As millions of travelers rode the rails during Spring Festival, a team of specialized divers was hard at work in the icy water beneath a bridge on the Xinyan railway connecting Xinxiang in Henan province with Yanzhou district of Jining, Shandong province.

Weighed down by more than 20 kilograms of equipment, divers from the China Railway Jinan Group's emergency rescue and survey unit conducted thorough inspections of the bridge's underwater piers, integrating traditional diving with cutting-edge robotic technology.

At a depth of 5 meters, with near-zero visibility in the turbid water, 28-year-old Gao Jiawang relied on experience and touch as he meticulously explored the pier surface inch by inch.

"My fingers act as my eyes. Any holes or spalling can be sensed through touch," Gao said. His diving mask bears numerous scratches, testimony to close encounters with riverbed rocks and submerged rebar.

This year, Gao has a new partner: an underwater inspection robot. The machine can swim like a fish and adhere to pier surfaces like a gecko, using high-definition cameras and sonar to rapidly scan and identify issues in turbulent waters. After the robot completes its preliminary screening, the divers perform manual checks on critical areas. The collaboration between humans and machine serves as a double safeguard for bridge safety.

The China Railway Jinan Group emergency rescue and survey unit, composed of 46 members, is the nation's only professional railway bridge underwater inspection unit. Beyond diving expertise, members must master bridge structural knowledge, interpret engineering blueprints, operate specialized equipment, including underwater cameras, and possess emergency skills such as underwater welding and cutting. Many of them have earned additional certifications, including welding engineer and diving supervisor qualifications during off-duty hours.

"Every dive presents a unique challenge," said Gao, whose deepest dive stands at just under 20 meters. "Underwater conditions vary dramatically across China's river basins. Northern waters require ice-breaking operations in winter, southern rivers conceal undercurrents in summer, mountain streams carry rolling rocks, while plain rivers accumulate deep silt."

Divers face potential entanglements in fishing nets, equipment failures, and sudden torrents."Maintaining calm judgment in absolute darkness and silence is a skill we must master," Gao added.

To date, the team has traversed 18 provincial-level regions and inspected more than 400 railway bridges across the country, accumulating an invaluable underwater structural database.

During the Spring Festival rush, inspection schedules intensified significantly.

"We must complete operations within limited time windows,"Gao said, referring to brief intervals between train services, typically lasting only two to three hours. "The most gratifying moment is hearing trains safely crossing the bridge after our inspection. It fills me with immense pride."

zhaoruixue@chinadaily.com.cn