The Hazmat Suit allows one to safely travel through irradiated zones, signified by Geiger counter style ticking. When the Suit is equipped, the wearer will be protected from most radioactive zones
It does not provide full protection in certain areas, such as in the main building at the Launch Site, or the broken cooling tower at the Nuclear Power Plant.
The main use of the Suit is to travel into irradiated zones, as its protective ability in combat is inferior to mid-tier equipment. However, in a pinch, it is better than being naked, unless one is trying to remain undetected as the bright yellow makes a person stand out against the landscape.