The 6600 Series Mask Interface with Anti-Asphyxiation valve and Calibrated Leak CPAP/Bi-Level with AAV -Anti-Asphyxia Valve (AAV) for patient safety - allows patient to breathe room air if the flow device malfunctions. Valve opens at mask pressures less than 3cm H2O -Swivel Port Micro Vent Holes dissipate CO2 -60° Dual Swivel Elbow Port with Detachable Swivel Port for improved patient freedom of movement. Color coded translucent blue