No one is certain what triggered the flyover collapse March 31 in Kolkata, India, leaving at least 25 dead and around 100 injured. But the tragedy has brought new scrutiny to India's construction safety standards.

In 2008, the Kolkata Metropolitan Development Authority, the statutory planning and development authority for the Kolkata Metropolitan Area, awarded the contract to construct the 2.2-km-long flyover structure or overpass in a congested area of West Bengal state’s capital city in East India. The winning bidder for the $24.5-million project was Hyderabad-based general contractor IVRCL.

Construction began in 2009 and was to be completed in 18 months. Since then, work has gone through three price escalations and missed seven completion deadlines.

“The incident happened on a bend. It looks like a steel girder along with slabs of around 40 meters got dislocated and came down. This is clearly an engineering design flaw and poor workmanship,” an engineer, who asked to remain anonymous, told ENR. “This is a vulnerable stage and it needs support of the pier. Looks like the balance too, was not correct,” said the source. “Material is important as proper pylons are required. This is where engineering comes in.”

Some 59 sections of a total length of 0.9 km have been completed successfully, noted IVRCL said in a statement. “The collapsed section is the 60th,” it adds. A spokesman talking to media at the site termed it as an “act of God.” Making matters worse, the work was being carried out during the day with peak traffic moving under the bridge.

“India does not follow safety standards stringently,” said Mohandas Pai, head of Aarin Capital Partners on NewsX, a local TV channel. “Four roads merge under this flyover. Who has certified it is safe to concrete and [also] allow traffic to move under?”

The accident led a concerned former chief minister of Jammu and Kashmir, to call “for a thorough safety audit of two flyover projects that are currently under implementation in the cities of Jammu and Srinagar.” The flyover located in South Asia’s most congested area with narrow streets and a sea of people made search and rescue by the National Disaster Relief Force tough as teams worked through the night using thermal cameras, acoustic equipment, gas cutters, and victim location breaching systems. Care had to be taken to ensure a fallen pier was not dislocated as residential homes were very close to the bridge, a phenomenon not alien to the choked city.

IVRCL has been blacklisted by the Indian Railways and three states for substandard quality, financial irregularities, and criminal negligence in a joint venture with a foreign company that did not perform any work.