Peoples Gas Light and Coke Co. said Monday that it is investigating whether human error caused the gas surge that led to a series of fatal Near Northwest Side explosions and fires.
Company officials raised the possibility after meeting with state utility regulators and acknowledging that one of its crews was overhauling pressure-regulating equipment in the neighborhood when the freakish accident occurred just before 4 p.m. Friday.
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The equipment, underground at West Erie and North Green Streets, was shut down when the gas surge occurred.
Peoples Gas officials said they were investigating whether the shutdown might have overloaded the pressure regulator that malfunctioned less than a half-mile away at West Chicago Avenue and North Carpenter Street.
The company has initially blamed the surge on the failure of the Chicago Avenue regulator and its backup, which are in the same underground vault.
Meanwhile, two victims of the accident were identified Monday through dental records by the Cook County Medical Examiner`s Office.
All three victims were pulled from the rubble of 824 N. Racine Ave., one of 18 buildings damaged in the explosions and fires, but the only one leveled. Alan Bass, 40, lived and operated a photo studio at 824 N. Racine. His body was found Friday. The bodies found later were identified as Stephen Hoenig, 19, of Glencoe, a customer at Bass` studio, and Victoria Opeka, 31, a studio makeup artist.
Peoples Energy Corp., the parent company of Peoples Gas, said Monday that it has ”adequate” insurance from a variety of carriers to deal with the inevitable damage and liability claims stemming from the accident.
Wall Street appeared to shrug off the news of the gas explosions as having limited or no effect on the company`s earnings. Peoples Energy stock closed Monday at $26.37, down 12 cents on the New York Stock Exchange.
Peoples Gas was looking at the possibility that human error caused the gas surge after telling officials of the Illinois Commerce Commission that company workers were performing an annual overhaul of the Erie Street regulator when the accident occurred.
Patrick Doyle, vice president of operations for Peoples Gas, said that when demand for natural gas is low in the summer the company frequently shuts down one of each pair of regulator vaults in the city because one is sufficient to supply homes and businesses. There are about 400 regulator vaults throughout Chicago, he said.
But Doyle and other company officials declined to say whether problems could arise from shutting down a regulator, even temporarily, on a bitter-cold day like Friday, when demand for gas to heat homes was high.
Peter Munoz, a Peoples Gas spokesman, confirmed that the Erie Street regulator was shut down for maintenance when the gas surge occurred.
Asked whether the shutdown might have overloaded the Chicago Avenue regulator, he said the scenario ”sounds good, but it`s too early in the investigation to say for sure.”
Workers had shut down the Erie Street regulator as part of an annual review in which they check the integrity of the valves, seals and other internal equipment, Doyle said. All of the utility`s regulators receive such annual checks, he said.
Peoples Gas also has said that the Chicago Avenue regulator believed to have caused the accident had undergone a less-rigorous weekly checkup Thursday.
In a weekly inspection, workers remove a paper chart on which pressure data and other information is recorded. That information shows the company whether the regulator is operating properly.
No problems were noted during Thursday`s review of the Chicago Avenue regulator, Peoples Gas has said.
Doyle said the Chicago Avenue regulator and its backup were manufactured in 1961. He said 31 years is not considered old for such equipment.
The Chicago Avenue and Erie Street regulators work in tandem to serve about 640 homes and businesses in a neighborhood between the Kennedy Expressway and the Chicago River and roughly along Chicago Avenue.
The vaults drop the pressure of gas flowing in from transmission lines at about 20 pounds per square inch to about 4 ounces per square inch, a level that furnaces and other gas-burning appliances can handle.
Because the pressure was not reduced Friday before it entered buildings, appliances were hit by a surge of gas about 80 times stronger than they normally receive. Gas blew out of appliances and exploded or caught fire wherever it met a spark or flame.
A system in which the gas pressure for a neighborhood is reduced at a common regulator is called a ”low-pressure” distribution system. About 88 percent of the 844,000 Chicago customers of Peoples Gas receive their natural gas through such a system.
The other 12 percent, as well as most suburban gas customers, are served by a more modern ”medium-pressure” distribution system, in which the pressure is reduced at each building`s individual gas meter.
Although the low-pressure system is not considered unsafe, the failure of a single pressure regulator in the medium-pressure system would have limited the damage to a single home.
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Most older U.S. cities remain at least partially dependent on low-pressure systems. Peoples Gas is switching to medium pressure slowly, but not for safety concerns, Doyle said. He said it is cheaper for the utility to switch because it can transport higher-pressure gas through less expensive smaller pipes.
Peoples Gas has converted to medium pressure in parts of Chicago where road resurfacing has made it easy to dig up old pipes, Munoz said.
Northern Illinois Gas Co., the gas utility for most of suburban Chicago, serves more than 90 percent of its customers through medium pressure, spokesman Scott Lewis said.
The only NI-Gas customers that continue to receive gas through low-pressure distribution live in scattered sections of close-in, older suburbs such as Evanston, Maywood and Oak Park, Lewis said.
North Shore Gas Co., which serves the north and far north suburbs, has almost entirely converted to medium pressure, a spokesman said.