(ANSA) - ROME, DEC 10 - The death toll of Monday's explosion at an Eni fuel depot at Calenzano, near Florence, has climbed to five after the bodies of three persons who had been unaccounted for were found on Tuesday.
    Nine people were injured in the blast.
    Three of them are in very serious 'code red' condition, suffering from severe burns and blunt-force trauma, the local health authority has said.
    The blast on Monday is believed to have been caused by a spill, according to an initial reconstruction of events.
    Some liquid was likely spilled while tanker trucks were being refilled, said investigators.
    An operator raised the alarm seconds before the explosion that killed five workers at the Eni fuels depot, investigative sources said.
    It all happened at platform number 6 of the loading area which has a total of 10 platforms, they said.
    At 10:21 and 30 seconds, the recorded time according to the investigators, an operator pushed the alarm button but in a few seconds there was the initial explosion, believed to have been caused by a spark igniting spilled fuel.
    This was followed by a chain of explosions involving at least five tankers, the investigators said.
    In the wake of the deadly explosion, labour unions representing workers at an Eni oil refinery in the Tuscan city of Livorno proclaimed a two-hour strike on Tuesday morning.
    The local chapters of engineering and metalworkers unions Fim, Fiom, Uilm and Rsu also organized a protest that started at 8:30 in front of the refinery in Livorno.
    At least 500 workers participated, the unions said, expressing "shock" for the victims of the blast and their families.
    "This is a silent war that never seems to end and only raises interest after tragedies like this one", they said, expressing "rage because it is not possible to die while working".
    Another two-hour strike has been organizerd by the unions on Wednesday morning at the Eni oil refinery of Stagno, Livorno.
    Meanwhile, the local chapters of Italy's three largest labour unions CGIL, CISL and UIL have proclaimed a four-hour provincial strike on December 11 and a protest at Calenzano over the deadly explosion.
    On Monday, the chief prosecutor of Prato opened a probe to ascertain "possible responsibilities" for the incident.
    Judicial sources Tuesday said the State attorney's office in Prato, which has jurisdiction over the area of Calenzano, is considering multiple manslaughter charges in the case, among others.
    It was unclear on Tuesday whether anyone has been officially placed under investigation yet in connection with the incident.
    Meanwhile, Prato prosecutors have appointed two expert consultants as part of the investigation into the explosion.
    They are explosives experts Roberto Vassale and Renzo Cabrino.
    Both worked as court-appointment consultants in the investigation into the 1992 "Capaci massacre", in which anti-mafia judge Giovanni Falcone, his wife Francesca Morvillo and three of their bodyguards were killed.
    Prato Chief Prosecutor Luca Tescaroli worked on the Capaci case when he was a prosecutor in Caltanisetta.
    Meanwhile energy giant Eni said in a note on Tuesday that it is cooperating with judicial authorities to "identify as soon as possible, in a rigorous manner through the required and indepth technical exams, the real causes of the explosion", adding it was yet impossible to speculate on their nature.
    The company expressed "its closeness to the families of the deceased people and to the people who were injured or involved", also stating that any information of relevance "will be made available by Eni to judicial authorities carrying out investigations, also to safeguard" the confidential nature of the probe.
    Petrol, diesel and kerosene was received and stored at the 170,300- square-metre Calenzano facility and then distributed from it.
    The plant is connected to Eni's Livorno refinery via two pipelines. Eni said the facility had been operating since 1956 and had 24 tanks and 10 loading platforms.
    The municipality of Calenzano has organized a commemoration ceremony for the victims on Wednesday, which will be attended by Mayor Giuseppe Carovani, among other local officials, and has declared it a day of mourning.
    Two of the victims, tanker truck drivers Vincenzo Martinelli and Carmelo Conso, both lived in nearby Prato and were originally from southern Italy.
    Vincenzo Martinelli, who was about to turn 57 and had a wife and two children, was the first victim to be identified by authorities. (ANSA).