NTSB Safety Recommendation Letter P-78-052

Page 1Official PDFNATIONAL TRANSPORTATION SAFETY BOARD WASHINGTON, D.C. M r . G. H. Lawrence President American Gas Association \ SAFETY RECDMMENDAT I ON (S) Arlington, V i r g i n i a P-78-52 'i --------________________________________-~ A t 2 p.m., e.d.t., on May 1 7 , 1978, a Columbia Gas of Ohio, Inc., (gas company) c o n s t r u c t i o n crew, mistaking an 8-inch, low-pressure steel gas main f o r an &inch, high-pressure steel gas main, d r i l l e d a small p i l o t b i t hole through t h e w a l l of t h e low-pressure gas main and began t o c u t i n t o t h e pipe w a l l with a l a r g e diameter b i t . The construction crew w a s making a "hot tap" t o complete t h e f i n a l t i e - i n of an &inch, replacement gas main t o t h e e x i s t i n g high-pressure system on t h e north s i d e of Glessner S t r e e t i n Mansfield, Ohio. The hot tap-was t o be made using a 3-way tapping tee which had its s i d e o u t l e t welded t o t h e I t l i v e , " high-pressure replacement gas main and its bottom o u t l e t mistakenly welded t o t h e low-pressure gas main. When the 1-inch p i l o t b i t on t h e Williamson tapping machine attached t o the top o u t l e t of t h e tee penetrated t h e w a l l of t h e low-pressure gas main, gas at 42 p s i g p r e s s u r e from t h e high-pressure gas system entered the 14-inch water column (w.c.) (approx- imately 1 / 2 p s i g p r e s s u r e ) , low-pressure gas main and r a p i d l y increased t h e pressure i n t h e low-pressure system i n a 4.8-square-mile area of Mansfield. Shortly a f t e r 2 p.m., t h e Mansfield F i r e Department began receiving r e p o r t s of f i r e s caused by excessively high appliance flames on gas appliances. A r e s i d e n t who l i v e d near t h e construction s i t e ran t o t h e gas company crew and t o l d them t h a t t h e p i l o t l i g h t on h e r gas range had f l a r e d 2 feet and then had blown out. The gas company crew immediately s h u t o f f a nearby valve on t h e high-pressure gas system, which stopped t h e flow of gas from the high-pressure system t o t h e low-pressure system. A t 2:06 p.m., t h e gas company d i s p a t c h e r received a r e p o r t t h a t a l a r g e volume of gas w a s being vented from a building t h a t housed a d i s t r i c t r e g u l a t o r s t a t i o n , which w a s 3/4 m i l e from t h e construction site. The man dispatched t o t h e s t a t i o n reported t h a t t h e pressure had exceeded t h e low-pressure recording gauge which recorded pressures up t o 30 inches W.C. ( s l i g h t l y over 1 p s i g ) . An o i l seal p r e s s u r e r e l i e f valve t h a t had been set f o r 32 inches W . C . a l s o had been overpressured and w a s 2414#

Page 2venting gas to the atmosphere through its 4-inch vent pipe. Seven other oil seal relief valves on district regulators within the 4.8-square-mile area also had been overpressured. By 2:20 p.m., after being overpressured for 20 minutes, the low- pressure distribution .- system returned to its normal pressure of 14 inches W.C. Gas was-physically shut off at approximately -2,000 meters or services out of the 12,300 meters in the 4.8-square-mile area. The shutoffs were made by firemen, police, gasmen, emergency response personnel, and residents. There were no fatalities or injuries requiring hospitalization because of this accident. Property damage to 16 houses resulted from the ignition of nearby combustibles by high pilot flames; 5 of these houses were extensively damaged. On April 28, 1978, the gas company construction crew had abandoned and capped an old main at its connection to the &inch, high-pressure gas main on the north side of Glessner Avenue, on the east side of Arthur Street. At that excavation there were two 8 5/8-inch outside diameter (O.D.), coated, wrapped, and welded steel gas mains, which were identical in appearance. The high-pressure gas main was 3 feet north of and about 10 inches higher than the low-pressure gas main. Before completing the final tie-in of the new replacement gas main to the existing 8-inch, high-pressure gas main on the west side of Arthur Street, the gas main atlas was consulted to verify the locations of the two gas mains. The atlas showed the El-inch, high-pressure and low-pressure mains traversing Arthur Street parallel to each other. The small-scale--1 inch to 200 feet--gas main atlas did not indicate the depths of the mains or their locations from the lot line, nor did it show the mains crossing each other. However, investigations after the accident showed that the two mains crossed in the Arthur Street inter- section. In the excavation for the final tie-in west of Arthur Street, approximately 75 feet from the first excavation, the mains appeared to be in the same relative position (3 feet apart), but the north main was 4 inches lower than the south main, which made the tie-in more difficult. The construction crew welded an %inch, 3-way tapping tee to the top of the north main, which they presumed was the high-pressure main, and welded the side outlet of the tee to the newly installed high-pressure gas main. Next they pressure-tested the tee and new main successfully and then filled them with gas at 42 psig from the high-pressure system. This was done so that the pressure between the newly installed main would be the same as that in the main to be tapped so the steel chips from the pipe-tapping operation would not blow up into the tapping and plugging apparatus and clog it.#

Page 3- 3 - The gas company procedure manual acknowledges t h a t it i s important t o recognize t h a t operating maps may n o t be c o r r e c t . The gas company's procedure f o r "By-Passing and Stopping Gas Flow " recommends t h a t p r e s s u r e gauges be i n s t a l l e d t o i n s u r e a g a i n s t l o s i n g p r e s s u r e and customer outages. However, t h e tapping s e c t i o n of t h e procedure does n o t contain p r e s s u r e gauge requirements and does not mention t h e p o s s i b i l i t y of overpressuring a low-pressure system. Gas company procedures f o r "Main Tie-Ins" state t h a t t h e s p e c i f i c tie-in plan, which includes t h e tapping operations, can be e i t h e r w r i t t e n o r o r a l . I n this accident, t h e workmen were t o follow an o r a l plan and d i d n o t consider t h a t t h e high- and low-pressure gas mains could c r o s s each other i n Arthur S t r e e t between the two excavations. Consequently, a p r e s s u r e gauge w a s n o t used t o determine which l i n e w a s t h e high-pressure gas main. After t h e accident t h e f i r s t excavation east of Arthur S t r e e t w a s re-opened and a pipe l o c a t o r w a s connected d i r e c t l y t o t h e high-pressure main. This main w a s touching another pipe i n Arthur Street and could n o t be traced e l e c t r o n i c a l l y . The two pipes were excavated where they were touching and were e l e c t r i c a l l y s h o r t - c i r c u i t e d ; they were then separated. When traced with t h e pipe l o c a t o r again, t h e high-pressure gas main was found t o have crossed t h e low-pressure gas main with two 45" elbows i n the Arthur S t r e e t i n t e r s e c t i o n . The gas company records d i d not contain f i e l d measurements of where these lines crossed and, consequently, the gas main atlases d i d not show this crossing. T i t l e 49 CFR 192.627 r e q u i r e s t h a t "Each t a p made on a p i p e l i n e under pressure must be performed by a crew q u a l i f i e d t o make h o t taps." The 1976 ASME Guide covering t h i s Federal code suggests t h a t : "When t h e pipe- line is exposed, it should be thoroughly examined t o (a) v e r i f y t h e i d e n t i t y of t h e p i p e l i n e t o be tapped by l o c a t i o n , s i z e , kind, type of coating, e t c . " In t h i s accident, t h e crew w a s q u a l i f i e d t o make hot taps, b u t it w a s d i f f i c u l t t o i d e n t i f y t h e c o r r e c t p i p e l i n e because t h e two l i n e s were i d e n t i c a l . However, t h e Safety Board concludes t h a t because of t h e s i m i l a r i t y of t h e two gas mains, a p r e s s u r e gauge t a p should have been made t o determine t h e exact l o c a t i o n of the high-pressure main. If t h e construction crew had n o t immediately shut o f f t h e valve on t h e Sigh- pressure gas main, and i f t h e low-pressure system had not had t h e e i g h t o i l seal r e l i e f valves t o relieve t h e high pressure, a c a t a s t r o p h i c accident could have occurred. Therefore, t h e National Transportation Safety Board recommends t h a t t h e American Gas Association:#

Page 4- 4 - Advise its member companies of the circumstances of this accident and urge them to keep accurate records of facilities and to instruct construction and maintenance crews in the importance of verifying these facilities before working on them. (Class T I , Priority Action) (P-78-52) KING, Chairman, McADAMS, HOGUE, and DRIVER, Members, concurred in the above recommendation. By: kR J es B. King W W#