13 Workers Die in Hydroelectric Plant Construction Project

Out of Ecuador is a report of a construction accident at a site for the new hydroelectric plant Coca Codo Sinclair.

Collapse Kills 13, Injures 12 In Chinese Hydroelectric Plant In Ecuador
QUITO, Dec 15 (BERNAMA-NNN-XINHUA) -- A tunnel collapse in a Chinese hydroelectric plant in Ecuador's Amazonian region Saturday night killed 13 workers, including three Chinese and 10 Ecuadorians, and injured another 12.

I do not work in the construction industry. I imagine the risks of construction and excavation on the level of a hydroelectric plant must be high.  But, I also imagine that there must be rigorous safety procedures.  The reports I could find so far do not detail the root causes of the incident.

BERNAMA-NNN-XINHUA reports that:

According to the National Risk Management Ministry, the accident was caused by a "collapse in a tunnel" that affected the high-pressure pipes inside the engine room.

Univision:

Ecuador's public radio said there had been a breakdown in a tunnel of the engine room of the plant and that the wounded were being treated at a hospital in the town of El Chaco, Napo.
"We are evaluating what's happened. It's a problem we're having in one of the penstocks," he told the AFP chief technical control of the project, Dennis Salgado.
He said that the accident occurred "in the area of ​​vertical well pipe pressure", which faces the underground powerhouse of hydropower.

The project is huge (Univision):

Coca Codo Sinclair, a work which cost about 2.245 million dollars will start operating in February 2016 and will generate 1,500 megawatts, 36% of the energy currently consumed Ecuador.The works are part of a network of eight hydroelectric construction with which Ecuador, an oil country, expected to stop importing electricity and become an exporter of clean energy.

This accident was not the only loss of life incident at the site(Univision):

Last April, four Chinese were killed in an explosion in the works of other hydroelectric being built in southern Ecuador, also funded by Beijing.
The victims were four technical explosives who perished during the expansion of an underground pit of Sopladora center, built by the China Gezhouba, as Tito Torres, business manager Hidropaute, the state company that manages the building.