Chinese President Xi Jinping visits medical staffers at the affiliated hospital of Qingdao University in Huangdao district, where the survivors from Friday's oil pipeline blast are being treated, in Qingdao, East China's Shandong province, on the afternoon of Nov 24, 2013. [Photo/xinhuanet.com]

However, in 2001, the Qingdao-based Peninsula Metropolis Daily reported that some buildings stand within 5 meters of the pipeline, which was laid in 1986 and predates the 2003 regulations. The residential section of Huangdao was built in the 1980s and 90s.

Guo Jishan, deputy secretary general of Qingdao municipal government, said that when it was laid, the pipeline conformed with the rules, but admitted that many pipelines run below Huangdao and they often overlap. "The pipeline system in Huangdao is very complicated — there are at least 11 different ones," he said.

Sinopec denied media reports that the 248-km-long pipeline, which runs across part of Shandong, from Dongying to Huangdao, was laid in August 2012.

The company said the pipeline was identified as a potential risk in 2011 and it plans to reroute five sections, including the 15 to 16 km running below Huangdao, plus two other pipelines in the province. However, it said the work has been stalled because the environmental impact of the plans is still under official assessment.

In a public announcement related to the first round of the environmental impact assessment in 2011, Sinopec said: "The area where the pipelines are located has become an extremely busy location, with many new buildings and a dense population. Some of the pipelines have been built over, making them inaccessible for repair and many of those we are able to reach are too close to buildings and it's difficult to maintain the erosion-resistant-layers. That makes them a potential safety hazard."

Sinopec conducted a nationwide safety inspection on an "unprecedented scale" in October, according to the company's website. Qingdao municipal government confirmed that the company inspected the pipeline at the center of Friday's tragedy, but was unable to give any further details.

No official warning

Many residents said they had been given no warning of the oil leak. "What I don't understand is why no one told us there was a leak on the oil pipeline, which is buried right next to my place of work, and why they didn't evacuate us when the repair work started?" said Li Baoli, an employee at a factory owned by Yihe Electrical Equipment Co, which is situated close by Zhaitangdao street — one of the worst-hit areas.

Li Baoli, who suffered a broken ankle in the blast, said that if the authorities had warned the factory about the possible danger, work could have been suspended for the day and many lives could have be spared.

"I wouldn't have worked here if I'd know that an explosion caused by leaking oil could be this severe. I've been working at this factory for 13 years, but I never knew that an oil pipeline ran underneath it," said the 45-year-old, speaking from his hospital bed.

He said he heard two loud bangs and was thrown to the ground by the shockwave. He attempted to run, but felt a sharp pain in his right ankle, which had been hit by flying masonry. "I had no choice but to ignore the pain. It felt as though death was chasing me when I heard a third loud bang," he recalled.

His colleagues took him to the hospital in a car with no windows — all the glass in nearby buildings and vehicles had been shattered by the explosion.

"My injury is nothing — some of my colleagues were killed. Many had blood all over their faces and people were lying on the ground in all sorts of horrible positions. It's such a tragedy," he said.