Workers injured in a December blast at a Chinese factory say that Apple inspectors toured the facility hours before the accident.

NPR spoke with 25 injured workers who criticized safety conditions at the plant and said they were instructed not to speak with the Apple contingent.

One of the injured employees, Zhang Qing, told NPR that workers were not informed about a similar blast seven months earlier at a factory in Chengdu, China, which was tied to a buildup of aluminum dust.

Another worker hurt in the explosion, Liu Hengchao, said he watched as inspectors wearing white gloves checked for dust levels. But he told NRP employees had been warned off by management not to interact with the Apple inspectors, who he said left after spending 10 minutes in the area.

Apple, which declined to speak with NPR about its report, is set to release its new iPad on Friday.