Editing Longwall mining (section)

==Ventilation==
Typically, intake (fresh) air travels up the main gate, across the face, and then down the tail gate, known as 'U' type ventilation. Once past the face the air is no longer fresh air, but return air carrying away [[coal dust]] and mine gases such as [[methane]], [[carbon dioxide]], depending on the [[geology]] of the coal. Return air is extracted by ventilation [[mechanical fan|fans]] mounted on the surface. Other ventilation methods can be used where intake air also passes the main gate and into a bleeder or back return road reducing gas emissions from the goaf on to the face, or intake air travels up the tail gate and across the face in the same direction as the face chain in a homotropal system.<ref>{{cite web|title=Homotropal Ventilation|url=http://eis.uow.edu.au/longwall/html/systems_homo.html|publisher=University of Wollongong|accessdate=2014-05-24|url-status=dead|archive-url=https://web.archive.org/web/20140524023310/http://eis.uow.edu.au/longwall/html/systems_homo.html|archive-date=2014-05-24}}</ref>

To avoid spontaneous [[combustion]] of coal in the goaf area, gases may be allowed to build up behind seals so as to exclude oxygen from the sealed goaf area. Where a goaf may contain an explosive mixture of methane and oxygen, nitrogen injection/inertisation may be used to exclude oxygen or push the explosive mixture deep into the goaf where there are no probable ignition sources. Seals are required to be monitored each shift by a certified mine supervisor for damage and leaks of harmful gases.<ref>Mine Safety and Health Administration 

[https://arlweb.msha.gov/seals/Final%20Rule%20Stakeholders%20Meetings.pdf]</ref>