Here's something I've been wondering...I've seen Gordon wear the HEV suit, but never the actual helmet. Does he wear the শিরস্ত্রাণ as well? He has telescopic vision and headcrabs can't mount his head, so he must wear it, right?
Thought about that too. Perhaps it is a localized force field generated দ্বারা the মণ্ডল ring? Also, those glasses have a built-in H.U.D.. BTW, the মণ্ডল force field also contains the controlled atmosphere needed to survive the toxic gases and breath on Zen, BUT it functions as a two-way sound damper with a defective (Acme)mic, therefore Gordon cannot verbally communicate. "...You're a man of few words..."