The Hong Kong Apartment Complex Fire

 

In the afternoon of Wednesday, November 26, it was windy in the part of Hong Kong where eight 31-story apartment towers called Wang Fuk Court were undergoing renovations.  As has been the custom for hundreds of years, exterior scaffolding made of bamboo was erected around the towers.  To prevent damage to the single-pane windows of the complex, workers had covered the windows with foam-plastic sheets.  Nylon safety nets surrounded the scaffolding.  What could go wrong?

 

The world found out when an unknown cause started a fire in the lower level of one of the scaffolds.  The flames quickly spread from high winds to the flammable plastic sheets over the windows.  Burning debris and flames spread from tower to tower until seven of the eight towers were engulfed.  About 40% of the residents were over 65, and the fire alarms in many of the buildings were later found to be out of order.

 

For the next day or so, the fire defeated efforts of thousands of firefighters to control it.  As of this writing, the confirmed death toll stands at 146, with dozens more missing.  About 4,600 people lived in the complex, so many got out alive.  But many others, probably including most of those who needed mobility assistance to escape, didn't make it.

 

News reports are calling this tragedy a "man-made disaster," and I couldn't agree more.  Authorities have arrested several officials of the construction company in charge of the renovations, Prestige Construction and Engineering Company, and have halted the firm's work on all other projects in order to conduct safety inspections. 

 

Whoever made the choice of protective window panels may have chosen low cost over safety.  In any event, that choice directly contributed to the fire perhaps more than anything else, although final conclusions will have to await a thorough investigation.  The use of nylon for safety netting and bamboo for scaffolding are also questionable, although China has a centuries-old tradition of bamboo scaffolding that has only recently come into question as metal scaffolding gradually supplants it.  Photos of the scene after the disaster seem to indicate that the scaffolding largely stayed in place, but was charred to the point of being structurally unsound.

 

As soon as I learned of this fire, I thought of the 2017 Grenfell Tower fire in London.  In that disaster, a refrigerator caught fire in a lower apartment and the flames spread to flammable exterior insulating sheathing that had been installed in an upgrade some years before.  The fire propagated behind the sheathing and was difficult to extinguish, and before it was all over, 72 people died and many more were injured.  Again, negligent planning and a failure to take account of the flammability of exterior sheathing was at fault, just as it appears to be in the Wang Fuk Court fire.

 

Engineering ethics requires imagination of a particularly informed type:  imagination bolstered by in-depth technical knowledge.  Engineers sometimes have a reputation for being dour pessimists who always jump to the worst-case scenario of a given situation.  But in the case of the Hong Kong fire, engineers were not pessimistic enough.  Nobody apparently imagined what would happen if one of the plastic window-sheathing panels caught fire, especially if it was on a lower floor of a building that happened to be upwind of most of the others on a blustery day. 

 

It's possible that workers were instructed not to smoke or to engage in operations that might lead to a fire.  That's all very well, but not everybody follows instructions. And even the best-intentioned workers can be using equipment that shorts out or otherwise becomes a source of ignition.  Good safety practitioners imagine that something statistically unlikely will nevertheless go wrong, and then draw conclusions from that premise. 

 

Judging from the number of residents listed and the casualty list, it's possible that about 5% of the listed residents died in the fire.  That means that 95% escaped either with no injuries or non-life-threatening ones, while however losing most of their worldly possessions.  No one I know would like to go through an unplanned experience that will strip you of your things and lead to a one-in-twenty chance of death.  So while fire escapes and other built-in safety features allowed most residents to escape the flames, over a hundred didn't.

 

Major renovation projects are routinely inspected by civil authorities, and I can't imagine that this project was an exception.  If a construction firm neglects to take due safety precautions, it is the civil authority's responsibility to step in and halt work if necessary in order for safety hazards to be addressed.  This obviously wasn't done. 

 

I don't know the nature of safety inspection services in Hong Kong, but among those to be held accountable should be whoever permitted the work to proceed.  Such officials can be subject to corruption pressures, and until a tragedy like this occurs, no light is shed on the fact that corners are being cut by paying off inspectors.  I have no reason to believe that this was the case here, but it is certainly an avenue worth investigating.

 

Disasters like this one can have the silver lining of making future safety regulations and inspections much more rigorous.  As the investigations proceed and the chain of causation is revealed, Hong Kong engineers, construction firms, and officials can all learn valuable lessons that are driven home by the horrible example of what can go wrong if safety measures are neglected.  My sympathy is with those who lost loved ones in the fire.  And my hope is that nobody anywhere in the world puts flammable sheathing on high-rises ever again.

 

Sources:  I referred to a BBC report at https://www.bbc.com/news/articles/cdxe9r7wjgro, a report from the news outlet livemint.com at https://www.livemint.com/news/world/hong-kong-apartment-fire-death-toll-climbs-to-146-probe-reveals-fire-code-violations-11764496767266.html, and the Wikipedia article "Grenfell Tower fire.

Alaska Airlines Plane Had Bolts Missing

 

Last month, we blogged in this space about the Alaska Airlines flight that lost a door plug and decompressed at 16,000 feet on January 5.  The aircraft involved was a Boeing 737 Max 9, and the door plug was recovered in the back yard of a Portland, Oregon resident.  Fortunately, no one was killed, although several minor injuries resulted, and the plane landed safely.

 

On last Tuesday, the U. S. National Transportation Safety Board (NTSB) announced that its investigators determined that the four bolts which retain the door plug in place were missing before it blew out.  Documents obtained from Boeing and its supplier Spirit AeroSystems show a sequence of events that points to a serious manufacturing problem, if preliminary indications are borne out by subsequent investigations.  At this point, here is what we know, based on news reports and a preliminary report by the NTSB.

 

The 737 fuselages are manufactured at a Spirit facility in Wichita, Kansas, which used to be owned by Boeing.  In 2005, Boeing spun it off to an investment firm, but it still makes fuselages and ships them via extra-long railcars to one of the main Boeing assembly plants in Renton, Washington State.  The fuselage of the plane in question arrived in Washington in August of 2023.

 

At the Renton plant, it was found that five rivets near the port-side door plug were damaged and had to be replaced.  To access the rivets, it was necessary to remove the door plug.  Except for the fact that it has no handle and other fittings that would make it a usable door, the door plug fits in the fuselage like a regular door.  There are twelve "stop pads" which engage with fittings on the plug, but in order for it to move like a door, the plug must be free to move away from these pads.  A regular door has a separate locking mechanism to keep it attached to the plane, but in the door plug, it appears that instead of a locking mechanism, four bolts retain it in place.  Without these bolts, the only thing keeping the door plug in place is the mechanical integrity of the stop-pad pins and other machinery that is not designed to keep it there, but to let it move when needed.

 

After the defective rivets were replaced by Spirit personnel at the Boeing plant, a photo was taken of the completed work.  This is the photo that shows three out of the four door-plug bolts were definitely missing (a fourth location was concealed by insulation, but that one was probably missing too, based on evidence from the recovered door plug). 

 

These events took place in September of 2003.  The aircraft was delivered to Alaska Airlines on Halloween of 2023, the end of October.  Somehow the door plug managed to stay in place for a number of flights through November and December, but by January 5, the stop pads and associated parts had fatigued with repeated pressurizations enough to fail at 16,000 feet.  If the plane had been at a cruising altitude of 35,000 feet when the plug blew, the depressurization could have sucked many passengers out and possibly crashed the plane.  So this incident was an extremely close call.

 

As a teacher, I am continually impressed with the need for an ability that is unique to humans:  the ability to pay attention.  I impress this need upon my students, but every time I grade exams, I discover what happens when attention is not properly directed, or directed on the wrong things.  Boeing and Spirit obviously have extensive procedures in place to manufacture, assemble, and inspect aircraft.  And nearly all the time, these procedures work.  But every procedure is useless if the human minds carrying them out do not perform them according to the rules. 

 

Clearly, it was someone's duty to document with a photograph the rework of the five damaged rivets.  But it is so easy to see how someone, even an inspector whose main job was to certify the correctnesss of a repair, would have his or her attention focused on the rivets, and not on the door plug only a few feet to the rear of the rivets.  The NTSB inspectors, focused as they were on the door plug, saw immediately from that photo that someone had forgotten to install the retaining bolts before the insulation and interior finish materials were installed.  And probably the first time the bolts were put in, before the rework procedure, somebody checked to make sure they were there.  But this time, because things were slightly out of the ordinary during the rivet rework, that small but critical act of looking to see if the bolts were in place was omitted.  And once everything was buttoned up, nobody could tell from outside that the bolts were missing.

 

This raises a question that occurs to a person who has disassembled and reassembled many pieces of equipment over the years.  When a technician removed the bolts to take out the door plug and gain access to the rivets, where did those bolts go?  On a workbench?  In a pile of similar bolts?  It seems like if they were just sitting around after the job was done, that would get somebody thinking about where they belonged.  This is the kind of seemingly unimportant detail that suddenly becomes significant, and I'm sure that some NTSB personnel are asking similar questions of the people involved in the rework.  I would not want to be one of the technicians who get grilled.

 

Modern technological means of documenting manufacturing processes have made it easier to trace actions such as the ones the NTSB is investigating.  In the old pre-digital-camera and pre-email days, investigators would have had to rely only on recollections of mechanics, and it's very unlikely anyone would have taken pictures at every step of the process or produced documents with as much detail as electronic data can include these days. 

 

Still, it's not robots who assemble airplanes, it's people.  And people (and robots) can make mistakes, especially when they are doing something out of the ordinary such as rework, where it is impossible to write procedures for every contingency and people are trusted simply to do the common-sense good thing.  The only problem here is, that wasn't quite good enough.  Fortunately, the consequences were a lot more benign than they could have been, and the accident can serve as a warning, or encouragement if you like, that no matter how trivial an inspector's work may seem, it can save lives—or lose them.

 

Sources:  I referred to an Associated Press report on the NTSB findings which appeared Feb. 6 at https://apnews.com/article/boeing-emergency-landing-report-alaska-airlines-8543c90b68b4d932a700cf57ff8f1b8e.  The preliminary NTSB report itself is at https://www.ntsb.gov/investigations/Documents/DCA24MA063%20Preliminary%20report.pdf.  I also referred to the Wikipedia article on Spirit AeroSystems.