CROSS Safety Report
Dismantling of tower cranes
This report is over 2 years old
The falling of two cranes during dismantling in 2019, one in the US and one in the UK, prompts reflections on crane safety on construction sites.
Key Learning Outcomes
For all built environment professionals, regulating authorities, owners, contractors, and suppliers:
Incidents involving tower cranes falling during erection and dismantling occur often and can be avoided by following proper procedure
During tower crane lifting and disassembly operations the temporary unbraced length of the tower crane is often the determining engineering consideration. These operations need to occur in acceptably low wind conditions
In most instances crane jumping and installation of new ties to the building occur together and involve numerous parties/participants. Participants’ experience and coordination are essential
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The reporter notes that there have been several instances over many years where tower cranes have fallen during erection/dismantling, citing two such events that occurred in 2019, one in the US and one in the UK.
In the US incident, the crane was being dismantled when it collapsed into the street, causing fatalities. At the time, gusty but not exceptional winds were reported in the area. The tower had been assembled in 20 ft (6 m) long, four-legged truss sections. An investigation by state authorities concluded that workers ignored the tower manufacturer’s dismantling procedures and prematurely removed the tower’s assembly pins.
The UK incident occurred at a construction site on an existing building. The crane was being dismantled when a 20m (66 ft) section of the crane separated and fell to the roof. Fortunately, no one was injured.
Expert Panel Comments
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The CROSS Expert Panel offers no additional opinions regarding the specific causes of the two incidents cited by the reporter, but general observations regarding crane site safety follow.
In NYC between 2006 and 2015 operations related to lifting/jumping or dismantling tower cranes accounted only for 10% of crane incidents, but they produced by far the largest number of casualties. This included seven fatalities that occurred during the jumping of a crane on East 51st St. in Manhattan, the deadliest crane construction accident in recent memory. Investigations by OSHA and the NYC Department of Buildings determined that the cause of the accident was human error (Report of OSHA's Investigation of Crane Collapse at 303 East 51st Street and City of New York Department of Investigation Remarks on East 51st Street Crane Indictment).
During tower crane lifting and disassembly operations the temporary unbraced length of the tower crane is the determining engineering consideration. These operations need to occur in acceptably low wind conditions.
In most instances crane jumping and installation of new ties to the building occur together and involve numerous parties/participants. Participants’ experience and coordination are essential. As a lesson learned from the accident on East 51st St., the NYC DOB introduced rules that require a pre–jump safety meeting and also several new responsibilities on the site – lift director and assembly/disassembly director. See NYC Building Code 2014 Section 3319 and NYC Local Law 14 of 2018 .
The risk associated with a crane collapse may be to adjacent infrastructure with disproportionate consequences such as equipment falling onto a railroad track in the path of a train. In the UK this was examined in a 2011 report Preventing catastrophic events in construction.
As always, key operations need to be under the control of qualified competent staff who work to procedures provided by crane suppliers. Correct procedures for erection and dismantling must be followed.
Factors that affect safety of tower crane installation/dismantling in construction industry examines factors that have contributed to accidents during tower crane installation/dismantling in Korea. A total of 38 fatal accident cases involving tower cranes occurred between 2001 and 2011. Accidents occurring during installation/dismantling of tower cranes accounted for 68.4% of all fatal accidents. Accident analyses identified ‘not following work procedures’ as one of the main causes of these accidents, followed by ‘unsafe acts of workers.’
In 1994 the ASCE Board of Direction approved ASCE Policy Statement 424 on crane safety on construction site. In July 13, 2019 the Board adopted an update to Statement 424.
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