Although on traditional tables the amount of decompression would vary according to time at depth, For example, using the US Navy diving tables (for air - ratio deco is predicated on the use of trimix - although the same basic considerations to time of exposure apply), a dive to 180 feet for 5 minutes would result in no decompression obligation at all, a 15 minute dive would result in total decompression obligation of 15 minutes, and a 30 minute dive would result in a total decompression obligation of 56 minutes.