The Mark IV Hazardous Environment Suit (or HEV Suit) is a full-body suit that was designed by Doctor Gina Cross for research in hazardous environments. The suit's protective qualities protect the user from radiation, energy discharges, and blunt trauma. Gordon Freeman sports one of these suits throughout the Black Mesa Research Facility before, during and after the Resonance Cascade.
The suit is essentially a powered exoskeleton, being powered by batteries and charging stations. While the suit is powered, the user is able to sustain much more damage. When fully powered, the user can sustain many gunshot wounds or even a direct hit from a RPG.
The suit itself is not made by the U.S. Government, but rather by a commercial developer [CITATION NEEDED] . The suit is equipped with a tracking device or devices, as affirmed by a scientist in the chapter Apprehension.
The Suit in Black Mesa
The developers have stated that at no time in the course of the game will Gordon wear the helmet for the HEV suit. It will only be found on dead survey team members on Xen and in the multiplayer mode of the game.
In 2010, The sound team had experimented with recording a new version of the HEV voice in order to replace the 8 bit sound files form the Source SDK Base with higher quality 16 bit. Victoria Teunissen was enlisted to recreate the "HEV lady" as closely as possible with her voice, as dialog editor Kevin Sisk worked meticulously to recreate the SFX process that gives the HEV voice its classic metallic "twang". While some of the first SFX test results sounded quite good, it was apparent that this was one of the few instances where "if it it aint broke, don't fix it." So It was opted to keep things "classic."
The vocalisation for the battery percentage count (scrapped in Half-Life 2 and Episodes) was kept in the mod .
The H.E.V. Container at Sector C test labs.
The developers went to great lengths to make sure the Mark IV appeared feasible by reviewing original Half-Life concept art and altering it to be more flexible and correctly proportioned.