GOVERNMENT health and safety officers yesterday launched an immediate inquiry into reports that dangerously high levels of the cancer-causing gas radon occurred in Mass Transit Railway tunnels at night. The Labour Department said it would work closely with the MTR to find out what was happening. 'Arrangements will be made with the management of the MTR for a detailed investigation to ensure that the radon will not accumulate to an unacceptable level,' a department spokesman said. More than 100 maintenance workers do regular overnight shifts in the tunnels after trains stop running. The MTR said its own surveys showed there was no threat to the health of either passengers or workers, but it was unable to say whether any of the tests had specifically measured radon levels in the tunnels after the ventilation was switched off. 'The present radon levels in MTR stations should not be considered as a cause for concern to commuters, employees and railway workers,' the company said in a statement. But scientists said tunnel workers should definitely be concerned by the new radon figures revealed in the Post yesterday. 'If I was an employee I would give serious consideration to urging my employer to take some counter-measures,' said Hong Kong University of Science and Technology radiation protection officer Dr Paul Chan Mok-wah. The figures from the Environmental Protection Department indicate that radon levels on the MTR soar dangerously high with the ventilation off.