No alarms went off in Columbia Gas Transmission's Charleston control room Tuesday afternoon, even as a massive explosion rocked one of the company's natural gas pipelines 15 miles away, the National Transportation Safety Board said Wednesday.Nor could Columbia quickly shut off the flow of gas fueling the nearby inferno, NTSB member Robert Sumwalt told reporters Wednesday evening.It took just over an hour for Columbia to manually stop the flow of gas to the pipe, even as fire roared through the hills, filled the sky and scorched the earth near Sissonville.Columbia is a subsidiary of Indiana-based NiSource.NTSB investigators will visit Columbia's control center along the Kanawha River this week to try to learn why no alarms sounded, Sumwalt said. Federal regulations go on at length about the efforts companies must make to manage their alarm systems, which are designed to alert companies when operations go awry.Companies that use automatic shut-off valves can stop the flow of gas "instantaneously, if not very, very quickly" during an emergency, Sumwalt said."Part of our investigation will be looking to see if this pipe was shut down in a reasonable and prudent fashion," he said.The NTSB has recommended companies install these automatic shut-off valves in "all 'high consequence' and relatively more populated areas," according to a March report by the Congressional Research Service. About 4,000 people live in Sissonville.Sumwalt said Tuesday's explosion created a crater 17-feet deep. It also caused a 20-foot, 7-inch gap in Columbia's interstate pipeline, which carries gas from the west to the east. Where did the chunk of pipe go?"Basically that part was ejected out of the crater about 40 feet," Sumwalt said. The 20-inch underground transmission line ruptured about 12:41 p.m. Tuesday. The flow of gas did not stop until about 1:45 p.m.The NTSB said the ruptured pipe was near two other Columbia-owned gas transmission lines: a 30-inch pipeline was 53 feet to its north and another 26-inch pipeline was also within 200 feet of the exploding pipeline. All three pipes had gas flowing through them at more than 900 pounds of pressure per square inch, Sumwalt said. The pipeline that ruptured was allowed to have no more than 1,000 pounds of pressure going through it."Even though it may seem they are closely spaced, the other ones were not even uncovered in the conflagration," Sumwalt said.Sumwalt provided few other details about the incident or about the nature of the pipe. He did not say the age of the pipe, when it was last inspected or if the explosion was connected to another Columbia pipeline explosion in the Kanawha Valley a decade ago. In early August 2002, one of the company's gas lines exploded on the Kanawha and Putnam county border, sending a cyclone of orange flames billowing hundreds of feet into the air. The site of that blast, in the community of Lanham near Cross Lanes, and Tuesday's blast are miles apart. But one regulatory filing suggests the pipes involved may be connected. Tuesday's explosion occurred on pipe known as SM-80, according to state authorities. The 2002 explosion occurred after a ground slippage on what is known as the "SM-80 loop," according to a federal regulatory filing by the company. Columbia did not comment Wednesday on whether the two incidents were on the same line.Aging systemTuesday's explosion comes as Columbia is asking federal regulators to approve a multi-billion dollar plan to modernize its underground transmission lines.In seeking approval for the plan, the company has been frank about the state of its aging pipeline system. Columbia owns 1,070 miles of "high risk" pipeline, according to a federal regulatory filing by the company. That is about a tenth of the pipeline the company owns. It is also the most miles of high-risk pipe owned by any gas company in the country.Columbia's system includes more than 11,000 miles of interstate transmission pipeline from Tennessee to New York. About half those miles were built before 1960. Modern federal pipeline regulations were created in 1968.NiSource Vice President Jimmy Staton told Kanawha County legislators Wednesday that the ruptured pipe near Sissonville had been laid in the 1990s, according to two lawmakers who attended that meeting.Pipelines are a bit like old cars: even if most of it is old, some parts are new.Columbia has been taking steps to upgrade its own high-risk lines. It is not clear if the Sissonville line is on the list to be upgraded. "We will be looking at that, but we don't know at this particular point," Sumwalt said.The company said higher risk pipes include pipes made only of bare steel. Columbia spokesman Shawn Tolle described the Sissonville pipe as "coated steel." He could not provide any other details Wednesday.Standard Oil originally constructed a "significant portion" of Columbia's current pipeline system in the early 1900s to transport oil, according to Columbia. InspectionsAmerican pipelines are regulated in a few different ways. But, at least in West Virginia, there appears to be infrequent inspections and those inspections depend, in part, on the work of companies themselves.In West Virginia, five staffers at the state Public Service Commission are tasked with regulating the 4,000 miles of transmission lines buried beneath the state. Transmission lines are the largest of the natural gas pipes. There are about 11,000 miles of smaller pipes -- known as gathering and distribution lines -- that also run across West Virginia.To cope, the PSC generally inspects gas companies once every three years. The U.S. Pipeline and Hazardous Materials Safety Administration approves the PSC's inspection plan, said PSC spokeswoman Susan Small.Columbia's transmission lines were last inspected by the state in 2011. Companies generally police themselves, and they have their work checked by the state regulators, Small said. State regulators also do spot checks of certain elements of the pipeline.The PSC's 2011 inspection found three problems at Columbia pipelines in the area. None of the violations are directly related to the structural integrity of pipes, according to a review of those inspection records.The federal pipeline administration, known as PHMSA, also does inspections of its own. So far this year, federal inspectors have done six inspections of Columbia facilities in the 13-state region that includes West Virginia, according to the agency's records. So far, inspectors issued one warning to Columbia as a result of an inspection near Cumberland, Md. Federal regulators said Columbia operations had failed to regularly inspect pipes for corrosion or ensure employees were properly trained for emergencies.Contact writer Ry Rivard at email@example.com or 304-348-1796. Follow him at www.twitter.com/ryrivard.