Source: http://www.capecodonline.com, April 5, 2009
By: Doug Fraser
For nearly 60 minutes, gas-fueled flames shot into the night sky at the Cape Cod Animal Hospital March 9, fed by a wide-open natural gas line that had blown off at the meter in an explosion that destroyed several rooms at one end of the sprawling clinic.
While firefighters battled the blaze from the opposite end of the building, work crews from National Grid, Cape Cod’s natural gas provider, struggled for an hour to locate their gas line and shut it off, at one point mistakenly following an underground television cable that was more than 50 feet from the real line, witnesses said.
In the end, not finding the gas line didn’t have a large impact on the outcome of the fire that killed four animals, said John Farrington, chief of the Centerville-Osterville-Marstons Mills Fire Department. The gas fed the flames on the south end of the building, which was already “pretty much gone,” he said.
Besides, firefighters aren’t as worried when the gas is burning. “When it’s up in flames we can see where it is,” Farrington said.
A bigger concern is when excavators puncture or damage a gas line while working on construction sites or in the street. When that gas escapes, sometimes there’s a deafening roar, but other times it travels underground — silent, unseen and potentially deadly.
The West Barnstable explosion, and the continuing problem of excavation incidents involving gas lines, raises questions about whether the gas companies know where their lines are, and whether private contractors and municipalities are taking every precaution to protect homeowners.
National Grid maintains a detailed electronic mapping system of all its underground lines, according to company spokesman David Graves. But neither the state nor local towns keep maps of gas lines when they are installed, altered or removed.
Excavation incidents happen “fairly routinely,” state Department of Public Utilities Executive Director Timothy Shevlin said. “But they don’t typically result in a home explosion.”
But sometimes they do. Recent news reports on a Somerset home explosion Feb. 19, which killed a 62-year-old woman, said investigators were examining a long section of gas pipe that may have been damaged when a sewer line was installed over 30 years ago. A 64-year-old man was killed and three homes destroyed in an excavation-related explosion in Plum, Pa., in 2008. A homeowner and a gas company employee were killed in a similar blast in Saratoga Springs, Wyo., in 2007. A 2003 explosion injured 14 in Wilmington, Del.
Shevlin said there are, on average, two home explosions due to natural gas a year in the state, although there have been five this past year.
A high number of excavation incidents nationally was the reason for the Dig Safe movement back in the 1970s. Dig Safe laws, which have been in place in Massachusetts since the late 1980s, require anyone doing excavation work to call a central switchboard, which notifies gas, electric, phone, water and cable utilities who then must clearly mark the route their underground lines take with color-coded flags and/or spray paint. Excavators also must use hand tools when working closely to the buried line, unless trying to penetrate rock or other hard surfaces. The contractor must stay at least 18 inches away from the marked lines with mechanical tools.
Although National Grid, Dig Safe and the state DPU could not provide any data, the National Transportation Safety Board recently estimated that excavation damage to pipelines, nationally, accounted for 50 to 60 percent of all pipeline accidents in the 1970s. That number dropped to around 25 percent since Dig Safe laws started being enforced.
In 2007, the DPU received more than 1,800 complaints of possible violations of Dig Safe laws, resulting in about $140,000 in fines to contractors and utility companies. Shevlin said the leading causes of excavation incidents are not waiting for the utility companies to mark the lines; digging too close with a backhoe; or lines wrongly marked by the utility or subcontractor hired to do the job. In some cases, utility companies, or their subcontractors, are using outdated maps or following the wrong line, Shevlin said.
“Sometimes they’ve said (the gas line) was on one side of the road, and it was on the other side,” Chatham Deputy Fire Chief Richard Hunter said.
Work crews from Enterprise Excavation in Plymouth struck a gas line earlier this winter following a marking that was off target by more than 15 feet, said Rory Kelleher, the company’s business manager.
In some cases, Dig Safe is “more of a curse than a blessing,” Kelleher said. “If you come out, and a utility company has marked a line in the wrong place, particularly if it’s significantly wrong, your crew might be digging, feeling comfortable with the fact that they’re nowhere near this utility line, and then hit it. “¦ If there’s that uncertainty, they’d probably be more cautious.”
“On the whole, they’re pretty accurate, about 98 percent of the time,” countered Tom O’Hara of Northeast Construction in Brewster. Chris Our, owner of Robert B. Our construction company in Harwich, agreed. If they are in doubt, Our said that his crews use their own metal-detecting equipment to test the accuracy of the Dig Safe marks, and will uncover the gas line with hand tools.
National Grid spokesman David Graves, in an e-mailed response, said that, out of 200,000 Dig Safe operations his company conducted in New England last year, “a few were noted for routine issues that required no follow up by the company or any state agency.”
Fire chiefs and other municipal officials say that sometimes the gas pipes are in a different spot than what’s shown on a map.
When he was supervising new sidewalk construction in downtown Orleans, Brewster DPW director Bob Bersin found some gas lines were close to the surface, not down to the minimum required depth of 18 inches. When Orleans DPW crews were trying to unplug storm drains a few years ago using high-pressure hoses, they found that gas lines had been trenched right through the corrugated steel culverts next to the roadway.
To complicate matters, each town decides which side of the road to put the gas lines. In Chatham, the gas lines are often right on top of the water lines, and water company workers have to work carefully, water department director William Redfield said.
When there is an excavation incident, a fire crew is typically called to the scene, where they take a reading with their gas-sniffing devices, establish a perimeter, evacuate everyone within that boundary, and wait for the experts from National Grid to shut off and repair the line. They don’t wait long, because help arrives within 20 to 30 minutes, said most departments.
But it’s a wait filled with unknowns. Natural gas is almost 90 percent methane but is only explosive when it has the right mix of gas to oxygen. It is too rich to explode flowing directly out of a pipe, and too lean to ignite when it’s dissipated into the atmosphere. But at some point in between, it reaches that explosive threshold.
Harwich Deputy Fire Chief Norman Clarke said he worries the gas might be pooling in a pocket of terrain, or, following the loose soil around a pipe, collecting in a basement, reaching that critical mix when a cell phone or pilot light will set off an explosion.
“Our instruments only detect the presence of gas,” Orleans Fire Chief William Quinn said. “It doesn’t give us a reading that warns us that it’s close to explosive.”
A natural gas leak in a street when the line is punctured by workmen, or a slower leak underground, is “an extreme challenge to us,” Clarke said. “The minute you get complacent, you’re in trouble.”
In December 2005, Bergenfield, N.J., firefighters thought they were responding to another routine gas leak. According to a National Transportation Safety Board investigation report, excavators removing an underground oil tank accidentally hit a gas line and pulled it loose at an unseen junction under the soil seven feet from an apartment building. The fire chief and firefighters testified they didn’t see, hear or smell the gas escaping underground and didn’t evacuate the apartment building. Within a half hour, it blew up, killing three residents and injuring five others.
The most insidious damage may be that done by an excavator who grazes a gas line and damages it without causing a leak. He may not even know he’s done the damage, and covers it up when the trench is backfilled. The leak, caused by corrosion, a broken seal or pressure on the damaged spot may not happen for years, even decades. In the Somerset explosion, the reported leak in a steel gas main took more than 30 years to develop.
“A fact of digging is that it can change soil structures. It may have seemed safe, but if it’s not tamped down correctly, settling can occur and cause disruption,” said David White, an injury attorney at Breakstone, White & Gluck in Boston. White has represented victims of natural gas explosions and is a past president of the Massachusetts Bar Association.
White compares excavation work to surgery. But the standard operating tool is not a scalpel but the powerful, and imprecise, bucket of a back-hoe.
Excavation contractors like Our and O’Hara said that safety resides in the experience of the person operating the backhoe.
Following Dig Safe requirements to stay at least 18 inches away from marked lines, using hand tools when operating close to lines, and digging by hand to locate them would reduce go a long way to minimize excavation incidents, contractors said.
But others questioned the incentive for a backhoe operator to report suspected damage when the consequences can be severe. Work comes to a standstill while the utility sends someone out to investigate. Significant fines can be assessed to the excavation company if they are at fault.
White thinks an independent inspection of all underground lines for damage should be required before a trench is backfilled. But excavators said that would be a logistical nightmare and costly, especially given the rare number of tragic incidents.
White doesn’t think the low number of incidents makes them less deserving of attention.
“You have no problems, and then there’s a big problem,” he said.