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Tests of soft floor coverings using a 25-foot tunnel furnace
NATIONAL RESEARCH COUNCIL OF CANADA DIVISION O F BUILDING RESEARCH
TESTS O F SOFT FLOOR COVERINGS
USING A 25-FOOT TUNNEL FURNACE
A . R o s e F i r e Study N o , 3 3 of the D i v i s i o n of Building R e s e a r c h Ottawa M a r c h 1974
TESTS O F SOFT FLOOR COVERINGS USING A 25-FOOT TUNNEL
FURNACE by A. Rose
ABSTRACT
The testing of c a r p e t s and vinyl r o l l flooring f o r f l a m e s p r e a d r a t e and smoke evolution i n the 25-foot tunnel furnace in the m a n n e r specified by ASTM E84 i s neither r e a l i s t i c n o r convenient. By m o d i - fying the f u r n a c e and the p r o c e d u r e t o p e r m i t testing on the floor instead
of on the ceiling, m o r e meaningful r e s u l t s a r e obtained a t reduced c o s t of m a t e r i a l s and in l e s s time. The r e s u l t s of testing a wide v a r i e t y of c a r p e t s in both m o d e s of mounting, with and without undercushioning
,
emphasize the d i f f e r e n c e s in behaviour of the m o r e important n a t u r a l and synthetic f i b r e s and blends. The a p p a r e n t advantages of testing on the floor of the f u r n a c e w e r e sufficient t o justify the incorporation of t h i s method in a new standard {CSA B54.9-1972), which is invoked in the control of floor covering h a z a r d s in c e r t a i n a r e a s of h i g h - r i s e build- ings in r e c e n t r e v i s i o n s of the National Building Code of Canada.ESSAIS DE REVETEMENT DE SOL MOUS E F F E C T U E S AU MOYEN D'UN FOUR A TUNNEL DE 25 PI p a r A. Rose
RESUME
L1ex6cution, selon la n o r m e ASTM E84, d f e s s a i s de t a p i s e t de r e v t t e m e n t s d e s o l en rouleau vinylique d a n s le but d f 6 t a b l i r l e u r indice d e propagation d e s f l a m m e s e t l e u r d6gagement de la furn6e d a n s un four
'a
tunnel de 25 pi, n t e s t n i r k a l i s t e n i commode. Une modification du four e t de l a m6thode'a
s u i v r e d e f a s o n'a
ex6cuter d e s e s s a i s au plancher a u lieu du plafond donne, e n un dClai plus rapproch6, d e s rCsultats plus s a t i s - f a i s a n t s e t'a
un coQt de m a t g r i a u x rkduit. L e s r 6 s u l t a t s d y e s s a i dlunevari6tC de t a p i s au moyen de s deux mCthodes d e montage soulignent l e s differences de comportement d e s f i b r e s n a t u r e l s e t synthgtiques e t d e s m 6 l a n g e s l e s plus importants. L e s avantages a p p a r e n t s dlun e s s a i a u plancher dtun f o u r ont Ct6 s u f f i s a n t s pour justifier lsincorporation de c e t t e m6thode d a n s une nouvelle n o r m e (CSA B54.9-1972) mentionn6e d a n s l e s
r6visions rCcentes au Code national du bdtiment du Canada,
'a
la Sous- section s u r l a d6fense contre l e s d a n g e r s de r e v t t e m e n t de s o l en c e r t a i n s e n d r o i t s d a n s l e s i m m e u b l e s de grande hauteur.TESTS OF SOFT FLOOR COVERINGS USING A 25-FOOT TUNNEL FURNACE
by A. Rose
The Associate Committee on the National Building Code of the National R e s e a r c h Council of Canada h a s been concerned f o r some t i m e with the potential contribution of finish floor m a t e r i a l s t o the g e n e r a l h a z a r d due t o combustible m a t e r i a l s in h i g h - r i s e buildings. The Committee on F i r e T e s t s of Building Construction and M a t e r i a l s of the Canadian Standards Association (CSA) h a s a l s o been i n t e r e s t e d in the development of a method of evaluating t h e i r contribution t o f i r e hazard in buildings of a l l types.
The ASTM E84-70 25-ft tunnel t e s t is the m o s t widely used North American method f o r determining the f l a m e - s p r e a d c l a s s i f i c a - tion (FSC), fuel contributed ( F C ) , and smoke developed (SD) of con- ventional building m a t e r i a l s . This t e s t , in which the sample is exposed f a c e down over the firebox, lacks both r e a l i s m and convenience in the evaluation of c a r p e t s and other soft floor coverings. Other methods, both s m a l l - and mediurn-scale, have been developed f o r testing c a r p e t s , but the values they produce a r e not readily r e l a t e d to other flame - s p r e a d
ratings o r t o the potential h a z a r d s involved, and they do not lend t h e m s e l v e s t o the m e a s u r e m e n t of smoke developed.
With the publication of CSA B54.9-1972, a modification of the E 84 tunnel t e s t h a s been accepted by some Canadian authorities a s an i n t e r i m approach t o the l a r g e - s c a l e testing of soft floor coverings f o r FSC and SD. This method, in which the sample is placed on the floor of the tunnel, i s now invoked in r e c e n t revisions of the National Building Code of Canada (NBC 1970) that affect finish floor m a t e r i a l s in c o r r i d o r s and exits of high-rise buildings.
The f i r s t p a r t of the work reported h e r e , covering 2 5 c a r p e t s and six undercushion m a t e r i a l s , was initiated at the request of the Sub-
committee on Miscellaneous F i r e T e s t s of the m a i n CSA c o m m i t t e e . At the t i m e of testing it was known that m a n y t e s t s of c a r p e t s glued to
1/4-in. high-density (125 lb/cu ft) a s b e s t o s - c e m e n t board (HDACB) with a silicate adhesive had been c a r r i e d out by Southwest R e s e a r c h
I n s t i t u t e (SwRI) on the ceiling of t h e i r E 8 4 tunnel f u r n a c e . T h e s c c a r p e t s w e r e t e s t e d t o a s s e s s t h e i r a c c e p t a n c e u n d e r t h e s t a n d a r d s f o r f l a m e s p r e a d e s t a b l i s h e d by t h e U . S. D e p a r t m e n t of H e a l t h , E d u c a t i o n and W e l f a r e and c e r t a i n s t a t e j u r i s d i c t i o n s f o r c a r p e t s
i n s t a l l e d in h o s p i t a l s and o t h e r public buildings. The r e s u l t s of s i m i l a r t e s t s on C a n a d i a n - m a d e c a r p e t s c a r r i e d out i n t h e
U.
S. A. had been s u b m i t t e d t o C a n a d i a n a u t h o r i t i e s f o r c o n s i d e r a t i o n . M o r e r e c e n t l y , U n d e r w r i t e r s 1 L a b o r a t o r i e s of C a n a d a ( U L C ) have l i s t e d s e v e r a l c a r p e t s 2 ( d e s i g n a t e d a s "wall c o v e r i n g s " ) t e s t e d in t h e s a m e m a n n e r .B e c a u s e t h e t e s t i n g of c a r p e t s on t h e ceiling by t h e E 84 method had been widely c r i t i c i z e d in t h e U . S . A . , C a n a d i a n a u t h o r i t i e s in t u r n q u e s t i o n e d t h e validity of s o m e of t h e r e s u l t s s u b m i t t e d t o t h e m a n d , like t h e CSA C o m m i t t e e , e x p r e s s e d the n e e d f o r a m o r e m e a n i n g f u l l a r g e - s c a l e c a r p e t t e s t t o s u p p l e m e n t t h e "modified p i l l t e s t . 1 1 3
B e f o r e t h e i n i t i a t i o n of t h e w o r k r e p o r t e d h e r e , a m o d e r a t e n u m b e r of t e s t s of c a r p e t s , linoleum and vinyl t i l e mounted on t h e f l o o r of t h e
tunnel had been c a r r i e d out a t SwRI, a s w e l l a s a few on c a r p e t s a t DBR. A f t e r reviewing t h e s e i t w a s d e c i d e d t o p r o c e e d with t h e t e s t i n g of a wide v a r i e t y of c a r p e t s m o u n t e d on both f l o o r and c e i l i n g , with a
l i m i t e d s t u d y of t h e e f f e c t s of u n d e r l a y m e n t s with both m o d e s of mounting.
M o d i f i c a t i o n s in P r o c e d u r e
-
F l o o r T e s t sIn addition t o t h e obvious s t e p of slanting t h e n o z z l e s of t h e T e e - b u r n e r f o r w a r d and downward a t 45 d e g . , and m i n o r c h a n g e s i n t h e ignition s y s t e m , no m o d i f i c a t i o n s t o t h e t u n n e l f u r n a c e w e r e n e c e s s a r y . A f t e r a few r u n s with f o a m - b a c k e d c a r p e t s i t w a s c o n s i d e r e d a d v i s a b l e t o i n t e r p o s e a s h e e t of No. 14 a s b e s t o s p a p e r ( 1 4 l b / ~ s q f t ) between c a r p e t and b r i c k t o f a c i l i t a t e c l e a n - u p . T h i s p a p e r w a s u s e d u n d e r a l l c a r p e t s and u n d e r c u s h i o n s i n t h e l a t e r s t a g e s of t h i s p h a s e of t h e w o r k . P r e l i m i n a r y t r i a l s with plywood on t h e f l o o r s u g g e s t e d t h a t i t w a s n e c e s s a r y t o r e t a i n t h e u s e of t h e s i x t u r b u l e n c e - i n d u c i n g G - 2 6 f i r e b r i c k s n o r m a l l y employed i n r e g u l a r t e s t s (Appendix A , Note 1 ) t o e n s u r e a r e a s o n a b l y s y m m e t r i c a l f l a m e p r o p a g a t i o n p a t t e r n in f l o o r t e s t s .
S o m e c a r p e t s , p a r t i c u l a r l y h e a v y nylon type
.;
with polypropylene p r i m a r y backing, t e n d t o "balloon" u n d e r t h e impingeing f l a m e and r o l l i n w a r d f r o m t h e e d g e s a t t h e s t a r t of t h e t e s t . T o m i n i m i z e t h eb u r n e r piping, s h o r t lengths of 1/2- by 1/2-in. s t e e l b a r o r 3/4-in. angle i r o n w e r e laid along t h e e d g e s and a c r o s s the width of the f l o o r behind the line of the b u r n e r n o z z l e s . In conjunction with the a f o r e
-
m e n t i o n e d b r i c k s , t h e s e u s u a l l y kept t h e c a r p e t in place until i t w a s n e a r l y consumed.Modifications i n P r o c e d u r e
-
Ceiling T e s t sIn t e s t s on the ceiling, the c a r p e t s and u n d e r c u s h i o n s w e r e glued and s t a p l e d t o 1/4-in. low-density (40 t o 45 lb/cu f t ) a s b e s t o s - c e m e n t b o a r d (LDACB). In the c a s e of f o a m - b a c k e d c a r p e t s t h e a d h e s i v e w a s a h i g h - s o l i d s n e o p r e n e l a t e x m a s t i c i n s t e a d of t h e thickened s i l i c a t e u s e d with jute -backed t y p e s .
When pronounced dripping w a s anticipated in t e s t i n g shag
c a r p e t s , No. 14 a s b e s t o s p a p e r w a s p l a c e d on the f l o o r . The p a p e r d o e s
-
i n c r e a s e the a p p a r e n t FSC f o r nylon s h a g s in m o s t c a s e s , a s w a sfound d u r i n g t h e National B u r e a u of S t a n d a r d s (NBS) round robin t r i a l s of 19724 and l a t e r w o r k h e r e .
Difficulties in O b s e r v a t i o n of Endpoint
In t e s t s of c a r p e t s of high s m o k e evolution ( e i t h e r c e i l i n g - o r f l o o r -mounted), o b s c u r a t i o n of the windows m a d e o b s e r v a t i o n of the f l a m e f r o n t and d e t e r m i n a t i o n of the "time t o 19. 5 ft" ( v i s u a l endpoint) difficult. T h i s w a s o v e r c o m e by i n s e r t i n g m i c a d e f l e c t o r s in the l a s t t h r e e o r f o u r window r e c e s s e s ( t h e windows a r e inside-mounted i n the DBR tunnel) t o k e e p c l e a r a s m a l l a r e a of t h e d o w n s t r e a m end of t h e h i g h - s i l i c a g l a s s . T h i s expedient g i v e s s a t i s f a c t o r y r e p e a t a b i l i t y .
When t h e f l a m e f r o n t did not r e a c h the end, a s in the c a s e of a c r y l i c o r wool c a r p e t s glued d i r e c t l y t o LDACB, fouling of the windows w a s u s u a l l y not bad enough t o hinder o b s e r v a t i o n of the f l a m e f r o n t a t m a x i m u m t r a v e 1.
D i s c u s s i o n of R e s u l t s ( C a r p e t s 1
-
25)The r e s u l t s f o r the c a r p e t s and c a r p e t -undercushion c o m b i n a - t i o n s a r e p r e s e n t e d in Table I, and f o r r e d oak flooring, low-density
c e l l u l o s i c f i b r e b o a r d and the s i x u n d e r c u s h i o n s in Table LA.
The v a l u e s f o r f u e l contributed ( F C ) a r e not included b e c a u s e t h e significance of t h i s v a l u e , p a r t i c u l a r l y in the c a s e of f l o o r c o v e r i n g m a t e r i a l s , i s c o n j e c t u r a l . T h e d e t e r m i n a t i o n of ignition t i m e ( I T , in
s e c o n d s ) i s not c a l l e d f o r in e i t h e r ASTM E 8 4 o r CSA B54.9, but i s c a r r i e d out routinely whenever p o s s i b l e and i s c o n s i d e r e d useful.
In the e a r l y s t a g e s of t h e w o r k r e p o r t e d h e r e the r e l a t i o n s h i p between the r e s u l t s f o r ceiling and f l o o r mounting without u n d e r
-
cushioning, even in t e r m s of ranking, a p p e a r e d e r r a t i c . A s m o r et e s t s with u n d e r c u s h i o n s w e r e r u n and the p e c u l i a r i t i e s i n the behaviour of t r i a c e t a t e , a c r y l i c and a c r y l i c / m o d a c r y l i c c a r p e t s b e c a m e m o r e obvious, the c o r r e l a t i o n a p p e a r e d m o r e p r o m i s i n g , b e a r i n g in m i n d t h a t t h e FSC values f o r s y n t h e t i c - f i b r e shag c a r p e t s t e s t e d on the ceiling m a y be high.
The c o n s i s t e n t l y low ignition t i m e s f o r t r i a c e t a t e , a c r y l i c and
wool c a r p e t s , r e g a r d l e s s of u l t i m a t e f l a m e - s p r e a d c l a s s i f i c a t i o n a r e note
-
worthy. A c r y l i c and a c r y l i c / m o d a c r y l i c c a r p e t s burn t o a h a r dr e s i d u e which, in s o m e tufted loop t y p e s , i s a l m o s t a c a r b o n r e p l i c a of the pile. Heavy p l u s h e s b u r n t o a f i r m p e r f o r a t e d c r u s t . Light- weight tufted wool c a r p e t s behave m u c h like a c r y l i c s , and like t h e m a s will be shown, give g r e a t e r i n c r e a s e s in smoke developed with u n d e r - c u s h i o n s than s t r u c t u r a l l y s i m i l a r nylon o r polypropylene c a r p e t a .
E x c e p t f o r heavy wool c a r p e t No. 1 , the f l a m e f r o n t always r e a c h e d the end of t h e tunnel in l e s s than 5. 5 m i n u t e s in t e s t s on t h e
f l o o r . In t h e c a s e of s o m e a c r y l i c s , e . g o
,
Nos. 3 and 5, and t r i a c e t a t e s , e . g . , Nos. 14 and 16, the advance of the f l a m e f r o n t , e i t h e r on t h e f l o o r o r with undercushioning on the c e i l i n g , w a s not smooth and w a s c h a r a c t e r i z e d by two o r t h r e e m a x i m a o r inflexions in the t e m p e r a t u r e - t i m e c u r v e( F i g . 1 ) A r a p i d advance a l m o s t t o t h e end, followed by a r a p i d r e c e s s i o n , m a d e a c c u r a t e d e t e r m i n a t i o n of t h e endpoint m o r e difficult due t o p a r t i a l o b s c u r a t i o n of t h e windows. B e c a u s e of deposition of soot on the vent-end t h e r m o c o u p l e , reading of the "time to 980°F", which i s a r e a s o n a b l e approximation in the c a s e of m a n y m a t e r i a l s of low SD, b e c o m e s a l e s s r e l i a b l e indication in t h e c a s e of c a r p e t s and p l a s t i c s , among o t h e r s .
The r e s u l t s of ceiling t e s t s without undercushioning f o r Nos. 3, 5, 14, 17 and 20 r e f l e c t s o m e of the d i f f i c u l t i e s e n c o u n t e r e d in the U.S.A. in t e s t i n g on HDACB and the r e s u l t a n t c r i t i c i s m s of the l a c k of r e p e a t a b i l i t y in t h i s m o d e . I t w a s suggested by 3 . H. M c G u i r e of DBR/NRC that a n "adjusted index" be applied when, in s u c h t e s t s on t h e c e i l i n g , the f l a m e f r o n t advanced r a p i d l y beyond the 10-ft m a r k (FSC>51) but f a i l e d t o r e a c h the end (19. 5 f t ) l a t e r . The index p r o p o s e d w a s :
2 5d
FSC - =
-
where
d
=
distance of flame spread, ftt
= t i m e t o maximum flame spread, min.
This adjusted index agreed much m o r e satisfactorily with the r e s u l t s f o r floor mounting and/or undercushioned ceiling mounting f o r the a c r y l i c s and t r i a c e t a t e s exhibiting anomalous behaviour, but i s not applicable in the case of No. 17 (heavy acrylic) and No. 20 (light nylon), where the advance was slow and regular.
In reviewing the r e s u l t s in Table I it should be emphasized
that, in addition to differences due t o changes in technique and improve- ments through t r i a l and e r r o r , the few duplicate runs reported m a y have been made weeks o r even months apart. In the e a r l y stages of the work, f o r example, the angle of the Tee-burner nozzles had not been made reproducible f r o m run t o run by m e a n s of indexing notches; asbestos paper was not always used in the t e s t s of jute-backed c a r p e t s on the floor; and the variability in FSC, SD and IT to be expected in a given r o l l of carpet was unknown.
The p r e s c r i b e d u s e of asbestos paper in B54.9 t e s t s can be justified on grounds other than those of convenience in clean-up and protection of the soft G-26 f i r e b r i c k floor. Insertion of the c a r p e t , o r carpet plus undercushion, repositioning of the bricks and steel weights, and adjustment of the angle of the Tee-burner nozzles appreciably i n c r e a s e the "soak timet' (the interval between placing of the sample and ignition of the burner) over that required for inserting top-mounted samples glued to ACB (usually in four equal sections). The asbestos paper insulates the samples f r o m the preheated brick of the floor ( p r e -
scribed surface temperature 95 t o 105OF). P a r a l l e l t e s t s with a heavy nylon carpet showed that i t increased IT f r o m 67 t o 82 s e c . , reduced SD from 473 t o 441, and did not change FSC at all. The minor effects of hair felt undercushioning on FSC and SD in floor t e s t s of nylon and polypropylene c a r p e t s support the reasonableness of this expedient and i t s use in subsequent work. It i s prescribed in CSA B54.9.
Examination of the r e s u l t s for red oak flooring and fibreboard (Table IA) and observation of the behaviour of c a r p e t s in many floor t e s t s led to the conclusion that the established techniques of warmup and calibration and the prescribed methods of calculating FSC and SD a s in E 84 t e s t s should be retained until m o r e information was available (Appendix A, Notes 2 and 3).
It should be noted in passing that c a r p e t s 2, 3, 7, 8, 9, 14, 15 and 16 failed the modified pill test.
F u r t h e r T e s t s
-
F l o o r MountingThe introduction in the 1970 edition of the National Building Code
of Canada of provisions concerning E 84 ratings of FSC and SD of
finish floor m a t e r i a l s in h i g h - r i s e buildings (Table
II)
was obviously a m a t t e r of concern t o the c a r p e t industry. In o r d e r t o a s s e s s theimplications of these r e q u i r e m e n t s and t o broaden the base of infor- mation on available Canadian c a r p e t s the industry supplied a number of c a r p e t s representing a reasonable c r o s s - s e c t i o n of c u r r e n t production. Of the 30 c a r p e t s supplied by the industry 1 5 w e r e nylon. Some w e r e t e s t e d on the ceiling with 40-02. h a i r felt (glued and stapled t o LDACB) with chicken w i r e support and additional stapling through c a r p e t and felt. Before publication of CSA B54.9 and i t s invocation in the NBC,all of the c a r p e t s w e r e t e s t e d on the floor over No. 14 a s b e s t o s paper. A few of the m o s t widely used contract types of floor covering w e r e a l s o t e s t e d on the ceiling on LDACB t o study t h e r m a l effects of board and adhesive.
Sufficient yardage had been m a d e available f o r replicate t e s t s on a few t y p e s , with e m p h a s i s on the repeatability of high SD ratings (floor mounted). Results of the r e p l i c a t e r u n s on nylon c a r p e t s
10-N-27 and 11 -N-33 on the floor (which a r e averaged in Table VI) a r e p r e s e n t e d in Table
III.
In addition, the t h i r t y - f i r s t c a r p e t , a heavy contract type (13-N-35) intended f o r d i r e c t glue-down on concrete f l o o r s in c e r t a i n f e d e r a l buildings in Ottawa and supplied by the Department of Public Works w a s t e s t e d in s i x different mounting a r r a n g e m e n t s (Table IV).Following a review of the accumulated r e s u l t s , and with publication of CSA B54.9 a s s u r e d , the Associate Committee on the National Building Code m a d e f u r t h e r revisions in the NBC r e q u i r e m e n t s f o r floor coverings in high-rise buildings (Table V).
In both CSA B54.9-1972 and the m o s t recent revisions t o the NBC 1970 it is stipulated that c a r p e t s be t e s t e d a s they a r e t o be
installed, e . g . , using a specific undercushion if such is called f o r in the
contract. In addition, the NBC c a l l s f o r t e s t s in t r i p l i c a t e .
Results
-
T e s t s on F l o o rThe r e s u l t s f o r c a r p e t s t e s t e d in this second s e r i e s and sub- sequent work a r e s u m m a r i z e d in Table
VI.
A comparison of r e s u l t s f o r shag c a r p e t s on the ceiling with sand and a s b e s t o s paper on the floor i s given in Table VII.The effects of various undercushion m a t e r i a l s on the r e s u l t s of B54.9 t e s t s , a recapitulation of relevant d a t a f r o m the f i r s t s e r i e s and
some m o r e r e c e n t work on two a c r y l i c c a r p e t s a r e s u m m a r i z e d in Table VIII. The l a r g e r i n c r e a s e s in SD f o r a c r y l i c and lightweight wool c a r p e t s v e r s u s nylon and polypropylene with even the most i n e r t
undercushioning a r e again evident. The high SD ratings f o r poly- propylene c a r p e t s a r e noteworthy.
All thirty-one c a r p e t s of this group p a s s e d the modified pill t e s t , according t o the staff of the Textile Flammability Group of the D e p a r t - m e n t of Consumer and C o r p o r a t e Affairs.
G e n e r a l Discussion
The disadvantages of the E 84 t e s t f o r c a r p e t s (using ACB backing) a r e evident f r o m a n examination of the r e s u l t s in Tables I, IV and VI. Backing of the c a r p e t with 40-0 z. h a i r felt eliminates some of the anomalies, p a r t i c u l a r l y in the c a s e of a c r y l i c c a r p e t s , gives b e t t e r a g r e e m e n t with B54.9 r e s u l t s f o r both FSC and SD and d e m o n s t r a t e s a "continuity of scalet' s i m i l a r t o that of B54.9. The s u p e r i o r i t y of the B54.9 t e s t over E 84 with felt backing l i e s in its seemingly g r e a t e r r e a l i s m , reduced effort in sample preparation, lower cost of mounting m a t e r i a l s , s h o r t e r conditioning t i m e and e a s i e r clean-up ( p a r t i c u l a r l y i n the c a s e of shag c a r p e t s ) .
Recent DBR work suggests that the B54.9 t e s t can detect the
effect on FSC and SD of m i n o r changes in pile weight, replacement of jute by polypropylene in p r i m a r y backings, and incorporation of f i r e
r e t a r d a n t s in the latex binder of a heavy nylon c a r p e t . In view of the high cost and l a r g e sample s i z e involved in the B54.9 t e s t , a s m a l l - s c a l e t e s t useful in both acceptance testing and development work is highly d e s i r a b l e , but it might not be capable of detecting the effects of t h e s e change s quantitatively nor m e a s u r e SD.
The recent revision of the National Building Code of Canada, calling f o r a m a x i m u m FSC of 300 f o r c o r r i d o r s and exits in h i g h - r i s e buildings, can be rationalized on the b a s i s of M c G u i r e r s work in the f u l l - s c a l e DBR c o r r i d o r facility. The application of the modified pill t e s t h a s led to the r e m o v a l of the m o r e readily ignitable c a r p e t s f r o m the m a r k e t ; FSC r a t i n g s over 250 a r e unlikely t o be found in the f u t u r e
except f o r experimental types of c a r p e t , o r f o r some vinyl r o l l flooring m a t e r i a l s , f o r which B54.9 h a s been shown t o give satisfactory r e p e a t -
ability f o r both FSC and SD.
The estimation of high SD values by integration of an obscuration- t i m e c u r v e ( F i g . 2) i s admittedly unsatisfactory. The variability of the
r e d oak standard itself, the differences f r o m one installation t o another in the type and location of the smoke-metering equipment, the un- c e r t a i n t i e s of d r a f t control, and the limitations of the r e c o r d e r involved a r e a l l valid r e a s o n s f o r c r i t i c i s m of t h i s method of evaluation. Repeat- ability of high SD values h a s been improved a t t h i s laboratory by installing a d i s c i n t e g r a t o r with digital readout on the 10 millivolt r e c o r d e r (one- second full-scale r e s p o n s e ) used f o r obscuration m e a s u r e m e n t s . The low v a r i a n c e in SD in the replicate t e s t s of a heavy nylon c a r p e t (Table Ill)
suggests that control of the furnace d r a f t by the u s e of both manual and b a r o m e t r i c d a m p e r s is s a t i s f a c t o r y in the DBR tunnel, but s t i l l p e r h a p s could be improved by installing automatic d r a f t control equipment.
Integration of a n optical density-time curve is a m o r e valid approach t o calculating high SD ratings (above 40 p e r cent maximum ob scuration) but one which, like standardization of smoke -mete ring and recording equipment, is unlikely t o be adopted by m a n y tunnel furnace o p e r a t o r s in the f o r e s e e a b l e future. Such integration would, of c o u r s e , give substantially higher SD values relative t o r e d oak than the p r e s e n t method.
Recent work h a s shown that m i n o r and justifiable changes in p r o - cedure would give even better a g r e e m e n t between SD values obtained by B 54.9 and E 84 r e s u l t s with 40 -02. h a i r felt cushioning.
The FSC values obtained using B54.9 t e s t s w e r e lower than
those obtained with E 84 t e s t s with h a i r felt cushioning which is in
harmony with the idea that a given m a t e r i a l is a l e s s e r h a z a r d on the floor than on the walls o r ceiling under comparable f i r e conditions. With a firebox height of only 12 in., the difference in r e s u l t s f o r a given c a r p e t of only 8 t o 40 p e r cent i s l e s s than would be expected in a full-scale
c o r r i d o r . This is compensated f o r in the NBC r e q u i r e m e n t s by setting FSC l i m i t s f o r floor coverings t e s t e d by B54.9 higher than those f o r wall coverings t e s t e d by E 84, e . g . , 300 by B54.9 f o r floor coverings in c o r r i d o r s and 150 by E 84 f o r wall coverings in other a r e a s in high-rise buildings.
R e f e r e n c e s
1. Canadian Standards A s sociation. CSA B54.9
-
1972. Standard Methodof T e s t f o r Burning C h a r a c t e r i s t i c s of Flooring and F l o o r Covering M a t e r i a l s .
2 . U n d e r w r i t e r s # L a b o r a t o r i e s of Canada. L i s t of Equipment and
M a t e r i a l s . Volume 11: Building Construction. Supplements, M a r c h
3. ASTM D2859-70T. Flammability of Finished Textile Floor Covering Materials.
4. L e e , T . G. and Huggett, C. Interlaboratory Evaluation of the
Tunnel T e s t (ASTM
E
84) Applied t o Floor Coverings. NationalBureau of Standards, NBSIR 73-125. March 1973.
5. McGuire,
J.H.
The Spread of F i r e in Corridors. F i r e Technology,M Q m m m r - 0 0 .D d ' m N V ) E - O \ O o N ~ m c m l d '
:
:
V I P - o d ' o 0 9 m m m ~ m .*-
9 9 N N p, p , m d ' * \ O d ' *z
:
2 25
0012
"
q m m o w m o s a m r c m a. t- r - * m u l m W m W O - - N * * 9 d' 9 -m g
-
d' -d W W N - N N N N - 4 4 4 m m - m m. . .
m a r -m a r - O O NT A B L E I
-
Tunnel F u r n a c e T e s t s on C a r p e t s 1 5-
25C a r p e t No.
Backing/Stiffening
F i b r e , Weave, Pile H e i ~ h t P r i m a r y Secondary
1/8 1. d.
V i s c o s e tufted l o w loop J u t e Urethane Foam Weight. oz/sq yd P i l e
-
-
Total Ceiling Mounting IT FSC Adj.-
-
- - -
IT F l o o r Mounting FSC SD ~ r i a c e t a t e / ~ ~ twist, 0. 25 in. J u t e J u t e A c r y l i c t u f ~ e d level loop As 17. with felt B P P tufted h i - l o loop Jute J u t e Jute J u t e As 18, with f e l t CPP tufted hi-lo loop (cf. 18) J u t e J u t e
As 19, with foam pad A (FSC = 408, SD = 270 on f l o o r )
As 19, with felt C
Nylon t u f t e d level loop PP J u t e
As 70. with felt I; As 20, with felt F ~ c r ~ l i c / m o d a c r ~ l i c low loop As 2 1 , w i t h felt B PP J u t e 23. 0 1/8 h. d. PP FR foam 34. 0 P P Latex, thin 2 0 . 0 1. d. foam
PP tufted level loop
PP tufted plush, 0. 15 in.
(indoor-outdoor type)
P P tufted Level loop (cf. 22) PP J u t e (FR 34.0
l a t e x ) AS 2-1, with felt B
TABLE I1
TABLE 3.2.6. Dl NATIONAL BUILDING CODE O F CANADA 1970
Maximum
Maximum Smoke Developed
Flame -Spr ead Rating Classification
Location
Wall Ceiling Floor Wall Ceiling Floor
Surface Surface Surface Surface Surface Surface
Exit stairways
,
vestibules t o exit s t a i r s and exit lobbies 25 25 25 C o r r i d o r s providing a c c e s s t o exits except within suites (1 ) (1 ) 200 100 25 300 Elevator c a r s and vestibules 25 25 200 100 100 300 Service spaces 25 25 25 25 25 25 Other rooms o r spacesTABLE XI1
REPEATABILITY
O F CSA B54.9-
1972TESTS
C a r p e t 10-N-27 Date
-
I T-
FSC T e x t u r e d nylon, PP/ J u t e 16 Nov. 7 0 150 backing, 1 8 oz. p i l e 2 6 J u n e 80 135 weight, 5. 6 Kilotex 2 6 J u n e 75 133 27 J u n e 84 138 1 Aug. 81 144 C a r p e t 11 -N-33 Nylon l o w l e v e l loop, 20 J u n e 55 163 J u t e p r i m a r y and s e c o n d a r y 2 0 J u n e 67 162 backing, 1 8 oz. p i l e wt., 20 J u n e 7 1 160 6.7 KilotexTABLE
IV
E F F E C T O F MOUNTING ON APPARENT FSC, F C AND S D
O F
HEAVY
NYLON CARPET 13-N-35C a r p e t Specification: Pile weight, o z / s q yd
- -
28. 0Total weight, o z / s q yd
-
-
80.5Kilotex/ sq c m
-
-
10.0P r i m a r y backing, 3 . 5 oz/sq yd polypropylene Secondary backing, 8. O o z / s q yd jute
P o s i t i o n Backing Adhesive
- - - -
I T FSC F C S DCeiling 4 0 oz. h a i r felt,
LDACB lino cement* 55 229 95 410
Ceiling
$
in. LDACB lino c e m e n t 70 160 9 6 315Ceiling
$
in. HDACB s i l i c a t e 75 72 35 150F l o o r No. 14 A s b e s t o s
P a p e r
F l o o r
5
in. LDACB lino c e m e n t 100 110 9 6 534F l o o r
$
in. HDACB s i l i c a t e 120 95 55 225*
lino c e m e n t-
lignosulfonate-
c l a y type, between f e l tand LDACB; c a r p e t stapled through both and a l s o supported by chicken w i r e .
TABLE V Location Exit stairways, vestibules t o exit s t a i r s and exit lobbies
TABLE 3.2.6. D, CHANGE SERIES NO. 2 NATIONAL BUILDING CODE O F CANADA 1970
Maximum
Maximum Smoke Developed
Flame -Spr ead Rating Classification
Wall Ceiling Floor Wall Ceiling Floor
Surface Surface Surface Surface Surface Surface
C o r r i d o r s providing a c c e s s t o exit except within suites (1 ) (1 ) 300 100 5 0 Elevator c a r s and vestibules 25 25 300 100 100 Service spaces and s e r v i c e rooms 25 25 25 5 0 5 0 Other rooms o r spaces (1
1
(1 (21
300 5 0(1) Appropriate FSC limits apply.
T A B L E VI - Results of T u n n c l T e s t s on 31 Carpets - S e c o n d Series No.
-
T U F T E D NYLON 1 -N-1 3-N-8 9-N-19 11 -N-33 13-N-35 5-N-14 7-N-16 9-N-21 10-N-27 8-N-18 8-N-17 1 0 - N - 2 4 8 -N-20 9 -N-22 9-N-23 WOOL 2-W-6 2-W-7 5-W-13 C o n s t r u c t i o n1
p i l eI
I
p i l eI
T o t a l Weight B a c k i n g P r i m a r y S e c o n d a r yLYE
PP PP PP J u t e PP PP J u t e J u t e PP PP PP J u t e J u t e J u t e J u t e J u t e J u t e J u t e J u t e J u t e J u t e J u t e J u t e J u t e J u t e J u t e L a t e x J u t e J u t e J u t e s q yd ~ u t e / c t n L a t e x ~ u t e / c t n L a t e x in. L o w L e v e l Loop I 1 II 11 I I H i - l o Loop T e x t u r e d I I II T w i s t P l u s h I I S h a g I* I $ Wilton Cut and h o p W i l t o n Plush PP J u t e 0. 1 4 0. 19 0. 1 4 0. 22 0. 25 0. 12-0. 32 0. 2 -0. 5 0. 44 0. 38 0. 63 1. 50 0. 77 2. 00 0. 31 0. 38 0. 2 5 20 23 2 1 1 8 2 8 18 2 0 18 1 8 2 0 2 0 45 2 6 2 6 22 40 33 T u n n c l F u r n a c e T e s t s C e i l i n g - C e i l i n g - LDACB F e l t C p e r s q crn* I Tufted Loop, 22 F l o o r No. 1 4 P a p e r I TFSC
S_D-
s q yd 11. 5 8 . 7 1 1 . 0 6. 7 10. 0 5. 4 5. 9 5. 0 5. 4 5. 1 5. 1 8. 8 16. 2 11. 5 8. 2 d e n i e r x p i l e ends/sq in. * Kilotex / sq c m = 5 & , 0 7 0 60 57 58 61 8 6 47 6 4 62 57 6 4 59 7 4 7 2 8 3 7 2 7 0 7 5 58 ContinuedT A B L E Vi - R e s u l t s of Tunnel Testa on 31 C a r p e t s
-
Second S e r i e s ( C o n t ' d )No.
-
w eACRYLIC, A C R Y L I C -
MODAC RYLIC [AM)
3 - A - 1 2 Tufted P l u s h 5-A-26 T u f t e d P a t - terned h a p 1 1 - A - 2 8 T e x t u r e d . Woven 1 0 - A h f - T u f t and Low 2 5 Loop (woven s e m i - s h a g ) POLYPROPYLENE I - P - 3 Low Level LOOP 6 - P - 1 5 1 1 4-P-I 0 Ncedlepunch POLY W T E R 1 - E - 2 Shag BLENDS, T U FTEDs* 1 - T P - 5 TTard T w i s t 1 I -AN- 29 I t
1 -EN-4 Low Level
L o o p
6-AN-30 I I
6 -AN-31 I I
*
Kilotex / s q c m58. 070 tc::' T - T r i a c e t a t e ; P - Polypropylene, A
-
Acrylic. E-
P o l y e s t e r ; N - NylonP i l e Weight o z / sq yd 28 22 'SO 46 2 0 2 8 47 45 3 1 36 3 6 2 4 d e n l e r = P l l p Fit. In. ' 0 38 0. 12-0.22 0. 16 0 22 1. 44 0 31 0 28 0 31 0 2 3 0 16 .c ? . l r C o n s t r u c t P i l e Density, Kilotex p e r sq c m * 8. 3 8 . 5 15. 7 1 1 . 3 10. 4 14. 6 3 . 9 1 2 . 7 1 0 . 5 13. 0 1 2 . 2 1 2 . 2 e n d s / s q tn. ion T o t a l Weight o z / sq yd 6 5 53 7 5 6 4 6 2 7 0 3 3 1 0 5 8 8 6 7 7 8 7 6 6 7 Backing P r i m a r y Secondary PP J u t e J u t e L a t e x ~ u t e / c t n ~ u t e / c t n L a t e x PP J u t e PP J u t e PP J u t e J u t e J u t e PP J u t e PP J u t e PP J u t e P P J u t e Tunnel I Ceiling
-
LDACB IT E C Adj. SD 1 4 61 500 360 8 51 500 191 20 61 250 373 10 55 375 413 50 197 NA 280 F u r n a c e T e s t s C e i h n g - Felt C 20 380 532 1 4 282 542 20 380 532 44 297 490 41 314 382 F l o o r No. 1 4 P a p e r IT FSCg
20 250 315 13 550 242 47 212 354 10 197 500 53 220 517 47 208 618 40 196 715 56 147 618 27 193 533 22 256 385 113 157 536 44 190 700 45 200 536TABLE VII Carpet NBS #5, 1 1 / 8 in. nylon 24 oz. p i l e wt. COMPARISON
OF
I N F L U E N C EO F
SANDVS.
# 14ASBESTOS PAPER
IN
TESTSOF
SHAG CARPETS (ASTM E 84)ASTM E 8 4 - 7 0 CSA B54.9
-
1972Ceiling
Floor- - - -
ITPSC
F C S D- -
IT
FSC--
FC
S D8-N-20,
1. 5 in. nylon, 4 5 oz. pile wt. 9 -N-22, 0.75 in. n y l o n , 2 6 o z . p i l e w t . 2 in. nylon, 22 o z . pile mt. 1 -E-22, 1 . 4 in. polyester, 47 o z . p i l e \vt. HtStW #14 paper 1 0 367 7 0 80 HtStW bare 1 5 1 4 5 45 84 79 172 108 400 HtStW s a n d 1 2 143 2 4 8 8 A t L#
14 paper 1 5 423 87 4 4 6 A t L t W b a r e 1 6 137 75 210 58 172 9 0 4 4 0 A t L t F t W sand 18 2 8 1 105 220 A t L # 14 paper 2 3 3 0 5 107 4 5 8 A t L t W sand 27 169 66 174 55 1 4 1 8 6 483 A t L t F t W sand 2 6 2 4 5 110 3 6 8 A t L fF 14 paper 11 4 4 0 84 384 AtL+W sand 16 1 3 7 75 210 67 172 84 4 3 0 A+L+F+W sand 16 282 9 4 325 AR
14 paper 15 275 60 405 A t L t W sand 18 9 8 57 3 7 0 56 147 9 4 618 A t L t F t W sand 25 257 7 8 4 0 0 H-
high-density ACB A - l o w - d e n s i t y ACB S - silicate glueL
-
linoleum c e m e n tF
-
40 02. hair f e l t W-
chicken w i r e supportTABLE VIII
-
Effect of Underlayment on R e s u l t s af CSA B 54-9 T e s t sP i l e
Fibre and Weight Pi1 e H t .
Construction oz/sq yd in.
Total Weight oz/sq yd
No. 1 4 P a p e r and Backing llnderlayment ~ s b e s t o s . P a p e r Underlayment P r i m a r y Secondary Used
- - -
IT FSC SD- - -
IT FSC SD Carpet No. First KiIotex per s q cm Series 10 Nylon t u f t e d shag 18 1 . 0 P P P P 45 216 495 60 225 6 3 7 Jute Jute 80 147 420 115 149 4 3 611 Nylon tufted textured 21
Jute Jute C - 4 0 oz, h a i r 58 200 445 45 187 427 f e l t
18 PP tufted textured 1 4
Jute J u t e A - 4 5 az. white 50 1 8 4 482 45 175 640
foam
19 PP tufted textured 18
20 Nylon low l e v e l loop 20 0. 1 4 P P J u t e F-25 o z . mixed 60 200 422 65 177 420
f i b r e
Second S e r i e s
9-N- 1 9 Nylon l o w level loop 21 0. 1 4 P P Jute P P Jute 10-N- N y l o n t u f t e d t e l d u r e d 18 0 . 2 - 0 . 6
27
~ u t e / c t n Latex C 2-W-6 Wool, Wilton cut 40 0. 31
and loop ~ u t e / c t n Latex C P P Jute C 2-W-7 Wool, Wilton p l u s h 3 3 0. 38 5-W-13 Woot, t u f t e d level 2 2 0 . 2 5 loop
1 1 -A- Acrylic textured 4 1 28 woven
11-AN- ~ c r y l i c / n y l o n h a r d
29 twist 3 1 0. 28 PP Jute C
Recent Work
Acrylic plush, similar to 5 -.4 -12, h e a v i e r pile
-
PP Jute CAcrylic level loop, similar to C a r p e t 17.
8 - -
4
6 - CARPET 5 - W - I 3 - W 4 - (WOOL) - I- 2 - - TEMP, x 100 OF l ~ l l ~ ' l l ! l ~ ~ CARPET ( NYLON ) (ACRYLIC) 2 '0 2 4 6 8 10 12 14 TEMP, X I 0 0 OFr
Z 6I
- CARPET 21 TEMP, x I 0 0 OF TEMP, X 100 OF 1 1 1 1 , 1 1 I , [ : , CARPET 5-A-13 - - TEMP, X I 0 0 OF TEMP, X I 0 0 OFFIGURE I TEMP TIME CURVES (CSA 854.9-1972)
MIL L 1 VOLTS MILLIVOLTS 10- - 1 I 10 i I I I (POLYPROPYLENE) SD- 618 2 4 6 8 I D MILLIVOLTS CARPET 5-A- 26 ( ACRYLIC
1
-
SD = 242 - - 8 - 1 6 - - g 4 - CARPET 10-AM-25 - I= ( ACRYLIC/MODACRYLIC SD.500 - 1 I 1 I 1 1 I I1
2 4 6 8 10 MILLIVOLTS 8 . ZE
6 . -6
4 --
I- 2 5 I I I I I I 10- I I Ir
- RED OAK 8 - - (E 8 4 ) CARPET 5-W-13 - SD= 100 --
( WOOL1
I- - 2 SD =467 --O b
I I i l l I I 1 I I I I I I1 4
2 4 6 8 10 OO 2 4 6 8 10 MILLIVOLTS MILLIVOLTS 4FIGURE
2 OBSCURATION TIME CURVES (CSA 054.9-1972)
L ,
APPENDIX A
Note 1. Use of Turbulence-Inducing B r i c k s
Seven of t h e e l e v e n tunnel f u r n a c e o p e r a t o r s p a r t i c i p a t i n g i n the NBS round robin t e s t s of 1972 u s e G-26 f i r e - b r i c k s t o induce t u r b u l e n c e i n the f u r n a c e . Usually t h i s i s done w h e r e t h e f u r n a c e h a s inside-mounted o r double windows, which produce l e s s t u r b u l e n c e than the o l d e r out s i d e
-
mounted d e s i g n with i t s t u r b u l e n c e - p r o d u c i n g d e e p window w e l l s .T h e n u m b e r and location of the b r i c k s in the DBR tunnel in routine t e s t i n g a r e i d e n t i c a l with t h o s e u s e d a t u n d e r w r i t e r s L a b o r a t o r i e s I n c . , Northbrook, i n 1968. The s i x G-26 f i r e b r i c k s r e s t on end with the
1
4 ~ - i n . f a c e a g a i n s t the w a l l . They a r e placed a t d i s t a n c e s ( m e a s u r e d f r o m t h e c e n t r e l i n e of the T e e - b u r n e r ) of 4.5, 9.5, and 1 5 . 5 ft along t h e blank wall and 7 , 12, and 20 ft along the window wall.
I t h a s been found t h a t the u s e of t h e s e b r i c k s i s e s s e n t i a l t o the
development of a r e a s o n a b l y s y m m e t r i c a l p a t t e r n of f l a m e f r o n t p r o p a g a - t i o n along t h e whole length of t h e tunnel in both E 84 and B54.9 t e s t s in o u r i n s t a l l a t i o n .
Note 2. W a r m - u p P r o c e d u r e and Use of A s b e s t o s P a p e r
M a n y c o m m e r c i a l and q u a s i - c o m m e r c i a l l a b o r a t o r i e s c a r r y out a 10 - m i n . w a r m - u p and s o m e t i m e s a 10 -min. blank run b e f o r e t e s t i n g t h e f i r s t s a m p l e of t h e day. In a l l c a s e s the f u r n a c e i s cooled a t high a i r velocity until a t h e r m o c o u p l e a t the p r e s c r i b e d location (14 ft f r o m the f i r e end and 1/8 in. below the f l o o r s u r f a c e ) r e g i s t e r s 1 0 0 ° F
+
5 ° F .I t h a s been the p r a c t i c e a t t h e Division of Building R e s e a r c h , a s w e l l a s a t s o m e o t h e r r e s e a r c h i n s t a l l a t i o n s , t o c a r r y out a 30-min. w a r m - u p and a 10-min. blank run, followed by the u s u a l cooling a f t e r e a c h , b e f o r e p r o c e e d i n g with t h e f i r s t t e s t of the day. If t h e cooling t o 1 0 0 ° F 5" i s v e r y r a p i d d u r i n g cold w e a t h e r t h i s p r a c t i c e p r o b a b l y l e a d s t o m o r e heat s t o r a g e in the b r i c k and s t e e l t h a n r e s u l t s f r o m the a b r i d g e d w a r m - u p p r o c e d u r e s u s e d e l s e w h e r e .
O b s e r v a t i o n of t h e t e m p e r a t u r e r i s e a t the b u r i e d t h e r m o c o u p l e d u r i n g positioning of c a r p e t s and u n d e r c u s h i o n s s u g g e s t s t h a t the s t o r e d h e a t m i g h t influence the r e s u l t s of the t e s t , and that t h e u s e of No. 14 a s b e s t o s p a p e r i s a r e a s o n a b l e expedient.
Note 3. Calibration and Calculations
Table
LA
shows that 3/4-in. r e d oak flooring and cellulosic fibreboardgive lower FSC and SD values in B54.9 t e s t s than i n E 84. It might be
argued that the f a c t o r s used in the calculation of FSC and SD f o r c a r p e t s
should be adjusted accordingly, i. e . , i n c r e a s e d by approximately 8 p e r cent f o r FSC (based on the quoted value of 92) and 1 5 p e r cent f o r SD (the inevitable outcome of lower consumption of the r e d oak fuel in t e s t s on the floor). The observed behaviour of c a r p e t s during t e s t s on the floor and the a r b i t r a r y nature of the methods of calculation employed when the flame front does not r e a c h 19. 5 ft, o r does s o in m o r e than
5.5 rnin., d e t e r r e d any change in the constants discussed below. The calculations involved in the E84 t e s t a r e a s follows:
(1) F o r m a t e r i a l s on which the flame s p r e a d s t o 19. 5 ft ( t
=
t i m e , min. ):( a ) in 5. 5 min. o r l e s s , the flame - s p r e a d classification i s : 1 0 0 ~ 5 . 5 550
FSC =
= -
t t
(b) in m o r e than 5 . 5 min. but l e s s than 10 m i n . :
27 5
FSC = 50 +-
-
t
( 2 ) F o r m a t e r i a l s on which the flame s p r e a d s l e s s than 19. 5 f t and c e a s e s t o advance ( o r r e c e d e s ) in the 10-min. t e s t , then
( a ) when the e x t r e m e flame s p r e a d distance, d , i s m o r e than 13.5 f t but l e s s than 1 9 . 5 ft FSC = 50 4- 1.41 d o r (b) when it i s l e s s than 13.5 ft 1 OOd FSC =
-
= 5.128d 19. 5Thus, the quoted FSC value of 92 f o r r e d oak on the floor in Table IA
i s actually derived f r o m a t i m e to 19. 5 ft of 6.60 min. If this r e p r e s e n t e d the average t i m e f o r a l a r g e number of r e d oak flooring decks which a l s o averaged 5 . 5 min. i n the E 84 t e s t , i t would be reasonable to i n c r e a s e
the FSC values f o r c a r p e t s and other m a t e r i a l s on the floor by 20 p e r cent.
the combustion c h a r a c t e r i s t i c s of carpets s o different from those of oak, that a correction of this o r d e r would be difficult to justify without further study.
The average SD for all
31
carpets in TableVI
i s higher for B54.9 than f o r E 84 t e s t s with 40-0s. h a i r felt cushioning. Because there i s no explanation of these differences and exceptions, the method of calculation i s again left unchanged f r o m that of E 84 based on the average SD of many calibration runs of r e d oak flooring.The calculation of SD i s a s follows:
where A A and A a r e the a r e a s under the obscuration-time curves for
4'
O
the samp e , r e d oak Booring and a blank run, respectively. A i s usually
about 10 p e r cent of A B