Correction: The story has been updated to correct the spelling of Carroll Dexter Wills’s name.
A malfunctioning jack or scaffolding extended beyond manufacturer recommendations may have caused a 43,000-pound concrete slab to collapse in a parking garage at the Westfield Montgomery Mall on May 23, killing one construction worker and seriously injuring another, according to an engineer’s report.
The findings are the result of an investigation by KCE Structural Engineers, hired by the mall’s owner, Westfield LLC. The 22-page report does not pinpoint a specific origin or cause of the accident but it describes a set of conditions that may have set the collapse in motion. It was delivered earlier this month to county officials, who must decide whether to cite the general contractor, Whiting-Turner, for possible violations of its construction permits.
The accident occurred as portions of the garage were being removed for a major renovation and expansion of the mall, on Democracy Boulevard west of Interstate 270.
A Whiting-Turner crew was lifting two 60-foot concrete slabs from the second to the third level of the garage. The first was lifted without incident, according to the report.
The second slab was elevated and then left supported by scaffolding while the crew went on a break. Workers told KCE that when they returned they noticed that a steel support on what is called the “safety tower” had partially buckled. They began jacking up the slab in an effort to free the beam and replace it. One of the workers, Carroll Dexter Wills, 57, called for a crescent wrench in an attempt to tighten the safety tower clamps.
But seconds later, workers told KCE, they heard a loud cracking noise. The slab fell about 18 inches, crushing Wills and seriously injuring a co-worker.
KCE, hired by the county last year to study the troubled Silver Spring Transit Center, noted problems with the jacks workers used in their attempts to stabilize the slab.
Three had pump pressure issues; two others were missing lifting devices that meant they were not the same height as the others. “We believe the ironworkers may not have known about” the defects, the report said.
The towers supporting the jacks may not have been properly centered, which may have left the jacks improperly aligned, investigators said. In addition, the legs on a shoring system used to support the towers were extended beyond their maximum rated load. The report said that for every inch beyond 12 inches, the shoring loses 5 percent of its strength. KCE engineers said the extensions measured 16 inches.
Whiting-Turner Vice President Chris Hoyson did not respond to phone and e-mail messages Monday.
Hadi Mansouri, chief of building construction for the county’s Department of Permitting Services, said the report — a condition of work resuming at the garage — answered at least some of the questions surrounding the incident. Late Monday morning, he lifted a “stop work” order that had been placed on the site.
“We understand the report and we are satisfied with the findings,” Mansouri said. He is scheduled to meet with Whiting-Turner officials in the next few days to discuss the report in detail.
A state investigation is continuing. Summar Goodman, a representative of the Maryland Department of Labor, Licensing and Regulation, said the agency could not comment on an ongoing inquiry.