NTSB Safety Recommendation Letter P-92-001 through P-92-005

Page 1Official PDFNational Transportation Safety Board Washington, D.C. 20594 Safety Recommendation mte: April 29, 1992 In reply refer to: P92-1 thraqh -5 Mr. E. H. lhnphaus President O k l a h m N a t u r a l Gas Ccenpany 100 w e s t 5th street Tulsa, O k l a h m 74103 A t 7:02 p.m. central stanclard the on July 5, 1991, at Tulsa, O k l a h m , high-pressure gas entered a lw-pressure, singlefamily a--service line coMBcted to a gas meter and regulator in a buried wncrete box near the custamerrs front propxty line. Gas at 4O-pig pressure was supplied to the regulator and meter a t 3805 East 98th street from a Z - i n c h - d i a m e t e r plastic gas main and a 1 1/4-inch-diameter plastic service line. ?he high-pmssmx gas enter& the gas fuel lines and appliances resulting in the escape of gas into the house. There w e r e no injuries, but the gas fm the furnaces and the water heatex ignited and fiieled fires that destroyed the rmiltilevel house. aopertY damage was estimated by the Tulsa F i r e Department at $540,000. Before the accident, a teenage girl was alone watching television in the family roam on the min level of the house when she head a laud noise. She believed that SDrmeOne was breaking in when the security alarm system SCIunded because a door s l d shut and a smoke detector w e n t off. She was unable to turn the alm off, so she opened the t r t i l i t y roam door to investigate and s a w the flames reflecting on the opposite w a l l . She closed the door and rep- the f i r e by telephonhg 911. As she left the house, she s a w fire and smoke throughout, including on the cedar shake roof. After arriving a t the scene, the Tulsa Fire Deparhnent closed a Z-inch abaveqx~t~~I gas valve on the line where it entersd the residence and then began extimpkhing the f i n . A t 8:25 p.m., the f h department notified the Oklahorra Natural Gas aanpany (QNGC) dispatcher about the incident. A t 8:37 p.m., a a- service technician arrived, and the fire mrshid told kim that the 2-inch gas valve at the house was &trt off. The service tezhician w e n t to close the meter valve in the buried concsete box, but he was unable to find it because it was cavered w i t h several inches of soil and sod. U s i n g a steel bar, the service technician pmbed the soil until the bar struck the steel-plate mtex box caver. After clearing and opening the cover, the technician s a w that it was filled w i t h soil, covering both the gas regulator and meter. H e remLNed erciqh soil to expose a 1-inch 5702#

Page 2valve between the regulator and meter and then closed that valve to shut off the gas flow frum the Fisher type 733A gas service regulator to the Amrican Imrlcase type 25B gas meter assembly. %e M c i a n remained on stanllby until the fire marshdl gave him permission to enter the residence to test the gas fuel lines in the hcuse for leaks. He closed a l l of the gas fuel line valves at the gas a&pliances and capped a funlace fuel line that had been s e v d during the fire. The r w r t mmiq, the ONGC cxwf installed a 100-pig gauge on the fuel piping a t an Outside Rheem gas furnace. The 1-inch valve downStream of the regulator ad irlside the concrete meter box was opened to supply mturdl gas for the test. The gauge registered 40-pig pressure, Wfsidi was the sam% as the pressure in the gas main. The oN(;c astoner service forenan concluded from this test that the regulator was faulty and mprted this to the fire mvshdl. The forerran then told the Senior meter and regulator technician to clear the soil from the regulator and meter and to check tlie gas pressure at the regulator inlet and outlet. E~th the inlet and outlet pressures were 40 p i g . Next, when the urtd- meter box was cleared of soil, tlle rqulator vent cap was found to be missing fm the regulator vent line. Soil was also remJved from the inside of the 1/4-hc!h regulator vent line, and the technician read the regulator inlet arld outlet pressures once mre. The inlet pressure was 40 p i g , and the outlet pressure was 1/4 p i g . The regulator and meter w e r e removed and taken to the ONGC service center for further examimtion. The Safety Board exam^^& ' thegasmeterandewrmned . andpressuretested the service regulator. The glass m e r over the Amricari Ironcase type 25B meter dial was broken, but no intenxd. damage to the meter was found. Examination of the Fisher 733A gas service regulator revealed that the built- in safety relief valve for the regulator was adjusted to the closed position, the wax seal was missing fm the relief valve spring adjustment hole a t the bottom of the safety relief valve body, the aluminum die-cast safety relief valve m e r was cozToded and heavily pitted, and the mtal upper diaphragm supprt within the regulator contained stains indicating a previous presence of water and soil. The Safety Board's r e v i e w of ONGC's gas servioe operat- arld mintenance practices and records revealed the following: o ONGC's records are inadequate to determine the manufacturer or type of service regulator installed on gas service lines. o WGC's pnxehres call for employees to conduct a visual && of the gas service replator vent "at every occasion that a campany employee is working on the property to see that it is free and open and not in a p i t i o r i that rainwater w i l l enter the requlator,99 and the ccarrpany's Itmrds hd.cate that the meter at 3805#

Page 33 East 98th Street had been read during the previous mnths. However, the employees that read the meter had not been trained i n these procedures and had not visually checked the regulator or reported the broken meter dial glass or soil that was accumulating in the meter box. o ONGC does not reqtLre regulator relief valves to be tested when main+xmance tests are perfomed or when service regulators are remnditioned. ?he investigation indicates that the Fisher type 733A gas service regulator failed to d i c e the gas deLivered to 3805 East 98th Street to a safe pressure. This most likely ormrred muse water and soil f m the undergrourd meter box entered the regulator thmugh its vent line, soil accumulated on top of the regulator diaphragm, and over time, soil sealed the regulator vent hole. The added w e i g h t on the diaphragm was sufficient to prevent the r q d a t o r fmm closing fully when the desired d m t r e a m pressure had been reached. Although the regulator had an intend relief valve to prevent excess pres- frum entering the cmtmx-service-line segrrwt, it could not operate because it had been adjusted to the closed position. M o s t likely the relief valve had been adjustea t o the closed position before installation because the adjustrrr?nt s c r e w could not be readily accessed after the regulator had been installed. The ONGC does not have a policy on the use of excess flow valves. It did install a f e w excess flaw valves as a pilot prcgram during the late 1960s and early 1970s, but it has not fornrulated a policy on the use of these valves or performxi an assessment of the current, in-p.mvea generation of excess flow valve designs since that early effort. Had an ex- flow valve been installed in the gas service line at the gas main before this accident, it would have rapidly stoppea the flow of gas that fueled the fires after the gas appliance and fuel line failures. The elimination of natural gas as a fuel source may have reduced the extent of the f i r e damage and reduced the spread of fire w i t k i n the residence. The National Transportation Safety Board determined that the probable cause of the accident was Oklahoma Natural G a s ccacpwlyrs failure to ensure that the gas service regulator safety relief valve was adjustea properly and operating as designed before being installed and that the regulator relief vent line wm not obstrticted after being installed. rnritributing to the extent of f i r e damage was the lack of an e,.cess flow valve on the gas senrice line, which would have rapidly stoppea the flow of gas into the house after the c m t m x ' s appliance and fuel lines ruptur&. As a result of its investigation, the National Transportation Safety Board mzmwrds that the Oklahcnm Natural Gas Capany: periodically inspect all gas service regulators installed underground to detmmbe whether the vent lines are obstructed and correct deficient coralitions identified. (Class 11, Priority Action) (P92-1)#

Page 44 C o ~ c t a one-time irlspection of Fisher type 733A and other qas service regulators w i t h adjustable relief valves to determire whether the relief valves are pmperly adjusted to protect dumstxwm gas piping from excessive pressures ard correct deficient corditions identified. ( C l a s s 11, Priority Action) (P-92-2) win all employees respnsible for viewing service line e a t o r installations to conduct visual inspections of m a t o r vents as Specifia i n ONGC prwxdwes anl instruct them on actions to take &en deficient corditions are identified. (Class 11, Priority Action) (P.92-3) Require service regulator technicians to test regulator relief valves when performins maintenance tests or reconditioning regulators to determine that these valves operate according to the miufacturer's specifications. (Class 11, Priority Action) (P-92-4) Install excess flow valves on new and rerlewed single- custamr residential high-pressure services that have operating conditions ccorpx3tible w i t h the rat& parameters of a t least one model of commercially available excess flow valve. (Class 11, Priority Action) (P.92-5) Ttie National Transportation Safety Board is an irdeperdent Federal agency w i t h the statutory responsibility I t t o p m t e transportation safety by conduding indepmdent accident investigations and by fonmrlating safety i n p r u v m t nxommdationstt (public Xaw 93-633). The Safety Board is vitally interest& in any action taken as a result of its safety mcammfiations. Therefore, it would appreciate a response from you rega?&q * action taken or coritemplated with respect to the -tiow i n this letter. Please refer to Safety Remmmdations P-92-1 thmugli -5 in your reply. cxxJGmm, Acting chainran, and IAuEm, m, HAMMERscHMIm, and KOISI'AD, Members, concurred i n these recammendations.#