Another badly corroded light found in Big Dig tunnel

A work crew removed another 110-pound light fixture from a Big Dig tunnel Thursday after it was found corroded and not fully secured to the tunnel ceiling, state transportation officials said.

The latest discovery came five months after an identical light fixture crashed down in the Tip O’Neill Tunnel, prompting transportation officials to conduct a system-wide inspection that quickly revealed nine more fixtures that were so corroded they were at risk of falling, too.

The fixture removed yesterday had been previously inspected in May, said transportation secretary Jeffrey B. Mullan, though it was unclear if the earlier inspectors had found corrosion.

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Workers driving through a ramp connecting Leverett Circle to the O’Neill Tunnel on Thursday noticed the light was vibrating from a nearby jet fan and askew. They removed it and found corrosion on five of 10 connecting clips. They then re-attached it using plastic straps, a remedy that’s been used on lights throughout the Big Dig since the February incident. Of the system’s 25,000 light fixtures, more than 9,000 have now been reinforced with straps.

Mullan, whose department came under criticism for not telling the public about the fallen light fixture for more than a month, announced the latest findings yesterday, unprompted, to reporters who came to ask about his decision to step down later this year. The Massachusetts Transportation Department also posted a full report about the incident online yesterday.

Earlier this week, Mullan suspended the Big Dig’s top engineer, Helmut Ernst, after he told the Globe that he and his colleagues were trained not to leave a paper trail about safety issues in the tunnels for fear of litigation.

Mullan could not say why the corrosion on the light fixture was not discovered during the May inspection.

“We’re working it. I don’t know. I don’t know exactly,’’ he said. “I know it was next to a jet fan. I’ve got my engineering team working on it right now.’’

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The incident report suggested that forced air from the jet fan may have caused the light to vibrate more than normal. The report also suggested that the testing conducted in May, which involved prying loose the clips that connect light fixtures to the ceiling, may have weakened those clips. That type of testing was suspended later in the month “because of the potential for damage’’ to the clips, according to the incident report.

The Globe reported on Sunday that the light clips at Leverett Circle in the southbound lane to I-93, where the light fixture was discovered, had a corrosion rate of 3.6 percent, nearly twice the systemwide average. That portion of the tunnel system has absorbed more leaks than others in the Big Dig, which could promote corrosion. The state pumped 400,000 gallons of water from Leverett Circle in 2010.

Mullan said all light fixtures near jet fans would be re-inspected. A spokesman, Adam Hurtubise, explained later that nine tunnels ramps in the Big Dig have a total of 35 jet fans. Fixtures in three of the tunnels, including the Leverett tunnel where the latest discovery was made, have now been fitted with support straps. Three others have been partially or mostly reinforced with straps. The final three ramps were scheduled to be visually inspected yesterday.

Mullan characterized the shaky light fixture discovered Thursday as the type of thing that comes up all the time in the sprawling transportation network overseen by the state. Asked if it represented a safety concern, he said the tunnels were under constant scrutiny.

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“I think we’ve done extensive testing inspections of it,’’ he said. “I think I’m happy that we’ve made good progress both on the inspections and on the strapping. I’ve been assured by my engineering team that they’re working on appropriate protocols and on a permanent fix.’’

Mullan also addressed his departure from Governor Deval Patrick’s administration yesterday, his first comments since he announced Thursday that he planned to leave for the private sector. He said his decision had “zero, absolute zero’’ connection to the criticism he faced over his handling of the light fixture incident.

“As much as I love this job, I’m committed to transportation reform, [and] the employees at DOT, my family comes first,’’ he said.

Mullan, who had said he would leave later this year, did not give a specific date for his departure. He said he would help Patrick find a replacement.

Patrick said yesterday that he had already begun looking for Mullan’s replacement.

“We’ve been working on that for a while,’’ Patrick said.

Mullan told Patrick in May that he planned to leave later this year because he needs more money, with three school tuitions for his children. Patrick declined Mullan’s request for a raise to his $150,000 salary, but reiterated his support for him yesterday.

“This has been an exceptional secretary of transportation,’’ Patrick said.

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