Preliminary analysis of a ceiling light fixture that fell into moving traffic in early February at Boston's Big Dig tunnel system suggests the fixture shows signs of severe corrosion caused by salt from snow and ice treatment.

Performed by West Boylston, Mass.-based Massachusetts Materials Research, the analysis indicates the fixture failed because of severe corrosion to the aluminum wire way at the locations where the light assembly was attached with stainless-steel clips, according to a Massachusetts Dept. of Transportation report released on April 13. The incident caused no injuries and no property damage.

In a report released on April 6, MassDOT Secretary Jeff Mullan says that, when the light fixture was attached to the aluminum wire way, the stainless-steel clips may have breached the protective coating covering the wire way. “This may have started the corrosion, which was then accelerated by the environment,” he notes.

Following the Feb. 8 incident, MassDOT electricians performed hands-on inspections of the tunnels' 25,000 light fixtures, said Adam Hurtubise, spokesman for MassDOT. The inspections, which are now complete, included pry tests on the 250,000 stainless-steel clips, the report notes. A total of 4,270 clips, or 1.7%, had failed or were failing due to corrosion. The failed clips were moved to another part of the light fixture and secured as necessary.

Since the fixture fell, MassDOT has changed its annual tunnel inspection protocols. The agency now requires a more detailed, hands-on inspection of each light fixture's components as well as the overall condition of the fixture itself, the ranking of the fixture and the ceiling connection, Mullan states.

While Los Angeles-based AECOM, which received $4.5 million under a three-year contract, missed the light-fixture problem, MassDOT does not consider the company negligent since the prior inspection protocol did not require hands-on inspection of the fixtures, Hurtubise says.

The report notes the revised policy has been forwarded to FHWA for review. In an e-mail, an FHWA spokesperson says that while the agency has not received written tunnel inspection protocols from MassDOT, it expects Mass DOT will incorporate the proposed changes regarding the frequency and method of inspecting the light fixtures. FHWA plans to conduct a review of the tunnel inspection program in June and will request the information in conjunction with that review.

Meanwhile, MassDOT has retained on-call consultant Transystems to engineer a light-fixture backup support system, scheduled for completion in 30 to 45 days, the report notes. The interim repair is intended to be reliable for up to five years; longer term, MassDOT will begin the process of selecting a consultant to evaluate the repair or replacement of permanent light fixtures. Transystems could not be reached for comment.

MassDOT is considering opotions for cost recovery from design, construction, manufacture and installation contractors, but the agency did not name specific any companies.