Tube staff working on the most polluted lines tend to be off sick more – but more research is needed to establish if there is a direct link between dust levels and ill health.
The largest-ever study into the potential impact of airborne Tube dust on London Underground workers found there was not yet enough evidence to be sure it caused them to fall sick.
But the Tube drivers’ union Aslef said the findings were “deeply concerning” as drivers were being exposed to particle pollution far above World Health Organisation safe limits.
However, Transport for London said the WHO – and UK Government - limits on air pollution only applied to “ambient” outdoor areas and not enclosed environments such as the Underground.
The study, led by Imperial College London, used 100 times more sample data than previous studies.
It found that staff who worked in areas with greater levels of fine dust – PM2.5 particulate matter, which can be harmful to health – tended to be off sick more.
Some drivers were exposed to more than twice as much dust as staff working on Tube station platforms.
The highest concentrations of PM2.5s were found in driver’s cabs on the Piccadilly line, where readings of 787 micrograms per cubic metre (µg/m3) were obtained.
By comparison, the District line had the lowest readings of 72 µg/m3.
Platform readings ranged from 17-310 µg/m3.
Dr David Green, from Imperial’s School of Public Health, said: “We found that exposure to dust varied widely among staff, even among those doing the same job, and depended largely on where they were working across the Tube network.
“For example, drivers who worked on older trains and on lines with deeper tunnels were exposed to more PM2.5 – as were customer service staff at stations with interchanges for multiple lines.
“There was some evidence to suggest that staff exposed to higher levels of PM2.5 took more days off sick, but this link wasn’t clear cut.”
Finn Brennan, Aslef’s London organiser, told the Standard: “The current World Health Organisation guidelines state that annual average concentrations of PM2.5 should not exceed 5 µg/m3, while 24-hour average exposures should not exceed 15 µg/m3 more than three to four days per year.
“But Tube drivers on the Piccadilly line are exposed to up to a shocking 787μg/m3 during a working shift.
“Aslef are insisting on an urgent meeting with TfL and medical experts to discuss what steps they are taking to deal with this issue.
“It’s just not good enough to say ‘more research is needed’. Action is needed now to make sure staff do not continue to be exposed in such a dangerous way.”
The researchers said that new trains with reduced braking emissions, platform screens doors – as found on parts of the Jubilee and Elizabeth lines - increased ventilation, air cleaning and surface cleaning can reduce concentrations.
The study, published in the journal Environment International, compared the anonymised sickness records of 29,744 staff employed between 2014 and 2019.
The researchers found that by comparison, TfL’s office staff “had lower sickness absence rates from all-causes and infections”, but they pointed out that it is “also common in similar places of work for office-based staff to have lower absence than operational staff (e.g. engineering or maintenance staff)”.
PM2.5 levels were taken from personal monitors and from monitors across the network.
The particles are emitted from train wheels and rails coming into contact, and from braking. A previous study found that PM2.5 levels on the Underground can be up to 15 times higher than in the air outside.
Drivers who experienced the highest exposure to PM2.5 worked on trains introduced before 2010 – such as those on the Bakerloo, Piccadilly and Central lines – and on lines with deeper tunnels.
TfL said it had increased its annual Tube dust cleaning budget by a third to £2 million.
Lilli Matson, TfL’s chief safety, health and environment officer, said: “The report did not establish a causal relationship between exposure to dust on the Tube and sickness absence from work.
“In addition, our own independent monitoring confirms that dust levels continue to remain well below occupational health limits set by the Health and Safety Executive and that most of our network is below the recommended limits advised by the Institute of Occupational Medicine, which are set significantly lower.
“TfL’s independent monitoring has shown that in-station dust levels have reduced by 19 per cent on the Tube since 2020 and that dust levels have reduced by 27 per cent in the driver's cab since 2019.”
