Publisher’s version / Version de l'éditeur:
Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n’arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca.
Questions? Contact the NRC Publications Archive team at
PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information.
https://publications-cnrc.canada.ca/fra/droits
L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site
LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB.
Paper (National Research Council of Canada. Division of Building Research); no.
DBR-P-1329, 1985
READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE. https://nrc-publications.canada.ca/eng/copyright
NRC Publications Archive Record / Notice des Archives des publications du CNRC :
https://nrc-publications.canada.ca/eng/view/object/?id=5e8d4f63-d283-4941-9b3b-55ee0716a826
https://publications-cnrc.canada.ca/fra/voir/objet/?id=5e8d4f63-d283-4941-9b3b-55ee0716a826
NRC Publications Archive
Archives des publications du CNRC
This publication could be one of several versions: author’s original, accepted manuscript or the publisher’s version. / La version de cette publication peut être l’une des suivantes : la version prépublication de l’auteur, la version acceptée du manuscrit ou la version de l’éditeur.
For the publisher’s version, please access the DOI link below./ Pour consulter la version de l’éditeur, utilisez le lien DOI ci-dessous.
https://doi.org/10.4224/40001805
Access and use of this website and the material on it are subject to the Terms and Conditions set forth at
Visibility of exit signs through smoke
Clark, F. R. S.; Rea, M. S.; Ouellette, M. J.
Ser
THl
TJ2ld
1 1 ~ 2 3 6
3 .
1329
National Research
Conseil national
c .2
Council Canada
d.
recherches Canada
BrnG
Division of
Division des
- - - ---
Building Research
recherche~
en batiment
Visibility of Exit Signs Through Smoke
by F.R.S. Clark, M.S. Rea and M.J. Ouellette
Appeared in
Pre-conference Proceedings
AWALV%?r?
International Conference on Building Use
and Safety Technolo y
p. 75-80
Rn
Los Angeles, CA., 12
-
14 arch 1985
(DBR Paper No. 1329)
Price $2.00
NRCC 25047
I - ~ S U M ~ ?
Gr3ce 3
16
observateurs, on a pu determiner les densites de
fumee ngcessaires pour reduire la visibilitg de
13 panneaux
"sortie" jusqu'aux seuils de reperage et de lisibilitg, avec
I
I
des eclairages ambiants fort et faible.
Connaissant les
caractgristiques de la fumge et de la vision humaine, on a pu
en tirer des conclusions concernant les facteurs qui influent
sur la visibilitg des panneaux "sortie" dans la fude.
- -
-
- - --- -
VISIBILITY OF EXIT SIGNS THROUGH SMOKE Ferrers R.S. Clark, Mark S. Rea, Michael J. Ouellette
National Research Council Canada Ottawa, Canada
ABSTRACT
Using 16 observers, the smoke densities required to reduce the visibility of each of 13 exit signs to threshold limits of detectability and readability were determined at both low and high ambient illuminations. Supported by known properties of smoke and the human visual system, some conclusions can be drawn from these data about the factors that influence exit sign visibility through smoke.
INTRODUCTION EQUIPMENT
The exit sign is an important component of modern fire protection systems in
buildings. It is expected to be visible through smoke.
Standards for exit signs are numerous and differ widely in details related to
visibility. The National Building Code of Canada (NBC) (1980) and the Canadian General Standards Board (CGSB) (19781, for example, differ in their requirements for sign luminance, colour and letter size.
A study of exit sign visibility through smoke, based on both photometric measurements and observations by volunteers, was conducted at the request of the CGSB by the Division of Building Research, National Research Council Canada. The procedures and results are presented here; more details are available in Rea, Clark and Ouellette. 1985.
The 13 signs used in this study are described briefly in Table 1. The majority were lighted by incandescent or fluorescent
lamps mounted behind translucent lenses which incorporated red or green lettering or symbols. Two "self-luminous" signs were also tested. Chemiluminescent tubes activated by beta emission from tritium gas provided illumination for these signs in the dark. The luminances of these two signs were greater in room lighting, due to diffuse luminous reflec- tion from the sign surface, than in the dark.
The signs were mounted at one end of a smoke chamber (Figure l), which could be filled with cosmetic oil dispersion smoke. The density of the smoke was measured with a
HeNe laser and a photodetector in the smoke chamber. A transparent (transmission = 0.92) plastic window separated the smoke chamber from a darkened observation chamber. Both
photometric measurements and visual evaluations were conducted from the observation chamber. It also contained controls for the smoke generator, the ambient illumination, the exit signs, and the smoke density monitor.
PHOTOMETRY Luminance
The luminance of a large circular area on the front of each sign was measured with a Pritchard photometer (Model 1980A), both with and without ambient illumination (Table 1).
'General luminance' refers to those measure- ments conducted without ambient illumination. Chromaticity
The CIE chromaticity coordinates (Wyzsecki and Stiles, 1982) for a white, transilluminated area of sign 1, were determined through several smoke densities
Table 1 Exit Sign Characteristics Large field
luminance (lights on,
Sign Script, lights off) Light No. Colours glyph (cd~rn-~) source
1 red, white 2 green 3 red, white
4
green 5 green 6 red 7 red EXIT/ SORTIE EXIT, triangle EXIT, triangle EXIT, arrow EXIT, triangle EXIT, triangle EXIT 292, 291 2 x 25w incandescent 18, 14 2 x 15w incandescent 51, 46 2 x 15w incandescent 12, 0.18 tritium 19, 0.61 tritium 170, 170 7w, 9w fluorescent 36, 22 2 x 15w 8 white, EXIT, 38, 29 red triangle 9 red EXIT, 231, 232 SORTIE 10 green EXIT, 391, 391 triangle 1 1 red, EXIT, 1272, 1277 white triangle 12 red EXIT 342, 281 13 white, EXIT, 506, 498 red triangle incandescent 2 x 15w incandeecent 2 x 25w incandescent 1 x 9w fluorescent 1 x 9w fluorescent 1 x 9w fluorescent 1 x 9w fluorescent(Figure 2). Values were based upon measure- ments through the broadband blue, red and green filters in the Pritchard photometer.
Fig. 2. CIE chromaticity coordinates for a white luminous region of sign 1 at different smoke densities. X and Y are dimensions in the CIE system used to characterize colours. The points are labelled in units of OD m-l.
PSYCHOPHYSICAL OBSERVATIONS Observers
Sixteen volunteers made threshold visibility evaluations of each sign through smoke. Ten of the observers had normal colour vision; four were protans (their sensitivity to long wavelengths was depressed relative to colour-normal observers) and two were deutans (their sensitivity to middle wavelengths was slightly depressed relative to colour-normal observers) (Wyzsecki and Stiles, 1982; Hsia and Graham, 1965). All observers had normal acuity in at least one eye, and wore
corrective lenses, if required, during visual screening and sign observations.
Test Protocol
The observer and the experimenter were seated in the dark observation chamber, ten minutes prior to making observations. The
experimenter presented the dimmest sign to the m N 9
P In observer with no light or smoke in the smoke
chamber. Threshold limits (critical smoke 1 . 0 ,
, , f . , ,
.
. , . , , , , ,densities) of readability and detectability were determined by slowly introducing and evenly distributing smoke in the smoke chamber (a sign became unreadable at a lower smoke
density than it became undetectable). 0 . 8 -
0
0
This procedure was continued with
successively brighter signs until the critical t
r
smoke densities had been recorded for each m
-
0 . 6 -sign, for both threshold conditions, both with z
and without room illumination. A total of 52 D
W
judgments were made by each observer, one Y
judgment per condition.
?
0 . 4 -"7 2 d RESULTS o
-
r-
The data were submitted to a three-way u 0 . 2 -
repeated measure analysis oE variance (ANOVA) (Table 2, Myers, 1972).
Sign Luminance
The ANOVA showed that the 13 signs were significantly different in their visibility
through smoke. A linear relationship
(r = 0.86) existed between critical smokc
density (averaged over all conditions of
threshold crlteria and ambient I. 1111minat Lon)
and log general 111minance (FLgure 3 ) . Cle~rly.
however, there ts varlatton aho~it thin slnglc', straight-line characterlzation (cross-l~atcl~~rl area, Figure 3 ) and therefore gelrer;il
luminance cannot he taken as n completely
adequate specificatton for sign vtsihi lity
.
Table 2 Analysis of Variwl~ce Eur Critical
Smoke Density* Source of Sum oE dE Variation Squares
--
S 20.7 12 R 16.0 1 C 1.34 L S x R 1.54 12 S x C 0.182 12 R x C 0.085 1 S x R x C 0.076 12 Mean Square---
1.73 16.0 1.34 0.128 0.015 0.085 0.006 S: exit sign R: ambient illumination C: threshold criterion*For an explanation of Analysis of Variance and the terms in this table, see any text on statistics (e.g. Myers, 1972).
1;INIRAL L U M I N A N C E , c d r n - 2
t . 3. Ik?lit?ndence of cr ttical smoke density
011 gt?nerill ll~mlrlance of exLt n i g n ~ (sign
ll~l~lllll!r* a1 top).
Ambient Illumination
Crltlcal smoke densities were
eignifica~~tly lower when the room lights were
'011' rather than 'oEf
',
because roomil Lr~minat ion increases the amount of scattered
Light in the smoke chamber (Figure 4). There
was also a significant interaction between the variables 'sign' and 'ambient illumination'
(S and K in Table 2). The interaction
demonstrated that some signs were more affected by scatter than others.
Ambient illlimination also influenced the critical smoke density required for
detectability diEferently from that required Eor readability. Figure 5 illustrates the significant interaction between the variables
'ambient illumination' and 'threshold
criterion'. The difference between the two
visibility criteria was greater when room lights were 'off' (0.10) than when they were 'on' (0.06).
Fig. 4. Critical smoke density as a Functioq of general luminance for both levels of ambient illumination (sign numbers at top).
R E A D A B I L I T Y DETECTABILITY
OFF 0 N
A M B I E N T I L L U M I N A T I O N
Fig. 5. Critical smoke density for both levels of ambient illumination and both threshold criteria.
Visibility Threshold
The ANOVA revealed a significant interaction between the two variables 'sign' and 'threshold criterion'. To help illustrate this interaction, Figure 6 includes a histo- gram of the differences in critical smoke den- sities for both criteria and for each sign; if there had been no significant interaction, the heights of all the columns would be the same.
The highest columns in Figure 6 are typically associated with electric signs that have: light-emitting apertures or 'down- lights', Luminous areas around the letters, nnn-uniform luminous d i s t r i b u t i o n s on the sign face, or low contrast or small letters. All o f these Factors served to reduce sign read- ability more than detectability, in smoke. Colour Vision
Observers with different spectral sensitivities were intentionally included in this study; colour normals, protans and
I
T H R E S H O L D C R I T E R I O NI
- 2
GENERAL L U M I N A N C E , c d rn
Fig. 6. Critical smoke density as a function of general luminance for both threshold criteria. Histogram at bottom shows, for each sign, the differences in critical smoke densities (Ad) between threshold criteria
deutans (Wyzsecki and Stiles, 1982; Hsia and Graham, 1965) were tested. Although not part of the three-variable experimental design, colour vision was included as a variable in a subsequent ANOVA. Critical smoke densities for colour normals and deutans were not significantly different, but the difference between the protans and the other observers was significant. The magnitude of this difference (Figure 7) was consistent with the literature (Wyzsecki and Stiles, 1982).
COLOUR VISION
0 NORMALS & DEUTANS
0 PROTAHS ---..---
R
Fig. 7. The effect of colour vision on sigli visibility (sign numbers at t o p ) .
Wavelength Dependent Scatter
Signs dominated by long wavelength emissions (i.e. red signs) were less
susceptahle to scattering by smoke. This was a relatively small effect, hut the shift in chromaticity values, recorded Erom the white area of sign 1, as smoke density increased, clearly demonstrated the preferential scatterring of short wavelengths by the cosmetic smoke (Figure 2). Jin (1978) measured the spectral transmission of several smokes and found scattering behaviour
consistent with the chromaticity shift
discussed here. He also found smokes that did
not exhibit this behaviour; differences in the scattering properties depend upon the kinds of smoke and their densities.
Observer Age
The age of the observers ranged from 19 to 63 years. A wide body of published data
(Wright and Rea, 1984) indicates that the human visual system deteriorates with increasing rate from the age of about 20 years. Although there is considerable variation within age groups, retinal illumination is reduced approximately
threefold between the ages of 20 and 60. Such detrimental effects of age were not evident in this experiment, perhaps because the small sample of observers is not representative of the population at large. Nevertheless, these inevitable and irreversible depreciations in visual capacity with age are worthy of consideration and future experimentation.
CONCLUSIONS
Tile results of this study suggest that several characteristics of currently recommended exit signs are not conducive to good visibility through smoke.
Sign brightness was found to strongly influence visibility; the brighter the sign the more visible it was through smoke. Thus Me contend that sign luminances should be high in smoke. This is at variance with sign recommendations in the USA (National Fire Protection Association, 1981) and the UK (British Standards Institution, 1978), where maximrim luminance levels are specified.
Yaximum luminance levels are set for aesthetic reasons and also to avoid loss of acuity of very distant signs. Our suggestion could be satisfied if signs were bright in smoke and dim at other times.
Extraneous light sources should be diminished in smoke to reduce the effect of scatter and the confusion between exit signs and other light sources. In particular, when smoke is in a building, ambient illumination near the sign should be extinguished or reduced; l~~~ninous regions surrounding lettered areas should be eliminated; and down-lights on signs should be extinguished.
Distinctive colours are probably useful for exit signs. Colour has been recognized as important, although there is little consensus, even within countries, for any given colour;
green and red are the most commonly recommended. Colour may, for example, aid occupants in discriminating between an exit sign and another luminous source, such as 4
fluorescent light fixture. Support for a particular colour has not been well grounded in theory or experimentation. Preferential scatter of short wavelengths by smoke would suggest that red signs should he used. Protans, however, who comprise about 2.5% of the Caucasian population (Hsia and Graham, 1965), will be less sensitive to red signs than colour normals. For protans, therefore, it would be better if exit signs were green. Most importantly perhaps, materials used for green sign faces will probably transmit more visible radiant energy to all occupants than will the materials used for red signs.
All things considered then, it is probably better not to have red exit signs. Nevertheless, it is impossible to make sensible statements about colour without proper experimentation and adequate
specification of the optical properties of the signs and smoke, as well as the visual
capacities of people. No sanctioning body presently takes these factors into account, but ultimately they must do so in order to make adequate recommendations for exit sign visibility. We hope this study poi~l, 111t J* to more adequate sperif i cat LOO? *,f e i i t sign
visibility 1 1 1 smoke.
The authors recognize the major contri- bution to this work by several colleagues, including Mr. Raymond Flaviani, Mr. George Williams-Leir and the 16 volunteer observers.
This paper is a contribution ~f the Division of Building Research, National
Research Council of Canada, and is p~iblishl~fl with the approval of the Director of the Division.
KEFEKENCES
British Standards Institution, SpeciFic?tions for Exit Signs (internally illumi~~ated), BS2560: 1978, London, 1978.
Hsia, Y. and Graham. C.H., Colour Blindness, in Vision and Visual Perception.
-
C.H. Graham, Ed., Wiley and Son, NY, 1965.
Jin, T., Visibility through Fire Smoke. J.
Fire and Flammability,
9,
135-155, 1978. Myers, J.L., Fundamentals of ExperimentalDesign. Allyn and Bacon, Boston, 1972. National Building Code of Canada 1980,
Sections 3.4.6 and 9.9.10, National Research Council of Canada, Ottawa,
1980.
National Fire Protection Association (USA), Code for Safety to Life from Fire in Buildings and Structures, NFPA 101-1981,
101-22, Quincy, MA, 1981.
Rea, M.S., Clark, F.R.S., and Ol~ellette, M.J., Photometric and Psychophysical
Yeasurements of Egress Signs through Smoke, to be published as a DBR Paper, Division of Building Research, National Kesesrch Council Canada, Ottawa, 1985. Yright, G.A. and Rea. M.S., Age, A Human
Fartnr in Lighting, &Proceedings of the
1984 I~lternational S?i6erence on
~c.,.trnat i~nal Ergonomics, Tnronto.
-
1,~ c e - 5 1 2
:
i 9 8 4 )Wyzsecki, G. and s t i i ~ , . W . S . , Zolor Science Wiley and Son, NY, 1982.
Canadian Government Specifications Board (now Canadian General Standards Board), Standard for Exit Lighting Fixtures,
r e p r i n t form by t h e D i v i s i o n of B u i l d i n g
R e s e a r c h ,
remains
t h e c o p y r i g h t
of
t h e
o r i g i n a l p u b l i s h e r .
It s h o u l d n o t
be
r e p r o d u c e d i n whole o r i n p a r t w i t h o u t t h e
p e r m i s s i o n of t h e p u b l i s h e r .
A
l i s t
of a l l p u b l i c a t i o n s a v a i l a b l e from
t h e D i v i s i o n
may
be o b t a i n e d by w r i t i n g t o
t h e P u b l i c a t i o n s S e c t i o n , D i v i s i o n of
B u i l d i n g
R e s e a r c h ,
N a t i o n a l
R e s e a r c h
C o u n c i l
of
C a n a d a ,
O t t a w a ,
O n t a r i o ,
K l A
0R6.
Ce document
est
d i s t r i b u g s o u s forme de
t