I dont wear a mask when im pouring jigs. But one thing i do is premelt all the lead outside before actually pouring jigs. The trash thats mixed in with the lead will often catch on fire and the resulting soot that enters the air will carry a lot of lead particles with it. So always remember to premelt outside and use adequate ventilation when pouring.
One of the best setups to have is a range hood with an electric fan located imediately above the melting pots. The hot air will naturally rise and carry the fumes upward and the fan will pull them out.