NTSB Safety Recommendation Letter P-79-001

Page 1Official PDFNATIONAL TRANSPORTATION SAFETY BOARD WASHINGTON, D.C. p,. ,/ 9 I S S U E D : April 11, 1979 M r . G . H . Lawrence President American Gas Association 1515 Wilson Boulevard Arlington, Virginia 22209 i M r . Jerome J. McGrath I President I n t e r s t a t e Natural Gas Association of America 1660 L S t r e e t , N.W. Washington, D.C. 20036 _____-________^_________________________- \ SAFETY RECOMMENDATION(S) P-79-1 A t 3:20 p . m . , c . s . ~ . , on January 2 7 , 1978, a s i g n a l was received a t the Robstown (Texas) Compressor Station of the Florida Gas Transmission Company. The signal came over the Radio Alarm Relay Systems (MARS) and indicated t h a t a u n i t of t h e company‘s remote Murdock Pass Compressor Station on Padre I s l a n d , Texas, had shut down. An investigator who went t o the Murdock Pass s t a t i o n t o check t h e indicated problem found t h e s t a t i o n was on f i r e . H e tripped t h e manual emergency shutdown (ESD) system a t 5 : 0 5 p.m. This action shut off the gas supply and “blew down” the s t a t i o n . Of the s t a t i o n ‘ s three compressor u n i t s , t w o were destroyed and t h e t h i r d was badly damaged. There were no i n j u r i e s . Records i n d i c a t e t h a t the compressor s t a t i o n maintained a steady flow from 8 : O O a . m . t o 2:40 p.m. The Safety Board’s examination of the damaged s t a t i o n and r e l a t e d MARS s i g n a l s and pressure/flow d a t a from an upstream o r i f i c e meter c h a r t determined t h a t , beginning a t 2:40 p . m ~ , a series of events took place t h a t caused the f i r e not t o be immediately reported t o the manned s t a t i o n a t Robstown. These events were: 1. A leak developed a t a flange on the bypass end of t h e suction header of u n i t N o . 2 , 2. Escaping gas gained access t o t h e only running compressor u n i t (No. 2 ) and was i g n i t e d , 3 . The r e s u l t i n g explosion caused u n i t No. 2 t o shut down by vacating combustion a i r to its engine, 2612#

Page 2- 2 - 4 . Monitored engine functions continued momentarily w i t h i n acceptable l i m i t s , 5. A n alarm was n o t s e n t v i a MARS when monitored engine functions did cease operating because the engine magnetos of t h e compressor u n i t a c t i v a t e MARS and t h e engine had shut down, 6. Flames being fed by the leaking gas a t t h e flange heated t h e P i n c h r i s e r on t h e d i s - charge s i d e of the bypass t o a p o i n t where it f a i l e d , 7 . Gas leakage r a t e increased due t o t h e f a i l u r e and fire damage became more extensive, and 8. The fire burned through a MARS u n i t cable causing an e l e c t r i c a l s h o r t , and a s i g n a l was s e n t t o Robstown indicating the shutdown of u n i t NO. 1 instead of a f i r e . An analysis of these events shows t h a t the emergency alarm system a t t h e Murdock Pass s t a t i o n was inadequate. The emergency s i t u a t i o n deactivated t h e alarm system before t h e a l a r m could be sent. Other gas compressor s t a t i o n emergency shutdown alarms e x i s t which could a l s o be circumvented. The Florida Gas Transmission Company took these actions t o make the alarm system more f a i l - s a f e : 1. An u l t r a v i o l e t l i g h t f i r e detection system has been ordered. This system w i l l be t i e d t o the ESD system. This t i e - i n w i l l cause automatic i s o l a t i o n and blow- down of t h e s t a t i o n i n t h e event of a f i r e i n or near t h e s t a t i o n . 2 . The ESD i s now t i e d t o o i l pressure-sensitive switches on t h e two replacement units. T h i s w i l l a c t i v a t e the ESD system i n t h e event t h a t one 01 both u n i t s a r e down f o r any reason, i n which case t h e s t a t i o n w i l l be i s o l a t e d and blown down. 3 . The MARS system has been revised t o be independent of t h e engine magnetos of t h e compressor u n i t . It is now t i e d t o an o i l pressure-sensitive switch on each u n i t .#

Page 3- 3 - I n order t o increase t h e o v e r a l l operational s a f e t y of t h e remote s t a t i o n , a 12-inch check valve has been i n s t a l l e d below ground i n the s t a t i o n discharge l i n e approximately 70 f e e t from the s t a t i o n . This check valve w i l l prevent a gas backflow from the l a t e r a l i n t h e event of a break. Therefore, the National Transportation s a f e t y B o a r d recommends t h a t the American Gas Association and the I n t e r s t a t e Natural Gas Association of America: Advise member companies of t h e circumstances of t h i s accident and urge them t o review t h e i r remote i n s t a l - l a t i o n alarm systems and t o c o r r e c t any d e f i c i e n c i e s found. (Class I , Urgent Action) (P-79-11 K I N G , Chairman, DRIVER, Vice Chairman, McA3AMS and HOGVE, Elembers, concurred i n the above recommendation.#