The International "Alpha" flag is mandated as the federal diver down flag. Federal law stipulates that the "Alpha" be flown when diving. Failure to do so may result in the loss of legal rights and/or courses of action against boaters in the event of an accident. Divers are encouraged to fly the "Alpha" flag when diving to help prevent accidents that involve boaters.

TERMS

Actual Bottom Time - The total time in minutes from the beginning of descent until the beginning of ascent
Decompression - The portion of a dive when the diver ascends toward the surface, decreasing the pressure.
Group Designation - A letter of the alphabet used in the dive tables to designate the amount of Residual Nitrogen in a diver’s body after a dive.
Hyperbaric - a term used to describe increased pressure over the pressure in one atmosphere.
NITROX - A combination of Nitrogen and Oxygen. Nitrox mixtures with percentages of oxygen greater than 21% are called Enriched Air Nitrox (EANx)
No Decompression Limits - The maximum Total Bottom Time, which can be spent at a depth without decompression.
Repetitive Dive - A dive made between 10 minutes and twelve hours of a previous dive. Dives made less than 10 minutes apart are considered a single dive.
Residual Nitrogen - Nitrogen remaining in the body after a dive. Twelve hours is required to eliminate excess nitrogen.
Residual Nitrogen Time - An amount of time, in minutes, added to the bottom time of a repetitive dive to represent the Residual Nitrogen of a previous dive. The amount is obtained from a table by using the Group Designation letter.
Total Bottom Time - The sum of the Residual Nitrogen Time and the Actual Bottom Time of a dive, used to determine a Group Designation after a repetitive dive.