Abstract : The purpose of the present report was to determine physiologically acceptable limits for work of breathing with heliox mixtures. The basis for the development was the limits for air breathing that Navy Experimental Diving Unit (NEDU) implemented in 2008. Two ways of converting the air limits to heliox were considered: empirical changes in breathing capacity and calculations of equivalent gas density. The reasons for choosing changes in breathing capacity are discussed. Limits are presented for diving with fixed concentrations of oxygen (e.g., open circuit diving) and fixed partial pressure of oxygen (e.g., electronic rebreathers). Tables give limits for common gas mixtures or ways to calculate the limits for custom gas mixtures. The results are compared to those from previous tests at NEDU. No restrictions will be put on existing equipment. Rather, in some situations the limits will increase, a result making the advantages of heliox increasingly obvious.