RIO DE JANEIRO – A heating unit at a Petrobras depot in Brazil used to treat fuel for ocean-going ships exploded on Wednesday, killing two workers, the state-run oil company said in a statement.

The blast and resulting fire broke out about 13:00 GMT, while workers were doing planned maintenance on the heating unit, said the press office of BR Distribuidora, the fuels distribution unit of Petroleo Brasileiro, as Petrobras is formally known.

The heating unit is used to raise the temperature and reduce the viscosity of bunker fuel, a heavy, sludgy refined petroleum product similar to heating oil. Heating the fuel makes it easier to load aboard ships.

The fire at the naval-fuels depot at the Port of Tubarão, near Vitória, Brazil, was brought under control by on-site firefighters and presents no immediate risk to anyone in the vicinity, BR Distribuidora said in a statement. The names of the dead workers were not immediately available, it said.

The fire is the third fatal accident this year at facilities owned by or operated on behalf of Petrobras in Brazil's Espirito Santo state, the country's second-highest oil and natural gas producer after neighbour Rio de Janeiro. Combined, the accidents have killed 13 and injured at least 26.

The accident comes just over a week after the board of Petrobras approved a plan for an initial public offering of up to 25% of the stock in BR Distribuidora, Brazil's largest service-station operator and fuels distributor.

The vote to approve the sale was opposed by chairperson Murilo Ferreira, who said the company needed to improve its management before a sale could be set.

Ferreira is also the CEO of Vale, the mining company that owns the Port of Tubarão, Brazil's largest port by tonnage moved.

The fuels unit at Tubarão supplies the bunker fuel needed for vessels including the giant dry-bulk carriers that ship Vale iron-ore at the port.

In February an explosion on the Cidade de São Mateus, an offshore oil and natural gas production ship operated on behalf of Petrobras by Norway's BW Offshore, killed nine and injured 26.

Two workers on a pier operated by Petrobras shipping unit Transpetro were killed in July when scaffolding at the site, in Aracruz, also in Espirito Santo state, collapsed into the ocean.