We've all seen them off and on over the years. The nitrogen canisters pop up on some street corner or another, remain there for a while, chained to a utility pole or a box covering access to phone lines, and then they disappear. It's been that way for so long that most people don't even notice, but Mason Ryder is fairly new to Houston, so when nitrogen canisters appeared on Scott Street near where he lives, he immediately wanted to know why the tanks were there and what they were being used for.
Ryder walked over to the man working on the canisters, an employee of Praxair Distribution, Inc., and asked what the canisters were for. "He told me they were none of my business, so I started taking pictures because I was determined to figure it out then," Ryder told the Houston Press.
He sent over the photos he snapped of the nitrogen cylinders. They do look ominous, huge tanks of nitrogen almost as tall as an adult, shackled to a phone company box. There were warnings printed on the side of each cylinder indicating that each container held refrigerated gas that "may cause cryogenic burns or injury" and "may displace oxygen and cause rapid suffocation."
A Praxair employee said the canisters are used by phone companies and entities like that to keep the wires and lines dry, and suggested we contact AT&T to find out more. We checked in with AT&T, and company spokesman Carlos Ramirez explained that AT&T uses the nitrogen tanks all the time to keep the underground facilities operational by maintaining a moisture-free environment. (And that's no easy feat considering how moist the swampy Houston environment usually is.)
As nitrogen leaves the canister, it turns to gas, expanding 175 times during this phase change, according to Popular Science. From there, this keeps the phone company equipment, the cables and the wires running underground at a high enough pressure to keep moisture out. In the case of AT&T, it keeps these canisters hooked up to equipment while employees work to repair or replace damaged equipment, Ramirez says. Once the equipment has been replaced, the tanks are removed, he says.
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Ramirez also says there have never been any issues with the nitrogen tanks. They may look formidable because of their size and those strident warnings on the side, but Ramirez says the canisters aren't volatile. Nothing impressive will happen if someone messes with a nitrogen tank, or if a canister is struck by a car. If the nitrogen in the tank is accidentally released, it will dissipate instantly, and that's about it, Ramirez stated via email.