FWIW, I have always heard and read that with a "conventional" heat source, you can't get lead hot enough to emit lead vapors or fumes...lead fumes or vapors are not to be confused with smoke.
I have to say I have a unit from a Turkey Deep Fryer that is operated by a high volume / high pressure propane regulator, as opposed to your typical Camping, RV, Motor Home propane low volume / low pressure regulator that will melt the bottom out of a Cast Iron pot, if I allow that pot to run out of lead....does that unit emit vapors?
I don't know, but you can be sure I am very careful in using that unit as a heat source.
Using conventional heat sources, such as a Lee, Lyman, Herters, or RCBS smelting pot, I never worry about vapors or fumes with pure lead.
I also use a lot of wheel weights, and some of the "crap" you get in that stuff smokes and stinks like the devil, and I am just as careful with that...normally that type of smoke can be lit and quickly burned off with one of the long BBQ lighters, but be careful when you do it, you will most likely get a "flash".
Of course any topic on casting should always contain the standard safety precautions and I don't want to neglect that.
Good common sense use of your casting pot, to include eye protection, is a must....along with protective clothing such as a long sleeve shirt, leather gloves, and even good sound foot wear can go a long way in providing you hours of enjoyment in this hobby.
Water and other liquids is something you want to be very careful with around molten lead.
For different reasons, I do "water-drop" some projectiles to increase hardness, and I keep a wet towel on my bench to drop the projectiles on...this not only cools the projectile quickly, without burning anything, it also allows me to touch the bottom and sides of the mould to it occasionally to keep the temperature of the mould down, should my rhythm get too fast.
My rhythm, or casting pace, is determined by the sprue puddle. With a little practice it is very easy to tell when your mould is getting to hot.
The wet towel is harmless, actually it's very helpful, but a bucket of water can be downright dangerous unless it is behind and to the side of both you and the pot, where you have to make an effort to get to it if you are water dropping......
I imagine I am preaching to the choir with most of my remarks, but safety is always first and foremost, and I hope we all adhere to basic safety precautions when we are casting.
Uncle Russ...