Radiation suit (also known as environment suit) can be used by agents to get through areas that have high radiation levels or toxic gas leaks. Your speed will be reduced and you won't be able to use your weapons while in a radiation suit however. Instead, the suit is equipped with integral welding tool that is typically used to patch up damaged material but also can be used in offensive manner and does deal damage, but not a lot of it. It's best to avoid the enemies (such as Protector Drones) while in the radiation suit. They can put on and taken off at radiation suit stations.
Radiation suits can be found in Megabase, Energeia, Arsia Mons Colony, and Neutrino.