Too funny rcmodel! Maybe that's why we act so crazy here
(I have been handling/inhaling lead all of my life)
Well, our indoor range has addressed the lead issue in the way of not using an angled steel plate back drop - they use ground tire bead mound instead and a very powerful ventilation system (It's like shooting in a strong breeze coming from your back). When you shoot lubed lead bullets, the smoke from the firing is immediately pushed down range. The range staff (who also own another range in neighboring state) confirms that shooting lead is permissible. I also shot at other California indoor ranges with steel plated back drops and they do not allow shooting of lead bullets, only jacketed or plated bullets (more on plated bullets later).
I work as a state health facilities inspector/surveyor and is the office respirator fit tester and it is my opinion that minimizing lead splatter and not inhaling lead vapor is the key. As long as the indoor ranges have good ventilation system, I believe harmful levels of exposure to lead vapor may be minimized. As to lead vapor venting to outside atmosphere, I do not believe regulations exist to mandate filtering before venting. If there were any established lead vapor concerns, I am quite certain OSHA/Cal-OSHA signs would be all over the indoor ranges.
I think the concern over lead may be more applicable to outdoor ranges shooting steel plates. I also shoot at several outdoor ranges for recreation/match shooting, and over time, more and more cardboard targets have been used and less and less steel plates for staging of targets. Even with good breeze, often it changes direction and the smoke/dust blows right back in our faces. Examining areas immediately adjacent to steel plates showed definite lead splatter, but surprisingly more from softer copper plated bullets than harder cast bullets (I shoot cast bullets with hardness of 18-24 - I think harder the better). The splattered lead fragments and dust on the ground may over time be picked up as wind blows and be breathed in. With the use of cardboard targets, bullets are mostly embedded in the dirt berms where they are less likely to fragment/dust and provide for safer outdoor shooting.
I do not believe wearing of masks in indoor range is practical. For actual filtering of lead vapor, respirator with filter cartrige rating specific to lead vapor is required and disposable paper masks (even N95) will help but not provide that level of protection.