Posted by Todd Somers [172.68.65.9] on Thursday, February 16, 2017 at 19:17:10 :
In Reply to: Re: Big Boy posted by Clint Dixon [108.162.216.73] on Wednesday, February 15, 2017 at 10:06:56 :
Tunnel ventilation is another facet of mechanical (HVAC) engineering. Like all engineering, it needs to be done very carefully. Every tunnel that is determined to be necessary to be provided with a ventilation system is carefully studied and designed before construction and many factors are taken into consideration for each specific tunnel project. The Moffat tunnel on the D&RGW RR (now Union Pacific) has a large roll-up door on the east portal which only opens to let a train enter or exit. When a train is inside the Fan House (also located on the East portal) provides forced air to the inside of the tunnel and the exhaust fumes are removed via vents through the top of the tunnel bore at intervals along the six mile + length. The idea is to remove the most of the fumes via the vents rather than just push them out them other end. The prevailing westerly winds supply a certain amount of fresh air to the west portal that also helps the ventilation system as well. All this considered, in my three trips through the tunnel there is still a still a small amount of fumes present that you can smell when riding the passenger train through the tunnel. This is a very simplified and incomplete explanation.
Spence