So, I know that this isn't really current... It's an older game, with a timeless debate - "Does Gordon Freeman wear a helmet?"
Well this is my answer... An intelegent person wouldn't go into a hazardous enviroment without full protection. And Freeman is an intelegent person. Yes, I know that there is an official helmet from Valve, but I don't like it... It seams to me as a combat oriented helmet, and not really something that a scientist would wear...
So the helmet is more or less a standard helmet, except that it has an oxygen connection in the back, and a transparent alumina (it exists, Google it) visor which swivles up... Also, on the side, in the circle is the flashlight.
forgot to comment...Well, at one point in Half-Life Barney asks Gordon to go get his suit and helmet, but there is no visible helmet on his HEV suit. We know a helmet exists for multiple reasons, because we saw other Hazard Workers in a helmet, and because there is an official one, but as many others suggest, maybe it was broken or just "sold seprately". Also, if you use the console command "thirdperson" on the PC version of the game,it takes you into thirdperson, and you can see he isnt wearing one, but instead sporting a small ponytail.
Regardless of if they are, I still like to add them. I think it helps people feel more appreciated, and I also wanted to contribute to the current thing that you were saying, so it works for both purposes on this instance.
I see where your coming from with the combat oriented thing, and I do believe this would be a more fitting helmet for the anomalous materials scientists, but as far as the Xen explorers go, the original seems as though it would fit more.
But this could be the mark 5 helmet.
Maybe Valve could use my design (a man can dream) for the Mk VI... If we ever see the mythical HL3.