The Fatal Dallas Crane Collapse

Two weeks ago, on Sunday June 9, a severe thunderstorm appeared over downtown Dallas, Texas.  Sudden thunderstorms are not uncommon in this region, and the residents of the Elan City Lights Apartments had no undue reason for concern.

But they should have been worried.  Around 2 PM that afternoon, a construction crane owned by Bigge Crane and Rigging Company toppled over onto the apartments, slicing through the buildings "like a hot knife through butter," in the words of one eyewitness.  One person, 29-year-old Kiersten Smith, died in her apartment, and five other residents suffered various degrees of injury.  More than 500 people have been temporarily made homeless while the building's safety is being assessed and repairs commence.

This is only the latest in a number of construction-crane accidents that have happened in the U. S. and elsewhere in recent years.  As a CNN report pointed out, from 2011 to 2015 Texas led the nation in the number of crane-related deaths, with nine occurring since 2011.  While this means you probably shouldn't take out a special crane-fatality rider on your life insurance, nine deaths, especially if they were not construction workers but ordinary citizens who were unable to do anything with regard to crane safety, is nine too many.

As crane-safety expert Thomas Barth pointed out in a CNN interview after the accident, there are things that crane operators can do to ensure that cranes won't blow over in case high winds arise.  The tower cranes so common in the skylines of modern cities can be designed and installed to withstand winds of up to 140 miles per hour (225 km per hour), which would occur during a moderate hurricane.  But the operators have to take certain precautions in the event of high winds.

           

One such precaution Barth cited was to attach a large weight to the working end of the crane.  With no load, such cranes are only marginally stable due to the large rear-mounted counterweight that compensates for the typical load the crane carries, and so pre-weighting the front adds to the crane's stability.  Another precaution taken by some operators is to release the rotation clutch and let the crane "windmill" in the wind, so that the long front part naturally points in the direction of the wind.  This also places the counterweight in such a position as to oppose the force of the wind and lessens the chances that the crane will blow over.

Apparently, neither one of these precautions was taken with the crane in Dallas.  Both live video shot during the storm and drone video of the accident's aftermath shows that the crane fell over nearly backwards, with the boom partly crosswise to the wind and partly pointing into the wind.  While definitive conclusions will have to await the results of the accident investigation, it appears that no one was on the construction site or charged with the responsibility of taking precautions with the crane if a storm arose. 

Some cities have regulations and licensing requirements for crane operators, but Dallas, in keeping with the general laissez-faire economic atmosphere of Texas, is not one of them.  Such regulations are not guaranteed to prevent crane accidents, as the 2008 crane collapse in New York City that killed seven people showed.  In general, the lawsuits and insurance-rate increases that follow a fatal accident like this can be enough incentive to make crane operators take reasonable precautions, but sometimes leaving safety to the commercial firms isn't enough.  All the regulations and policies in the world won't make a difference if the people on the ground doing the work either get careless, or simply are not told what the safe thing is to do, and get paid for doing it. 

In the case of the Dallas crane accident, either the crane operator or the construction general contractor would have had to pay somebody to be responsible for putting the crane into a safe mode in the event of threatening weather.  In retrospect, the few hundred dollars this might have cost would have been money well spent if it had prevented the accident.  And perhaps Bigge Crane and Rigging has learned its lesson, although news reports say it has been cited some eighteen times by the U. S. Occupational Safety and Health Administration in the last ten years. 

Such a record may be typical for a large, busy firm with extensive operations in numerous states.  And some of the citations may be for fairly trivial matters, such as mislabeled safety equipment.  But we now know that in at least one case, inattention to crane safety has led to the loss of one life, the injury of several bystanders, the loss of an expensive piece of equipment, and untold damage to property.

There is an aspect to this accident that gets almost no attention these days, but deserves it nonetheless.  It concerns the wider society's attitude toward "lowly" jobs such as construction workers, even those who operate costly pieces of equipment and hold the responsibility for dozens of lives in their hands.  The same thing could be said about airline pilots.  Pilots are respected, treated with deference, and in turn receive good pay and job security, while the operator of a construction crane is unknown to everyone except perhaps his family and co-workers, certainly gets paid less than the lowliest supervisor on the job, and may not know if he has a job at all after the current project is over. 

This situation reminds me of a saying attributed to Lyndon Johnson's Secretary of Health, Education, and Welfare, one John W. Gardner.  In a 1961 book called Excellence:  Can We Be Equal and Excellent Too? he wrote, "The society which scorns excellence in plumbing as a humble activity and tolerates shoddiness in philosophy because it is an exalted activity will have neither good plumbing nor good philosophy: neither its pipes nor its theories will hold water."  As a society, I think we both tend to scorn lowly but important activities such as crane operation, and exalt others, not just philosophy (think sports and entertainment?) that don't necessarily deserve such exaltation.  If crane operators and their ilk were more respected, they might feel a little more responsible, and companies employing them might act more responsibly too.

Sources:  I referred to news reports on the Dallas accident from the websites of Channel 5 News at https://www.nbcdfw.com/weather/stories/Dallas-Crane-Collapse-Multiple-Injuries-511045081.html and CNN at https://www.cnn.com/2019/06/10/us/dallas-crane-collapse/index.html.  I also referred to Wikipedia articles "303 East 51st Street" for the New York crane collapse and https://en.wikiquote.org/wiki/John_W._Gardner for the quotation about plumbers and philosophy. 

Mecca Construction Crane Tragedy

Construction sites can be dangerous places.  That is why under most circumstances, access to the sites is strictly limited to workers who presumably know what they're doing, and even then, worksite injuries and deaths can occur as temporary structures or machinery such as cranes can get out of control. 

But what if the site you're working on is regarded as sacred by your religion, and in a few weeks hundreds of thousands of pilgrims are going to visit it?  Putting up "closed for construction" signs isn't an option. 

This is the dilemma that those in charge of the Grand Mosque (Masjid al-Haram, in Arabic) in Mecca faced as this year's hajj (obligatory pilgrimage) approached.  When upwards of a million people are expected to crowd into a few dozen acres of ground, the potential for disaster is always present.  And in years past, stampedes of pilgrims have on occasion led to the deaths of hundreds of people caught in panic-stricken rushes.  Improvements to the structures used can help with crowd control, and so areas near the Grand Mosque have seen a lot of construction activity in recent years.  That is one reason why the Grand Mosque was surrounded by numbers of tall construction cranes last Friday, Sept. 11, shortly before the time of evening prayer at 6:30.  At least one of these was a "crawler crane" mounted on a mobile platform that could move on tank-like treads. 

Around 5 PM, a thunderstorm approached the city and brought heavy rain, lightning, and high winds.  Although the central part of the Grand Mosque surrounding the Kaabah (the black cube at the center) is open, much of it is covered by in a ring-shaped multistory structure that affords protection from the weather.  

While details are not yet clear and await investigation, apparently about 5:30, winds became strong enough to overbalance one of the crawler cranes stationed just outside one of the Grand Mosque's walls.  Videos shot at the time show the crane as it toppled onto the roof of part of the mosque, crashing through the ceiling and landing with its top  inside the mosque's inner open area.  Unfortunately, hundreds of people were in the path of the collapse and were killed or injured when the crane knocked down masonry as it fell.  As of Sept. 13, the death toll had risen to 107, with over 200 injured.  King Salman of Saudi Arabia has stated that once an investigation of the tragedy is complete, the findings will be made public.

First, our prayers and sympathy are with the injured and the relatives and friends of those who died.  Accidental deaths are always tragic, but especially so when victims were engaged in a religious pilgrimage made obligatory by one's faith.  There is some comfort at least in the knowledge that the pilgrims who died were engaged in what they considered to be a holy act. 

From an engineering point of view, this incident has several lessons that can be learned. 

First, crawler-type cranes can be less stable than other types with bases that are anchored to the ground.  The crawler crane is obviously more flexible and easier to position, but this convenience comes with a price:  less stability, unless great precautions are taken to ensure that the crane's rated load and maneuvering envelope are strictly observed.  And even if this is done, unpredictable wind loads such as are present in a thunderstorm can tip the balance of forces away from stability. 

Prudence might have suggested that with all the cranes around, someone should have kept an eye on the local winds and issued an evacuation order if the wind exceeded a certain speed.  But that might not have helped, for a number of reasons.  First, winds in a thunderstorm can change minute by minute, and it's possible that a sudden gust was responsible for the crane's collapse.  But evacuating a complex as large as the Grand Mosque would have presented its own problems, including the possibility of inducing exactly the kind of panic that has led to deaths in stampedes in the past.  So although evacuating the area might have prevented some loss of life, it might have contributed to it as well.

The other alternative would have been to use only cranes that could withstand higher winds.  This might mean either using only stationary ground-mounted units, or shorter crawler cranes that are sturdier in high winds.  While either of these options would cost something in terms of workplace efficiency and schedules, in retrospect it would have been a price worth paying.

Like airports in expanding metropolitan areas, the Grand Mosque complex in Mecca is likely to be under construction in some sense for an indefinite time.  Given that it is, the authorities in charge of it are under an obligation to see that nothing like this tragedy can ever happen again.  Unlike the whims of mobs, engineering involves calculation, prediction, and the ability to plan ahead.  While engineers cannot foretell every eventuality that could lead to disaster, the investigation of the Mecca crane collapse may show how it could have been prevented.  If it does, the engineering staff in charge have their work cut out for them to make sure that pilgrims can worship safely in the holiest city of Islam.

Sources:  I referred to news articles on the collapse carried by several outlets:  CNN at http://www.cnn.com/2015/09/12/middleeast/saudi-arabia-mecca-crane-collapse/, the BBC at http://www.bbc.com/news/world-middle-east-34236662, Al Jazeera at http://www.aljazeera.com/news/2015/09/saudis-probe-deadly-mecca-crane-collapse-150912125336576.html, and The Guardian at http://www.theguardian.com/world/video/2015/sep/11/aerials-of-mecca-crane-collapse-reveal-damage-video, which has a cellphone video showing the crane falling amid heavy rain.  I also referred to the Wikipedia articles on the Grand Mosque and the climate of Mecca.