Two workers employed by a drain-cleaning contractor were trapped and drowned on Oct. 21, when a punctured main sent water flooding into a 12-ft-deep trench where they were working, according to the Boston Fire Dept.

The bodies of Kelvin Mattocks, 53, of Brockton, Mass., and Robert Higgins, 47, of Warren, R.I., were recovered hours after the frantic scene unfolded in front of pedestrians on a bustling thoroughfare.

The owner of a drugstore adjacent to the worksite, Gary Einsidler said, “All hell broke loose” at 1:06 p.m., when water started to come down the street. “Water was coming out of the hole,” he said. “I saw a worker coming out of the hole all wet, all panicked. Everyone was running all around.”

As emergency responders descended on the scene, water was removed with a large vacuum. Then, a trench box was lowered to prevent the walls from collapsing, a Fire Dept. spokesman said.

Fire Dept. officials said they still have not determined how the accident occurred. Water-main ruptures are common in cities with aging infrastructure, but accidental punctures of both water and gas lines pose special dangers to workers. Many utilities provide a special contact number so contractors can verify locations before digging.

An Occupational Safety and Health Administration spokesman said the agency opened an inspection of the incident on Oct. 21. He said Roslindale, Mass.-based Atlantic Drain Service Co. Inc., the contractor performing the work, has been cited for 23 violations since 2007, including 14 “serious violations.” The firm also has $95,660 in current penalties that remain uncollected, according to an agency spokesman.

None of OSHA’s information could be immediately confirmed. Several messages left with Atlantic’s answering service weren’t returned at press time.