Bangalore : Two construction workers allegedly asphyxiated after they fell into a 14-ft deep dry manhole at Saraipalya in Nagavara on Wednesday.

The deceased Sridhar (22), a native of Bellary, and Bandri (25), a native of Davangere, both living in Geddalahalli here, were working on a pipeline in the area. They opened the manhole, located next to a storm-water drain off the Thanisandra Main Road, to measure the depth and check if the pipeline could be connected to the drain through the manhole.

The accident occurred around noon when Sridhar, who was trying to measure the depth, fell into the manhole. Bandri, who rushed to his rescue, also fell in.

“As the manhole had not been opened for a very long time, we suspect gases, such as carbon monoxide, had accumulated. Sridhar may have inhaled the fumes as he bent towards the manhole and lost consciousness, leading to him falling into the manhole. The two could have asphyxiated owing to the high concentration of gases inside,” an investigating police official said.

The supervisor, Chandrashekhar, who witnessed the accident, screamed for help. Passersby on the road, around 60 metres away, heard him and helped him alert the police and fire and emergency services. Eight firemen rushed to the spot and one of them was lowered into the manhole with protective gear. After 20 minutes, the bodies were lifted out of the manhole using ropes, fire officials said. The bodies have been sent to Dr. Ambedkar Medical College and Hospital for post-mortem.

Chandrashekhar told the police that Sridhar seemed to lose consciousness before falling into the manhole. The police are awaiting the medical report.

The police took Chandrashekhar to the hospital for a check-up.

Meanwhile, Bangalore Water Supply and Sewerage Board (BWSSB) engineer-in-chief T. Venkataraju said the manhole was part of the 2D Karnataka Municipal Reforms Project (KMRP) package work entrusted on contract to M/S GKC Projects Ltd, who had sublet it to another contractor. He said work on the stretch was still going on and the manhole had not yet been connected to the main drain or any other drainage lines.

He said as per Supreme Court guidelines, a compensation of Rs. 5 lakh each had to be paid to the families of the deceased. “We will first issue a notice to the contractor seeking an explanation as to why the workers were sent to work on a government holiday and that too without any safety gear. An inquiry will be conducted and suitable action will be initiated against the contractor.”

The Hennur police have booked a case of negligence against the contractor.