Do you want to spend more time underwater? By diving with enriched air rather than normal breathing air you can considerably extend your no-decompression limits.
The PADI Enriched Air Specialty course is designed to teach recreational divers to use enriched air (nitrox), for fun, safe, no-stop recreational diving. The course addresses the use of enriched air with 22-40% oxygen, with emphasis on the enriched air of 32% & 36%.
