Photo by Associated Press
A 1,350-tonne Liebherr LR 11350 fell on Mecca's Grand Mosque during a violent rainstorm.

A supercrane that collapsed during a Sept. 11 rainstorm into the Grand Mosque in Mecca, Saudi Arabia, represents the deadliest crane accident in decades and perhaps in modern construction history, according to a forensic engineer who studies such failures. The accident claimed the lives of at least 100 pilgrims and injured more than 230 others.

The toll is higher “than any I can remember,” says Jim Wiethorn, chairman and principal engineer for Sugar Land, Texas-based Haag Engineering Co., which has compiled a database of more than 800 crane accidents since the firm began studying them in 1983. A March 2008 tower-crane collapse in midtown Manhattan killed six craftworkers and one bystander—the deadliest accident Haag had recorded to date and still the highest for fatalities in the U.S.

The Grand Mosque failure was a “result of natural factors—strong wind, severe storms and heavy rains,” according to the state-owned Saudi Press Agency. The Saudi government says it will investigate the accident and publicize its findings. The crane is one of many in use for a multibillion- dollar expansion of Islam’s holiest site.

Officials at German crane manufacturer Liebherr confirm the model is an LR 11350, with a lifting capacity of 1,350 tonnes. "As the crane manufacturer Liebherr does everything in its power to help bring the accident investigation to a speedy and logical conclusion," a spokesman for Liebherr told ENR.

One industry source, who asked not to be named, said that investigators likely would look at how the crane was stowed prior to the storm. Workers usually lower the boom to an angle of 60° or less and, if equipped with a luffing jib, rest the tip on a dolly on the ground, the source said. If there is not enough room to stow the jib, workers would secure the structure with guy wires.

Although the crane was not in operation at the time, workers appeared to have left the boom and jib in the working position.

Initial Findings

On September 15, the government of Saudi Arabia announced their preliminary findings on the accident, saying in a release through the state-owned Saudi Press Agency that "the main reason for the accident is the strong winds while the crane was in a wrong position."

The focus now shifts to the main contractor on the site, Saudi Binladin Group (SBG). The Saudi government has announced a suspension of work by the contractor in the country, after the initial inquiry found it had not "respected the norms of safety." A travel ban was also issued for SBG senior leadership, pending further investigation.

SBG did not respond to inquiries from ENR.

This article was updated on Sept. 18, 2015.