Comments about technological history, system fractures, and human resilience from James R. Chiles, the author of Inviting Disaster: Lessons from the Edge of Technology (HarperBusiness 2001; paperback 2002) and The God Machine: From Boomerangs to Black Hawks, the Story of the Helicopter (Random House, 2007, paperback 2008)

Monday, October 5, 2015

Crane Down at Masjid al-Haram, September 11

About the crane disaster last month in Makkah (Mecca in its westernized spelling). A Liebherr L-11350 crawler crane tipped backward in a windstorm, killing 109 people in what forensic folks call the laydown zone. The worst area of destruction was where the 100-ton mast and jib dropped on the roof of a very long building on the east side called the Massa. The upper end of the jib crashed onto pedestrian areas on the other side of this building (photo AFP)

When the crawler crane fell over it also came close to destroying a tower crane, a Liebherr 335, also located on the east side of the Massa.

Here's how the roof damage looked: 

The "W"-shaped object above the Massa roof, projecting into it, is where the two jib struts join up with the upper end of the main boom, and the lower end of the jib (see below for a diagram). The jib struts provide a support for the jib. As the crane fell over backward, the two jib struts acted like twin piledrivers, smashing into the third and second floors of the Massa

Here's a link to the only public video I've seen of the crane going down (but I'm sure the Saudis have a lot of CCTV footage):

Here's a diagram of the basic components, before and after:

How big was it? As this crane was rigged (called an SDW arrangement in the manual), the tip of the L-11350's upper structure called the "luffing-fly jib") reached more than 600 feet off the ground. 

It's classed as a super-crane: while not the world's biggest crawler crane, it's close. The lift capacity under ideal conditions is 1,350 metric tons. It's a popular crane for refinery turnarounds and wind-farm projects. 

How long had it been on the plaza? More than three years. It was part of a big Saudi purchase from Liebherr in 2012. 

What was the crane doing there? It had been parked and inactive for some time. Details on usage are fuzzy; given past photos taken by pilgrims and posted online, the crane hadn't gotten much use lately. We're told that it was to be used again after the September 2015 Hajj, as part of ongoing expansion of the Masjid al-Haram and the Massa in particular. Here's a diagram of the location. 

What do the initial reports say? Authorities have been interrogating employees of the contractor, Saudi Binladin Group, which has filed an insurance claim. While this particular windstorm was unusually powerful, the crane manufacturer says it was a mistake to park the crane with its boom at such a high angle (85 degrees), where it could catch the wind. 

What about the cleanup? Because the 2015 Hajj pilgrimage was to begin less than two weeks after the wreck, work went on around the clock. Experts decided structural damage to the plaza at the base of the crane was so severe that the removal of the lower chassis (called the car body) would have to wait until after the Hajj, so this area was screened off from pilgrims. 

The focus was on removing the main boom and derrick mast from above the eastern plaza, and pulling the jib and jib struts off the roof -- and without causing more damage to the Massa, which is heavily used by pilgrims. 

If there's interest I'll post on how a team from Aramco got this done, with advice from heavy-life expert Mammoet, which I mentioned in this post about strand jacks


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