Final answer:
ADCI standards specify that the maximum allowable depth for surface supplied mixed gas is approximately 450 feet, specifically for heliox gas mixtures.
Step-by-step explanation:
The ADCI (Association of Diving Contractors International) standards specify the maximum allowable depth for surface supplied mixed gas. These standards vary depending on the type of gas mixture being used. One commonly used gas mixture is heliox, which is a combination of helium and oxygen. ADCI standards state that for heliox gas mixtures, the maximum allowable depth is approximately 450 feet. This is because at greater depths, helium becomes narcotic and can cause impairment, so the concentration of helium in the mixture needs to be minimized.