SHANGHAI — An explosion that killed 3 workers and injured 15 others last week at a Chinese factory that supplies products to Apple was caused by combustible dust, according to a preliminary investigation by the local authorities.

The explosion, which occurred Friday in the southwestern city of Chengdu, has led to the partial shutdown of a facility operated by Foxconn, one of the world’s biggest contract electronics makers and a major supplier to companies like Hewlett-Packard, Dell, Sony and Apple.

The shutdown has created worries about supply disruptions for some Apple products, including the iPad, which experts say was being produced at the Chengdu facility. The aftermath of the explosion is also the latest problem facing Foxconn, which was hit last year by a rash of worker suicides at several of its Chinese facilities.

Apple and Foxconn, a division of Hon Hai Group, based in Taiwan, issued statements after the explosion last Friday saying that they regretted the tragic accident and that the cause of the blast was under investigation.

City officials in Chengdu said the explosion had been caused by combustible dust in an air duct at a polishing workshop.

Foxconn and Apple each declined to say which products were being produced at the Chengdu facility. Foxconn is one of Apple’s biggest suppliers, and the Chengdu complex is a relatively new facility, with 80,000 employees.

IHS iSuppli, a research group, said Monday that the explosion at the Chengdu facility could result in the loss of production of 500,000 Apple iPad 2 tablet computers during the second quarter of this year. IHS iSuppli said that while most of the iPad 2 production was taking place at another Foxconn facility, in the southern Chinese city of Shenzhen, that facility might not be able to compensate for the disruption in Chengdu.

Foxconn has been moving aggressively over the past year to expand its operations in central and western China to keep up with production demands and to recruit more workers from the poorer, inland provinces.

Apple has a longstanding relationship with Foxconn, which struggled last year to cope with a rash of worker suicides. Some labor rights groups say they believe the suicides were the result of harsh working conditions at Foxconn.

Foxconn, however, insists it treats its workers well. Following the suicides, it hired counselors and put large nets up on some buildings to prevent suicides.

Apple later praised Foxconn’s efforts, saying the company had “definitely saved lives.” But Apple, like other global companies, has to deal with continuing problems that crop up in China’s massive factory zones. Apple has a strict code of conduct for its global suppliers, audits facilities every year and publishes its findings.

Last year, Apple said its audits found that nine supplier factories in China had hired workers below the age of 16, the legal working age, and that other facilities had falsified audit materials and even coached workers on how to respond to questions from auditors. Apple also said in its report that at a supplier factory in the city of Suzhou, 137 workers were exposed last year to the toxic chemical n-hexane, causing adverse health effects.

Some labor rights activists say Foxconn’s working conditions are poor and that Apple and Foxconn have failed to address complaints by workers.

On Monday, a Hong Kong-based labor rights group called Students Scholars Against Corporate Misbehavior said that it had noted a problem with “aluminum dust” in Foxconn’s Chengdu facility last March, when it issued a report on the company’s working conditions there.

The group said workers at the Chengdu facility had complained earlier this year that “the ventilation of the department is poor. Workers polish the iPad cases to make them shiny. In the process, there is lots of aluminum dust floating in the air. Workers always breathe in aluminum dust even thought they put on masks. When workers take off their cotton gloves, their hands are covered with aluminum dust.”

After the statement was released by the group, Foxconn issued its own statement saying it was “unfortunate” that the Hong Kong group was seeking to “capitalize on the tragic accident” with a statement that misrepresented “Foxconn’s commitment to the health and safety of our employees.”

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