s e reduce e x i t s i g n v i s i b i l i t y i n smoke. S i m i l a r l y , an automated
l i g h t i n g c o n t r o l s y s t e m c o u l d e x t i n g u i s h t h e e x i t s i g n downlights, p e r h a p s u s e f u l i n c l e a r , no-smoke c o n d i t i o n s , b u t d e l e t e r i o u s i n smoke-filled i n t e r i o r s .
It seems i m p o r t a n t t o develop i n t e g r a t e d f i r e p r o t e c t i o n s t r a t e g i e s
based upon sound p r i n c i p l e s of v i s i b i l i t y . More work o b v i o u s l y needs t o b e
done i n t h i s a r e a , b u t t h i s s t u d y h a s a l r e a d y l e d t o u s e f u l g u i d e l i n e s t h a t c o u l d be i n c o r p o r a t e d i n t o a f i r e p r o t e c t i o n s t r a t e g y f o r b u i l d i n g s i n Canada and abroad.
Acknowledgements
The a u t h o r s a r e g r a t e f u l t o t h e members of t h e DBRINRCC s t a f f who
v o l u n t e e r e d a s s u b j e c t s f o r t h i s experiment. Technical a s s i s t a n c e from
R. F l a v i a n i and c o n c e p t u a l i n p u t from G. W i l l i a m s - k i r , b o t h of DBRINRCC,
a r e a l s o g - a t e f u l l y acknowledged. Thanks a r e a l s o extended t o A. Robertson
and B. C o l l i n s f o r comments on a n e a r l i e r manuscript. F i n a l l y , t h e a u t h o r s
wish t o thank t h e v a r i o u s o f f i c i a l s and manufacturers who were k i n d enough t o s u p p l y t h e s i g n s f o r t h i s s t u d y .
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