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A firefighter sprays water at a liquid propane fire simulating a blown flange between two pipes. The training was part of a gas fire course held at the Massachusetts Fire Academy in Stow that Harvard firefighters attended in October 2008.(Courtesy photo by Bob Mignard)
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| Firefighter Justin Warren stand in front of a pool of liquid natural gas as it responds to water being sprayed on it.(Courtesy photo by Bob Mignard) |
For several days this September, news of the explosion that leveled a section of San Bruno, Calif., dominated local headlines, TV newscasts, and Internet buzz. Though the cause is still being investigated, the blast measured 1.3 on the Richter earthquake scale, killed eight people, sent dozens to local hospitals, some with serious burns and injuries, and set off fires that destroyed 37 homes. Experts who have seen photographs of the site say the event most likely began with the "catastrophic failure" of a section of 54-year-old natural gas pipeline owned by Pacific Gas and Electric (PG&E). Residents have told reporters and investigators they had no idea such a large transmission pipe ran unseen through their community.
Here in oil-dominated New England, natural gas has become an increasingly important fuel over the past half century, so news of any explosion inevitably raises the question of whether one could happen here, and particularly in Harvard. The answer, the Press has learned, is that while accidents do happen, an explosion like the one in San Bruno is unlikely. No major transmission lines pass through the town. Reported gas leaks have declined over the past 10 years. And according to Harvard Fire Chief Bob Mignard, none of the major fires to which the Harvard Fire Department has responded during his six-year tenure has been a gas fire, nor has he heard of any before his time. "When there is a serious fire," Mignard said in a recent interview, firefighters "will talk about it for generations," but such a story, he said, is not part of local lore.
"Every energy source has a certain level of risk," National Grid spokesman David Graves told the Press in a phone interview last week, but gas explosions and fires are "relatively rare" events. And while accidents do happen, he said, with proper precautions they are unlikely.
The number of Harvard buildings that use gas for heating or cooking is relatively small, and unlike the concentrated community of San Bruno, they are spread along the town's main thoroughfares and back roads on two-acre lots. The elementary school and new library run on natural gas, but the Bromfield School, Town Hall, the General Store, and other buildings continue to burn oil. The Harvard Energy Advisory Committee (HEAC) has recommended that all municipal buildings convert from oil to gas because of its greater efficiency and smaller carbon footprint, and Bromfield is likely to do so in 2011, if the town can find the money.
National Grid, an investor-owned utility, is the sole town gas utility. Graves says his company has roughly 341 customers inside Harvard's historical boundary, which includes Devens. Mignard and Harvard Gas and Plumbing Inspector Jim Bakun say that a growing number of Harvard's roughly 2,000 homes and buildings, especially new ones, are choosing to operate on propane gas, which is delivered by independent distributors to 500- to 1,000-gallon underground tanks or in pressurized bottles, rather than via underground gas lines.
National Grid gas is piped to customers through underground gas mains and street-to-meter service. National Grid in turn buys its supplies from the Tennessee Gas Company, a subsidiary of energy giant El Paso, which delivers gas to New England from Louisiana and Texas through large-diameter transmission pipelines at high pressure. A branch of the Tennessee transmission pipeline skirts the southern edge of the Harvard town line and travels along the western boundary of Devens and is the largest pipe close to the town. There are gateways in Clinton, Acton, and Lunenburg, which local utilities such as National Grid tap for their supplies.
Ferreting out the exact location of Harvard's gas mains, or distribution pipelines, as they are known, has become difficult since the events of 9/11. The Department of Transportation has removed detailed maps from its National Pipeline Mapping website, where formerly it was possible to search for local maps by zip code. Town Hall does not have maps either, nor do the police or fire departments. It turns out that only National Grid can tell you exactly where its pipelines run, but is not anxious to share the information with the public. Once the Fire Department confirms with its meters that a site is leaking gas, the first call it makes is to National Grid.
The roughly 37 miles of gas mains in Harvard enter the town from Ayer along Route 110/111 (Ayer Road) and from Boxborough along Route 111. Anecdotally, additional mains are known to extend from the center of town down Littleton Road to Whitney Lane; up Bolton Road to West Bare Hill Road (where the line bears right and continues downhill to Scott Road); and out Still River Road as far as the Girl Scout camp.
More than two-thirds of the pipeline—26 miles' worth—consists of coated steel pipe; the rest is plastic. Both materials are safer than the cast iron mains installed by many utilities early in the last century, mains that the state of Massachusetts wants utility companies to replace as rapidly as possible. Unlike the 30-foot-wide, high-pressure transmission line that exploded in San Bruno, the gas mains in Harvard are narrower and operate at lower and less dangerous pressures that never exceed 200 psi (pounds per square inch). Most, says Graves, operate at 30 to 60 psi. Within a house, pressures are typically 1.5 psi, says Bakun.
Statistically, the risk of an explosion involving a gas main or house service line is extremely low. The Pipeline and Hazardous Materials Safety Administration (PHMSA), a department of the federal Department of Transportation, classifies gas explosions as "significant" when damage exceeds $50,000 (in 1984 dollars) and "serious" when they result in a fatality or an injury that requires hospitalization. There have been no incidents of either type in Harvard in at least 20 years, according to records kept by PHSMA and the state Department of Public Utilities (DPU). In all of Massachusetts, there were only 12 significant and eight serious incidents between 2004 and 2009, which were responsible for two fatalities, six injuries, and more than $4 million in damage.
Nevertheless, as infrequent as such events are, when natural gas ignites, the results can be devastating. Earlier this week a Bridgewater family was surprised when a 50-pound gas bottle containing what the Boston Globe described as "compressed natural gas" crashed through the roof of their home, after exploding in a nearby dump and hurtling 600 feet through the air. Three years ago, an explosion leveled a house in nearby Groton and showered neighboring homes with flaming debris after a National Grid worker accidentally pierced a buried gas line that fed the structure. The cause of the accident, in which no one was hurt, is still under investigation.
The most common cause of an explosion is a leak provoked by a contractor, a property owner, or sometimes a gas company worker, according to literature distributed by the industry and the agencies that regulate it. In 2009, alarmed by a spate of six explosions between 2007 and 2009, the DPU reexamined seven closed cases from earlier in the decade to search for a pattern of causes, but could find none; each was unique.
According to National Grid, 75 leaks have been reported in Harvard over the past 10 years, 25 called in by residents and the rest found by the company as part of its ongoing inspection programs. Between 2000 and the end of fiscal 2005, 63 leaks were reported in town; from 2006 through the end of fiscal 2010 (Mar. 31, 2010) there were 12 reported leaks. "These numbers would tell me that this is a very safe system and over the past several years, it has gotten even safer," wrote Graves in an e-mail to the Press.
The Massachusetts Dig Safe law is meant to prevent the kind of damage to a pipe that can cause a leak. The law requires anyone who plans to excavate in an area served by gas to call the DPU and local utilities 72 hours ahead of time. The utility is required to visit the site and mark the location of its mains or service lines. The plans that the Town Center Sewer Building Committee is preparing, for example, are based on maps provided by National Grid, the Water Commission, and Verizon, says Project Manager John Potts of Weston & Sampson. "I can assure you that we have copies of the maps," he told the Press.
"It's not just major construction that can pose a risk, adds Graves, "it's also the homeowner, who may just be digging a hole for a fence post." The best way for homeowners to avoid an accidental leak is to follow the Dig Safe law, he said, a violation of which can lead to a $1,000 fine.
As the years pass, pipes and connections are also subject to normal wear and tear. National Grid is responsible for the mains, services lines, and meters in town. Meters must be inspected once every three years. The company inspects its mains roughly once a year. "We patrol the mains in specially equipped vans that have air-testing equipment to detect leaks," said Graves. "We also have individuals on foot, using hand-held air-testing devices to take readings. The frequency of this testing depends on a number of factors, such as the life expectancy of the main, frequency of excavation in the vicinity of the main and its maintenance history," he says.
If a leak does occur, however, you're likely to smell it before it becomes dangerous. The gas that National Grid delivers is mixed with an odorous material that you can smell at extremely low concentrations. If you think you smell a leak, says Mignard, you should do two things: call the fire department immediately, then get away from the source until help arrives.
If you've accidentally dug up a service line to your house, says Graves, let it vent; whatever you do, don't try to rebury it. The mantra is, "When in doubt, pull it out," he adds.
"I'll take 100 false phone calls to avoid a big one," says Mignard, especially when it's a 'street fed' house. Don't feel guilty, he says. If you do, "just pull out your tax bill."
The key to prevention, adds Mignard—who heats and cooks with gas in his own home—is "a proper installation by a licensed professional, inspected by me and the [town] gas inspector. Properly installed and properly maintained, it's quite safe."