Running a science lab in video-game land

[prog]

The Half Life games explain away the protagonist's (genre-typical) ability to get shot and blown up a zillion times over the course of play by putting him in an "HEV suit", explained as a scientific tool for working with dangerous lab materials, and which happened to be handy when bad things started happening in his lab at the start of the first game.

What isn't explained is why it repels the vulcan-gun fire from helicopters and the slavering jaws of alien brainslugs with ease, but the moment you step into an actual hazardous environment (like the radioactive goo that's ubiquitous in at least one major chapter of Half Life 2) it starts yelling and falling apart.