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Estimates of formaldehyde emission from urea formaldehyde foam
insulation based on a thermal cycle and a barometric pressure cycle
Richardson, J. M.; Sereda, P. J.
NATIONAL RESEARCH COUNCIL OF CANADA DIVISION OF BlllLDlNG RESEARCH
DBR INTERNAL REPORT NO. 505
ESTIMATES OF FORMALDEHYDE EMISSION FROM UREA FORMALDEHYDE FOAM INSULATION BASED ON A THERMAL CYCLE AND A BAROMETRIC PRESSURE CYCLE by
J.M.
Richardson andP.J.
SeredaA N A L Y Z E D
Checked by: Approvrdby: L.W. Gold Oats: September 1985
Pnparrd for: Records Purposes
ABSTRACT
This note undertakes to estimate the rates of formaldehyde emission due to a thermal cycle and a barometric pressure change.
These rates are compared to the assumed concentration of formaldehyde in the living space of 1.00 ppm.
ESTIMATES OF FORMALDEHYDE EMISSION FROM UREA FORMALDEHYDE FOAM INSULATION BASED ON A THERMAL CYCLE
AND
A BAROMETRIC PRESSURE CYCLEJ.M. Richardson and P.J. Sereda
INTRODUCTION
Experience and e x p e r i m e n t s a t t e s t t o t h e f a c t t h a t formaldehyde i s e m i t t e d from UFFI foams. Various c o n c e n t r a t i o n s of formaldehyde have been measured i n t h e l i v i n g s p a c e i n houses i n s u l a t e d w i t h UFFI foams.
S i m i l a r l y , v a r i o u s h i g h e r c o n c e n t r a t i o n s have been measured i n t h e w a l l c a v i t i e s ( s t u d s p a c e s ) where t h e foams a r e found. F i n a l l y , e x p e r i m e n t s have been conducted where foams have been exposed t o v a r i o u s c o n d i t i o n s of RH and t e m p e r a t u r e and e m i s s i o n r a t e s of formaldehyde have been measured. D e t a i l s of t h i s i n f o r m a t i o n a r e g i v e n i n o t h e r UFFI n o t e s , i n c l u d i n g "UFFI
C h a r a c t e r i s t i c s Update" by C.J. S h i r t l i f f e and P.J. Sereda. These UFFI n o t e s a r e , o r w l l l b e , i n t h e form of DBR I n t e r n a l Reports.
Various mechanisms f o r t h e d e l i v e r y of formaldehyde from t h e foams i n t o t h e house, have been c o n s i d e r e d . I n o r d e r t o account f o r and t o p r e d i c t t h e r a n g e of c o n c e n t r a t i o n s t h a t have been observed o r t h a t may o c c u r i n a
house, i t i s n e c e s s a r y t o u n d e r s t a n d t h e mechanism r e s p o n s i b l e f o r t h e d e l i v e r y of t h e gas.
I n l a b o r a t o r y e x p e r i m e n t s t h e h i g h e s t r a t e s of e m i s s i o n of formaldehyde from foams have been observed when t h e a i r i n t h e c e l l s of t h e foam was d i s p l a c e d by t h e "sweeping" a c t i o n of mass a i r f l o w t h r o u g h t h e foam. The
h i g h p r e s s u r e drop ( r e s i s t a n c e t o a i r flow) t h a t h a s been measured f o r most foams p r e c l u d e s t h e p o s s i b i l i t y t h a t s i g n i f i c a n t a i r f l o w c a n be caused by wind p r e s s u r e o r s u c t i o n . T h i s f a c t h a s l e d t o t h e c o n c l u s i o n t h a t a
d i u r n a l t h e r m a l c y c l e ( d u r i n g t h e h e a t i n g p a r t ) o r a warming e p i s o d e i n t h e w e a t h e r , and a l s o a b a r o m e t r i c p r e s s u r e c y c l e ( i n v o l v i n g a d e c r e a s i n g
p r e s s u r e ) , s h o u l d c a u s e a s i m i l a r d i s p l a c e m e n t of a volume of a i r and r e s u l t i n t h e h i g h e s t r a t e of e m i s s i o n of formaldehyde from t h e foam.
T h i s n o t e u n d e r t a k e s t o e s t i m a t e t h e r a t e s of formaldehyde e m i s s i o n due t o a t h e r m a l c y c l e and a b a r o m e t r i c p r e s s u r e change. These r a t e s a r e
compared t o t h e assumed c o n c e n t r a t i o n of formaldehyde i n t h e l i v i n g s p a c e of 1.00 ppm. ( I t i s r e a l i z e d t h a t t h i s l e v e l i s a b o u t 10 times h i g h e r t h a n t h e normal l e v e l s found i n most UFFI houses b u t t h e v a l u e s o b t a i n e d i n t h i s e x e r c i s e can be r e a d i l y a d j u s t e d t o any l e v e l . )
PART 1
-
This s e c t i o n c o n s i d e r s what r a t e of r e l e a s e of formaldehyde from UFFI i s needed t o m a i n t a i n a c o n c e n t r a t i o n of 1.00 ppm i n a house when t h e r e is one a i r change p e r hour. These r e l e a s e r a t e s a r e t o be compared w i t h
e x p e r i m e n t a l l y determined e m i s s i o n r a t e s from samples of UFFI c o n d i t i o n e d a t
95%
RH.
The i n i t i a l e m i s s i o n r a t e s r a n g i n g from 700 t o 10 000 ng/min/g were o b t a i n e d from samples by sweeping w i t h a i r p a s s i n g t h r o u g h t h e foam a t al i n e a r v e l o c i t y of a b o u t 0.72 m / d n ( 1 L / d n t h r o u g h a f u n n e l 42 mm i n d i a m e t e r ) . (Assumptions and d e r i v a t i o n s a r e g i v e n i n t h e appendix.)
For a h o u s e of 9600 f t 3 (271 m3) a n d one a i r change p e r h o u r , mass of
a i r = 5091 g/min. I f t h e formaldehyde c o n c e n t r a t i o n i s t o be m a i n t a i n e d a t 1.00 ppm i t uust be s u p p l i e d a t t h e r a t e of 5091 x 1.00 x =
0.005 g/min. T h i s formaldehyde must be p r o v i d e d by i t s e m i s s i o n from 72.2 kg of foam. I f t h e foam i s e m i t t i n g a t t h e r a t e of 10 000 ng/min/g, t h e maximum e m i s s i o n r a t e would be 0.7 g/min, which is a b o u t 100 t i m e s h i g h e r t h a n r e q u i r e d . I f t h e foam i s e m i t t i n g a t t h e l o w e r r a t e of
700 ng/min/g, t h e n t h e r a t e would be 0.05 g / d n which is a b o u t 10 t i m e s h i g h e r t h a n r e q u i r e d . (The i n i t i a l h i g h r a t e of e m i s s i o n of formaldehyde
from foam c a n n o t be m a i n t a i n e d f o r a l o n g time b e c a u s e i t d e c a y s t o a s t e a d y v a l u e of a b o u t 1/10 of t h e i n i t i a l v a l u e i n s e v e r a l h o u r s . )
The above c a l c u l a t i o n s i n d i c a t e t h a t t h e UFFI i n a h o u s e h a s t h e p o t e n t i a l t o s u p p l y t h e r e q u i r e d amount of formaldehyde t o m a i n t a i n a
c o n c e n t r a t i o n of 1.00 ppm p r o v i d e d t h e UFFI h a s been c o n d i t i o n e d t o t h e h i g h h u m i d i t y and i t i s b e i n g "swept" o u t by a i r f l o w i n g t h r o u g h t h e foam a t c e r t a i n l i n e a r v e l o c i t y t o a f f e c t a c e r t a i n volume of a i r change.
PART
2T h i s s e c t i o n w i l l examine w h e t h e r t h e d i u r n a l t h e r m a l c y c l e c a n e f f e c t a n a d e q u a t e volume of a i r d i s p l a c e d t o sweep t h e r e q u i r e d amount of
formaldehyde from t h e foam. (Assumptions and d e r i v a t i o n s a r e g i v e n i n t h e appendix. )
Assuming t h a t t h e maximum mean t e m p e r a t u r e of t h e foam i s 30°C and minimum mean t e m p e r a t u r e i s 20°C f o r summer c o n d i t i o n s , t h e volume of a i r t h a t w i l l be e x p e l l e d from t h e 226.8 f t 3 (6.42 m3) o f foam i s 7.74 f t 3
(0.219 m3 = 219 L). I t i s assumed t h a t t h i s volume of a i r w i l l be e x p e l l e d u n i f o r m i l y o v e r a 12-hour p e r i o d , a t a r a t e of 0.304 L / d n .
From e x p e r i m e n t s i t was found t h a t 1 L/min of a i r p a s s i n g t h r o u g h one UFFI foam c o n d i t i o n e d a t 95%
RH
e m i t s a peak v a l u e of 10 000 ng/min/g of formaldehyde. Assuming t h i s v a l u e i s a p p l i c a b l e t o t h e foam i n a w a l l andi s p r o p o r t i o n a l t o t h e a i r f l o w r a t e , t h e n 72.2 kg of foam would e m i t
0.219 g/min of formaldehyde, c a r r i e d by t h e volume o f a i r f l o w i n g o u t d u r i n g t h e h e a t i n g c y c l e . T h i s c o r r e s p o n d s t o 43.1 ppm i n t h e a i r i n t h e l i v i n g s p a c e (one a i r c h a n g e p e r h o u r ) . T h i s r e s u l t i s f o r t h e peak v a l u e which d e c r e a s e s t o a b o u t 1/10 a f t e r s e v e r a l h o u r s . T h i s v a l u e s h o u l d be f u r t h e r d e c r e a s e d by a f a c t o r of a t l e a s t f o u r b e c a u s e of t h e l o s s t o t h e o u t s i d e of t h e h o u s e a n d b e c a u s e e m i s s i o n o c c u r s f o r o n l y t h e h e a t i n g p a r t of t h e d i u r n a l t h e r m a l c y c l e . These combined e f f e c t s would r e d u c e t h e e m i s s i o n o v e r 24 h o u r s t o t h e o r d e r of 1 ppm. T h i s would i n d i c a t e t h a t t h e proposed mechanism i n v o l v i n g t h e t h e r m a l c y c l e s h o u l d c a r r y o u t from t h e foam more t h a n enough formaldehyde t o m a i n t a i n t h e l e v e l s t h a t have been observed.
A s i m i l a r c a l c u l a t i o n was c a r r i e d o u t f o r w i n t e r c o n d i t i o n s . Assuming a maximum mean t e m p e r a t u r e of 7.5OC i n t h e day and minimum mean of -2.5OC a t n i g h t , t h e volume o f e x p e l l e d a i r was found t o be 8.38 f t 3 (0.237 m3) and
t h e r a t e of a i r e x p e l l e d was 0.33 L/min. However, t h e r a t e of f o r m a l d e h y d e e m i s s i o n w a s n o t d e t e r m i n e d a t t h e low t e m p e r a t u r e s i n v o l v e d i n w i n t e r and f o r t h i s r e a s o n t h e c a l c u l a t i o n of t h e f o r m a l d e h y d e e m i t t e d i n w i n t e r i s n o t v a l i d . It i s e x p e c t e d t h a t a d e c r e a s e i n t e m p e r a t u r e would d e c r e a s e t h e r a t e of formaldehyde r e l e a s e a n d t h i s a g r e e s w i t h t h e measured l e v e l s , which a r e found t o be c o n s i d e r a b l y lower i n t h e w i n t e r . However, a s w i l l be shown i n P a r t 3, t h e l a r g e s t b a r o m e t r i c p r e s s u r e c h a n g e s o c c u r i n w i n t e r , which may be t h e main mechanism f o r d e l i v e r y of formaldehyde.
PART
3T h i s s e c t i o n w i l l c o n s i d e r w h e t h e r a b a r o m e t r i c p r e s s u r e change c a n a c c o u n t f o r some o r most of t h e r e q u i r e d e m i s s i o n of formaldehyde from t h e foam.
It w a s p o i n t e d o u t a t t h e b e g i n n i n g o f t h i s n o t e t h a t mass a i r f l o w t h r o u g h t h e foam r e s u l t s i n t h e h i g h e s t r a t e of e m i s s i o n of formaldehyde.
It i s o b v i o u s t h a t t h e p r i n c i p a l p r o c e s s r e s p o n s i b l e f o r s u c h a i r exchange i s i m m a t e r i a l and i t h a s been shovn t h a t a t h e r m a l c y c l e c a n produce t h e r e q u i r e d mass a i r flow. S i m i l a r l y , a b a r o m e t r i c p r e s s u r e c h a n g e w i l l a l s o c a u s e mass a i r f l o w from o r t o t h e c e l l s of t h e foam.
M e t e o r o l o g i c a l r e c o r d s i n d i c a t e t h a t t h e l a r g e s t b a r o m e t r i c p r e s s u r e changes do o c c u r d u r i n g t h e w i n t e r months and t h a t s u c h changes c a n have a magnitude a s h i g h a s 8% i n a p e r i o d of 24 h o u r s .
S i n c e volume c h a n g e s a r e d i r e c t l y p r o p o r t i o n a l t o t h e p r e s s u r e c h a n g e s , a n 8% p r e s s u r e change w i l l r e s u l t i n a n 8% volume change, 0.08 x 226.8 f t 3 =
18.1 f t 3 , which i s g r e a t e r t h a n t h e 7.74 f t 3 c a u s e d by a 10°C t h e r m a l c y c l e . From t h i s i t i s o b v i o u s t h a t even a 3.4% change i n b a r o m e t r i c p r e s s u r e would c o r r e s p o n d t o t h e e q u i v a l e n t volume change. The c a l c u l a t i o n s c a r r i e d o u t i n P a r t 1 and 2 a r e a p p l i c a b l e t o a r r i v e a t t h e e x p e c t e d amount of formaldehyde d e l i v e r e d o u t of t h e foam d u r i n g any e p i s o d e o f b a r o m e t r i c p r e s s u r e
d e c r e a s e . It i s v a l i d t o c o n s i d e r t h e p o s s i b i l i t y t h a t a n i n c r e a s i n g ambient t e m p e r a t u r e e i t h e r d u e t o t h e d i u r n a l c y c l e o r a warming t r e n d may be c o i n c i d e n t w i t h a d e c r e a s i n g b a r o m e t r i c p r e s s u r e s o t h a t t h e e f f e c t of t h e two e v e n t s i s a d d i t i v e a n d a n e x p u l s i o n of rmch g r e a t e r volume of a i r from t h e foam c o u l d o c c u r c a u s i n g a n e p i s o d e of major i n c r e a s e i n t h e formaldehyde e m i s s i o n .
CONCLUSIONS
The a u t h o r s w i l l r e a d i l y acknowledge t h a t t h i s a t t e m p t a t c a l c u l a t i n g t h e e m i s s i o n of formaldehyde by a t h e r m a l c y c l e , a warming t r e n d i n t h e w e a t h e r o r a n e p i s o d e of a d e c r e a s i n g b a r o m e t r i c p r e s s u r e , may o v e r s i m p l i f y a complex p r o c e s s and may l a c k t h e r i g o r o u s a n a l y s e s t o test i t s v a l i d i t y . However, i t is b e l i e v e d t h a t t h e r e s u l t s of t h e s e c a l c u l a t i o n s i n d i c a t e t h a t t h e s e mechanisms o f f e r t h e p o s s i b i l i t y t o d e l i v e r a l a r g e q u a n t i t y of
formaldehyde o u t of t h e foam, i n f a c t rmch more t h a n i s r e q u i r e d t o m a i n t a i n t h e l e v e l s t h a t h a v e been o b s e r v e d . For t h i s r e a s o n t h e s e mechanisms of t e m p e r a t u r e c h a n g e s a n d / o r b a r o m e t r i c p r e s s u r e changes r m s t be s e r i o u s l y c o n s i d e r e d as t h e ones most l i k e l y r e s p o n s i b l e f o r t h e d e l i v e r y of
In view o f this conclusion, monitoring of formaldehyde levels In houses and especially those of the wall cavitles should be coordinated with
APPENDIX Volume of house: 1200 f t 2 x 8 f t = 9600 f t 3 . Volume of a i r ( a t 1 a i r change p e r h o u r ) = 9600 f t 3 / h . Mass o f a i r / m i n 9600 f t 3 0.07 l b a i r 1 kg 1000
g
1 h_
5091 g/min. h f t 3 2.2 l b kg 60 min Volume of one s t u d s p a c e : 33 x 143 x 914 = 2.68 f t 3 . Volume of t o t a l s t u d s p a c e : P e r i m e t e r 140 f t-
0.2 (140) window s p a c e = 112 f t a t 3 s t u d s p a c e s / 4 f t = 84 s t u d s p a c e s . Volume of 84 s t u d s p a c e s x 2.7 f t 3 = 226.8 f t 3 . Mass of foam i n t h e s t u d s p a c e s : 226.8 f t 3 x 0.7 i b foam 1 kg g. 72,16 kg. f t j 2.2 l b The d i l u t i o n r a t i o , s t u d s p a c e : l i v i n g s p a c e = 16:l (From DBR B u i l d i n g P r a c t i c e Note No. 23)The i n i t i a l r a t e o f e m i s s i o n of formaldehyde from 9 s a m p l e s , c o n d i t i o n e d a t 95% RH ranged from 700 t o 10 000 ng/min/g.
For summer c o n d i t i o n s , maximum o u t s i d e w a l l s u r f a c e t e m p e r a t u r e assumed t o be 40°C. Minimum o u t s i d e w a l l s u r f a c e t e m p e r a t u r e assumed t o be 20°C.
Indoor a i r t e m p e r a t u r e c o n s t a n t a t 20°C.
Average d a y t i m e t e m p e r a t u r e f o r i n s u l a t i o n = 30°C. Average n i g h t t i m e t e m p e r a t u r e f o r i n s u l a t i o n = 20°C.
To o b t a i n volume i n c r e a s e due t o t e m p e r a t u r e changes:
V 2 / V l = T3/T,, where V l = 226.8 f t 3 ,
