# Why Nitrogen canisters on sidewalk boxes? **URL:** \ **Category:** Factual Questions\ **Created:** [September 24, 2007, 5:06am UTC](https://boards.straightdope.com/t/why-nitrogen-canisters-on-sidewalk-boxes/420271 "2007-09-24T05:06:57Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![Cardinal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cardinal/32/4000_2.png) [@Cardinal](https://boards.straightdope.com/u/Cardinal)\ **Post date:** [September 24, 2007, 5:06am UTC](https://boards.straightdope.com/t/why-nitrogen-canisters-on-sidewalk-boxes/420271/1 "2007-09-24T05:06:57Z")
My buddy and I have encountered a few gas canisters on sidewalk metal boxes that we presume to be electrical in nature. He hopped out and found a label IDing the can as being compressed N2. All I can figure is that there’s a thermostat in the box, and if there’s a fire, an inert gas will flood it and kill the fire. Why not on all such looking boxes? Why not CO2? Why such a big “party sized” canister? ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [September 24, 2007, 5:52am UTC](https://boards.straightdope.com/t/why-nitrogen-canisters-on-sidewalk-boxes/420271/2 "2007-09-24T05:52:32Z")
The nitrogen is pumped into the underground conduit to keep it free from moisture that will corrode the wires. ---
**Author:** ![chorpler](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chorpler/32/2888_2.png) [@chorpler](https://boards.straightdope.com/u/chorpler)\ **Post date:** [September 24, 2007, 9:51am UTC](https://boards.straightdope.com/t/why-nitrogen-canisters-on-sidewalk-boxes/420271/3 "2007-09-24T09:51:15Z")
[QUOTE=Joey P] The nitrogen is pumped into the underground conduit to keep it free from moisture that will corrode the wires. [/QUOTE] I thought it was to displace air so that any moisture wouldn’t have any oxygen to react with. But I didn’t listen that closely when we were hooking them up, and it was many years ago, so I could be way off. ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [September 24, 2007, 1:04pm UTC](https://boards.straightdope.com/t/why-nitrogen-canisters-on-sidewalk-boxes/420271/4 "2007-09-24T13:04:45Z")
[QUOTE=chorpler] I thought it was to displace air so that any moisture wouldn’t have any oxygen to react with. [/QUOTE] I thought about that, but if all they wanted to do was displace air, they could use ANYTHING, so, in that case, why nitrogen? ---
**Author:** ![essell](https://avatars.discourse-cdn.com/v4/letter/e/34f0e0/32.png) [@essell](https://boards.straightdope.com/u/essell)\ **Post date:** [September 24, 2007, 1:10pm UTC](https://boards.straightdope.com/t/why-nitrogen-canisters-on-sidewalk-boxes/420271/5 "2007-09-24T13:10:13Z")
[QUOTE=Joey P] I thought about that, but if all they wanted to do was displace air, they could use ANYTHING, so, in that case, why nitrogen? [/QUOTE] WAG: It’s the most abundant gas in the atmosphere so the fractional distilation of air produces plenty. Thus it’s non-reactive and cheap. ---
**Author:** ![Booker57](https://avatars.discourse-cdn.com/v4/letter/b/b9e5f3/32.png) [@Booker57](https://boards.straightdope.com/u/Booker57)\ **Post date:** [September 24, 2007, 1:13pm UTC](https://boards.straightdope.com/t/why-nitrogen-canisters-on-sidewalk-boxes/420271/6 "2007-09-24T13:13:16Z")
O2 is nasty stuff, corrosoin and stuff. Keep it away with N. We need spellcheck. I know it is wrong but don’t know how to fix it. ---
**Author:** ![postcards](https://avatars.discourse-cdn.com/v4/letter/p/8e8cbc/32.png) [@postcards](https://boards.straightdope.com/u/postcards)\ **Post date:** [September 24, 2007, 1:45pm UTC](https://boards.straightdope.com/t/why-nitrogen-canisters-on-sidewalk-boxes/420271/7 "2007-09-24T13:45:48Z")
[QUOTE=Booker57] O2 is nasty stuff, corrosoin and stuff. Keep it away with N. We need spellcheck. I know it is wrong but don’t know how to fix it. [/QUOTE] We have spellcheck.. See the red lines under the suspect words when you’re posting? Right-click for the proper spelling. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [September 24, 2007, 1:59pm UTC](https://boards.straightdope.com/t/why-nitrogen-canisters-on-sidewalk-boxes/420271/8 "2007-09-24T13:59:39Z")
Specifically, those dry nitrogen canisters are connected following line repair work (which, by necessity, allows moist ambient air into the lines.) They are left in place long enough to pump out all the moist air and drive out any remaining condensation and once that’s accompished, the cannisters are disconnected and the line pressure is maintained by dehumidifying pumps located at the CO. ---
**Author:** ![zoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zoid/32/336_2.png) [@zoid](https://boards.straightdope.com/u/zoid)\ **Post date:** [September 24, 2007, 2:13pm UTC](https://boards.straightdope.com/t/why-nitrogen-canisters-on-sidewalk-boxes/420271/9 "2007-09-24T14:13:54Z")
[QUOTE=postcards] We have spellcheck.. See the red lines under the suspect words when you’re posting? Right-click for the proper spelling. [/QUOTE] Funny - I don’t get those. What browser are you using? ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [September 24, 2007, 2:30pm UTC](https://boards.straightdope.com/t/why-nitrogen-canisters-on-sidewalk-boxes/420271/10 "2007-09-24T14:30:21Z")
[QUOTE=zoid] Funny - I don’t get those. What browser are you using? [/QUOTE] Bet it’s a Mac… OS X has built-in spellcheck for all text dialogs. ---
**Author:** ![essell](https://avatars.discourse-cdn.com/v4/letter/e/34f0e0/32.png) [@essell](https://boards.straightdope.com/u/essell)\ **Post date:** [September 24, 2007, 2:34pm UTC](https://boards.straightdope.com/t/why-nitrogen-canisters-on-sidewalk-boxes/420271/11 "2007-09-24T14:34:31Z")
[QUOTE=zoid] Funny - I don’t get those. What browser are you using? [/QUOTE] There’s inline dictionary add-ons for Firefox 2. I love em. ---
**Author:** ![chorpler](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chorpler/32/2888_2.png) [@chorpler](https://boards.straightdope.com/u/chorpler)\ **Post date:** [September 24, 2007, 4:31pm UTC](https://boards.straightdope.com/t/why-nitrogen-canisters-on-sidewalk-boxes/420271/12 "2007-09-24T16:31:15Z")
[QUOTE=Q.E.D.] Specifically, those dry nitrogen canisters are connected following line repair work (which, by necessity, allows moist ambient air into the lines.) They are left in place long enough to pump out all the moist air and drive out any remaining condensation and once that’s accompished, the cannisters are disconnected and the line pressure is maintained by dehumidifying pumps located at the CO. [/QUOTE] Thanks, **Q.E.D.**. I remember being told that while installing them now. My bad. ---
**Author:** ![Rayne\_Man](https://avatars.discourse-cdn.com/v4/letter/r/df705f/32.png) [@Rayne\_Man](https://boards.straightdope.com/u/Rayne_Man)\ **Post date:** [September 24, 2007, 6:10pm UTC](https://boards.straightdope.com/t/why-nitrogen-canisters-on-sidewalk-boxes/420271/13 "2007-09-24T18:10:33Z")
Nitrogen is also used to purge natural-gas pipe-lines of air before the gas is introduced. This is to avoid creating an explosive mixture. This procedure is used on new gas pipes and whenever the flow of gas has been interrupted, for instance when a pipe has been damaged.