The regulations may be different in other countries, but in the US, there are actually occupational safety and health laws concerning the usage of a respirator. The "real" respirators rated for fumes require medical evaluation and fit testing. The reason why medical evaluations are done because unless you are using powered or supplied air (the outfit cost about US$500 and up), wearing a respirator makes it more difficult to breathe because you have to literally "suck through the filters". You will end up with less air per breath and your lungs will have to work harder. Fit testing ensures that there are no gaps and openings between the respirator and your face, which would negate the purpose of wearing a mask.
Wearing respirators is part of my job requirement and I have to get a full physical (part of that is also to make sure that I am not exposed to too much heavy metals/toxins) once a year, a fit test once a year or anytime I gain or lose more than 10% of my body weight or have any dental work done.
If you think I am making this up, scroll down to 1910.134(e):
http://www.osha.gov/pls/oshaweb/owadisp ... =standards
Now, that is not to say people cannot just go to a hardware store and get one and slap it on. If so, please limit the time of wearing the respirator to an absolute minimal. Stir your lye in the water, put it away, and take off the respirator. That also goes without saying if you feel light-headed or short of breath, stop what you are doing, walk away, take off the respirator and go outside for some fresh air.
Another thing I routinely do to minimize fumes is use half water, half ice in making up the solution. If the formula calls for 400 g/ml water, weight out approximately 200g of ice, the rest in water. Since you keep the temperature lower, there will be less fume.
