The most significant friction point involves PHMSA and SCBA Fully Wrapped Carbon-Fiber Reinforced (CFFC) aluminum-lined cylinders on Special Permit 16320 and the use of Modal Acoustic Emission (MAE) testing to extend the life of composite cylinders. Fully Wrapped Carbon-Fiber Reinforced (CFFC) aluminum-lined cylinders have a 15-year service life. PHMSA has investigated and granted limited special permits allowing life extensions (up to 30 years) when non-destructive MAE testing demonstrates structural integrity.