Four years after undergoing a transplant to replace his lungs, which were destroyed by pneumoconiosis, Zhang Haichao now lives a healthy and normal life.

"I feel fine. My lung functions are back to normal," he said. "Before the surgery, I could barely walk 50 meters, but now I can even climb mountains."

Zhang, 37, began displaying symptoms of pneumoconiosis, such as harsh coughing, in 2007 while working at a dusty workshop producing fireproof materials in Xinmi, Henan province.

The condition is caused by the inhalation of dust.

He traveled to the provincial capital, Zhengzhou, for a checkup and was diagnosed with tuberculosis by the Zhengzhou Occupational Disease Control and Prevention Institute.

However, after seeking a second opinion at the First Affiliated Hospital of Zhengzhou University, one of the city's top hospitals, doctors ruled out TB and diagnosed pneumoconiosis.

"I went to many hospitals after that, including in Beijing. All the hospitals agreed that I didn't have TB," he said.

Yet the feedback from those hospitals had no legal effect in allowing Zhang to claim compensation from his employer. Of all his local clinics, only the Zhengzhou institute is certified to diagnose occupational diseases such as pneumoconiosis, yet Zhang said it has refused to confirm his diagnosis.

He underwent exploratory chest surgery at the Zhengzhou University hospital in June 2009, and it showed without doubt he had the disease. But the institute still refused to back the results.

Eventually, Zhang's story was picked up by local and national media, which prompted public outrage and applied pressure on the institute and local authorities to accept the diagnosis.

He went on to receive 1.2 million yuan ($190,000) in compensation from his employer, and in mid-2013, he underwent a lung transplant at Wuxi People's Hospital in Jiangsu province.

After two years of recovery, Zhang found work as a bus driver in Xinmi.

"I don't really want to be a driver, as my doctor told me to stay away from crowds to prevent infection," he said. "But I have to make a living. I get up at 5 am, even in temperatures as low as - 13 C in winter. I'm really afraid of catching a cold."

Zhang's wife left him in 2012, and now he lives with his 13-year-old daughter, who studies at primary school.

"As a pneumoconiosis patient, I know I'm very lucky because I got compensation that covered my treatment," he said. "Most migrant workers with the disease I know can't get compensation, either because their employers didn't buy insurance for them or they didn't sign an employment contract."

Fortunately, local governments have attached more importance to the prevention and control of the disease, and are improving support for patients.

"Migrant workers in some places can even have their medical bills completely reimbursed," Zhang added. "I hope those working in hazardous environments can learn to protect themselves and stay healthy."