I want to electrolyze water to get oxygen and hydrogen. I want to mix them in a regular balloon and ignite it. How much hydrogen would you need in a 2:1 ratio with air for it to be dangerous? Is this generally a safe experiment?
In case FriendofKim can still read this...
First, let me say that I've enjoyed many times exploding soap bubbles of about one milliliter filled with hydrolysis gas. That is 1 cubic centimeter. That will give you a sound that rings in your ears in a decent sized living room. You may wish to use ear protection for the experiment.
50 ml will have an effect in a lecture hall that not only wakes up everyone, but also may make people complain.
Now while the explosive limits of hydrogen in air range from about 18 -- 60 % the flammable limits are from 4 -- 75 %, in oxygen the limit of flammability goes all the way from 4% to 95% read: for practical purposes, hydrogen in oxygen is always at least a flammable mixture.
However, you start with a stochiometric mixture which is ideal for explosion (after all, that's why you do it, right?), and it is in oxygen, not in air. So even if you "only" have a flammable mixture reaching an ignition source (e.g. electric switch), chances are quite high that as the ignition proceeds through the mixture, it can reach a zone where the gas/air mixture is explosive. Also, because hydrogen is so much lighter than air, it tends to accumulate under the ceiling, so even if there is enough air in the room that an ideal mixture would not be explosive, chances are that there is an explosive layer of gas. (Same with gasoline or, practially more relevant: solvent from glue for parquet floor tiles)
The safety relevant points are:
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UVic, three party balloons, each to be tied to a ring stand: 1) Pure hydrogen. Flame on balloon. Whoosh, it burns. 2) Hydrogen plus demonstrator's breath to inflate. Demonstrator puts on helmet, ignites from a yardstick. BOOM!!! Dust falls from ceiling. 3) Hydrogen plus oxygen 2:1. I'm about 50 feet back, in the vary last row of a filled auditorium, snugged in the corner of the AV extension. It puffed me. DON'T DO IT.
Enough that I wouldn't recommend trying a home-experiment.
In all honesty you'd probably be fine, as long as you're careful. I personally wouldn't do this at home or anywhere near something I didn't want near an explosion, and I'd still make sure you were behind something when you started it.
I also have a question for you:
Have you ever heard of the Hindenburg?
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