Last week, Buildings Commissioner Robert LiMandri released the findings of the year-long investigation into the tower crane collapse that occurred on March 15, 2008, at 303 East 51st St. in Manhattan, according to a press release. The investigation concluded that improper rigging operations caused an 11,000-pound steel collar to fall while it was being connected to the building under construction. When the collar fell, it struck and severely damaged the crane’s lower connections to the building, which resulted in the collapse of the entire tower crane structure. The collapse killed six construction workers and one civilian, demolished a four-story brownstone on East 50th Street, and damaged more than a dozen buildings in the East Side neighborhood.

“Crane assembly is a highly technical activity that requires great skill and adherence to the crane manufacturer’s instructions. Deviation from those instructions can have catastrophic results. This investigation shows the consequences of taking shortcuts on the job site,” said Commissioner LiMandri. “In the coming days, we will convene a series of meetings with the construction industry to review the report’s findings and identify ways to prevent tragedies like this from happening again.”

DOB hired Ove Arup & Partners Consulting Engineers PC (Arup) to provide expert engineering and investigative services in connection with the crane collapse. Arup’s investigation included structural laboratory testing and computer analyses of the tower crane’s components, related equipment and slings. In addition, investigators reviewed thousands of documents and photographs, as well as the final report on the collapse from OSHA. Based on this comprehensive review, the investigation concluded the collapse was caused by a number of critical errors, including:

• Four synthetic slings were used instead of the required eight chain blocks specified by the manufacturer to support the 11,279-pound steel collar;
• One of the slings used to support the collar had prior physical damage;
• Slings were not attached at the collar points specified by the manufacturer;
• Slings were attached to the mast in a way that compromised their capacity; and
• Padding for the slings at the mast’s sharp edges was not provided.

Arup’s investigation concluded that the tower crane installation design met industry standards and was not a cause of the crane collapse. In addition, Arup found that the DOB crane inspection and permitting protocols would not have identified the rigging errors that caused the collapse.

DOB Inspectors and Engineers worked with Department of Investigation (DOI) and the Manhattan District Attorney’s Office on the investigation into the collapse, and in January, Manhattan District Attorney Robert Morgenthau announced the indictment of the tower crane rigger and his company on multiple charges of manslaughter, criminally negligent homicide, assault, and reckless endangerment. DOB continues to work with the District Attorney and DOI to prosecute the case.

DOB issued vacate orders for 18 buildings following the collapse. Most of the vacate orders were lifted within days, but three buildings remain vacated due to outstanding repair work required to make them safe for occupancy. DOB revoked the permit for construction of the new building at 303 East 51st Street, and a Stop Work Order remains in effect.

Over the past three weeks, DOB Inspectors performed a citywide safety sweep of all tower cranes undergoing jumping operations. Of the 18 jumps performed, Inspectors found that all were in compliance with new crane safety laws enacted last year: all contractors held the required safety meetings before their operations began, all provided detailed rigging plans on site during the inspections, and synthetic slings were not used during any operation. Over the past year, DOB has worked with Mayor Michael R. Bloomberg and Council Speaker Christine Quinn to enact 12 new laws designed to increase construction safety and regulatory oversight.

Last month, Commissioner LiMandri announced the results of the High-Risk Construction Oversight study to increase safety during crane, hoists, concrete, and excavation operations. As part of the $4 million study, DOB worked with nearly 100 industry stakeholders to develop 41 steps that will improve construction operations throughout the City. DOB is in the process of implementing those recommendations.

A copy of the 298-page report, titled “51st Street Crane Investigation Report,” is available at www.nyc.gov/buildings.