CBRN is a helmet attatchment for Halo: Reach, Grunts however have used it all the time.
Most CRBNs look cool, but you just look like you're sucking a dick on some.
It stands for:
Crappy attitude. Chemical.
Barf Zones. Biological.
This is worn by people with Gruntiness. A CBRN is for Operations in Hazard Zones, like Grunts. They usually come with HUL/CNM. HUL is for flashing Grunts. CNM is for Spec-Op Leaders. The Gruntiness of helmets, the CBRN is not worn by people of Halopedia. Of course we wear them. How would we have survived the Grunt Invasion?