Editing London Underground (section)

===Ventilation and cooling===
{{see also|London Underground infrastructure#Ventilation and cooling|label 1=London Underground infrastructure: Ventilation and cooling|London Underground cooling}}
When the Bakerloo line opened in 1906, it was advertised with a maximum temperature of {{convert|60|F}}, but over time the tube tunnels have warmed up.{{sfnp|Croome|Jackson|1993|pp=253–254}} In 1938 approval was given for a ventilation improvement programme, and a refrigeration unit was installed in a lift shaft at Tottenham Court Road.{{sfnp|Croome|Jackson|1993|pp=253–254}} Temperatures of {{convert|117|F}} were reported in the [[2006 European heat wave]].<ref>{{Cite news |url=http://news.bbc.co.uk/1/hi/england/london/5191604.stm |title=Baking hot at Baker Street |work=BBC News |date=18 July 2006 |access-date=31 March 2013 |last=Griffiths |first=Emma |archive-date=1 January 2016 |archive-url=https://web.archive.org/web/20160101055245/http://news.bbc.co.uk/1/hi/england/london/5191604.stm |url-status=live }}</ref> It was claimed in 2002 that, if animals were being transported, temperatures on the Tube would break European Commission animal welfare laws.<ref>{{cite news |url=https://www.telegraph.co.uk/news/1405628/Londons-Tube-unfit-for-animals.html |archive-url=https://ghostarchive.org/archive/20220111/https://www.telegraph.co.uk/news/1405628/Londons-Tube-unfit-for-animals.html |archive-date=11 January 2022 |url-access=subscription |url-status=live |title=London's Tube 'unfit for animals' |work=The Daily Telegraph |location=London |date=28 August 2002 |access-date=31 March 2013}}{{cbignore}}</ref> A 2000 study reported that air quality was 73 times worse than at street level, with a passenger inhaling the same mass of particulates during a twenty-minute journey on the Northern line as when smoking a cigarette.<ref>{{cite web |url=http://128.40.58.147/web/ben/Tube.htm |title=Environmental Quality in Underground Railways |publisher=University College London |date=4 December 2003 |access-date=5 November 2013 |author=Croxford, Ben |url-status=dead |archive-url=https://archive.today/20131016210006/http://128.40.58.147/web/ben/Tube.htm |archive-date=16 October 2013 }}</ref><ref>{{cite news |url=https://www.standard.co.uk/news/passengers-choke-on-the-tube-6304049.html |title=Passengers choke on the Tube |work=London Evening Standard |author=Murray, Dick |date=23 August 2002 |access-date=31 March 2013 |archive-date=8 November 2020 |archive-url=https://web.archive.org/web/20201108125625/https://www.standard.co.uk/news/passengers-choke-on-the-tube-6304049.html |url-status=live }}</ref> The main purpose of the London Underground's ventilation fans is to extract hot air from the tunnels,{{sfnp|Croome|Jackson|1993|pp=253–254}} and fans across the network are being refurbished, although complaints of noise from local residents preclude their use at full power at night.<ref>{{cite web |url=http://lurs.org.uk/documents/pdf%2008/jan/jan%20MEETING%20REPORT.pdf |title=Meeting Report: Cooling the tube |date=8 May 2007 |author1=Westgate, Stuart |author2=Gilby, Mark |publisher=LURS |access-date=31 March 2013 |archive-date=5 October 2013 |archive-url=https://web.archive.org/web/20131005010257/http://lurs.org.uk/documents/pdf%2008/jan/jan%20MEETING%20REPORT.pdf |url-status=live }}</ref>

In June 2006 a groundwater cooling system was installed at [[Victoria station (London)|Victoria station]].<ref>{{cite news |url=http://news.bbc.co.uk/1/hi/england/london/5058362.stm |title=Water pump plan to cool the Tube |work=BBC News |date=8 June 2006 |access-date=31 March 2013 |archive-date=6 July 2006 |archive-url=https://web.archive.org/web/20060706000031/http://news.bbc.co.uk/1/hi/england/london/5058362.stm |url-status=live }}</ref> In 2012, air-cooling units were installed on platforms at Green Park station using cool deep groundwater and at Oxford Circus using chiller units at the top of an adjacent building.<ref>{{cite press release |url=http://origin.tfl.gov.uk/corporate/media/newscentre/archive/22885.aspx |archive-url=https://archive.today/20140327171415/http://origin.tfl.gov.uk/corporate/media/newscentre/archive/22885.aspx |url-status=dead |archive-date=27 March 2014 |title=Work begins to cool the platforms at two major central London stations |publisher=Transport for London |date=17 February 2012 |access-date=27 March 2014 }}</ref> New air-conditioned trains have been introduced on the sub-surface lines, but were initially ruled out for the tube trains due to space being considered limited on tube trains for air-conditioning units and that these would heat the tunnels even more. The [[New Tube for London]], which will replace the trains for the Bakerloo, Central, Waterloo and City and Piccadilly lines, is planned to have air conditioning for the new trains along with better energy conservation and regenerative braking.<ref name="Connor" /><ref name="MR">{{cite news |work=Modern Railways |date=January 2013 |pages=38–41 |title=Sub-surface renewal |last=Abbott |first=James}}</ref><ref>{{Cite web|title=Improving the Tube – What we're doing – Improving the trains|url=https://www.tfl.gov.uk/campaign/tube-improvements/what-we-are-doing/improving-the-trains|access-date=21 August 2021|website=[[Transport for London]]|language=en-GB|archive-date=15 August 2021|archive-url=https://web.archive.org/web/20210815084031/https://tfl.gov.uk/campaign/tube-improvements/what-we-are-doing/improving-the-trains|url-status=live}}</ref>

In the original Tube design, trains passing through close fitting tunnels act as pistons to create air pressure gradients between stations. This pressure difference drives ventilation between platforms and the surface exits through the passenger foot network. This system depends on adequate cross-sectional area of the airspace above the passengers' heads in the foot tunnels and escalators, where laminar airflow is proportional to the fourth power of the radius, the [[Hagen–Poiseuille equation]]. It also depends on an absence of turbulence in the tunnel headspace. In many stations the ventilation system is now ineffective because of alterations that reduce tunnel diameters and increase turbulence. An example is Green Park tube station, where false ceiling panels attached to metal frames have been installed that reduce the above-head airspace diameter by more than half in many parts. This has the effect of reducing laminar airflow by 94%.

Originally, air turbulence was kept to a minimum by keeping all signage flat to the tunnel walls. Now, the ventilation space above head height is crowded with ducting, conduits, cameras, speakers and equipment acting as a baffle plates with predictable reductions in flow.<ref>{{Cite journal |last1=Demartini |first1=L. C. |last2=Vielmo |first2=H. A. |last3=Möller |first3=S. V. |title=Numeric and experimental analysis of the turbulent flow through a channel with baffle plates |journal=Journal of the Brazilian Society of Mechanical Sciences and Engineering |volume=26 |issue=2 |pages=153–159 |doi=10.1590/S1678-58782004000200006 |year=2004 |doi-access=free |hdl=10183/75781 |hdl-access=free | issn=1678-5878}}</ref> Often, electronic signs have their flat surface at right angles to the main air flow, causing choked flow. Temporary sign boards that stand at the top of escalators also maximise turbulence. The alterations to the ventilation system are important, not only to heat exchange.

==== Air quality ====
The [[Committee on the Medical Effects of Air Pollutants]] (COMEAP) has reported on the relative risks of breathing air pollution in different situations. In January 2019, for example, it reported that pollution from [[particulates]] is up to 30 times higher on the London Underground than on streets in the roads above, with the [[Northern Line]] having the worst air quality.<ref>{{cite news |last1=Finnis |first1=Alex |title=One hour on the tube is as toxic as standing next to a busy road for an entire day |url=https://inews.co.uk/news/uk/air-pollution-london-underground-tube-equivalent-busy-road-244546 |work=iNews |date=10 January 2019}}</ref><ref>{{cite news |last1=Oglesby |first1=Kate |title=Dust and air pollution higher on Northern Line than any other part of the Underground |work=The Times |date=12 January 2019}}</ref>{{needs update|date=October 2024}}