This is not the first time Foxconn has reported major fires at its manufacturing plants. The most serious incident, a May 2011 explosion in the company’s Chengdu plant, killed four workers and injured 18. Later that year, another fire broke out in a plant in the Shandong province, with no casualties reported.

In both this latest fire and in the large blaze in Chengdu, officials pointed to issues with ventilation ducts. Explaining the most recent fire, the Wall Street Journal reported (paywall) that it “began in the central air conditioning fan and ventilation ducts.” Apple’s own conclusion to the May 2011 explosion in Chengdu was to increase the effectiveness and safety of the factory’s ventilation system (pdf).

Better ventilation was necessary to remove small particles suspended in the air which could explode in the right circumstances. Apple’s report, also referring to an explosion at a Shanghai factory run by another contractor, said:

While the causes of these two incidents—as well as many of the corrective actions taken afterward—were different, both explosions involved combustible dust. Many materials, including ones normally considered noncombustible, can burn rapidly when small particles are suspended in air in the right concentration and ignited.

Small particles of aluminum dust were particularly problematic. Such dust is produced while milling and polishing the casings of various Apple gadgets.

Below is a (Chinese language) 2012 video tour of the Zhengzhou plant. It was created by Chinese news website iFeng and features Foxconn chief Terry Gou.

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