Firefighters have accused ministers of attempting to house asylum seekers on a “potential deathtrap” after health and safety officials prompted a further delay to the use of a giant barge until next week. The Fire Brigades Union (FBU) said it is planning to write to the Home Office about overcrowding and access to fire exits on the vessel. The health and safety officials’ intervention had already led to the postponement of the arrival of the first men who were due to stay on the 222-bedroom Bibby Stockholm in Portland, Dorset. Rishi Sunak is now under increasing pressure to explain why the government persists in planning to use the barge, which has been condemned by refugee organisations for being costly, cruel and inhumane. A Home Office source confirmed that there would be further delays in the use of the barge until sign off from health and safety officials is obtained. “The Bibby Stockholm will not be taking new arrivals tomorrow [Wednesday]. It could now be next week as the council’s guidance is that they don’t want new services beginning on a Thursday or Friday close to the weekend. “Delay is because working practices for port workers have to be signed off for the Health and Safety Executive. There are no fire safety issues,” the source said. But the FBU’s assistant general secretary, Ben Selby, said he is writing to the Home Office about claims of overcrowding and access to fire exits after members raised concerns over safety. “As the only professional voice, firefighters believe the Bibby Stockholm to be a potential deathtrap,” he told the Guardian. The barge has 222 cabins along narrow corridors over three decks, with two main exits. The evacuation point for those onboard is a compound on the quayside, which councillors have described as “completely inadequate” for about 550 people. Councillors who visited the barge last week were told there are no lifejackets onboard and have expressed concerns that locked gates could cause a crush in an emergency. Carralyn Parkes, the mayor of Portland, said she was not surprised by the delay. “The Home Office has been inconsistent and opaque in their decision making and their attempt to rush through the barge without proper consultation and consideration, which was always going to create problems,” she said. “The Bibby Stockholm is not a suitable place to house asylum seekers. It is still not too late to stop this. Human beings belong in communities,” she told the Guardian. The Home Office was due to send the first group of people to the accommodation on Tuesday, but there were serious fire safety concerns about the facility. The Guardian first reported that the arrival date had been pushed back to Wednesday to give more time for final inspections. Speaking at a beer festival in west London, the prime minister attempted to reassure the public that the checks were part of normal procedure. “All migrant accommodation has to go through a series of checks and inspections to make sure it complies with regulation, that’s what’s happening in this case,” he said. Facing questions on Sky News, transport minister Richard Holden said he “can’t put a timeframe” on when people will board the Bibby Stockholm in Portland. It is the first time a large floating structure has been used to accommodate asylum seekers in long-term housing. One report from the NGO One Life to Live has raised concerns about fire safety on the barge following a Home Office decision to place two asylum seekers in cabins which previously only accommodated one. The report warned that the barge could become a “floating Grenfell” and raised concerns about the narrow corridors on the barge which could leave people crushed. Campaigners have called for clarity about whether land or maritime laws apply to various aspects of the scheme. A statement from the Dorset & Wiltshire Fire Service said it is the responsibility of the Home Office and the vessel operator to complete a fire risk assessment and to ensure that the necessary fire safety measures are in place. The Home Office was asked on Tuesday morning who had legal responsibility for fire and other health and safety checks on the Bibby Stockholm, but did not respond. The latest figures show that the average number of people crossing the Channel in every small boat last month was the highest on record. About 3,299 people made the journey in July in 63 boats – an average of about 52 migrants per vessel. This is the highest average since records began in 2018, according to PA news agency analysis of government data. More than 50 national organisations and campaigners, including the Refugee Council, Asylum Matters and Refugee Action, have called the government’s plan “cruel and inhumane”. They said the vessel was “entirely inappropriate” and would house traumatised migrants in “detention-like conditions”. A Home Office spokesperson said: “The Bibby Stockholm is undergoing final preparations to ensure it complies with all appropriate regulations before the arrival of the first asylum seekers. “This is part of the government’s plan to reduce the use of expensive hotels and offer alternative accommodation that is more manageable and better value for communities, just like our European neighbours are already doing. “We continue to work closely with Dorset and Portland councils, as well as the local NHS and police services, to manage any impact in Portland, including providing substantial funding to local services, to address the local community’s concerns.”