London Assembly Committee Commences ‘Tube Dust’ Investigation

Approximately 4.8 million[i] commuters use London’s Tube network on a daily basis[ii] and, in edition 217 of BC Disease News (here), we reported on the issue of excessive noise exposure on the Tube.

More recently, however, exposure to potentially toxic dust has been a more widely reported public health concern in the media.

Dr Samantha Walker, Director of Research and Policy at Asthma UK, has stressed that an estimated 489,200 asthma sufferers are particularly at risk of poor air quality on the Tube, with the charity having previously called for amendments to be made to the Clean Air Act 1993.

The Institution of Mechanical Engineers is another body that has called for ‘urgent action’ to be taken on ‘dangerous’ levels of Tube pollution in recent months, in conjunction with its publication: A Breath of Fresh Air: New Solutions to Reduce Transport Emissions.[iii]

Why Is the Tube Dusty?

The Underground transport system, in London, is the oldest in the world, with deep, poorly ventilated tunnels. As a result, dust ‘tends not to disperse’.

What Is the Dust Composed of?

Previous studies have found high levels of iron-based pollutants, which are created by wear on train brakes and friction between the wheels and tracks. Other pollutants present include traces of chromium, manganese, copper, nickel, vanadium, arsenic, cadmium, cobalt, zinc and quartz.

Pollutant-based particulate matter (PM) 2.5 is heavier and larger than above ground carbon particles.

Leading air quality expert, Professor Stephen Holgate, identifies that:

‘Metals from the rail and break friction are highly reactive and will damage the delicate lining cell of the lung, like welding fumes do’.

Nonetheless, an Institute of Occupational Medicine Research Report, published in 2003, concluded that because concentrations on the underground are well below allowable workplace concentrations for welding fumes, they are ‘unlikely to represent a significant cumulative risk to health of workers or commuters’.[iv]

What Is the London Assembly Doing to Further Investigate ‘Tube Dust’?

Last Thursday, the London Assembly’s Environment Committee opened an inquiry into ‘tube dust’ on the Underground and the knock-on health effects of cumulative exposure.

Committee Chair, Caroline Russell stated:

‘The Environment Committee is committed to finding out the content of tunnel and other dust on the Underground but also what the impact of Tube dust is on the health of workers and passengers’.

This latest investigation is expected to build on the Committee on the Medical Effects of Air Pollutants (COMEAP) Report, commissioned by TfL, which was the first research since 1998 on this specific issue.[v]

The Government Advisory Body’s Report[vi] used unpublished findings from King’s College London academics, in the field of air quality, which found that the Northern Line had the highest concentration of PM 2.5. On 10 days of testing,[vii] Hampstead, the deepest Northern Line station, situated 60 metres (200 feet) below ground, contained 30 times more PM 2.5 [492 micrograms per cubic metre (μg/m3) of air] than an average roadside monitoring site on a busy London road (16 μg/m3 of air).[viii]

Essentially, COMEAP found that passengers are exposed to the same concentration of particulates in 1 hour on the tube as they are during a full day above ground in ambient London air, or a 7.5 hour bus journey (one-third of the pollution on a 2.5 hour journey):

‘Given that there is strong evidence that both long- and short-term exposure to particle pollutants in ambient air are harmful to health, it is likely that there is some health risk’.

In the face of evidence that tube dust levels are hazardous, Director of Asset Operations at TfL, Peter McNaught, has assured that dust levels on the Tube are ‘closely monitored ... through a wide range of measures, ensure that particle levels are well within Health & Safety Executive [HSE] guidelines’. In fact dust pollution levels are 4 times lower than the HSE limit (4mg/m3 for respirable dust).[ix]

However, some argue that the HSE currently sets an ‘informal target’ to limit dust exposure, which means that dust levels well-under the limit are still not safe.

In recognition of this, TfL Director of Health, Safety and the Environment, Jill Collis, has pledged that the institution is working towards stricter targets of less than 5mg/m3 for inhalable dust and less than 1mg/m3 for respirable dust.[x]

What Measures Can Be Taken to Reduce Dust Exposure?

In 2014, plans to unveil a specialist tunnel-cleaning train were scrapped as ‘unviable’, but in 2017, as part of another cleaning-centred regime, so-called ‘magic wands’ were released as a means to reduce dust at 46 London Underground stations.

A spokesperson for the Mayor of London, Sadiq Khan, revealed that:

‘Trials at over 40 of the worst stations and tunnels resulted in pollution levels falling by up to 40 per cent on days when deep cleaning was used’.

Aside from cleaning measures, TfL is developing techniques for track replacement, which should create less dust. Also, new signalling on the Northern and Jubilee Lines is reducing the need for drivers to break so defensively, which, at least in theory, should generate less PM 2.5.[xi]

The Jubilee Line, being the most modern line on the network, has been upgraded in recent years through the implementation of Platform Edge Doors (PED) at Westminster, Waterloo, Southwark, London Bridge, Bermondsey, Canada Water, Canary Wharf and North Greenwich Stations[xii] – see the image below.


[Sources: Wikipedia and Wikimedia Commons (as edited by BC Legal)]

Although PED were not originally intended to operate as a health and safety mechanism, the London Assembly Committee, in collaboration with (COMEAP), will monitor the benefits of barrier doors on PM 2.5 levels, along with the perceived benefits of electrostatic precipitators (using electrical forces to collect particles) and enhanced tunnel ventilation (using fans).

A disadvantage of PED is that they are not in contact with the ceiling and are therefore not a total barrier to tunnel air. However, in Barcelona, full-height Platform Screen Doors (PSD) have been trialled on the metro system, which fully obstruct the tunnel from the platform.[xiii]

We will continue to follow up on this emerging EL/PL risk as the London Assembly inquiry continues.


[i] ‘Air quality on London Underground '30 times worse than congested roads above' (10 January 2019 The Independent) <

> accessed 5 July 2019.

[ii] Tom Batchelor, ‘‘Tube dust’: London launches investigation into potentially dangerous substances detected on Underground’ (26 June 2019 The Independent) <> accessed 5 July 2019.

[iii] Martin Coulter and Sean Morrison, ‘More research needed on effect of breathing in dust on Tube, report warns’ (23 January 2019 The Independent) <> accessed 5 July 2019.

[iv] JF Hurley et al., Assessment of health effects of long-term occupational exposure to tunnel dust in the London Underground’ Research Report TM/03/02 December 2003 <> accessed 5 July 2019.

[v] Jessica Taylor, ‘Tube pollution: How toxic is London Underground air and how to breathe cleaner air on your commute’ (10 January 2019 Evening Standard) <> accessed 5 July 2019.

[vi] ‘Particulate air pollution on London Underground: health effects’ (9 January 2019 GOV.UK) <> accessed 5 July 2019.

[vii] ‘Tube particle pollution '30 times higher than by roads'’ (10 January 2019 BBC) <> accessed 5 July 2019.

[viii] Gwyn Topham, ‘Report sparks concerns over poor air quality on London Underground’ (9 January 2019 The Guardian) <> accessed 5 July 2019.

[ix] Ashleigh Webber, ‘London Underground air quality ‘likely’ to present health risks’ (16 January 2019 Personnel Today) <> accessed 5 July 2019.

[x] ‘Air pollution: How bad is your commute?’ (25 June 2019 BBC) <> accessed 5 July 2019.

[xi] Tom Batchelor, ‘‘Tube dust’: London launches investigation into potentially dangerous substances detected on Underground’ (26 June 2019 The Independent) <> accessed 5 July 2019.

[xii] ‘Improving the trains’ (TfL) <> accessed 5 July 2019.

‘New Tube for London: Feasibility Report’ (October 2014 TfL) <> accessed 5 July 2019.

[xiii] ‘Barcelona Metro to test vertical platform screen doors’ (Spanish Railway News) <> accessed 5 July 2019.