Karl Townsend fired this volley in
:

Is working in front of a fan enough to keep the lead fumes safely
away?

It's counter-intuitive, but don't have the fan behind you, or even behind
at an angle. Have it blow R-L or L-R across your pot.

As far as concerns "lead fumes" -- WHAT lead fumes? At correct casting
temperatures, no significant or harmful amount of anything lead-bearing
will get into the air that you don't throw into the air with your tools.

The flux fumes may or may not be injurious, depending upon what you use.

Chronic breathing of even simple animal grease smoke ain't all that good
for you.

LLoyd