For years I've wondered what those nitrogen tanks are doing hanging out on NYC corners like some sort of futuristic snowman having a cigarette break.
I rooted around a bit but seemed to find a different explanation everywhere I looked - cooling telecommunication lines; cooling electric transformers; preventing corrosion of copper lines; identifying leaks in sewage pipes; plugging leaks, and so on.
Alas, while I can not reveal my sources, I've learned the nitrogen is used to keep moisture out of telecom cables. The tanks slowly push the gas into the copper phone lines, keeping them somewhat dry. The tanks are replaced every couple of days and they aren't dangerous, though they look it. Apparently they've been nailed by cars a few times and held together fine and didn't blow up Manhattan.
Another reason to love New York; there can be two or three giant nitrogen gas tanks on every corner and we think nothing of it.