Zhang Zaigui, who has been monitoring coal mine safety for two decades, understands that if he gives the go-ahead to a dangerous project, he may end a miner's life.

"We can't put miners' lives at risk at any time," the 55-year-old said.

Zhang works at the Shandong Provincial Bureau of the National Mine Safety Administration, looking for hidden dangers in coal mines to ensure safe production.

He is dubbed by people in the sector as Iron-faced Baogong, which means he is selfless, impartial, and not afraid of threatening situations, just like Baogong, an upright official known for stressing the dignity of law in the Song Dynasty (960-1279).

He earned the name with a bunch of cases that he strictly dealt with according to laws and regulations.

One case was in 2015 when Zhang and his colleagues were checking a coal mine in Shandong province. He found the amount of explosive materials handed out was higher than the number recorded on the books.

"The person who oversaw handing out the explosives couldn't explain where the explosives were used. What he said was ambiguous, so I suspected there might be concealed operational sites," Zhang said.

He went into the coal mines and found three illegal sites after walking over 10 kilometers underground. He turned down bribes from the coal mine operator and handed out a fine to urge the mine operator to rectify the problems immediately.

"If I showed mercy to the mine operator, then many workers' lives would have been put in danger," he said.

During the past two decades, Zhang has gone down into the mines more than 3,000 times. He walked underground, looking carefully for any hidden dangers such as rock bursts, water inflows or harmful gases. He has removed more than 10,000 hidden dangers, according to the bureau.

During a conference in October 2015, Zhang noticed the head of a coal mine leaving after a brief phone call. Sensing there might be a problem, Zhang went to the control room, where he observed on surveillance devices that there was water leaking into an underground area where 150 miners were working.

As the head of the mine hesitated about whether to stop all work, Zhang issued an enforcement order to evacuate all people underground. The mine flooded only minutes after all the workers were evacuated to safety.

During Spring Festival last year, when the COVID-19 epidemic was spreading, Zhang suspended his holiday and returned to his post to oversee coal mine production at an intelligent platform.

"The platform, which contains monitoring systems including those tracking workers' positions, microseismic rock bursts and mine hydrological conditions, helped us to know underground conditions during the epidemic, when we weren't able to go down underground frequently," Zhang said.