NTSB Safety Recommendation Letter P-77-043

Page 1Official PDF% P - 87 NATIONAL TRANSPORTATION SAFETY BOARD WASHINGTON, D.C. ---------..-----.-." _ - _ _ _ _ _ I Forwarded to: Mr. Byron W. Cain President Southern Union Gas Company 1201 Elm Street SAFETY P-77-43 R E C O M M E N D A T I O N ( S ) Dallas, Texas 75270 About 1:OO p.m., m.d.t., on August 9, 1 9 7 7 , n a t u r a l gas under high pressure was b r i e f l y allowed t o e n t e r a low-pressure n a t u r a l gas d i s t r i b u t i o n line and overpressured more than 750 customer s e r v i c e lines i n a seven- block area i n E l Paso, Texas. Flames from gas p i l o t s and the burners of appliances burned out of control and caused fires i n nearby flammable materials. There were a few minor i n j u r i e s and some minor property damage, but no f a t a l i t i e s . Within a few minutes t h e f i r e department arrived and, w i t h t h e help of t h e p o l i c e department, s t a r t e d t o s h u t off gas meters a t houses and businesses. Some commercial establishments were evacuated f o r about 2 hours u n t i l their area w a s cleared of gas odor. A t t h e time of t h e accident, a Southern Union Gas Company street crew w a s replacing a s e c t i o n of 10-inch cast-iron, low-pressure gas main operating a t 6 ounces per square inch (02.) downstream of a pressure- reducing (regulator) s t a t i o n . The s t a t i o n had an i n l e t pressure of 20 psig . The s e c t i o n t o be replaced was f i r s t i s o l a t e d by closing two valves on the main, approximately 70 f e e t a p a r t . Next, a stopple f i t t i n g w a s i n s t a l l e d t o i s o l a t e t h i s section from t h e regulator s t a t i o n . A 2-inch bypass w a s i n s t a l l e d around t h e stopple f i t t i n g and one of t h e i s o l a t i n g valves i n order t o supply t h e system while t h e replacement work was being performed. 2216#

Page 2Although the gas company was aware t h a t the s e c t i replaced contained the pressure-sensing l i n e s s t a t i o n and its monitor, the company apparent p o t e n t i a l hazard of i s o l a t i n g the pressure-se make t h e two regulators inoperative. It was estimated t h a t the pressure was a low-pressure system f o r 4 t o 7 minutes before the st by the sound of an increased flow of gas thro something unusual had happened and opened the stopple f i t t i n were no pressure gauges on t h e low-pressure s m a x i m u m pressure put i n t o the system; however, the pen of recording gauge located approximately seven blocks away a regulator s t a t i o n went off the chart a t 1 2 oz. This accident did not cause a f a t a l i t y o r extensive p damage; however, it did have the p o t e n t i a l t o the circumstances were s i m i l a r t o those involved i n an accident i vestigated by the Safety Board on June 3, 196 i n which 7 houses were destroyed and 45 other Therefore, the National Transportation Safety Board recomm the Southern Union Gas Company: Evaluate the e f f e c t s upon the gas system p r i o r t o placing any portion out of s e r v i c e and take a c t necessary t o assure continued s a f e operation. Appendix G - 1 2 of the ASME Guide f o r Gas Transmis and Distribution Piping Systems - 1976, provides guid t o aid i n accomplishing these actions.(Class 11, P r i o Action)@-77-43) BAILEY, Acting Chairman, McADAMS, HOGUE, and KING, M i n the above recommendation. By: Kay Bailey Acting Chairman .- -___ _. 1/ "Pipeline Accident Report-Low-Pressure Na System, Gary, Indiana, June 3, 1969,"adopt#