Dozens of bags of fireworks were stored in the same hangar as thousands of tonnes of ammonium nitrate at Beirut’s port and may have been a decisive factor in igniting the explosive chemical compound that fuelled Tuesday’s huge explosion, a former port worker and other sources have told the Guardian. As angry Lebanese plan a major protest in central Beirut on Saturday, scrutiny has focused on how 2,750 tonnes of the dangerous material could have been stored so close to residential neighbourhoods for years – despite repeated warnings of the risk it posed. A former port worker, Yusuf Shehadi, told the Guardian he had been instructed by the Lebanese military to house the chemicals in warehouse 12 at the port despite repeated protests by other government departments. “We complained a lot about this over the years,” said Shehadi, who worked at the port until emigrating to Canada in March this year. “Every week, the customs people came and complained and so did the state security officers. The army kept telling them they had no other place to put this. Everyone wanted to be the boss, and no one wanted to make a real decision.” In addition, the hangar housed a quantity of fireworks, Shehadi said, which customs had confiscated in about 2009-10 and which he said he had personally seen delivered on a forklift. “There were 30 to 40 nylon bags of fireworks inside warehouse 12,” he said. “They were on the left-hand side when you entered the door. I used to complain about this. It wasn’t safe. There was also humidity there. This was a disaster waiting to happen. The port workers did not put the chemicals there in the first place. That outrage rests with the government.” A second source has confirmed the fireworks’ presence, which was also the subject of media reports in Lebanon on Friday. The emerging new picture of the circumstances that led to the blast comes as investigators and media organisations continue to try to piece together the cause of the fire and subsequent blast. The claim that fireworks were being stored in the same warehouse as the ammonium nitrate appears to be confirmed by phone footage, apparently filmed by a port worker from the roof of the grain silos that overlooked the seat of the biggest blast – now a 150-metre-wide crater of seawater. In the brief section of footage posted on social media, a long warehouse – running parallel to the grain silo and separated by a road – is visible, with smoke coming out of the windows on its west side and from the roof. Geotagging by the investigative website Bellingcat and the Guardian, and comparison of features, strongly suggests that this warehouse is located at the very centre of the devastating blast –locating the initial fire and subsequent explosions in the same area of warehousing. As the person on the silo roof films the north end of the warehouse from their vantage point, the smoke thickens and then a dozen or so white flashes can be seen occurring in rapid succession inside, triggering thicker red flames that quickly spread southwards before detonating a major explosion in the building within seconds that causes the person filming to duck for cover. Shehadi said he had spoken to former colleagues at the port who said workers were attempting to fix a gate outside warehouse 12 with an electrical tool ahead of the blast. “This was at 5pm, and after 30 minutes they saw smoke. Firefighters came, and so did state security. Everyone died.” A video posted to social media depicted firefighters tackling a small blaze in a warehouse that resembled a port building. “It is my belief that this repair work led to this catastrophe,” Shehadi said. The Lebanese investigation into the disaster is expected to report to the national cabinet by Sunday. Sixteen people linked to the port including its general manager have been placed under house arrest, but figures including the French president, Emmanuel Macron, have called for an independent international inquiry. The country’s president, Michel Aoun, said the cause of the blast was still unclear and did not rule out the possibility of a hostile act. “The cause has not been determined yet,” Aoun said. “There is a possibility of external interference through a rocket or bomb or other act.” The Lebanese Red Cross estimated that dozens of people could still be buried under debris from the blast, mostly port employees who worked in and around the hangar.