ATA means atmospheres absolute, a measure of total ambient pressure. About 1 ATA is normal sea-level pressure. A treatment stated as 2 ATA uses roughly twice that absolute pressure, but ATA alone does not describe the complete oxygen dose.

Soft and hard chambers are not interchangeable labels for the same treatment. Construction, rated pressure, intended use, oxygen delivery, monitoring, and regulatory status can differ, so the model and protocol matter more than appearance.