State transportation officials have discovered corrosion in some of the lighting fixtures throughout Boston's Big Dig tunnel system after one of the 110-pound fixtures crashed onto the road in early February, missing cars traveling below.
No one was injured.
Transportation Secretary Jeffrey Mullan said workers have inspected 95 percent of the 23,000 light fixtures, including all the fixtures located over roadways. He said some corrosion was detected in less than 2 percent of the fixtures, and there's no danger to the public.
"This is a relatively isolated incident, but it's something that we're taking very seriously," Mullan told reporters Wednesday. "The tunnels remain safe."
Mullan said the fixture is the first lighting element to fall since the $15 billion network of tunnels, bridges and roadways transformed downtown Boston. The project officially came to an end in 2007.
Mullan said the state has notified the Federal Highway Administration about the problem and has contacted the manufacturer of the fixtures, NuArt Lighting in Fullerton, Calif.
A call to NuArt Lighting was not immediately returned.
The Big Dig was the most expensive highway project in U.S. history, prompted criticism of pork barrel spending, and was plagued by cost overruns and design problems, including leaks.
The most serious incident occurred in July 2006, when several 4,600-pound ceiling panels in another portion of the tunnel system broke free, crushing a passing car.
The accident killed 38-year-old Milena del Valle of Boston. In 2008, contractors who worked on the project agreed to pay more than $450 million to settle a lawsuit stemming from the tunnel ceiling collapse and to cover the costs of leaks and design flaws.
The National Transportation Safety Board concluded the accident occurred because the wrong type of epoxy was used to hold bolts that anchored the ceiling tiles in place.
In the aftermath, then-Gov. Mitt Romney ordered a full review of the project to ensure its safety. The $4.5 million report was issued in November 2006 and found the highways, tunnels and bridges in downtown Boston were well built overall but needed some safety improvements.
Mullan said each of light fixtures consists of two 8-foot powder-coated aluminum components clamped to the ceiling with 10 stainless steel clips.
He said where corrosion was detected in the aluminum sections, the clamps were moved to a non-corroded portion. He said the state is working on permanent fix for the problem.
Mullan said the corrosion is linked to the installation and manufacturing process combined with the weather and the salt used to treat roads in the winter. The fixture that fell was located on Interstate 93 northbound near the portal of the Thomas P. O'Neill Jr. Tunnel.