Sgt. Caleb Renner, the chief chemical, biological, radiological, and nuclear instructor with II Marine Headquarters Group, gives an hour-long class on how to properly wear and function in a M50 gas mask at Marine Corps Base Camp Lejeune, N.C., Jan. 8, 2016. The chamber is a routine exercise to ensure the durability of each Marines gear while exposed to chlorobenzylidene malononitrile, or CS gas, which is a bi-annual qualification requirement for Marines. - Sgt. Caleb Renner, the chief chemical, biological, radiological, and nuclear instructor with II Marine Headquarters Group, gives an hour-long class on how to properly wear and function in a M50 gas mask at Marine Corps Base Camp Lejeune, N.C., Jan. 8, 2016. The chamber is a routine exercise to ensure the durability of each Marines gear while exposed to chlorobenzylidene malononitrile, or CS gas, which is a bi-annual qualification requirement for Marines.