If you are in an area where Radon can be a problem, test for it. They sell kits for it everywhere. I took steps with my house thinking I'd have a problem in a heavy limestone area - but several tests show no issue. You can install a vent pump, What I did, based on some expert advice, is lay some pvc inch pipes with holes drilled in them around the rough center of the crawlspace UNDER the sealed plastic. The pipes all connect to a vertical pvc pipe that goes up through the house inside a wall and out the roof. Any gases are vented. I found I didn't have any real issues but had already installed the system. (I capped it for the tests.)
