Hydrogen detection and electro

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DougH

Member
While I'm fine in the warm months, I'm not going to be able to run my electro tank outdoors in the winter. I've got a few ideas of homemade vent hoods bouncing around my head so I could safely run the tank indoors. However, while I'm certainly very handy at projects like this, I'm not an expert. I would really feel better about the idea if I had a hydrogen detector set up, like a smoke detector. A quick google search makes it seem like these exist. Does anyone have any experience with these? Or with venting requirements to run a tank safely indoors.

I don't know if this can be done safely or not, and I'm just in the thinking about it stage. But I'd like to have a better test than lighting a match [emoji95] [emoji91]
 
Doug, I think that you will be fine without a sensor. I believe that you are over estimating the amount of H2 that is evolved. In an electrolysis cell that is running at 100% efficiency, it take about 100 watt hours to produce 1 cu ft of hydrogen (11.7 MJ/cu meter). For example in my cell, I run at 20 amps with a cell voltage of about 2.5 volts. (remember to measure the cell voltage at the anode and cathode). this is 50 W. Therefore at 100% efficiency I could generate 0.5 cu ft of H2 per hour. The lower explosive level (LEL) is about 4% by volume of H2. I'm running on my basement lab that is about 600 sq ft, with an 8 ft ceiling giving me about 4800 cu ft. 4800 * .04 = 192. Therefore if the room was perfectly sealed and the process was 100% efficient, it would take 384 hours (57 days) to reach LEL. H2 is an extremely small molecule and wants to creep though just about anything. I also enter and exit the lab, opening the door when I do. :)

All this being said, I probably wouldn't run the cell in a small closet with the door closed. I definitely wouldn't run the cell with a cover on.

I run NaOH as an electrolyte to protect my anodes (remember that the solution around the anode becomes acidic and around the cathode becomes basic) so I potentially have a higher efficiency than a Na2CO3 cell.

tl;dr
Don't worry about it unless you run in a very small enclosed room, cover the cell, or are running at an industrial scale. Spills and skin contact are more of a problem that H2 concentrations.
 
Awesome, Shawn. Thank you very much for the detail. That's exactly the kind of thing I don't know and needed to for comfort's sake. I will still plan on running an exhaust fan of some sort over it, but the knowledge here is very helpful for my peace of mind.
 
ShawnE said:
I'm running on my basement lab that is about 600 sq ft, with an 8 ft ceiling giving me about 4800 cu ft. 4800 * .04 = 192. Therefore if the room was perfectly sealed and the process was 100% efficient, it would take 384 hours (57 days) to reach LEL.
Click to expand...

Ooops.. 384/24 = 16. This ignores stratification. I also assumed efficiency and H2 egress was a wash with stratification.

Running a fan isn't a bad idea, or crack a window once in a while. I have a bathroom in my basement with an overhead exhaust fan. I run it every so often anyway. Considering that H2 will rise, I would guess that it would exhaust what little H2 is produced.

Nothing wrong with being safe, but a little math will tell you when it isn't cost effective to go overboard.

This stuff is fun isn't it??
 
Thanks ShawnE for running the numbers. While I'm relieved I don't need to worry about explosions, I'm kind of deflated by the realization that I won't be able to fill up my own blimp with the waste hydrogen from my e-tank....
 
No Hindenburg then huh?? :) You could do it, but it would take a while. :(

By running the numbers it is obvious why H2 for transportation isn't done by electrolysis using excess power from renewables. Round trip efficiency sucks. Commercial H2 is generated from natural gas (methane).
 
ShawnE said:
Ooops.. 384/24 = 16. This ignores stratification. I also assumed efficiency and H2 egress was a wash with stratification.
Click to expand...

Great, clearly I can't trust you with these obvious mistakes. This is basically a guarantee that I'll blow up my house [emoji3]

Based on your explanations, and as drafty as this old house is, I probably couldn't cause an explosion if I tried to. Still, I have an unused dryer vent in the basement wall, so I'll probably rig a cheap bath fan or something to it and call it plenty.
 
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