CO2 is a compressed gass in the lifejacket so yeah its classed as a dangerous good on the aircraft. but its essential we have them on board. A lot of things we carry on the a/c are restricted for passengers, or not allowed at all ie Dry Ice, CO2, Oxygen, and the main one, is BCF's... not allowed to be used on the ground at all, banned, but in the air they are our best bet in fighting fire.