April 9, 2008
A 200-ft-tall construction crane collapsed on New York City’s East Side on Saturday, killing seven people. Hardly a freak accident, this tragedy marks the latest in a slew of crane accidents that have taken place across the country over the past few years. Engineers may wonder whether the fault lies in the design of the cranes themselves. Yet the cause of most crane accidents can usually be found out on the job site.
In this recent fatal accident, a tower crane working on a new 43-story residential building at 303 East 51st Street toppled onto a property across the street. As the crane broke apart during the fall a roughly 75-ft section demolished a building over on 50th street and damaged at least six other nearby buildings.
According to a statement sent by Carly Sullivan, assistant press secretary for the New York City Department of Buildings, a preliminary investigation indicates the accident occurred while workers were adding tower sections to extend the crane upwards, a process known as “jumping” or “jacking.”
“While crews were jumping the crane to the 18th floor, a heavy-duty steel collar, which wrapped around the mast of the crane and used to tie the crane to the side of the building, fell as workers attempted to install it. When the steel collar fell, it damaged a lower steel collar, installed at the 9th floor. The collar installed at the 9th floor served as a major anchor securing the tower crane to the building under construction. With the elimination of the support provided by the steel collar at the 9th floor, the counter-weights at the top of the crane’s tower caused the entire structure to fall southward,” the statement says.
Owned by New York Crane and manufactured by the Favelle Favco Group, the tower crane has been inspected at least five times during its operation at 305 East 51st Street. The most recent inspection of the crane occurred on just a day before the accident when inspectors from the Building Department’s Cranes & Derricks Unit inspected the mast sections that would be used to jump the crane upward. The Building Department issued no violations as a result of that inspection, and a prior inspection earlier this month found the crane had been erected in accordance with the city’s crane permit.
As of yesterday, the Buildings Department engineers were working with the New York City Police Department to recover the crane parts needed for a forensic investigation into the accident. With this evidence destined for lab testing and analysis, it may be some time before the cause of the accident comes to light.
But crane experts say it’s unlikely the the crane will be found to have failed due to any inherent design flaws. “Cranes are designed well by their manufacturers. In all the accidents I’ve investigated over the past 12 years, not one of them was the fault of the crane itself,” says Thomas Barth of Barth Crane Inspections, a firm that provides crane operator training as well as crane inspections and accident investigation services.
“Accidents usually occur when someone does something with the crane that the manufacturer did not intend the crane to do,” Barth says.
Often times that someone can be an operator. Barth argues many operators don’t have nearly enough training or experience to understand how to lift the loads safely and within the design limits of the crane. “Some of them don’t know jack about the cranes they’re operating,” he says.
According to Barth, one particularly common class of problems relates to a lack of awareness about the crane’s maintenance needs. For example, he says he’s seen many crane operators fail to account for wear in the crane cables, which they should do by measuring the cable and applying wear tolerances.
Graham Brent, executive director of the National Commission for the Certification of Crane Operators (NCCCO), likewise says the operator error can result in crane mishaps. He says these errors can involve trying to lift loads in ways the crane can’t tolerate. Modern cranes do have load sensors that in theory would prevent too heavy a load from being lifted. “But controls can be bypassed,” says Brent. “And sometimes a load that’s safe to lift in one quadrant of the crane’s operating envelope could be unsafe in another,” he says.
To minimize the occurrence of operator-induced problems, the NCCCO develops voluntary certification programs for all kinds of crane operators, including those who run the big tower cranes. Fifteen states have adopted the NCCCO’s certification guidelines as part of their formal crane licensing programs, and Brent says the organization has helped train “thousands more” operators across the country.
Training programs still have a ways to go. Barth says operators when he began in the crane business needed 4,000 hours of training to become certified on the most complex types of equipment. Nowadays he runs across employer training programs that seek to train crane operators in as little as few hours — though that short a period wouldn’t be common for the tower cranes.
New York State’s Labor Department has also run across training deficiencies. Last November, the department suspended 129 Crane Operator’s Certificates after discovering licenses were issued to individuals who failed the state’s practical exam.
Other crane toppling problems have nothing to do with the operator and everything to do with the on-site engineering. Barth cites a November 2006 Bellevue, WA crane accident that killed one man as an example. “The report on the Bellevue accident found that crane went down because it used a homemade steel base that did not meet the crane manufacturer’s criteria,” he says. The Washington Department of Labor and Industry’s investigation into the accident found the crane’s foundation, which should have been concrete, was designed to withstand only about one-fourth of the 210-ft tower’s load requirements.
Brent also says installation mistakes represent a leading cause of tower crane failures. “But the recent rash of tower crane accidents is unusual in that they occurred once the crane was erected,” he says, explaining most toppling accidents take place while the crane is being installed. “Once properly installed, tower cranes tend to be free of toppling accidents,” he says.
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