Highway Accident Report - Ceiling Collapse in the Interstate 90 Connector Tunnel

Boston, Massachusetts
July 10, 2006

NTSB Number: HAR-07-02
NTIS Number: PB2007-916203
Adopted July 10, 2007
PDF

Executive Summary

About 11:01 p.m. eastern daylight time on Monday, July 10, 2006, a 1991 Buick passenger car occupied by a 46-year-old driver and his 38-year-old wife was traveling eastbound in the Interstate 90 connector tunnel in Boston, Massachusetts, en route to Logan International Airport. As the car approached the end of the Interstate 90 connector tunnel, a section of the tunnel's suspended concrete ceiling became detached from the tunnel roof and fell onto the vehicle. Concrete panels from the ceiling crushed the right side of the vehicle roof as the car came to rest against the north wall of the tunnel. A total of about 26 tons of concrete and associated suspension hardware fell onto the vehicle and the roadway. The driver's wife, occupying the right-front seat, was fatally injured; the driver was able to escape with minor injuries.

Probable Cause

The National Transportation Safety Board determines that the probable cause of the July 10, 2006, ceiling collapse in the D Street portal of the Interstate 90 connector tunnel in Boston, Massachusetts, was the use of an epoxy anchor adhesive with poor creep resistance, that is, an epoxy formulation that was not capable of sustaining long-term loads. Over time, the epoxy deformed and fractured until several ceiling support anchors pulled free and allowed a portion of the ceiling to collapse. Use of an inappropriate epoxy formulation resulted from the failure of Gannett Fleming, Inc., and Bechtel/Parsons Brinckerhoff to identify potential creep in the anchor adhesive as a critical long-term failure mode and to account for possible anchor creep in the design, specifications, and approval process for the epoxy anchors used in the tunnel. The use of an inappropriate epoxy formulation also resulted from a general lack of understanding and knowledge in the construction community about creep in adhesive anchoring systems. In addition, Powers Fasteners, Inc., failed to provide the Central Artery/Tunnel project with sufficiently complete, accurate, and detailed information about the suitability of the company's Fast Set epoxy for sustaining long-term tensile loads. Contributing to the accident was the failure of Powers Fasteners, Inc., to determine that the anchor displacement that was found in the high-occupancy vehicle tunnel in 1999 was a result of anchor creep due to the use of the company's Power-Fast Fast Set epoxy, which was known by the company to have poor long-term load characteristics. Also contributing to the accident was the failure of Modern Continental Construction Company, Inc., and Bechtel/Parsons Brinckerhoff, subsequent to the 1999 anchor displacement, to continue to monitor anchor performance in light of the uncertainty as to the cause of the failures. The Massachusetts Turnpike Authority also contributed to the accident by failing to implement a timely tunnel inspection program that would likely have revealed the ongoing anchor creep in time to correct the deficiencies before an accident occurred.

The safety issues identified during this investigation are as follows:

  • Insufficient understanding among designers and builders of the nature of adhesive anchoring systems;
  • Lack of standards for the testing of adhesive anchors in sustained tensile-load applications;
  • Inadequate regulatory requirements for tunnel inspections; and
  • Lack of national standards for the design of tunnel finishes.

As a result of its investigation of this accident, the National Transportation Safety Board makes safety recommendations to the Federal Highway Administration; the American Association of State Highway and Transportation Officials; the departments of transportation of the 50 States and the District of Columbia; the International Code Council; ICC Evaluation Service, Inc.; Powers Fasteners, Inc.; Sika Corporation; the American Concrete Institute; the American Society of Civil Engineers; and the Associated General Contractors of America.

Recommendations

As a result of its investigation of the July 10, 2006, ceiling collapse in the I-90 connector tunnel in Boston, Massachusetts, the National Transportation Safety Board makes the following safety recommendations:

To the Federal Highway Administration:

In cooperation with the American Association of State Highway and Transportation Officials, develop standards and protocols for the testing of adhesive anchors to be used in sustained tensile-load overhead highway applications. These standards and protocols should consider site-specific ultimate strength values as well as the creep characteristics of the adhesive over the expected life of the structure. (H-07-15)

Prohibit the use of adhesive anchors in sustained tensile-load overhead highway applications where failure of the adhesive would result in a risk to the public until testing standards and protocols have been developed and implemented that ensure the safety of these applications. (H-07-16)

Seek legislation authorizing the Federal Highway Administration to establish a mandatory tunnel inspection program similar to the National Bridge Inspection Program. (H-07-17)

Once provided with legislative authority to establish a mandatory tunnel inspection program as indicated in Safety Recommendation H-07-17, develop and implement a tunnel inspection program that will identity critical inspection elements and specify an appropriate inspection frequency. (H-07-18)

In cooperation with the American Association of State Highway and Transportation Officials, develop specific design, construction, and inspection guidance for tunnel finishes and incorporate that guidance into a tunnel design manual. (H-07-19)

To the American Association of State Highway and Transportation Officials:

Work with the Federal Highway Administration to develop standards and protocols for the testing of adhesive anchors to be used in sustained tensile-load overhead highway applications, and incorporate those standards and protocols into the AASHTO Construction Quality Assurance Guidelines. These standards and protocols should consider site-specific ultimate strength values as well as the creep characteristics of the adhesive over the expected life of the structure. (H-07-20)

Use the circumstances of the July 10, 2006, accident in Boston, Massachusetts, to emphasize to your members through your publications, Web site, and conferences, as appropriate, the risks associated with using adhesive anchors in sustained tensile-load applications where failure of the adhesive would result in a risk to the public. (H-07-21)

In cooperation with the Federal Highway Administration, develop specific design, construction, and inspection guidance for tunnel finishes and incorporate that guidance into a tunnel design manual. (H-07-22)

To the Departments of Transportation of the 50 States and the District of Columbia:

Prohibit the use of adhesive anchors in sustained tensile-load overhead highway applications where failure of the adhesive would result in a risk to the public until testing standards and protocols have been developed and implemented that ensure the safety of these applications. (H-07-23)

Review the use of adhesive anchors in highway construction within your jurisdiction and identify those sites where failure of the adhesive under sustained load could result in a risk to the public. Once those sites have been identified, implement an inspection and repair program to ensure that such failures do not occur. (H-07-24)

To the International Code Council:

Require creep testing for the qualification of all anchor adhesives. (H-07-25)

Disqualify for use in sustained tensile loading any adhesive that has not been tested for creep or that has failed such tests. (H-07-26)

Revise your building codes, qualified materials listings, and product labeling guidelines to clearly address the possibility for creep in polymeric anchor adhesives and to make end users aware of the potential lack of correlation between short- and long-term performance of these adhesives. (H-07-27)

Use your building codes, qualified materials listings, test criteria, or other mechanisms to make end users aware of the strong potential for creating voids in the adhesive during the overhead installation of adhesive anchors and of the need to account for the reduction in effective embedment depth associated with the use of seal plugs in such applications. (H-07-28)

To ICC Evaluation Service, Inc.:

Revise evaluation report ICC ESR-1531 to state explicitly in the text and in the bond strength tables that the Fast Set formulation of Powers Power-Fast epoxy is approved for short-term loads only. (H-07-29)

To Powers Fasteners, Inc.:

Revise the packaging, for all distributors, of your Power-Fast Epoxy Injection Gel Fast Set formulation to state explicitly that this formulation is approved for short-term loads only. (H-07-30)

To Sika Corporation:

Revise your product literature and packaging to state explicitly that Sikadur Injection Gel AnchorFix-3 epoxy is approved for short term loads only. (H-07-31)

To the American Concrete Institute:

Use your building codes, forums, educational materials, and publications to inform design and construction agencies of the potential for gradual deformation (creep) in anchor adhesives and to make them aware of the possible risks associated with using adhesive anchors in concrete under sustained tensile-load applications. (H-07-32)

To the American Society of Civil Engineers:

Use the circumstances of the July 10, 2006, accident in Boston, Massachusetts, to emphasize to your members through your publications, Web site, and conferences, as appropriate, the need to assess the creep characteristics of adhesive anchors before those anchors are used in sustained tensile-load applications. (H-07-33)

To the Associated General Contractors of America:

Use the circumstances of the July 10, 2006, accident in Boston, Massachusetts, to emphasize to your members through your publications, Web site, and conferences, as appropriate, the need to assess the creep characteristics of adhesive anchors before those anchors are used in sustained tensile-load applications. (H-07-33)