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→In history: "summit tunnel" sounds better than "vertex tunnel" Tags: Mobile edit Mobile web edit |
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[[File:Scene with Fabric Tunnel - Srimangal - Sylhet Division - Bangladesh (12904860703).jpg|thumb|A fabric tunnel in [[Moulvibazar District]], [[Bangladesh]]]]
A tunnel is relatively long and narrow; the length is often much greater than twice the [[diameter]], although similar shorter excavations can be constructed, such as cross passages between tunnels.
A tunnel made by an animal is commonly referred to as a [[burrow]] and may or may not have multiple portals.
The definition of what constitutes a tunnel can vary widely from source to source. For example, in the United Kingdom, a road tunnel is defined as "a subsurface highway structure enclosed for a length of {{convert|150|m|ft}} or more."<ref>{{cite book |url=https://www.standardsforhighways.co.uk/tses/attachments/987a669b-13a1-40b9-94da-1ea4e4604fdd |title=Highway Structures & Bridges Design CD 352, Design of road tunnels (formerly BD 78/99) |publisher=The Department for Transport |year=2020}}</ref> In the United States, the [[National Fire Protection Association|NFPA]] definition of a tunnel is "An underground structure with a design length greater than {{convert|23|m|ft|abbr=on}} and a diameter greater than {{convert|1800|mm|ft}}."<ref>{{cite book|title=NFPA Standard for Safeguarding Construction, Alteration, and Demolition Operations|publisher=National Fire Protection Association}}</ref>
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{{see also|History of water supply and sanitation}}
{{Expand section|date=March 2013}}
Some of the earliest tunnels used by humans were [[Paleoburrow|paleoburrows]] excavated by prehistoric mammals.<ref>{{Cite journal |last=Frank, de Carvalho Buchmann, Gonçalves de Lima, Caron, Lopes & Fornari |date=2011 |title=KARSTIC FEATURES GENERATED FROM LARGE
PALAEOVERTEBRATE TUNNELS IN SOUTHERN BRAZIL |url=https://www.ufrgs.br/paleotocas/Frank_et_al_2011b.pdf |journal=Espeleo-Tema |volume=22 |issue=1}}</ref>[[File:Joralemon Street Tunnel postcard, 1913.jpg|thumb|Joralemon Street Tunnel on 1913 postcard, part of the [[New York City Subway]] system]]
Much of the early technology of tunneling evolved from [[mining]] and [[military engineering]]. The [[etymology]] of the terms "mining" (for mineral extraction or for [[mining (military)|siege attacks]]), "military engineering", and "[[civil engineering]]" reveals these deep historic connections.
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Predecessors of modern tunnels were [[adit]]s that transported water for [[irrigation]], drinking, or [[sewerage]]. The first [[qanat]]s are known from before 2000 BC.
The earliest tunnel known to have been excavated from both ends
In [[Ethiopia]], the [[Siqurto foot tunnel]], hand-hewn in the Middle Ages, crosses a mountain ridge.
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Rail tunnels usually require fewer [[air changes per hour]], but still may require [[Ventilation (architecture)|forced-air ventilation]]. Both types of tunnels often have provisions to increase ventilation under emergency conditions, such as a fire. Although there is a risk of increasing the [[rate of combustion]] through increased airflow, the primary focus is on providing breathable air to persons trapped in the tunnel, as well as [[firefighter]]s.
The [[Aerodynamics|
When there is a parallel, separate tunnel available, airtight but unlocked emergency doors are usually provided which allow trapped personnel to escape from a smoke-filled tunnel to the parallel tube.<ref>{{cite journal | last1 = Fridolf | first1 = K. | last2 = Ronchi | first2 = E. | last3 = Nilsson | first3 = D. | last4 = Frantzich | first4 = H. | year = 2013 | title = Movement speed and exit choice in smoke-filled rail tunnels | journal = Fire Safety Journal | volume = 59 | pages = 8–21 | doi = 10.1016/j.firesaf.2013.03.007 | bibcode = 2013FirSJ..59....8F }}</ref>
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