Fact and fiction in the Mecca crane disaster

A lot of misinformation is being circulated about the crane accident on Friday which killed more than 100 people at the Grand Mosque in Mecca during a storm. Several spurious claims have gained credence simply because no one bothered to check them against the abundant photographic evidence.

One example was a story circulated on social media saying the crane in question was manufactured in China. This seems to have been based on a popular belief that any red-painted crane, like the one in the accident, is Chinese. 

That claim could have been instantly laid to rest by taking a careful look at photographs of the toppled crane. A name-plate saying "Liebherr" can be seen attached to its side, and it only takes a quick check on Google to find that Liebherr is a Swiss/German company and one of the world's leading crane manufacturers.

From the point of view of establishing what happened to the crane, the most useful collection of photographs – showing the wreckage from a variety of angles – is on the website of Heavy Lift News. There is also a video of the crane as it toppled. 

From these images three key facts can be established:

FACT 1: The crane toppled backwards, not forwards.

The Associated Press mistakenly reports that one of its journalists saw the wrecked crane with "its base tipped forward".

Similarly, the Jeddah-based Arab News says:

"There have been umpteen photographs in the media showing the Liebherr crane with its base tipped forward."

That is the exact opposite of the truth. All the photographs – without exception – show that its base tipped backward. This is a crucial point because it relates to the crane's stability (or lack of it).

Tipping forward when lifting heavy objects is an obvious risk that manufacturers and crane operators are well aware of and take steps to prevent. The risk of tipping backward seems less obvious and, consequently, tends to receive less attention. However, mobile cranes, including the crawler type involved in the Mecca accident, are more vulnerable than others where backward stability is concerned.

In a post about the accident on Sunday, I included a quote from an engineering blog which is worth repeating.

"Backward stability for cranes has always been a serious consideration and often misunderstood or overlooked. The tendency is to carefully study the capacity charts to assure frontward stability when planning a lift. 

"It is somewhat counter intuitive to worry about backward stability as all the lifting is being done over the front. In fact, there are almost as many crane accidents that are a result of 'loss of backward stability' as there are for all the rest combined.

"All mobile cranes are subject to a loss of backward stability ..."

The basic point here is that it would take a lot less force to tip the crane backward than it would to tip it forward.

FACT 2: The crane's base was not weighted at the front

Citing unnamed sources, Arab News says the crane "was fixed to the ground with four foundations, each weighing 1,000 tons". 

This was a mobile crane and its base would have been weighted at the rear to prevent it from tipping forward. If it really was "fixed to the ground with four foundations", none of its fixings appear to have been at the front.

The photographs show no evidence of weights at the front of the crane's base that might have helped to prevent it falling backwards, though there are two stabiliser arms at the front (again to prevent it tipping forward) which can be seen pointing into the air after the accident. 

FACT 3: The crane's hook was able to swing in the air.

The heavy hook may have added to the crane's instability. An unidentified engineer employed by the contractors (the Saudi Binladin Group) told AFP that the hook began swaying [in the wind] and moved the whole crane with it, toppling it on to the mosque.

This explanation is partly supported by a video which shows hook swinging freely and striking the crane with a clang as it topples.

On the other hand this video, together with photographs of the wreckage, casts doubt on another reported claim – that the crane fell when one of its arms broke.

THERE IS little doubt that strong winds were what caused the crane to topple. The question is why this particular crane fell when numerous others in the same area survived the storm intact. Was there a design fault or had the operators set it up incorrectly?

The operators and the manufacturers will no doubt seek to blame each other. For Saudi Arabia, this is a particularly sensitive matter because the man ultimately accountable for safety at the Grand Mosque is King Salman, in his role as Guardian of the Two Holy Shrines.

  • Note for crane-spotters: A spokesman for Liebherr quoted in Arab News today implies (without directly saying so) that the crane was Liebherr's LR-13000 model. In my blog post on Sunday I suggested it was the LR-11350. I'm still not sure which it is. A drawing of the LR-11350 can be seen in Sunday's blog post. A drawing of the LR-13000 is below:

Posted by Brian Whitaker
Tuesday, 15 September 2015