Vent shafts

[farecard]

What's the longest span between vent/exit shafts?
I'm guessing the Potomac tube, but then I wondered if there was one somewhere on Teddy R's island.

Is there a list of them?

[Sand Box John]

"farecard"
What's the longest span between vent/exit shafts?
I'm guessing the Potomac tube, but then I wondered if there was one somewhere on Teddy R's island.

Don't know what pairs are furthest apart but I would hazard a guess the Potomac River tunnels would be the furthest between shafts.

There is no shaft on Teddy Roosevelt Island as the tunnels pass under the river north of the island along the tangent of I Street west of Pennsylvania Avenue. The shafts on either side of the river are in south end of Thompson's Boat House and inside the loop ramp from southbound George Washington Parkway to Key Bridge.

Is there a list of them?

Yes, as I recall, but not a comprehensive one, I recall seeing partial lists in various contract document related to replacement and or upgrade fire standpipe.

Hell, I could probably create one from memory using google maps to identify their locations.

Some of them are marked with signs and chaining locations.

[farecard]

Could you SWAG the # of fans or fan locations? I assume most/all shafts have fans.

How big/small are the fans: dia & horsepower?

[Sand Box John]

"farecard"
Could you SWAG the # of fans or fan locations? I assume most/all shafts have fans.

How big/small are the fans: dia & horsepower?

Typical configuration:

• Shaft at the ends of station are always vent shafts, blow out shafts, tunnel walls and or roofs tapered to direct the air pushed by trains out the shaft instead of into the station.
• First shaft beyond a station is always a fan shaft.
• Second shaft beyond a station is always a vent shaft provided there are 3 or more shafts between station pairs.
• CFM and the number of fans varies depending on the shaft. 2 or 3 fans is typical some have 4. In the older parts of the system, pre 2000, the fans are 4' and are rated at 4,000 CFM.
• Post 2000 sections of the system have 2' fans (fan jets) I believe they have the same CFM rating as the older larger fans.
• As far as I know all of the fans only blow air out of the tunnels.
• There are dome relief shafts in the crown of the station vaults, typically 4 spaced evenly along the length of the station, the dome relief shafts are used to allow the hot air to escape from the crown of the station vault. In cut and cover stations the dome relief shaft openings are typically behind the curb along the street the station is under, if the cut and cover station is not under the street they are along the center line of the station. In station bored out of the bed rock the dome relief openings in the crown of the vault vents into a air plenum that runs the length station to shafts that are adjacent to blow out shaft openings.*
• All shafts have automatically or remotely controlled dampers in them to control the direction and flow of air.

*The dome relief shafts in the Farragut North station have been sealed shut, not sure why, but my guess is because motor vehicle exhaust gases were being sucked into the station when the dampers were open as the surface openings are along the center line of Connecticut Avenue.