The man's hand is twisted into a claw, crushed, he says by a metal press at the Foxconn factory in Shenzhen, where Apple's luxury electronics are assembled. He is looking at an iPad – he has never seen one switched on. His mangled hand strokes the screen, bringing it to life.

Back at the factory, where the buildings are swathed in nets after 12 workers committed suicides in a single year, a young girl emerges from the gates. Her job is to clean the iPhone screens before they are packaged. She says she is 13.

These are a few of the many shattering images in performer Mike Daisey's account of his 2010 visit to China. After hearing about the Foxconn suicides, he determined to meet members of Apple's largest subcontracted workforce.

What he discovered ultimately led to the firm's announcement this month that it would throw open its factories to independent auditing by the Fair Labor Association (FLA). A non-profit group founded in 1999 after sweatshop scandals, it already audits Nike, Adidas and H&M. Apple is its first tech industry member.

"In high tech to date there hasn't been anything like external independent assessment, which is what makes Apple's decision such big news," says FLA president Auret van Heerden.

Apple has been auditing itself since 2007. Working hours are a major issue. In China, 12 and 16 hour shifts are common. In 2008, 82% of factories violated Apple's limits – a 60 hour week with no less than one day off. By 2011, the number was 68%. In 2008, half violated wages codes by deducting salary as a disciplinary measure, or not providing pay slips. The figure was 30% last year.

Apple has ordered retribution. Factories discovered employing children must return the youngsters to their families, fund their education and continue to pay their factory wage too. Employers have been made to reimburse wage deductions and settle unpaid overtime.

But six active and 13 historical cases of underage labour were discovered at five factories last year. Mandatory pregnancy tests were imposed at 24 Apple facilities.

When Daisey visited, he found worker dormitories where people slept in bunks stacked five or six high, so closely there was no room to sit. There were cameras in the rooms, in the corridors.

He found workers whose hands shook uncontrollably by their late 20s because of repeating the same motions at the same production line post, year after year.

The FLA visited China at Apple's request on a test project in 2010, following the Foxconn suicides. Van Heerden describes what he found: "The whole campus has got excellent facilities. The problem is that [it] still doesn't touch the human being inside. You are at a work station all day – you can't talk to anyone else.

"Then you go back to your dorm and you might not know anyone there either, they might not even speak the same dialect. You are in a situation where you might go days without anything resembling human contact."

He seems to suggest that in China at least, the problem is less about basic human rights and more about HR.

Foxconn has much to learn about human resources, judging by a recent comment from the chair of its parent company, Hon Hai Precision Industry. Terry Gou told an end of year party, at which the director of Tapei Zoo was asked to share his management techniques: "Hon Hai has a workforce of over one million and as human being are also animals, to manage one million animals gives me a headache".

Managing its supply chain will for now remain one of Apple's biggest headaches.