On Thursday night, November 16, 2006, a 210-foot tower crane, used in building construction, collapses in downtown Bellevue, damaging three buildings and killing Matthew Ammon in his top-floor apartment. After a six-month investigation, Washington State Department of Labor and Industries will determine that the collapse was due to catastrophic failure of a custom-designed, non-standard base. The tragedy will spur the state legislature to pass a crane-safety law that will be among the nation’s strictest.
Unaccustomed Base
The giant construction crane had been set up in September 2006 by Northwest Tower Crane Services, Inc. at the southwest corner of NE 4th Street and 108th Avenue NE in Bellevue, the site of Tower 333, a new 20-story office building. Manufactured in Germany by Liebherr International AG of Bulle, Switzerland, the 210-foot-tall tower crane, operated by Ness Crane Services, sat in an excavation five stories deep. Attached to the top of the vertical mast was the slewing unit, the gear and motor that allow the crane to rotate, and the operator’s cab. The crane’s horizontal jib, or working arm, extending 154 feet forward of the slewing unit, had a maximum lifting capacity of 22 tons. The shorter horizontal machinery arm, extending aft, contained the crane’s motors, electronics, and the large concrete counterweights.
Typically, the entire apparatus is anchored to a huge concrete pad, weighing some 200 tons, with large anchor bolts, ensuring its stability. But the base for the tower crane at Tower 333 was different. Designed by the Seattle engineering firm Magnusson Klemencic Associates (MKA), at the behest of the project’s general contractor, Lease Crutcher Lewis, the tower crane was bolted onto a custom-designed cross-frame made of steel I-beams. The empty space beneath the crane was used for parking and storage.
The Fall
At about 7:45 p.m. on Thursday, November 16, 2007, the tower crane suddenly toppled across 108th Avenue NE, a major downtown Bellevue arterial. The falling mast demolished the entire northeast corner of the Plaza 305 office building. The machinery arm hit the Civica Office Commons, damaging the northeast corner on the fifth and sixth floors, and the adjacent Melting Pot Restaurant. The jib crashed directly onto the top of Pinnacle Bell Center, a five-story, 248-unit condominium building with retail stores on the ground level.
When the Bellevue Fire Department arrived at the scene, they found the crane operator, Warren Taylor Yeakey, age 34, of Tacoma, trapped in the operator’s cab, some 30 feet from the ground. Yeakey was able to extract himself from the cab and was rescued by firefighters with a ladder. He was transported to nearby Overlake Hospital, suffering only minor injuries from the nearly 200-foot fall.
Meanwhile, Bellevue firefighters and police, assisted by King County Search and Rescue personnel and dogs, began searching the debris and damaged buildings for casualties. Miraculously, they found only one. He was identified as Matthew Quay Ammon, age 31, a Microsoft patent attorney who was living in the fifth-floor Pinnacle Bell Centre apartment crushed by the crane’s jib. Tim Waters, Director of Communications for the City of Bellevue remarked: "If this had occurred between eight and five, we could have been looking at a tragedy of much farther-reaching consequences" (The Seattle Times).
Aftermath
On Friday, November 17, rescue workers continued searching through the wreckage and large piles of debris until they were sure all the possible victims had been located. Private contractors lifted the fallen jib and machinery arm away from the damaged buildings and placed them in the street. There the equipment was dismantled into sections and hauled away on flatbed trucks. The crane’s mast remained in place, lying across the wreckage of the Plaza 305 office building and blocking 108th Avenue, so that three health-and-safety inspectors from Washington State Department of Labor and Industries (L&I) as well as four Liebherr International engineers, who had flown in from Germany, could examine the accident scene.
By Monday, November 18, L&I inspectors had completed their examination of the crane’s wreckage. They determined that the mast had broken off about 15 feet above the base, evidenced by broken welds and sheared horizontal bolts. The next step in the investigation was to determine the cause of the failure.
The crane’s operator, Warren Yeakey, told L&I investigators that as he was securing the crane for the night, he heard cracking noises and then the crane toppled. As part of its standard procedures, the Ness Crane Services gave Yeakey a drug test after the accident, and he passed. Operator error was eliminated as the cause of the accident.
Untoward Leaning
Photographs of the crane, taken in October by a visitor to Bellevue, seemed to show the tower crane leaning as much as three feet at the top, when it should have been vertical. According to national industry standards, tower cranes are allowed to lean one inch for every 40 feet in height. The tower crane at the Tower 333 site, at 210 feet, should not have been leaning more than five-and-a-quarter inches, so, early in the investigation the non-standard, custom-designed base came under close scrutiny.
Investigators found that dozens of horizontal bolts had sheared and three welds had failed in base. Among the possible causes contributing to the collapse were water trapped and freezing inside the tubular structure, recent high winds, possibly inducing metal fatigue, inherent structural or metallurgy problems, and improper assembly.
To help resolve this complex situation, L&I hired Professor Anthony de Sam Lazaro, a mechanical and forensic engineer at Saint Martin’s University in Lacey, Washington, who had helped the state agency reconstruct the crane accident inside the Kingdome in Seattle that had killed two construction workers on August 17, 1994. "It's never just one thing -- it's just a whole series of things that causes an accident of this nature," he observed (Seattle Post-Intelligencer).The New Crane-Safety Law
On February 9, 2007, two crane-safety bills were introduced in the Washington State Legislature: Senate Bill 5990, sponsored by Senator Jeanne Kohl-Welles (D-Seattle) and House Bill 2171 sponsored by Representative Deborah Eddy (D-Kirkland). The bills passed through the House and Senate without difficulty and was signed into law by Governor Christine Gregoire on April 10, 2007, making the state's new crane-safety regulations into some of the nation's strictest. Department of Labor and Industries was assigned responsibility for the implementation, administration, and enforcement of the new act, and given 11 new positions. Statewide, L&I has 42 health and safety inspectors who conduct about 7,000 inspections a year, about half on construction sites.
Effective January 1, 2010, the Crane Safety Act requires cranes to be load-tested, inspected, and certified at least annually, after any significant modification or repair of structural parts, and before and after each setup at a new site. Crane owners are required to have an independent professional engineer review and approve plans for any non-standard tower crane base. Crane operators are required to have a valid operators certificate issued by a nationally recognized accrediting agency, have up to 2,000 hours of documented experience, and pass a substance abuse test.Meanwhile, work continued on the 20-story Tower 333 construction project. On January 21, 2007, a brand new Liebherr tower crane, shipped from Germany in December was installed on the site. This time the crane was anchored to a new concrete foundation, designed by MKA structural engineers, rather than fastened to steel I-beams.
A Flawed Crane Base
On Friday, May 11, 2007, L&I released their final report, which stated that the Bellevue crane collapse was caused by a flawed engineering design of the base. The foundation, engineered by MKA, was designed to withstand only about one quarter of the pressures the tower crane required. Metal fatigue of the steel base frame, I-beams configured in an H-pattern, led to the collapse of the structure. The investigation found no evidence that high winds the previous day contributed to the collapse of the tower crane or that operator error was a factor. The crane operator, Warren Yeakey, was well-experienced and was operating the crane correctly.
MKA was cited for “failing to ensure that the design specifications met the specific recommendations of the crane manufacturer,” and fined $5,600. Lease Crutcher Lewis, the project’s general contractor, was cited for “failing to conduct periodic inspections to determine that the crane’s deflection limits were not exceeded as specified by the manufacturer,” and fined $5,600. The firm was also cited and fined $3,600 for "attaching to the tower crane structure advertising banners that exceeded the size recommended by the manufacturer" which could "potentially affect the control and operation of the crane." None of the other companies involved in the Tower 333 project were found to be in violation of L&I’s workplace safety regulations.
