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.