A seven-member expert team has submitted a preliminary report to Bangladesh’s Ministry of Industries on the toxic-gas incident that killed 10 workers at Ferdous Steel Shipyard in Bhatiary, Sitakunda, Chattogram. The report initially identifies hydrogen sulfide dissolved in water inside a ship’s tank as the likely cause of the August 14 accident during work on an old vessel.

Investigators believe the gas was released as ballast water was drained from the tank, exposing workers to a lethal concentration. The accident occurred while work was under way in the vessel’s third tank; the ship has four tanks, and work in one had already been completed. Five workers died at the scene and another five died while receiving hospital treatment.

The team inspected the site several times and collected data before filing the preliminary report on Wednesday. Its head, BUET Chemical Engineering Professor Dr Yasir Arafat Khan, said the investigation remains ongoing and declined further comment. Samples from the ship have been sent to a laboratory in Dhaka for analysis of how hydrogen sulfide was present in the water and how it may have formed or accumulated.