Thanks, especially FlyFish, for the interesting input. Just one more question concerning lead: Of which quantities of shooting do we speak here? Is there a significant amount of lead expectable after 50 or 100 shots or are we talking something in the ranks of 1.000+ shots after this becomes a real issue?
That's a tough one, Simon, and I don't have a straight answer for you but perhaps I can give you some idea of the amount of shooting that can result in problematical exposure to airborne lead.
The amount of shooting necessary to increase airborne lead to levels that can result in elevated serum (blood) concentrations high enough to be a health risk (10 micrograms per deciliter [mcg/dl] is the generally accepted "safe" upper limit for adults here in the US) depends on a number of factors, such as: centerfire vs. rimfire (and based on both your original post and my personal experience, what we'll be talking about is .22LR), the amount (volume) of air in the range, and the effectiveness of any ventilation.
Most of my data comes from a very poorly ventilated range - essentially one box window fan in the wall - with 10 lanes (maybe 12 meters wide?) and about 3 m ceiling height, with a length of about 20 m. My pistol team either competed (in season) or practiced (in off season) once per week, with about 7 shooters shooting perhaps 100 rounds each per session.
That amount of exposure was enough to raise the serum lead of our team captain, who probably had shot in that range for several years at the time, to 62 mcg/dl, which is dangerously high by any standard. My own serum lead was at 26 mcg/dl, which in Massachusetts, where I was at that time, is sufficiently high that it has to be reported to the state Department of Public Health, who then issues you a letter discussing occupational exposure and your rights as an employee, obviously of no particular value in this case.
We both started wearing half-face respirators with the pink P100 pancake filters - exactly like
this one, but otherwise didn't change our shooting habits. In my case I also took particular care to wash my hands well after shooting because ingestion is another source of exposure, but I'd pretty much been doing that all along anyway. After one year, his serum lead was down to something in the 20s (can't quite remember exactly) and my own had come down to about 12 mcg/dl. I relocated at around that time, so I know nothing of his history after that. In my case, after two more years I was tested again and was down to 7.6 mcg/dl and I've remained under 10 since then.
I'm shooting in a range with somewhat better ventilation now, but I still wear the respirator, as do most of the other shooters on my pistol team. For me, it's simply a part of my protective equipment, no different from my ear muffs and glasses, and I'd feel naked without it.
I also did "wipe" samples of surfaces in the range and found, much to my surprise frankly, that they were only slightly elevated for lead and well within applicable guidelines. We also sampled the air when the range was not active, and there were no problems there either. So, from all of that I concluded that the issue is really airborne lead rather than particulate lead on the floor and other horizontal surfaces, though I'm sure enough shooting can result in problems with that as well. Our range was a multipurpose room that was only used as a range the one night each week that we were there, so that may be why we didn't see problems on surfaces.
My guess is that if you can get some good ventilation going - the NRA guideline is a minimum flow of 1 foot-per-second downrange - and limit your basement shooting to a few rounds every now and again you're probably going to be OK. I wanted to shoot a bit more than that in my own basement, primarily as practice for competition, so I went the air gun route and now I can shoot as much as I want without worrying about any of it. It's also relatively simple, here at least, to add lead to the list of analytes for your annual physical so you can check on things and get some early warning if you're getting too much exposure, then make adjustments as necessary.
My range is only a couple years old and claims to have a great top dollar state of the art ventilation system. However in the pistol side of the range I've noticed when shooting some of my .22lr handguns (buckmark or single six for example) I'll get a pretty decent cloud of "smoke" from the 6-10 shots I just fired. The cloud will pool up and swirl around, frequently back into my face before it finally thins out and is carried down range.