How to safely handle AVGAS (100LL)?
If you don't crawl underneath and breathe in the exhaust fumes from the engine, you'll be fine.  If you do crawl underneath and breathe in the exhaust fumes, you'll be dead from carbon monoxide poisoning long before any harmful effects from the tetraethyl lead combustion byproducts in the fuel.
While you don't want to ingest lots of lead, that won't really happen being around airplanes with engines running.  The old saying in toxicology is, &quot;The poison is the dose&quot;, and whatever dose you get from casual exposure is too microscopic to matter.
My advice, as an old-timer who likes a clean world as much as the next guy, is don't become so hyper-sensitized (by mostly media coverage) to environmental exposure to chemicals that you can't enjoy life. It's not worth it.