One of the more divisive subjects in technical diving concerns using compressed air as a breathing gas on dives below . Some training agencies still promote and teach courses using air up to depths of 60m. These include TDI, IANTD and DSAT/PADI. Others, including NAUI Tec, GUE, ISE and UTD consider that diving deeper than , depending upon agency, on air is unacceptably risky. They promote the use of mixtures containing helium to limit the apparent narcotic depth to their agency specified limit should be used for dives beyond a certain limit. Even though TDI and IANTD teach courses using air up to depths of 60m, they also offer courses include "helitrox" "recreational trimix" and "advance recreational trimix" that also use mixtures containing helium to mitigate narcotic concerns when the diving depth is limited to 30-45m.