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Example of the spread of fire by radiation
R e f S e r
no,
NOT FOR PUBLICATION
NA'TIONAL
RESEARCH
COUNCIL
CANADADIVISION O F BUILDING RESEARCH
BUILDING RESEARCH
(
T
I
NATlONAL RESEARCH COUMCfC
AN EXAMPLE OF THE SPREAD OF FIRE BY RADIATION
BY
J. H. McGUlRE A N D G. W. SHORTER
THIS REPORT HAS AND IS NOT
BEEN PREPARED FOR INFORMATION TO BE CITED AS A REFERENCE I N AND ANY RECORD PURPOSES PUBLICATION. OTTAWA AUGUST 1958
NATIONAL
RESEARCH
COUNCIL OF CANADADIVISION OF BUILDING
RESEARCH
A14 EXAMPLE OF !EIE
SPREAD
OFFIRE
BY RADIATION byJ.H. M o G u i r e and G.W. Shorter
Report No.
145
of the
Division
of Building ResearchOttawa
PREFACE
It i~ of importance in the field
of fire
technology to be able to predict the space separa-
tions between buildings whioh will prevent a fire
In one building from spreading to another,
Des-
pite this, there is little reliable information on
which such predictions can be based.
!hesenior
author, a member of the staff of the Joint Fire
Research Organization in Great Britain, on an official
visit to the Division, recognized the opportunity
provided in the case of a local fire which was
visited
to obtain useful information on fire spread.-
!be
observations which were made and the conclusions
drawn
are now recorded.
Ottawa
August 1958
N.B, ~utcheon
AN EXAMPLE OF THE SPREAD OF FIRE
BY
RADIATION J.H. McGuire-x and G.W. S h o r t e r On December 30, 1957 a t l2:O5 p.m. t h e F i r e S e c t i o n o f t h e D i v i s i o n o f B u i l d i n g Research was n o t i f i e d of a f i r e i n A l t a V i s t a i n a new r e s i d e n t i a l a r e a i n t h e s o u t h e r n s e c t i o n o f O t t a w a . The f i r e occurred d u r i n g t h e c o n s t r u c t i o n of adomestic d w e l l i n g and was o f p a r t i c u l a r i n t e r e s t i n t h a t it s p r e a d t o t h e two neighbouring d w e l l i n g s , both of which were completed and occupied ( F i g , 1). The s e p a r a t i o n s between t h e d w e l l i n g s exceeded 1 4 f e e t and r a d i a t i v e h e a t t r a n s f e r was c l e a r l y e s t a b l i s h e d as t h e mechanism by which t h e f i r e
s p r e a d from t h e one house t o t h e o t h e r two. The way i n which t h i s occurred i s c o n s i d e r e d i n t h i s r e p o r t .
The I h e l l i ~ ? ~ s Involved
The dwelling i n which t h e f i r e s t a r t e d w a s a timber- framed, one and a half s t o r y s t r u c t u r e . The framing had been completed, i n f i l l e d w i t h 3 i n . of m i n e r a l wool and s h e a t h e d e x t e r n a l l y w i t h a s p h a l t - f a c e d f i b r e i n s u l a t i o n board. A c o n c r e t e b r i c k e x t e r i o r f i n i s h had been e r e c t e d up t o first f l o o r l e v e l . The r o o f had been completed, t h e sub f l o o r s l a i d and a l l t h e windows i n s t a l l e d . For con- venience t h e d w e l l i n g s have been d e s i e n a t e d A , B and C i n
t h i s r e p o r t as f o l l o w s :
A
-
d w e l l i n g t o t h e l e f t of one i n which f i r e o r i g i n a t e d , as viewed from t h e road i n f r o n t of a l l 3 dwellings.B
-
d w e l l i n g i n which f i r e o r i g i n a t e d .C
-
dvrelling t o t h e r i g h t of one i n which f i r e o r i g i n a t e d .The l o c a t i o n of t h e exposed d w e l l i n g s ( A and C ) i n r e l a t i o n t o d w e l l i n g B i s shown i n Fig. 2 , and diagrams of t h e p e r t i n e n t s i d e w a l l s a r e shown i n F i g s .
3
and 4 ,*
Member of s t a f f of B r i t i s h J o i n t F i r e Research O r g a n i z a t i o n , Boreham Wood, H e r t s , England.Cause o f t h e F i r e
The f i r e s t a r t e d j u s t a f t e r noon i n d w e l l i n g B
when a p o r t a b l e o i l space h e a t e r being used t o h e a t t h e d w e l l i n g d u r i n g c o n s t r u c t i o n w a s overturned. About t h r e e g a l l o n s o f f u e l o i l were s p i l l e d and i g n i t e d . !The whole b u i l d i n g w a s r a p i d l y enveloped i n f i r e and t h e exposed
c l a p b o a r d i n g on t h e a d j a c e n t s i d e w a l l s of t h e neighbouring houses i g n i t e d w i t h i n 1 5 min. A s h o r t time l a t e r , t h e f i r e w a s e x t i n g u i s h e d by t h e f i r e department. Wind a t t h e time w a s n e g l i g i b l e and one w i t n e s s s a i d t h a t flames from house
B d i d n o t impinge on t h e s i d e s of houses A and C.
Observations Subsequent
t o
t h e F i r eIt w a s i n t e r e s t i n g t o n o t e t h a t t h e secondary f i r e s on t h e s i d e w a l l s of t h e two neighbouring d w e l l i n g s had o n l y been i n i t i a t e d on t h e v e r t i c a l f a c e s d i r e c t l y exposed t o r a d i a t i o n from t h e burning dwelling. The u n d e r s i d e s of t h e e a v e s were o n l y d i s c o l o u r e d where flames from t h e
secondary f i r e had played upon them; t h e under edges o f c e r t a i n exposed boards were n o t d i s c o l o u r e d a t a l l .
It was concluded, t h e r e f o r e , t h a t t h e s p r e a d o f f i r e t o houses A and C r e s u l t e d from r a d i a t i v e h e a t t r a n s f e r . R a d i a t i o n Level and Temperature P r e d i c t i o n s
Timber w i l l i g n i t e spontaneously when s u b j e c t e d t o a r a d i a t i o n l e v e l i n e x c e s s o f 0.8 cal/cm*/sec. . A t r a d i a - t i o n l e v e l s of between 0.3 and 0.8 cal/cm2/sec.
,
i t w i l l a l s o i g n i t e if a h i g h t e m p e r a t u r e i g n i t i n g s o u r c e i s n e a r it.
The i n f o r m a t i o n o b t a i n e d i l l u s t r a t e s t h a t t h e one s i d e o f b o t h d w e l l i n g s A and C w a s s u b j e c t e d t o a l e v e l o f r a d i a t i o n g r e a t e r t h a n a c e r t a i n minimum. The f a c t t h a t an a r e a o f board t o t h e r e a r o f t h e s i d e of house A ( M g .5 )
was o n l y d i s c o l o u r e d and d i d n o t i g n i t e , shows t h a t a t t h i s
p o s i t i o n t h e l e v e l o f r a d i a t i o n w a s l e s s t h a n a c e r t a i n maximum.
The c o n f i g u r a t i o n f a c t o r i n t h e r e g i o n of t h e un- damaged t i m b e r a t t h e back of t h e west s i d e of house A may be computed most e a s i l y by c o n s i d e r i n g t h e r a d i a t i n . g a r e a t o approximate one h a l f a s q u a r e , t h e r e c e i v i n g element being l o c a t e d on t h e normal t o one c o r n e r of t h e square. Expres- s i o n s and t a b l e s g i v i n g t h e c o n f i g u r a t i o n f a c t o r f o r t h i s
a p p r o x i m a t e l y 0.1 w a s o b t a i n e d , The maximum c o n f i g u r a t i o n f a c t o r may a g a i n be c a l c u l a t e d approximately by c o n s i d e r i n g it t o be h a l f t h e v a l u e g i v e n by a s q u a r e r a d i a t o r , t h e r e c e i v e r i n t h i s c a s e b e i n g l o c a t e d on t h e normal t o t h e c e n t r e o f t h e s q u a r e . The t a b l e s r e f e r r e d t o above g i v e a r e s u l t o f 0.2 a p p r o x i m a t e l y , f o r t h e c a s e c o n s i d e r e d h e r e .
S i n c e t h e undamaged t i m b e r must have been s u b j e c t e d t o a
l e v e l o f r a d i a t i o n l e s s t h a n 0 . 3 cal/cm2/sec. it f o l l o w s
t h a t t h e maximum l e v e l o f i n t e n s i t y i n c i d e n t on t h e s i d e
o f house A must have l a i n between 0.3 and a b o u t 0.6 cal/cm2/sec. It i s l i k e l y t h a t t h e l e v e 3 o f r a d i a t i o n on t h e undamaged
t i m b e r exceeded 0.2 cal/cm /sec. which r e d u c e s t h e l i m i t s s t i l l f u r t h e r .
Worn t h e above i n f o r m a t i o n t h e b l a c k body t e m p e r a t u r e o f t h e b u r n i n g s i d e o f B c a n be c a l c u l a t e d provided it i s assumed t h a t t h e f l a m e s above t h e burning house c o n t r i b u t e d much l e s s h e a t t o t h e d i s c o l o u r e d p i e c e of t i m b e r o n l t h e
exposed s i d e of house A t h a n d i d t h e b u r n i n g a r e a of t h e s i d e of house B. The e m i s s i v i t y and c o n f i g u r a t i o n f a c t o r s o f t h e s e f l a m e s would have been much lower t h a n t h o s e
a s s o c i a t e d with t h e b u r n i n g a r e a s . The a d o p t i o n of t h i s assumption maximizes t h e c a l c u l a t e d v a l u e of t h e b l a c k body t e m p e r a t u r e . The b l a c k body t e m p e r a t u r e of a s u r f a c e i s
t h a t t e m p e r a t u r e which, i f a t t a i n e d by a g e o m e t r i c a l l y similar s u r f a c e with a n e m i s s i v i t y f a c t o r of u n i t y ( i . e . a "black" s u r f a c e ) , would emit t h e same i n t e n s i t y o f r a d i a - t i o n . The s p e c t r a l d i s t r i b u t i o n o f t h e r a d i a t i o n from two s u r f a c e s w i t h t h e same b l a c k body t e m p e r a t u r e might be q u i t e d i f f e r e n t . Considering t h e i n t e n s i t y o f r a d i a t i o n on t h e t i m b e r which w a s d i s c o l o u r e d b u t n o t i g n i t e d :
whence
T =
890°Cf
60°C.To reduce t h e maximum r a d i a n t i n t e n s i t y on t h e s i d e s
o f h o u s e s A and C by a f a c t o r 2 and hence t o ensure t h a t
t h e r e w a s no s p r e a d o f f i r e by r a d i a t i o n , a s e p a r a t i o n of 24 f e e t would have been n e c e s s a r y . A l t e r n a t i v e l y , o f c o u r s e , t h e c o n c r e t e b r i c k s i d e w a l l s o f house B could have been c a r r i e d up t o t h e r o o f l e v e l t o reduce t h e r a d i a t i n g a r e a . Conclusions
The s p r e a d of f i r e from B t o t h e one s i d e of b o t h t h e neighbouring houses was t h e r e s u l t o f r a d i a t i v e t r a n s f e r i n t h e presence o f l o c a l h i g h t e m p e r a t u r e i g n i t i n g s o u r c e s ,
incident upon the clapboard portion of the side of house A was not sufficient to cause spontaneous ignition.
On the assumption that the radiation incident on the piece of timber which did not ignite originated largely from
the burning areas of house
B,
the black body temperatureof these areas has been calculated to be 890°C
f
60°C.If
this assumption were not valid the true black body tempera- ture would be lower than .this.
The pilot ignition of the wood on the one side of both the neighbouring houses would have been prevented had the separations between the houses been greater than 24
feet, or had the concrete-brick side walls of house
B
beencarried up to the roof. References
1. McGuire,
J.H.,
Heat transfer by radiation, Department of Scientific and Industrial Research (DSIR) and Fire Offices' Committee, Fire Research Special ReportNo. 2.
H.M.
Stationery Office. London 1953.2. Hamilton, D.C. and
W.R.
Morgan, Radiant-interchangeconfiguration factors.
U.S.
National AdvisoryCommittee for Aeronautics, Technical Note 2836. December 1952.
BR 7605
F i g u r e 1 Front view o f d w e l l i n g o r i g i n a l l y i n v o l v e d i n f i r e and t h o s e on e i t h e r s i d e which were i g n i t e d by r a d i a t i o n .
R O A D
FIGURE 2 PLAN V I E W
NOT SEVERELY
WINDOWS I N T A C T
W. S I D E , HOUSE B E. S I D E , HOUSE C
FIGURE 3 ADJACENT END WALLS, WEST SlDE
CHARRED T I M B E R
FIBREBOARD SHEATHING C O R N I C E BOAR0
AREA S L I G H T L Y
W. S I D E , HOUSE A E . S I D E . HOUSE B
BR 7606
F i g u r e
