A ventilation structure built to route one airstream underneath another without allowing them to mix. It consists of a sealed tunnel or duct excavated into the floor of a mine working, typically used to pass return air safely beneath an intake airway or haulage road.
Heard on the job
The engineers are pouring concrete for the new undercast so we can route the return air below the main haul road.
Do not mix it up with
- Overcast: An undercast routes air below the floor, while an overcast routes it above the roof.
Related terms
Overcast
An enclosed bridge built to allow one ventilation air current to cross over another without mixing.
Airway
Any underground gallery, drift, or shaft designated specifically for routing ventilation air through a mine.
Return
An underground passage that carries exhausted or contaminated air away from the working face.