The explosion occurred in the morning hours at a mooring in the Zanja H area, on the right bank of the river opposite the Costanera Sur, a waterfront road linking the capital city of Asunción with the neighbouring city of Lambaré. The vessel had six workers on board at the time. Five were killed. The sixth, outside the barge when the blast occurred, was pulled to safety with minor injuries.   The vessel was a tanker barge owned by a private Paraguayan company, which specialises in the fluvial transport of fuels, gases and bulk. These types of tanker barges have no engines of their own, and are pushed along river routes by tugboats. The barge was not carrying any cargo at the time of the incident and had workers on board who were working on maintenance.   Several specialised units were deployed to the location by Paraguay’s Prefectura General Naval (the country’s naval authority) and the surrounding area was closed off due to the risk of residual gases still inside the vessel’s cargo compartments.     The fire was brought under control by three units of Bomberos Voluntarios, the volunteer fire brigade of Paraguay. The stricken barge was anchored near to an island in the river.   A formal investigation is under way into the cause of the blast. Authorities believe the most likely trigger was a degassing operation – the process of clearing flammable vapours from cargo tanks before hull repair or welding work can begin. Although a tanker barge may be completely empty of liquid fuel, its enclosed compartments may still contain combustible vapour. Any spark from maintenance equipment in that process can be enough to trigger a catastrophic explosion.      Investigators have yet to establish the definitive cause of the incident, calling in naval forensic experts and the country’s Fiscalía (prosecution office) to determine the precise circumstances.      Paraguay’s Ministry of Public Works and Communications has also opened a parallel investigation through its Dirección General de Marina Mercante to establish whether the maintenance work being carried out was duly authorised and whether the ship’s operator and the contracted repair team had the permits required by maritime regulations.      The Costanera Sur mooring is on the Paraguay-Parana Hidrovia, the vast inland waterway which runs for more than 3,400 kilometres through the heart of South America carrying grain, fuel and minerals from landlocked countries to export terminals on the Atlantic. The incident will bring attention to safety protocols for maintenance operations on fuel-carrying vessels across the system.