Lead vapour is extremely toxic. Here are a few things to take into consideration...
Melting lead in large quantities and casting lead bullets offers more opportunity for lead to enter the body and there are some special lead handling precautions that are particular to lead casting.
Always cast lead bullets outside. Do not contaminate your home or workshop with lead residue which can persist for years and provide a continuous source of exposure to lead.
Before starting to cast lead, cover all work surfaces with heavy duty aluminum foil. At the conclusion of that casting session, gently roll up the aluminum foil with all the lead contaminates and dispose of it properly.
Keep the temperature on the lead pot as low as possible. Lead melts at 621°F. Lead boils at 3180°F, but significant amounts begin to evaporate above 900°F. Any lead vapor quickly forms a very fine lead oxide powder and can be inhaled. If your bullets have a frosty appearance, the lead is hotter than needed. This also causes slower cycle times as you must wait longer for the lead to solidify before dropping it from the mold, and you are more likely to drop the bullet while it's still soft, causing it to deform. If the molten lead doesn't fill the mold at temperatures low enough that the bullets aren't frosted, try adding 1/2% tin to the alloy to lower the surface tension. It's also possible that the lead is contaminated with zinc and must be discarded.
Fluxing is the process of adding a pea sized chunk of flux while stirring the molten lead and skimming off the grayish brown powdery contaminate residue that floats to the surface. This dross contains a large percentage of lead oxides in a fine powder that can be aerosolized and inhaled. Wearing a dust mask is a good idea, but you can limit exposure by keeping your head well away from the dross at all times, not breathing while skimming the dross, and keeping the dross in a glass jar or metal can with a lid.
Position yourself so you are upwind of the casting operation. This allows the wind to carry the lead contaminates away from you instead of carrying them toward you. When designing an outside area for lead casting, keep in mind that in the northern hemisphere the prevailing winds flow from west to east.
After casting lead, it's a good idea to take a shower, being sure to thoroughly wash your hair, and wash your clothes.
Special Precautions For Women and Children
Male reproductive processes are damaged by high serum lead levels, but female reproductive processes are more permanently damaged by exposure to lead.
Children and fetuses are developing, and lead interferes with proper physiological development. Nerve cells are particularly affected by high levels of lead, and most structures of the body rely on nerve cells to function properly. There is no safe level of lead for a child's mental development. Average serum lead levels correlate to lower IQ when compared to children with below average serum lead levels. The less lead, the better.
The human body slowly excretes lead, but it also stores lead in bones. It's possible for serum lead levels to return to normal after a large exposure, and then spike again when the body uses the store of bone calcium to heal a fractured bone or during pregnancy when a developing fetus increases the requirement for calcium. There have been documented cases where a woman was exposed to high levels of lead, recovered, and later had a child with lead poisoning because the prior exposure stored lead in her skeletal system.
more on lead exposure here...
http://www.tacticoolproducts.com/leadsafety/