Two hours into Mr. Lai’s second shift, the building started to shake, as if an earthquake was under way. There was a series of blasts, plant workers said.

Then the screams began.

When Mr. Lai’s colleagues ran outside, dark smoke was mixing with a light rain, according to cellphone videos. The toll would eventually count four dead, 18 injured.

At the hospital, Mr. Lai’s girlfriend saw that his skin was almost completely burned away. “I recognized him from his legs, otherwise I wouldn’t know who that person was,” she said.

Eventually, his family arrived. Over 90 percent of his body had been seared. “My mom ran away from the room at the first sight of him. I cried. Nobody could stand it,” his brother said. When his mother eventually returned, she tried to avoid touching her son, for fear that it would cause pain.

“If I had known,” she said, “I would have grabbed his arm, I would have touched him.”

“He was very tough,” she said. “He held on for two days.”

After Mr. Lai died, Foxconn workers drove to Mr. Lai’s hometown and delivered a box of ashes. The company later wired a check for about $150,000.

Foxconn, in a statement, said that at the time of the explosion the Chengdu plant was in compliance with all relevant laws and regulations, and “after ensuring that the families of the deceased employees were given the support they required, we ensured that all of the injured employees were given the highest quality medical care.” After the explosion, the company added, Foxconn immediately halted work in all polishing workshops, and later improved ventilation and dust disposal, and adopted technologies to enhance worker safety.

In its most recent supplier responsibility report, Apple wrote that after the explosion, the company contacted “the foremost experts in process safety” and assembled a team to investigate and make recommendations to prevent future accidents.

In December, however, seven months after the blast that killed Mr. Lai, another iPad factory exploded, this one in Shanghai. Once again, aluminum dust was the cause, according to interviews and Apple’s most recent supplier responsibility report. That blast injured 59 workers, with 23 hospitalized.

“It is gross negligence, after an explosion occurs, not to realize that every factory should be inspected,” said Nicholas Ashford, the occupational safety expert, who is now at the Massachusetts Institute of Technology. “If it were terribly difficult to deal with aluminum dust, I would understand. But do you know how easy dust is to control? It’s called ventilation. We solved this problem over a century ago.”

In its most recent supplier responsibility report, Apple wrote that while the explosions both involved combustible aluminum dust, the causes were different. The company declined, however, to provide details. The report added that Apple had now audited all suppliers polishing aluminum products and had put stronger precautions in place. All suppliers have initiated required countermeasures, except one, which remains shut down, the report said.

For Mr. Lai’s family, questions remain. “We’re really not sure why he died,” said Mr. Lai’s mother, standing beside a shrine she built near their home. “We don’t understand what happened.”