Its also used to make soap.
From what I know and have used of lye, the amount of concentration is where the dangers become higher. Low solutions (Water and lye) are not as dangerous. I have had it on my skin many times in low concentrations (Do not try this). Oven cleaners are commonly made of lye as there active ingredients. I use oven cleaner to clean burnt motor oil off of (steel) auto parts before machining. Works better than any degreaser that I have tried. I can tell you that it will eat your skin if left for 10 seconds or more. Its not ever given me any pain, just some new shinny skin. I assume it just eats at the first layer, and if left to long could eat several layers. If you do get it on you Quickly rinse with water thoroughly. I would recommend you wear eye protection. And don’t stick your face directly over the solution breathing the fumes. Use some pliers to pick the object in and out of the solution or a stiff wire (coat hanger).
Warning : Don’t touch the stuff just because I did, your concentration could be higher causing burns.
.
The lower concentrations of a lye solution like used to dissolve anodizing is quite weak. I only use about a teaspoon for 1/2 gallon of water. I add more if the anodizing seems to be going slowly. If you would like to make smaller amounts of solution, just add very little lye and see how it reacts in 5 minutes if it doesn’t seem to be doing much add a little more, then check again until the desired stripping is achieved. Rinse in water thoroughly once done.
.
As for the hydrogen fumes, The lower the concentration the lower the fumes. I would think if you de-anodized beside a open window where air is flowing, you would be fine. Hydrogen is lighter than air so it goes up. I don’t really think there’s much danger from the hydrogen unless you where in a closed up room and de-anodized for a long period of time. Where the hydrogen could concentrate at the ceiling.
.
I consider de-anodizing some what dangerous. But take precautionary measures to try and keep it safe. The eyes being the most important part needing protection. Gloves would not be a bad idea either but you should really not be touching the stuff any way, if you use something to take the item in and out of the solution. Don’t touch it because I did with the oven cleaner, your concentrations could be higher. Don’t take safety to lightly.
.
This is just my 2 cents on de-anodizing with lye.