Editing Tunnel (section)

== Safety and security ==
{{Redirect|Tunnel fire|the 1991 wildfire in California|Oakland firestorm of 1991|the 2022 wildfire in Arizona|Tunnel Fire (2022)}}
[[File:Alma tunnel Paris.jpg|thumb|left|The entrance to the [[Pont de l'Alma]] tunnel, the site where the car carrying [[Diana, Princess of Wales]], [[Death of Diana, Princess of Wales|hit a Fiat and then the wall]]. There was no proper barrier and this contributed to her death.]]

Owing to the enclosed space of a tunnel, fires can have very serious effects on users. The main dangers are gas and smoke production, with even low concentrations of [[carbon monoxide]] being highly toxic. Fires killed 11 people in the [[Gotthard Road Tunnel#History|Gotthard tunnel fire]] of 2001 for example, all of the victims succumbing to smoke and gas inhalation. Over 400 passengers died in the [[Balvano train disaster]] in Italy in 1944, when the locomotive halted in a long tunnel. [[Carbon monoxide poisoning]] was the main cause of death. In the [[Caldecott Tunnel fire]] of 1982, the majority of fatalities were caused by toxic smoke, rather than by the initial crash. Likewise 84 people were killed in the [[Paris Métro train fire]] of 1904.

Motor vehicle tunnels usually require [[ventilation shaft]]s and powered fans to remove toxic [[exhaust gas]]es during routine operation.<ref name="Mishra">{{cite journal
  | last1 = Mishra
  | first1 = V K
  | title = Dynamics of ultrafine particles inside a roadway tunnel
  | journal = Environmental Monitoring and Assessment
  | volume = 187
 | issue = 12
  | pages = 756
  | year = 2015
  | url = https://www.researchgate.net/publication/284172320 
  | doi = 10.1007/s10661-015-4948-x
  | pmid = 26577216
  | last2 = Aggarwal 
  | first2 = M L
  | last3 = Berghmans
  | first3 = P
  | last4 = Frijns
  | first4 = E
  | last5 = Int Panis
  | first5 = L
  | last6 = Chacko
  | first6 = K M
| bibcode = 2015EMnAs.187..756M
 | s2cid = 207140116
 }}</ref>

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|aerodynamic]] [[Longitudinal wave|pressure wave]] produced by [[High-speed rail|high speed trains]] entering a tunnel<ref>{{Cite journal|last1=Kim|first1=Joon-Hyung|last2=Rho|first2=Joo-Hyun|date=1 March 2018|title=Pressure wave characteristics of a high-speed train in a tunnel according to the operating conditions|journal=Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit|language=en|volume=232|issue=3|pages=928–935|doi=10.1177/0954409717702015|s2cid=125620030|issn=0954-4097}}</ref> reflect at its open ends and change sign ([[Compression (physics)|compression]] wavefront changes to [[rarefaction]] wavefront and vice versa). When two wavefronts of the same sign meet the train, significant and rapid air pressure<ref>{{Cite journal|last1=Niu|first1=Jiqiang|last2=Zhou|first2=Dan|last3=Liu|first3=Feng|last4=Yuan|first4=Yanping|date=1 October 2018|title=Effect of train length on fluctuating aerodynamic pressure wave in tunnels and method for determining the amplitude of pressure wave on trains|journal=Tunnelling and Underground Space Technology|volume=80|pages=277–289|doi=10.1016/j.tust.2018.07.031|bibcode=2018TUSTI..80..277N | s2cid=116606435 |issn=0886-7798}}</ref> may cause ear discomfort<ref>{{Cite journal|last1=Xie|first1=Pengpeng|last2=Peng|first2=Yong|last3=Wang|first3=Tiantian|last4=Zhang|first4=Honghao|date=April 2019|title=Risks of Ear Complaints of Passengers and Drivers While Trains Are Passing Through Tunnels at High Speed: A Numerical Simulation and Experimental Study|journal=International Journal of Environmental Research and Public Health|volume=16|issue=7|pages=1283|doi=10.3390/ijerph16071283|issn=1661-7827|pmc=6480231|pmid=30974822|doi-access=free}}</ref> for passengers and crew. When a high-speed train exits a tunnel, a loud "[[Piston effect#Tunnel boom|Tunnel boom]]" may occur, which can disturb residents near the mouth of the tunnel, and it is exacerbated in mountain valleys where the sound can echo.

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>

Larger, heavily used tunnels, such as the [[Big Dig]] tunnel in [[Boston, Massachusetts]], may have a dedicated 24-hour staffed [[operations center]] which monitors and reports on traffic conditions, and responds to emergencies.<ref>{{cite journal|last=Johnson|first=Christine M.|author2=Edward L. Thomas|title=A Case Study Boston Central Artery/Tunnel Integrated Project Control System, Responding to incidents Rapidly and Effectively|journal=Metropolitan Transportation Management Center|date=October 1999|page=12|url=http://ntl.bts.gov/lib/jpodocs/repts_te/11063.pdf|access-date=4 April 2014|archive-date=9 March 2013|archive-url=https://web.archive.org/web/20130309164537/http://ntl.bts.gov/lib/jpodocs/repts_te/11063.pdf|url-status=dead}}</ref> [[Video surveillance]] equipment is often used, and real-time pictures of traffic conditions for some highways may be viewable by the general public via the Internet.

A database of seismic damage to underground structures using 217 case histories shows the following general observations can be made regarding the seismic performance of underground structures:

* Underground structures suffer appreciably less damage than surface structures.
* Reported damage decreases with increasing over burden depth. Deep tunnels seem to be safer and less vulnerable to earthquake shaking than are shallow tunnels.
* Underground facilities constructed in soils can be expected to suffer more damage compared to openings constructed in competent rock.
* Lined and grouted tunnels are safer than unlined tunnels in rock. Shaking damage can be reduced by stabilizing the ground around the tunnel and by improving the contact between the lining and the surrounding ground through grouting.
* Tunnels are more stable under a symmetric load, which improves ground-lining interaction. Improving the tunnel lining by placing thicker and stiffer sections without stabilizing surrounding poor ground may result in excess seismic forces in the lining. Backfilling with non-cyclically mobile material{{clarify|What is non-cyclically mobile material?|date=October 2021}} and rock-stabilizing measures may improve the safety and stability of shallow tunnels.
* Damage may be related to peak ground acceleration and velocity based on the magnitude and epicentral distance of the affected earthquake.
* Duration of strong-motion shaking during earthquakes is of utmost importance because it may cause fatigue failure and therefore, large deformations.
* High frequency motions may explain the local spalling of rock or concrete along planes of weakness. These frequencies, which rapidly attenuate with distance, may be expected mainly at small distances from the causative fault.
* [[Ground motion]] may be amplified upon incidence with a tunnel if wavelengths are between one and four times the tunnel diameter.
* Damage at and near tunnel portals may be significant due to slope instability.<ref>{{Cite journal |last1=Hashash |first1=Youssef M.A. |last2=Hook |first2=Jeffrey J. |last3=Schmidt |first3=Birger |last4=Yao |first4=John I-Chiang |date=2001 |title=Seismic design and analysis of underground structures |url=https://www.sciencedirect.com/science/article/abs/pii/S0886779801000517 |journal=Tunnelling and Underground Space Technology |volume=16 |issue=4 |pages=247–293 |bibcode=2001TUSTI..16..247H |doi=10.1016/S0886-7798(01)00051-7 |s2cid=108456041 |via=[[Science Direct]]}}</ref>

Earthquakes are one of nature's most formidable threats. A magnitude 6.7 earthquake shook the San Fernando valley in Los Angeles in 1994. The earthquake caused extensive damage to various structures, including buildings, freeway overpasses and road systems throughout the area. The National Center for Environmental Information estimates total damages to be 40 billion dollars.<ref>{{cite web|url=https://www.ngdc.noaa.gov/hazel/view/hazards/earthquake/event-more-info/5372|title=Significant Earthquake Information|last=National Geophysical Data Center / World Data Service (NGDC/WDS): NCEI/WDS Global Significant Earthquake Database. NOAA National Centers for Environmental Information|year=1972 |publisher=NOAA National Centers for Environmental Information|doi=10.7289/V5TD9V7K}}</ref> According to an article issued by Steve Hymon of TheSource – Transportation News and Views, there was no serious damage sustained by the LA subway system. Metro, the owner of the LA subway system, issued a statement through their engineering staff about the design and consideration that goes into a tunnel system. Engineers and architects perform extensive analysis as to how hard they expect earthquakes to hit that area. All of this goes into the overall design and flexibility of the tunnel.

This same trend of limited subway damage following an earthquake can be seen in many other places. In 1985 a magnitude 8.1 earthquake shook Mexico City; there was no damage to the subway system, and in fact the subway systems served as a lifeline for emergency personnel and evacuations. A magnitude 7.2 ripped through Kobe Japan in 1995, leaving no damage to the tunnels themselves. Entry portals sustained minor damages, however these damages were attributed to inadequate earthquake design that originated from the original construction date of 1965. In 2010 a magnitude 8.8, massive by any scale, afflicted Chile. Entrance stations to subway systems suffered minor damages, and the subway system was down for the rest of the day. By the next afternoon, the subway system was operational again.<ref>Hymon, Steve. "Designing A Subway to Withstand an Earthquake." The Source. N.p., 2017. Web. 11 November 2017. http://thesource.metro.net/2012/08/10/designing-a-subway-to-withstand-an-earthquake/
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