Train workers at a mainline station in east London have been given pollution masks after a report showing high levels of mould, yeast and bacteria sparked health fears.
Drivers on the Great Northern route are refusing to take trains to Moorgate station because of their concerns about inhaling "potentially harmful air".
Trains have been diverted to King’s Cross station instead, one worker said.
According to the report, the amount of airborne bacteria in the station is "50 per cent above recommended levels while yeast and mould levels are also above the ideal limit."
At these levels “it is possible that there is a danger to human health,” the report warned.
A spokesman for Great Northern told the Standard that potential issues for staff from prolonged exposure to dust, bacteria, airborne yeast and mould were being monitored and that the masks were offered as a "precautionary" measure.
One worker, who asked to remain anonymous, claimed the lack of cleaning in the tunnels has turned the station into a “death trap”.
When trains speed through the tunnel, it stirs up the dust and harmful air into the platforms, he said.
“Quite frankly, people are being allowed to go work in these conditions,” the source said. “People are asking the company and they say everything’s fine.
“We have got a large number of drivers refusing, even now, to take trains into Moorgate.”
When asked by worried passengers on social media why staff were wearing masks, rail operator GTR said there were “no health fears” and that were workers were offered the masks because "they are exposed to dust when cleaning."
A Great Northern spokesman later told the Standard: “Dust levels are well below workplace exposure limits and there is no risk to passengers as confirmed by an independent specialist report we commissioned.
“There are no formal limits for bacteria, airborne yeast or mould and the bacteria samples at Moorgate were the same as outside the station, in the open air of central London as was yeast and mould at other stations.
“Potential issues for staff from prolonged exposure – however minimal – are being managed and as part of a series of precautionary measures, we have made masks available to local staff.”
Network Rail said it is planning to carry out a full clean of the tunnels, while Great Northern said they are looking to “enhance the cleaning regimes of ventilation systems in stations and offices”.
A Network Rail spokesman said: “In 2016, the walls of all stations within the Northern City Line tunnel were cleaned thoroughly and we are currently arranging another round of cleaning.
“We have also developed a specialist cleaning unit for use in the tunnel which is currently going through our product acceptance process for use in the future.”
It comes after a report in February this year found people who use the Tube are exposed to eight times more air pollution than those who drive to work.
The study, carried out by the University of Surrey, found Tube passengers are exposed to 68mg of PM10 – tiny particles of soot – while car drivers only inhaled 8.2mg.