A crack in a steel beam that forced the closure of the Interstate 40 bridge connecting Arkansas and Tennessee for three months likely began when the span was built in the 1970s and went undetected for years, according to a report released Thursday by Arkansas’ Transportation Department.

According to a forensic investigation conducted by an outside firm hired by the department, the crack occurred during the fabrication of the bridge in a weld between two plates. Because of the type of steel and welding method used at the time, those welds were more prone to cracking, according to the department. “The cracking in the weld most likely occurred within hours of its completion but was not detected by any post-weld repair fabrication testing and remained unchanged for a number of years,” according to the department’s report.

The crack was visible in 2016, and a department inspector who missed it was fired in May. According to the report, the weld fracture was initially not visible by conventional inspection and was not detected by an ultrasonic inspection in 1982.

Inspectors discovered a crack in one of two 900-foot (275-meter) horizontal steel beams critical to the structural integrity of the I-40 bridge over the Mississippi River on May 11. During the repairs to the I-40 bridge, traffic was diverted to the nearby Interstate 55 bridge, which is about 3 miles (4.8 kilometers) south of the I-40 bridge. In August, the bridge reopened completely.

As part of its announcement of changes to its bridge inspection program, the department released the forensic investigation, its review of the crack, and a review conducted by the Federal Highway Administration. The inspector general of the United States Department of Transportation is also conducting an investigation and has interviewed Arkansas bridge inspection employees.

“We will now move forward with confidence and make the necessary changes to improve our program so that the past does not repeat itself,” Arkansas DOT Director Lorie Tudor said in a statement.

When ultrasonic testing was performed on the bridge’s girder welds in 1982 due to defects discovered with similar bridges, the problems with the weld were not detected. The initial fracture occurred on the interior face of the box, where it could not be seen using conventional inspection. According to the report, the fracture spread in stages, beginning with the weld and ending in May.

According to a department spokesman, two inspectors, state heavy bridge maintenance engineer Michael Hill and staff engineer Stewart Linz, retired on Wednesday. The department announced that it is reorganizing the inspection program and putting its heavy bridge maintenance section under new management. The Arkansas Democrat-Gazette first reported the reports and retirements on Thursday.

In 2016, 2017, 2019, and 2020, the fired inspector had missed the crack. Another inspector who missed the crack in 2018 had never inspected that section of the bridge before, according to the department, and has been “verbally counseled.” “as well as additional training

According to the report, the agency’s failure to adequately respond to employees who were concerned about the fired inspector’s job performance “perpetuated a culture in which team members did not feel they had the authority or support to question a lead inspector’s procedures or thoroughness.”

The department also stated that “fracture critical” bridges, such as the I-40 span, will no longer be inspected by the same person on consecutive occasions.

I-40 connects North Carolina and California. Manufacturers and shippers rely on interstate transportation to transport goods and materials across the Mississippi River. A typical day sees approximately 50,000 vehicles cross the bridge. Arkansas is in charge of bridge inspections, while Tennessee is in charge of maintenance and repairs.

The closure was costly for the trucking industry, with the Arkansas Trucking Association estimating that it cost the industry around $2 million per day at one point. Arkansas estimated that the bridge repairs and inspections following the closure cost $10 million.

According to the Arkansas report, a similar crack on the bridge is “highly unlikely,” but the bridge’s welds will continue to be inspected at arm’s length and ultrasonic testing should be done on a regular basis.