Related to MAKE 05, MakeShift
MakeShift 05: Woody's Solution
by Woody Norris
July 07, 2006
Almost everyone realized the solution would in some way involve using the vent tube. The problem is, the tube is too long to merely exchange air by breathing through it directly.
Sectioning the tube to have one side bring in good air and the other expel bad air is problematic unless you could split the tube far enough along its length to be sure the air wasn't merely making a round trip before it made it all the way to the top (exit).
Here's the crux of the problem: except for the overhead vent, the room is sealed (that's the case with almost any good vault). That requires some consideration for equalizing the air pressure in the room, whichever solution one comes up with.
The key is two-fold. First off, there is about enough air in the room to take you 24 hours. Secondly, you finish off the time using electrolysis. My setup is a little different from the solutions proposed—sometimes it's the little things that make the big difference.
In electrolysis, there will be two streams of bubbles making their way upwards from the carbon electrodes. The fine bubbles formed at the negative (-) terminal in the drawing below are hydrogen (H2); the others (+) are the good stuff, oxygen. That way, you know you're not breathing hydrogen, which would not be fun.
If the electrodes are plain old metal, such as a hammer/toolbox combo, contamination will take place, stopping the process as well as producing other gasses that may not be wanted. I'd be real concerned that whatever method you use, you don't fill the room with hydrogen…dangerous. A spark, etc., could be the end.
Here are a few facts to consider in solving the problem: hydrogen is the lightest of all gases so it will easily vent through the hose to the ceiling (see illustration). CO2 is heavier than O2, so it will accumulate from the floor up. With these things in mind, take a look at the drawing and see how it works.
Notes to Drawing:
- Cut apart two of the individual cells from a battery that powers the emergency lights. Remove the carbon rod from each cell. Wipe the rods as clean as you can. A bit of electrolyte residue will not hurt; in fact, it will probably enhance the electrolysis process.
- Cut the hose into two pieces appropriate to the items described below.
- Hydrogen is the lightest of all gasses, so it will quickly exit easily through the hose to the outside. Notice the paper cup on the left in the water reservoir is positioned above the water line. That is so that not only hydrogen can exit up the tube but also CO2 picked up from the floor. The cup on the right is below the water line.
- CO2, being heavier than the other gasses in the room, will begin to accumulate from the floor up. That's why CO2 sensors for the home always mount near the floor.
- O2 will accumulate higher up in the room. Take the second piece of hose and get on top of the table, where you position the hose and where the freshest air is going to be.
- Wrap wire taken from the dead telephone cord around each rod and position the other end outside the water tank connected to batteries obtained from the other lights. Note that even though the phone is dead, there is AC power in the room charging the batteries in the emergency lights. This is an alternative to using the batteries, but a description of how to rectify and split the voltage is too complex for this discussion.
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- Battery electrode problem
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Sorry to nitpick, but if the batteries in the emergency lights are rechargeable, you won't likely have any carbon rods to use as electrodes - those are typically only present in zinc-carbon dry cells. Rechargeable batteries in most systems are sealed, gelled or valve-regulated lead-acid batteries. Looking at a galvanic series, the copper wire is likely to be your best bet as an electrode to minimize the amount of oxygen being "stolen" by the oxidization of your electrode. Unless you can find some stainless steel bolts to use, or one of the safe deposit boxes happens to be open and have some gold or platinum bars in it... Adding a bit of the elecrolyte from the batteries to the water would probably help the circuit, as you mention. If there are any pencils in there, the graphite from them might be useful as well as electrodes.
Also note that if there are rechargeable batteries in the emergency lights and a circuit to recharge them, they are already set up with rectifiers, so it's just a matter of observing correct polarity to make use of the incoming power to the room.
Otherwise, very neat solution to the problem. I especially like harnessing the "lightness" of the H2 produced during electrolysis to help draft CO2 laden air up off the floor and out through the vent tube.
Mayhaps I'll enter one of the future "MAKEShift Challenges". For now, I'll just lurk and comment.
Posted by cajunfj40 on July 17, 2006 at 10:01:53 Pacific Time
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