Wikipedia: Military protective kit (OZK) is a personal protective equipment designed to protect a person from toxic substances, biological agents and radioactive dust. OZK is in service with the Armed Forces of the Russian Federation, many countries of the former USSR and is an individual defense tool for servicemen of all types of armed forces and combat arms. Used in conjunction with a respirator or gas mask.

How it looks in real life:


I also added an unusual gas mask PMG "Nerekhta"