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Fire propagation tests of foamed plastic insulation within a wall cavity
NATIONAL RESEARCH COUNCIL OF CANADA DIVISION OF BUILDING RESEARCH
FIRE PROPAGATION TESTS OF FOAMED PLASTIC INSULATION WITHIN A WALL CAVITY
M.V. D I S o u z a
Internal Report No. 424 o f the
Division o f Building Research
OTTAWA February 1976
PREFACE T h i s r e p o r t d e s c r i b e s a t e s t a p p a r a t u s developed t o e v a l u a t e t h e s u i t a b i l i t y of p l a s t i c foams f o r u s e a s thermal i n s u l a t i o n w i t h i n w a l l c a v i t i e s . A specimen i s completely surrounded w i t h i n a c a v i t y , t h e d e p t h o f which i s a d j u s t - a b l e t o s u i t t h e t h i c k n e s s o f t h e m a t e r i a l and o f t h e i n t e r v e n i n g a i r s p a c e , and i s heated by a flame from below. F i r e propaga- t i o n over a s p e c i f i e d h e i g h t o f t h e specimen i s t a k e n a s t h e c r i t e r i o n f o r f a i l u r e .
S e v e r a l t e s t s were conducted on p l a s t i c foams having ULC S102 flame s p r e a d r a t i n g s r a n g i n g from 20 t o 550. In g e n e r a l , m a t e r i a l s having a r a t i n g i n excess o f 20 were n o t s u i t a b l e f o r u s e i n a s s e m b l i e s w i t h an i n t e r v e n i n g a i r space. I n a s s e m b l i e s w i t h a nominally z e r o a i r s p a c e , a l l t h e m a t e r i a l s t e s t e d were c o n s i d e r e d a c c e p t a b l e , w i t h t h e e x c e p t i o n o f p o l y s t y r e n e beadboard. Ottawa February 1976 C . B . Crawford D i r e c t o r , DBR/NRC
FIRE PROPAGATION TESTS OF FOAMED PLASTIC INSULATION WITHIN A WALL CAVITY
M.V. DVSouza
INTRODUCTION
I t h a s been t h e p r a c t i c e i n b u i l d i n g codes, f o r b u i l d i n g s c l a s s i f i e d a s non-combustible c o n s t r u c t i o n , t o t r y and p r e v e n t t h e p r o p a g a t i o n o f f i r e by thermal and sound i n s u l a t i o n i n c a v i t i e s , by s e t t i n g l i m i t s on t h e flame s p r e a d r a t i n g s o f t h e m a t e r i a l s t o b e used a s determined by t h e ASTM-E84 (1) o r ULC-S102 (2) t e s t s .
These t e s t s a t t e m p t t o a s s e s s t h e burning c h a r a c t e r i s t i c s o f m a t e r i a l s under c o n d i t i o n s i n which t h e i r s u r f a c e s a r e exposed t o a f r e e atmosphere. A s s u c h , t h e y do n o t a c c u r a t e l y r e p r e s e n t
c o n d i t i o n s encountered d u r i n g f i r e p r o p a g a t i o n by i n s u l a t i o n w i t h i n a c a v i t y . In o r d e r t o circumvent t h i s p r o b l e m , e a r l i e r s p e c i f i c a t i o n s invoked a wide margin o f s a f e t y by c a l l i n g f o r v e r y low r a t i n g s o f 25 o r l e s s . With r e c e n t t r e n d s towards r e l a x i n g t h i s l i m i t f o r
a s s e m b l i e s i n which t h e i n s u l a t i o n i s p l a c e d between two l a y e r s o f non-combustible m a t e r i a l without an i n t e r v e n i n g a i r s p a c e , t h e q u e s t i o n o f t h e a p p l i c a b i l i t y of t h e t e s t s becomes c r u c i a l . The c r i t i c a l n a t u r e o f t h i s q u e s t i o n h a s i n c r e a s e d w i t h t h e advent o f p l a s t i c foam i n s u l a t i o n because E84 r a t e s p l a s t i c foams a s b e i n g l e s s flammable t h a n e x p e r i e n c e o r o t h e r t e s t s would s u g g e s t .
The work d e s c r i b e d i n t h i s p a p e r was undertaken a s p a r t of t h e development o f a t e s t i n t e n d e d t o be s u i t a b l e f o r e v a l u a t i n g t h e hazard o f f i r e p r o p a g a t i o n by i n s u l a t i o n i n c a v i t i e s , b o t h w i t h and w i t h o u t a i r s p a c e s .
DESCRIPTION OF TEST APPARATUS T e s t Compartment
The t e s t c a v i t y c o n s i s t e d o f a v e r t i c a l r e c t a n g u l a r
compartment 72 i n . h i g h by 24 i n . wide, made of 1 / 2 - i n . l i g h t w e i g h t a s b e s t o s board ( F i g u r e s 1 6 2 ) . Three o f i t s s i d e s were f i x e d
r i g i d l y t o a framework w h i l e t h e f o u r t h was a d j u s t a b l e t o s u i t t h e m a t e r i a l t h i c k n e s s and geometry ( a i r gap) under i n v e s t i g a t i o n .
In t h e c o u r s e of d e v e l o p i n g t h e a p p a r a t u s , f o u r h o r i z o n t a l s l o t s were c u t a l o n g t h e width of t h e movable f a c e f o r a i r admission. T h e i r purpose i s d i s c u s s e d l a t e r .
When t e s t i n g assemblies t h a t r e q u i r e d a zero a i r gap a l l s l o t s were closed with ceramic f i b r e .
Gas Burner
The burner was comprised of two p i p e s arranged i n tandem along t h e bottom edge of t h e compartment and s u p p l i e d s e p a r a t e l y with n a t u r a l gas and a i r . Each p i p e had a s e r i e s of r a d i a l h o l e s d r i l l e d along i t s length and arranged with r e s p e c t t o t h e o t h e r p i p e s o t h a t a mixture of f u e l and a i r , capable of s u s t a i n i n g s t a b l e flames, was achieved by j e t impingement. More d e t a i l s of t h e burner a r e shown i n Figure 3.
Instrumentation
F i r e propagation over a given h e i g h t was adopted a s t h e c r i t e r i o n f o r f a i l u r e . I t was necessary t h e r e f o r e t o provide a p o s i t i v e method of determining t h e exact moment flames reached a
given p o i n t r a t h e r than j u s t r e l y i n g on v i s u a l o b s e r v a t i o n . Thermo- couples and f u s i b l e metal s t r i p s o r wires were r e j e c t e d because o f t h e i r c o s t and t h e r e l a t i v e l y high thermal i n e r t i a of each system.
I n s t e a d , a l e n g t h of number 10 c o t t o n t h r e a d , s t r u n g o u t under t e n s i o n along t h e width of t h e specimen, was used t o i n d i c a t e , by breaking, t h e passage of flame (Figure 4 ) . When t e s t i n g assemblies with an a i r space t h e t h r e a d was l o c a t e d a t t h e top edge of t h e specimen, while f o r c a s e s with no a i r space t h e 3 6 - i n . l e v e l was chosen, t h e t h r e a d being recessed i n a shallow groove c u t i n t h e movable f a c e of t h e compartment. During t h e course of a "blank", 30-minute d u r a t i o n run, when temperatures n e a r t h e t o p o f t h e t e s t apparatus a t t a i n e d 210 O C ,
t h e t h r e a d remained i n t a c t .
Average gas temperatures a t e n t r y and e x i t were measured with chromel-alumel thermocouples, whose o u t p u t s were recorded on a
2-channel l i n e r e c o r d e r . The e x i t thermocouples had a p e n e t r a t i o n depth equal t o t h e t h i c k n e s s of t h e specimen.
The a b i l i t y of t h e apparatus t o g i v e r e p r o d u c i b l e r e s u l t s i s i l l u s t r a t e d i n Figure 5 , which compares t h e temperature-time h i s t o r i e s a t t h e top o f t h e compartment from two t e s t s with a polyurethane foam, assembled with a 1 - i n . a i r space. Although t h e d e t a i l s a r e d i f f e r e n t , t h e g e n e r a l t r e n d s displayed i n t h e two t e s t s a r e remarkably s i m i l a r .
TEST SPECIMENS
The specimens were secured mechanically t o t h e f i x e d f a c e of t h e compartment, with c a r e taken t o prevent t h e specimen from p u l l i n g away from t h e a s b e s t o s board during a t e s t . A l l specimens were 69 112 i n . long by 23 718 i n . wide with 1 - i n . nominal t h i c k n e s s . Table 1 l i s t s p a r t i c u l a r s of t h e m a t e r i a l s and geometries t e s t e d .
I t i s n o t p o s s i b l e t o g i v e a r e a l i s t i c r a t i n g f o r m a t e r i a l N O . 6 because of t h e manner i n which p o l y s t y r e n e foams burn. When h e a t e d most foams of t h i s t y p e melt r a p i d l y , i g n i t e and d r i p o n t o t h e f l o o r w h i l e flaming and c o n t i n u e t o burn a s a pool o f l i q u i d f u e l . TEST CONDITIONS
S i n c e a i r e n t r a i n m e n t i n t o t h e compartment d u r i n g a t e s t i s
dependent on t h e a r e a of t h e bottom opening, exposure c o n d i t i o n s could be expected t o vary from t e s t t o t e s t depending on t h e geometry b e i n g i n v e s t i g a t e d . Rather t h a n compensate f o r t h i s v a r i a t i o n by a d j u s t i n g t h e b u r n e r flow r a t e s , it was d e c i d e d , i n t h e i n t e r e s t s o f s i m p l i c i t y , t o develop a s e t o f t e s t c o n d i t i o n s f o r a s i n g l e geometry and t o m a i n t a i n b u r n e r o p e r a t i o n c o n s t a n t a t t h e s e c o n d i t i o n s f o r a l l subsequent t e s t s .
Gas flows c a p a b l e o f producing a mean compartment e n t r a n c e t e m p e r a t u r e (To) o f 980 O C with an a i r space of 1 1 / 4 i n . and no
specimen i n s t a l l e d (blank r u n ) were considered s u i t a b l e a t f i r s t . However, d u r i n g p r e l i m i n a r y t e s t i n g with t h e s e s e t t i n g s and no e x t r a a i r added, mean compartment e x i t t e m p e r a t u r e s (Te) a s h i g h a s 450 O C were r e c o r d e d , and a l l foams burned e a s i l y , i n c l u d i n g t h e low
r a t i n g i s o c y a n u r a t e l i s t e d a s No. 1 i n Table I . T h i s i s n o t e n t i r e l y s u r p r i s i n g , s i n c e thermogravimetric a n a l y s e s show t h a t , f o r p l a s t i c foams, r a p i d wcight l o s s due t o thermal decomposition becomes
s i g n i f i c a n t above about 220 O C . This v a l u e t h e r e f o r e , was s e t a s
t h e maximum f o r To and was achieved by reducing To t o 800 O C (below
which flame s t a b i l i t y problems were encountered) and i n t r o d u c i n g e x t r a a i r through s l o t s i n t h e movable f a c e o f t h e compartment. F i g u r e 2 shows t h e f i n a l arrangement; Table I 1 l i s t s c o n d i t i o n s imposed.
TEST RESULTS
D e s c r i p t i o n o f Events f o r T e s t s with 2 - i n . A i r Gap M a t e r i a l No. 1 (Table I )
An important f e a t u r e of t h i s m a t e r i a l from t h e f i r e p o i n t o f view was i t s a b i l i t y t o s w e l l i n s i z e when h e a t e d . Within 25 seconds from t h e s t a r t of t h e t e s t flames were n o t i c e d momentarily a t s l o t 3 (27 i n . from t h e bottom), b u t t h e s e dropped back r a p i d l y a s t h e m a t e r i a l s w e l l e d t o e f f e c t i v e l y block o f f a s much a s 75 p e r c e n t of t h e gap a t t h e bottom by t h e 3:00 minute mark. Burning t h e n proceeded very slowly up t h e two open s i d e s , with t h e flames b a r e l y r e a c h i n g s l o t 2 (12 i n . from t h e bottom) a t 10:OO minutes. Some flame p e n e t r a t e d through t o t h e back of t h e specimen a s it cracked o r warped. Burned p i e c e s o f m a t e r i a l f e l l through t o t h e f l o o r a f t e r about 15:OO minutes. Smoke formation was r e l a t i v e l y l i g h t throughout No f a i l u r e occurred w i t h i n t h e t e s t p e r i o d .
About 18 i n . o f t h e m a t e r i a l had completely burned away i n t h i s t i m e . Heavy c h a r and some s h r i n k a g e was noted up t o a h e i g h t o f 30 i n . , w i t h a t h i n v e n e e r of unburned m a t e r i a l beneath t h e c h a r . Immediately above t h i s p o r t i o n t h e specimen was swollen w i t h no c h a r beyond. The t o p was s t i l l 1 i n . t h i c k .
M a t e r i a l No. 2 (Table I )
A l l t e s t s conducted w i t h t h i s m a t e r i a l produced t h i c k
brownish smoke and a " s u r f a c e f l a s h " i n which flames t r a v e l l e d r a p i d l y o v e r t h e s u r f a c e of t h e m a t e r i a l l e a v i n g a l i g h t c h a r . The a v e r a g e t i m e f o r i s s u a n c e o f flames (about 10 i n . long) from t h e t o p o f t h e compartment was 20 s e c o n d s . The c h a r a p p a r e n t l y s e r v e d a s a
p r o t e c t i v e c o v e r f o r t h e unburned m a t e r i a l c a u s i n g t h e flames t o drop back by 45 seconds. Burning proceeded s l o w l y a f t e r t h i s w i t h moderate smoke f o r m a t i o n .
A f t e r a 20-minute t e s t p e r i o d t h e specimen had burned c o m p l e t e l y t o a h e i g h t of 24 i n . Beyond t h i s it was buckled and h e a v i l y c h a r r e d t o about 36 i n . , t h e c h a r forming i n l a y e r s w i t h a l a c e y appearance. The remaining p o r t i o n o f t h e specimen had s u r f a c e c h a r o n l y .
M a t e r i a l No. 3 (Table I )
The o v e r - a l l behaviour o f t h i s m a t e r i a l was s i m i l a r t o t h a t o f m a t e r i a l No. 2. The f i r e developed r a p i d l y w i t h flames (12 t o 18 i n . long) i s s u i n g from t h e t o p o f t h e compartment w i t h i n 7 seconds. The smoke formed was moderately d e n s e , brownish and a c r i d . T h i s
s i t u a t i o n p r e v a i l e d t i l l about 1 : 4 5 minutes i n t o t h e t e s t , a t which t i m e t h e flames dropped back and t h e smoke a b a t e d . Slower s t e a d i e r burning followed f o r t h e remainder o f t h e t e s t p e r i o d .
The f i r s t 12 i n . o f m a t e r i a l c o n s i s t e d of l i g h t a s h and t h e remainder o f t h e specimen was c h a r r e d . The t h i c k n e s s o f t h e unburned p o r t i o n a t t h e t o p was 3/8 i n .
M a t e r i a l No. 4 (Table 11
T h i s m a t e r i a l was covered on both s i d e s w i t h aluminium f o i l . Thick smoke accompanied a r e l a t i v e l y slow p r o g r e s s i o n o f flame up t h e c a v i t y . A t 30 seconds t h e c o t t o n t h r e a d broke b u t no flames were e v e r n o t i c e d a t t h e t o p . Flame and smoke a c t i v i t y s u b s i d e d w i t h i n 60
s e c o n d s . A t 5:00 minutes t h e specimen had p u l l e d away from t h e a s b e s t o s board t o a h e i g h t o f 24 i n . p a r t i a l l y b l o c k i n g t h e compart- ment, and a t 9:00 minutes t h e f o i l s t a r t e d t o m e l t and d r i p . The t e s t was t e r m i n a t e d a f t e r 10:OO minutes.
Underneath t h e f o i l t h e m a t e r i a l had burned t o a h e i g h t of 24 i n . The s u r f a c e was c h a r r e d t o 42 i n . The t o p o f t h e specimen was v i r t u a l l y unchanged.
M a t e r i a l No. 5 (Table I )
Without t h e aluminium f o i l , m a t e r i a l No. 4 burned more r a p i d l y . Flames were n o t i c e d a t t h e t o p o f t h e compartment by 14 seconds and c o n t i n u e d f o r a f u r t h e r 70 seconds, even though flaming a t t h e lower l e v e l s had ceased. A l l flaming and smoke s u b s i d e d by 100 seconds and s t e a d y burning ensued.
The specimen had burned completely t o a h e i g h t o f 30 i n . w i t h o n l y a l i g h t a s h remaining. A c e l l u l a r t y p e c h a r followed t h i s t o a h e i g h t o f 42 i n . a t which p o i n t t h e unburned m a t e r i a l measured about 1 i n . t h i c k . The specimen was b a d l y d i s t o r t e d .
M a t e r i a l No. 6 (Table I )
M a t e r i a l No. 6 e x h i b i t e d a l l t h e c h a r a c t e r i s t i c s o f a
p o l y s t y r e n e foam. The t e s t began innocuously w i t h r a t h e r t h i c k s o o t y smoke. Flames r e a c h e d s l o t 4 (42 i n . from t h e bottom) momentarily, b u t receded s h o r t l y a f t e r . A t 5:00 minutes t h e t e s t was t e r m i n a t e d a s t h e f i r e on t h e f l o o r showed s i g n s of g e t t i n g o u t o f c o n t r o l . The c o t t o n t h r e a d d i d n o t f a i l w i t h i n t h i s time. Only a s m a l l s t r i p o f m a t e r i a l (70 s q / i n . ) remained i n t h e compartment. EFFECT OF GEOMETRY T e s t s w i t h a 1 - i n . a i r s p a c e showed l i t t l e change i n behaviour from t h o s e on s i m i l a r m a t e r i a l s w i t h a 2 - i n . s p a c e . I n g e n e r a l , burning proceeded a t a f a s t e r pace f o r t h e 2 - i n . a i r s p a c e . I t f o l l o w s t h a t , i f t h i s t e s t were adopted a s a s t a n d a r d f i r e t e s t , t h e t h i c k n e s s o f t h e i n t e r v e n i n g a i r s p a c e should b e t h e maximum f o r which approval i s s o u g h t .
In c o n t r a s t t h e r e was v e r y l i t t l e d i f f e r e n c e between t h e burning p a t t e r n s o f m a t e r i a l s 1 t o 5 when t e s t e d w i t h an a i r s p a c e t h a t was nominally z e r o . Although t h e r e was heavy smoke f o r m a t i o n i n i t i a l l y , burning proceeded s t e a d i l y and, on t h e a v e r a g e , c h a r r i n g o f t h e m a t e r i a l extended up t o 30 i n . w i t h i n t h e 20-minute t e s t
p e r i o d , w i t h t h e f i r s t 10 i n . o r s o of m a t e r i a l reduced completely t o a s h . No f a i l u r e s of t h e c o t t o n t h r e a d were r e c o r d e d .
o n l y m a t e r i a l No. 6 d i f f e r e d , f o l l o w i n g t h e p a t t e r n d e s c r i b e d f o r t h e 2 - i n . a i r s p a c e ; f a i l u r e o c c u r r e d i n 45 seconds. By 5:00 minutes about 80 p e r c e n t o f t h e m a t e r i a l i n t h e c a v i t y had e i t h e r been consumed o r was b u r n i n g i n a pool on t h e f l o o r .
CONCLUSIONS
I n v e s t i g a t i o n s i n d i c a t e t h a t t h e t e s t a p p a r a t u s and proce- d u r e d e s c r i b e d h e r e would be s u i t a b l e f o r e v a l u a t i n g t h e h a z a r d o f f i r e p r o p a g a t i o n by i n s u l a t i o n i n c a v i t i e s , b o t h w i t h and w i t h o u t a i r s p a c e s .
The r e s u l t s o f t e s t s conducted t o d a t e with assemblies of p l a s t i c foam w i t h i n c a v i t i e s with an i n t e r v e n i n g a i r s p a c e have shown
flame p r o p a g a t i o n t o be s i g n i f i c a n t when m a t e r i a l s having a flame s p r e a d r a t i n g g r e a t e r t h a n 20 a r e used. However, with a s s e m b l i e s i n which t h e i n t e r v e n i n g a i r space i s nominally z e r o , s a t i s f a c t o r y behaviour was observed f o r m a t e r i a l s whose flame s p r e a d r a t i n g s a r e
f a r i n e x c e s s of 100. These f i n d i n g s a r e i n agreement w i t h t h o s e o f Lie ( 3 ) .
P o l y s t y r e n e beadboard was a n o t a b l e e x c e p t i o n , a p p e a r i n g s u i t a b l e f o r u s e i n "opent' c o n s t r u c t i o n but n o t i n c l o s e d . However, t h i s m a t e r i a l , p r e s e n t e d an extreme f i r e hazard when it melted and burned on t h e f l o o r of t h e t e s t a r e a .
REFERENCES
1. S t a n d a r d methods of f i r e t e s t s f o r s u f a c e burning c h a r a c t e r i s t i c s o f b u i l d i n g m a t e r i a l s . ASTM Designation E-84-70. 1971 Book o f ASTM S t a n d a r d s , P a r t 1 4 , p. 395.
2. S t a n d a r d method o f t e s t f o r s u r f a c e burning c h a r a c t e r i s t i c s o f b u i l d i n g m a t e r i a l s . ULC-S102-1975, U n d e r w r i t e r s ' L a b o r a t o r i e s o f Canada.
3 . L i e , T.T. C o n t r i b u t i o n o f i n s u l a t i o n i n c a v i t y w a l l s t o
p r o p a g a t i o n o f F i r e . N a t i o n a l Research Council o f Canada,
D i v i s i o n of Building Research, F i r e Study No. 29, November 1972. (NRCC 12878)
TABLE I
No. Material Type Density ASTM-E84 Geometry-Air Gap (in.) lb/ft Rating 0 1 2 1 Isocyanurate 1.97 2 0
/
/
/
2 Polyurethane A 1.82 55/
/
/
3 Polyurethane B 2.06 5 0/
/
/
4 Polyurethane C-
275/
-/
(with aluminium foil both sides)5 Polyurethane C 2.57 550
/
-/
(with aluminium foil removed) 6 Polystyrene Bead- 0.92 -/
-
/
board - Regular TABLE I1Test Conditions Develo~ed from "B1ank"Runs
Fuel Flow 1.1 SCFM
Air Flow 0.9 SCFM
Temperature at bottom of cavity: 800 OC approximately
Temperature at top of cavity: 210 OC 10 OC
Flame Height: 14 in. approximately Air gap for "Blank" run: 1 1/4 in.
The duration of each test was 20 minutes, unless premature failure occurred.
F I G U R E 1
A L ' T H E R M O - C O U P L E S B O A R D S I D E S A I R A D M I S S I O N S L O T S 1 2 - 1 9 S W G C H - A L T H E R M O - C O U P L E S F I G U R E 2 F R O N T E L E V A T I O N
S P E C I M E N
7
F I G U R E 3
F I G U R E 4
