New York City - Local: Liquid nitrogen tanks on NYC streets?

Walking around the city, I frequently see large tanks of liquid nitrogen chained to a lamppost, with a rubber hose leading from the tanks into a manhole cover.

Does anyone know what these are for?

Walking around the city, I frequently see large tanks of liquid nitrogen chained to a lamppost, with a rubber hose leading from the tanks into a manhole cover.

Does anyone know what these are for?

See:
http://gothamist.com/2008/01/31/nitrogen_tanks.php

They've been around a while!

FYI Question NY Times (http://www.nytimes.com/1995/08/20/nyregion/fyi-753995.html)

If this works so well to keep cables dry, why don't we see them in other cities?

They've been around a while!

FYI Question NY Times (http://www.nytimes.com/1995/08/20/nyregion/fyi-753995.html)

If this works so well to keep cables dry, why don't we see them in other cities?You've never seen them before? I remember as a kid, in a small town, seeing liquid nitrogen containers (painted, not shiny like those in the link, similar in size/shape to the oxygen tank you'd see hooked to an acetylene torch, for those of you for which that rings a bell) tied to a utility pole, with a hose running up to the overhead line. It's not something new or unique to NYC.

See:
http://gothamist.com/2008/01/31/nitrogen_tanks.php

They've been around a while!

FYI Question NY Times (http://www.nytimes.com/1995/08/20/nyregion/fyi-753995.html)

If this works so well to keep cables dry, why don't we see them in other cities?

I was given a completely different explanation when I asked a VZ worker in the street. He said that sometimes their lines are very close to gas pipes so the practice is to blow out manholes with nitrogen which supposedly forces the methane gas out. Knowing very little about chemistry, I believed him.

As I think about this, however, I don't think I see nitrogen tanks too often in Brooklyn whereas they are all over Manhattan. Could the fact that Manhattan has lots of underground steam lines have anything to do with this?

I've never noticed them outside the city although apparently they're out there...

Nitrogen Gas Tanks on Plano Roadsides? (http://www.city-data.com/forum/dallas/1483464-nitrogen-gas-tanks-plano-roadsides.html)

It makes sense they would be used mainly in humid areas or places with lots of steam tunnels.
Perhaps the density of cables means no room for the dewars in Manhattan's crowded utility tunnels.

Liquid Nitrogen plumbing (http://toilet-guru.com/ln2.php)