Debris rains on vehicles in tunnel

One day after federal officials declared the Big Dig's tunnels safe, rocks and other debris rained down from an overhead vent in the Interstate 93 southbound tunnel yesterday and damaged at least five vehicles, including an ambulance transporting a patient from Massachusetts General Hospital.

The debris, which witnesses described as ranging from pebbles to rocks smaller than a golf ball, poured down near the Purchase Street exit between 11 a.m. and 11:30 a.m., cracking windshields, damaging mirrors, and denting car roofs, according to motorists and the State Police.

Mariellen Burns -- a spokeswoman for the Massachusetts Turnpike Authority, which manages the tunnels -- said rocks and sand poured through a shaft that leads from an above-ground vent building that workers are demolishing. Burns said the debris was not falling from the tunnel ceiling and said the episode did not suggest that the Big Dig is structurally unsafe.

''This is not a tunnel issue; it's an issue of demolition going on up above," Burns said.

There were no reports of injuries, but an executive with the company that owns the ambulance, American Medical Response, said he would no longer send vehicles through the tunnels until he was certain the Big Dig is safe.

One motorist, Maura Vogel of Somerville, said a rock slightly smaller than a golf ball whizzed through the open sunroof of her BMW and landed on the empty passenger seat, while other rocks caused two small holes in her windshield.

''I was pretty startled," Vogel said. ''I worried that the tunnel was going to implode."

''It was like a bolt of lightning," said Timothy F. Mahoney, whose 1994 Chevrolet Blazer was left with several pebble-sized holes in the windshield and a softball-sized dent in the roof after traveling through the tunnel around 11:15 a.m. yesterday.

The vent that discharged the debris had once been part of the air-cleansing system for the former Dewey Square tunnel, which was rehabilitated and renovated as part of the Big Dig, Burns said. The vent was connected to a ventilation building that is being demolished and replaced by a new structure, but the contractors doing the demolition work, Modern Continental Construction Co., failed to close off the vent before starting the demolition work, Burns said.

The area above the I-93 tunnels will continue to be an active construction and demolition zone for months, as workers build parks and other structures. But Burns said project officials and contractors would redouble efforts to keep debris from falling into the tunnel and endangering motorists.

Modern Continental issued a statement yesterday taking responsibility for the accident and apologizing to the motorists involved.

''First and foremost, we want to underscore that this was an isolated incident and is in no way related to the structural integrity of the tunnel," the statement said. ''Modern Continental takes full responsibility for this matter, and wants to express sincere apologies to the motorists who were affected.

''This incident appears to have resulted from demolition work being conducted on an active construction site adjacent to the tunnel," the company statement said. ''This work caused dirt and gravel to become dislodged and fall onto the roadway. The company is conducting a complete investigation into this matter to ensure that this does not happen again."

A State Police spokesman said troopers shut down two lanes of the tunnel for about 15 minutes yesterday so Turnpike Authority engineers could assess the situation.

There was a pile of what looked like sand in the roadway when Turnpike officials arrived, but no other overt evidence of what had transpired, Burns said. They determined, however, that the debris came from the vent.

Modern Continental was also responsible for the tunnel wall section that had a gushing leak in September, as well as for dozens of other defective spots in the walls. The Cambridge-based firm, which has performed more work on the $14.6 billion Big Dig than any other company, was on the verge of bankruptcy last year when its insurers took control of its financial obligations and competitor Jay Cashman Inc. took over its remaining state contracts.

Recent disclosures that the walls are peppered with defects, that hundreds of leaks riddle the tunnels' roof, and that fireproofing material on the ceiling was compromised by the water had already shaken the faith of many motorists. The situation was made worse when two independent engineers recently told reporters that turnpike officials had denied them crucial documents related to an inquiry into the leaks and that, as a result, they could no longer vouch for the tunnels' safety.

The news turned positive on Monday for Turnpike Authority chairman Matthew J. Amorello when the Federal Highway Administration released a report saying that the tunnels are structurally sound and safe for drivers to use.

Amorello, whom Governor Mitt Romney asked to resign over the leak problem, also told reporters, ''If the road wasn't safe, I'd shut it down immediately."

Brian Keeter, spokesman for the Federal Highway Administration, said the agency was standing by its assertion that the I-93 tunnels are safe for drivers.

''This incident is unrelated to our leak assessment of the project and the findings that the project is structurally sound," Keeter said yesterday.

Nonetheless, motorists involved in the situation yesterday said they were shaken.

Kevin Prendergast -- vice president of Northeast operations for American Medical Response, which owns the largest private ambulance fleet in the nation -- said his vehicles will not use the I-93 tunnels until he is convinced that his drivers will not be put at risk. The firm has roughly 150 ambulances on the region's roads on typical weekdays, he said.

''My thinking is, the public ought to have a safer means of traveling through the city," Prendergast said.

''My ambulances are in the tunnel dozens of times a day. Our communications center has advised all vehicles operating in the Boston area now to avoid the tunnels until further notice."

Prendergast said that the ambulance driver, who had swerved to avoid the falling debris, pulled over to assess the damage to the windshield and continued toward Fall River, where the patient was being discharged. Prendergast described the damage as ''star cracks," like those created by small rocks.

Mahoney, a retired English teacher who lives in Arlington, was traveling to Cape Cod when his SUV's roof and front windshield were hit by falling debris. ''It was so quick; I didn't see anything coming down," Mahoney said. ''It wasn't like it was falling and I drove into it. It was just like bang!"

He said that since his Blazer is 11 years old, he does not carry collision insurance for the vehicle. ''So it's either going to be me or the Turnpike Authority who pays for it," he said.

Vogel, who was driving her partner's BMW 328i, said she was rattled by the falling debris, but considers the tunnels indispensable for commuting from Somerville to her auto-detailing business in Whitman.

But she did question the federal government's unqualified assertion that the tunnels are safe.

''I don't know what qualifies as safe, but this rock is really sharp," she said, examining a stone during a telephone interview. ''It could have smacked somebody right in the head."