Basic Technical Diving Manual: The Basic Training Manual for Technical Scuba Divers.
Because there needs to be a safe beginning to becoming a technical scuba diver this manual has been written. The premise is that in order to properly satisfy the several definitions of technical scuba diving acceptable preliminary limits need be established so that student divers can gain the relevant important basic technical skills and knowledge safely. In other words (to use a sage expression), one needs to crawl before one can walk. The other analogy we like to quote is: one needs to learn to fly a Piper Cub long before one can fly a jet fighter.
Scuba divers (technical or otherwise) carry a finite amount of air (gas) with them. That amount of gas determines how long they can stay at any depth. No-Decompression diving, that style of diving done by the majority of recreational scubas, doesn't require that air be held in reserve for controlled, staged ascents. Technical diving on the other hand carries with it the absolute need to know how much air (gas) will be required for a particular excursion, including any for decompression (to avoid the bends). A technical diver must not rely solely on the readable output of a dive computer... when the read-out of his or her device dictates that an ascent be made, he or she must have sufficient gas to safely complete that ascent.
The three definitions of technical diving (deeper than 130 feet...and/or...decompression diving...and/or...mixed gas diving) can all involve the need to do stage decompression. Any dive that will not allow for a direct ascent to the surface must only be undertaken by scuba divers who carry sufficient gas for controlled decompression.
Where as the trademark of many so-called "technical divers" is the seemingly excessive amount of equipment they drag through the water, the real critical measure of a technical diver is that he or she knows how much air/gas will be needed (for the decent, for the time at depth, for the ascent, for any decompression that may be required, and for whatever reserve has been considered appropriate).
The BASIC TECHNICAL DIVING MANUAL discusses: decents to depths to 180 feet; times at those depths that may require decompression; ascents on air; with decompression being carried out while breathing nitrox. The manual cites "aluminum 80s" as example cylinders, and assumes that 80 cubic feet are contained when the cylinder pressure is registering 3000 psig. Air and gas requirements for the descents, times at depth, ascents, and stage decompression are calculated.
By Fred Calhoun PE.