The iPhone may be one of the world's most successful consumer items, but its production has involved poor working conditions, serious damage to health and even death for the Chinese workers who make it.

The number of violations by Apple's suppliers, who help it make the iPhone and the iPad, doubled year-on-year in 2010. Those included the use of underage labor, unsafe working conditions, inadequate safety measures and improper handling of hazardous chemicals, Apple said in an annual Supplier Responsibility report yesterday.

The report noted suicides at the South China factory of Foxconn in the first half of 2010 and 137 workers poisoned following exposure to dangerous chemicals in the Suzhou facility of Wintek.

Apple sent its chief operating officer, Tim Cook, to Shenzhen last June to talk to Foxconn about making changes in conditions to "prevent impulsive suicides," the California-based firm said.

In 2010, Apple audited 127 supplier facilities, revealing 37 core violations, compared with 17 in 2009. They included 18 facilities where workers had paid excessive recruitment fees; 10 facilities where underage workers had been hired; two instances of worker endangerment; four facilities where records were falsified and one case of bribery, according to the report.

Apple has supplier facilities worldwide, but most of its products are assembled on the Chinese mainland.

Industry insiders said the popularity of Apple devices had brought considerable profits for the company while suppliers had been forced to take measures to cut costs and improve efficiency, sometimes to the detriment of workers welfare and working conditions.

Ten Foxconn workers in Shenzhen died after jumping off buildings at the company's plants in the first half of last year. The deaths were blamed on discontent about wages and benefits.

The Wintek workers were poisoned after exposure to hexane, a chemical in cleaning agents.

"We discovered that the factory had reconfigured operations without also changing their ventilation system," the report said.

Similar violations occurred in Shanghai where eight women at a factory making parts for iPhones were diagnosed with peripheral neuropathy, a disease caused by exposure to hexane.

Apple said it will improve its supplier system in the areas of labor and human rights, health and safety, the environment, ethics and management commitment.

Apple terminated its business with one facility at which management "presented falsified payroll records" and with another at which a facility manager "offered cash to Apple's third-party auditors, asking them to reduce the number of audit findings."