NTSB Safety Recommendation Letter P-73-037 through P-73-046

Page 1Official PDF- 17 - 6. It i n i s d i f f i c u l t c a s t - i r o n CFR 192.459. p i p e t o d e t e r m i n e t h e by t h e v i s u a l e x t e n t of e x a m i n a t i o n e x t e r n a l r e q u i r e d c o r r o s i o n by 49 7. S i n c e AGL r e c o r d s d i d n o t i n d i c a t e o f f a i l u r e s o f c a s t - i r o n m a i n s , t o a s s e s s t h e problem a c c u r a t e l y t h e f r e q u e n c y and i t was and p l a n d i f f i c u l t f o r remedial c a u s e s AGL a c t i o n . V . PROBABLE CAUSE The N a t i o n a l T r a n s p o r t a t i o n S a f e t y Board d e t e r m i n e s t h a t t h e p r o b a b l e c a u s e o f t h e e x p l o s i o n was t h e i g n i t i o n o f g a s t h a t leaked from a c a s t i r o n main c r a c k e d by uneven s o i l s e t t l e m e n t which a p p l i e d a b e n d i n g f o r c e t o t h e p i p e i n an a r e a weakened by g r a p h i t i z a t i o n . C o n t r i b u t i n g t o t h e e x p l o s i o n was t h e f a i l u r e by t h e g a s company t o check f o r g a s i n t h e b u i l d i n g , t o s h u t o f f t h e flow o f l e a k i n g g a s , and t o n o t i f y p o l i c e and f i r e o f f i c i a l s . V I . KE~C.C@GNDATI.ONS The N a t i o n a l T r a n s p o r t a t i o n S a f e t y Board recommends t h a t : 1. The O f f i c e of P i p e l i n e S a f e t y o f t h e Department of T r a n s p o r t a t i o n : Improve t h e a c c i d e n t - r e p o r t i n g i n o r d e r t o o b t a i n a b e t t e r of t h e c a u s e s of f a i l u r e s (Recommendation No. P-73-37) r e q u i r e m e n t s u n d e r s t a n d i n g o f c a s t - i r o n mains. In c o o p e r a t i o n w i t h t h e v a r i o u s S t a t e r e g u l a t o r y a g e n c i e s , d e t e r m i n e t h e d e g r e e of na tionwi.de compliance w i t h 49 C F R 192.615, w r i t t e n emergency p r o c e d u r e s , and t a k e enforcement a c t i o n a c c o r d i n g - l y . (Recommendation No. P-73-35) In c o o p e r a t i o n w i t h t h e v a r i o u s S t a t e r e g u l a t o r y a g e n c i e s , encourage g a s d i s t r i b u t i o n o p e r a t o r s t o r e v i e w t h e f a c t o r s t h a t c a u s e f a i l u r e s i n c a s t i r o n mains i n t h e i r s y s t e m s , and t o t a k e n e c e s s a r y a c t i o n t o r e d u c e t h e h a z a r d t u t h e p u b l i c . (Recommendation ao. P-73-39) Give t h e of and a d d i t i o n a l r e g u l a t o r y c o n s i d e r a t i o n t o e f f r c t s of g r a p h i t i z a t i o n on t h e r e s i s t a n c e c a s t - i r o n mains t o e x t e r n a l l o a d s . L o c a l i z e d g e n e r a l g r a p h i t i z a t i o n should b e d e f i n e d . (Recommendation No. P-73-40)#

Page 2- 18 - 2 . The American S o c i e t y of Mechanical E n g i n e e r s Gas P i p i n g S t a n d a r d s Committee: ( a ) Develop c r i t e r i a which can be u s e d by g a s d i s t r i b u t i o n o p e r a t o r s f o r r e d u c i n g t h e p o t e n t i a l h a z a r d s from b r e a k s i n c a s t - i r o n mains. The c r i t e r i a s h o u l d c o n s i d e r r e p l a c e m e n t o r r e p a i r of mains, based on p i p e s i z e , g r a p h i t i z a t i o n , e x t e r n a l l o a d s , t r a f f i c , s o i l c o n d i t i o n and s t a b i l i t y , and gas p r e s s u r e . (Recommendation No. P-73-41) (b) Develop g u i d e l i n e s f o r d e t e r m i n i n g t h e e x t e n t of g r a p h i t i z a t i o n of c a s t - i r o n p i p e by means of v i s u a l e x a m i n a t i o n , a s r e q u i r e d i n 49 CFR 192.459, and t h e e f f e c t s of such g r a p h i t i z a t i o n on p o s s i b l e f u t u r e l e a k s o r f r a c t u r e s . (Recommendation No. P-73-42) 3 . The A t l a n t a Gas L i g h t Company: P r e p a r e w r i t t e n emergency p r o c e d u r e s and a p p r o p r i a t e o p e r a t i n g and maintenance a c q u a i n t employees w i t h t h e p r o c e d u r e s . (Recommendation No P-73-43) Improve its r e c o r d - k e e p i n g system s o t h a t the number and c a u s e s of c a s t - i r o n main b r e a k s c a n be r e a d i l y o b t a i n e d . (Recommendation No. P-73-44) Take reduce mains. of t h o s e w h a t e v e r r e m e d i a l a c t i o n i s t h e p o s s i b i l i t y of breakage This a c t i o n s h o u l d i n c l u d e s e c t i o n s o f c a s t - i r o n main n e c e s s a r y t o of c a s t - i r o n r e p l a c e m e n t s u s c e p t i b l e t o f a i l u r e . (Recommendation No. P-73-45) Develop a s e c t i o n a l i z i n g program of i t s p r e s s u r e d i s t r i b u t i o n system so t h a t p r o c e d u r e s a r e a v a i l a b l e t o i s o l a t e any h i g h - p r e p l a n n e d s e c t i o n of i t s system i n an emergency. (Recommendation P -73 -46)#