Nitrogen Tanks-NYC-Untapped CitiesLiquid nitrogen tanks on the street are not dangerous, says Verizon.

Have you ever seen these out-of-place nitrogen tanks in the city and wondered how safe they are? In today’s Cities 101 feature, we’ve looked into these tanks of liquid nitrogen and found out that Verizon is responsible for them. According to Kate Ascher, author of The Works, the 40-gallon silver nitrogen tanks are used by Verizon to prevent moisture from the steam and heating systems from damaging the phone lines underground.

Each tank stores the liquid nitrogen at -300 degrees Fahrenheit and delivers it below ground via a small rubber tube running through a manhole cover. As it is released, the nitrogen heats up to -280 degrees and becomes gas, providing pressure that travels along the voice and data cables and keeps them dry.

Verizon says these tanks are perfectly safe sitting out there on the street, “if a tank was punctured, nitrogen would dissipate in the air without harming anyone around it, or the environment.” The tanks only last 3 days, says Ascher and then have to be replaced. Read more from our Cities 101 series about how stuff works in the city, including the remote monitoring of the NYC sewer system, space for the dead in NYC cemeteries, and double-lettered subway trains.