A type of SCUBA diving involving deeper water and longer bottom times than standard recreational diving. A tech diver is easily distinguished from a normal recreational diver by his equipment. A typical tech diving outfit consists of:
  • A drysuit, to keep the diver warmer in deep water than the more common wetsuit, which compresses at depth.
  • Two eighty or one hundred cubic foot tanks filled with compressed air or, for deeper dives, a bottom gas such as trimix. Trimix contains less nitrogen than standard air, giving the diver less risk of nitrogen narcosis at depth.
  • A smaller pony bottle filled with nitrox, for use as a medium-depth decompression gas and possibly as a descent gas. Trimix, due to its reduced oxygen content, may become hypoxic above about ten feet of depth if a mixture with less than the standard 16% O2 is used.
  • A second pony bottle filled with compressed pure oxygen, for use as a shallow decompression gas. This cannot be used at depths greater than about twenty feet, since the increased partial pressure at these depths makes pure oxygen toxic.
Most tech divers are wreck divers who want to explore deeper and more challenging wrecks. The extra gear gives a tech diver the ability to remain at depths of over 250 feet for up to an hour or more, as compared to the practical recreational diving limit of about 130 feet. At this depth, a recreational diver on compressed air can stay only ten minutes before requiring decompression to avoid DCS. For even greater bottom times a rebreather can be used, though they are often prohibitively expensive and are much more prone to mechanical failure; rebreathers for consumer use have only appeared on the open market in the last five years, meaning most of the current designs are young and unproven, though the technology is quite old. The extra gear a tech diver wears gives him (or her -- Janet Beiser comes to mind) far more redundancy than the standard tank-and-two-regulators provides. This may give a false sense of security in more dangerous environs, as evidenced by the rash of fatalities associated with the Andrea Doria.

The popularity of technical diving has surged in the past decade but still remains a niche sport compared to recreational open-water diving. Most technical divers I know consider this a good thing, since there is (at the time of this writing) no internationally-recognized certification authority for technical divers as there is for recreational divers (PADI, NAUI, and others). The number of fatalities involved in this sport has some worried that the government may seek to regulate it, which would involve regulating all of SCUBA. Therefore, most boat captains require divers they are unfamiliar with to make a few simple dives to demonstrate their skill before they are allowed into more dangerous situations. At the very least, the captain will ask to see your logbook before allowing you to dive, and will almost certainly require a PADI Advanced Open Water license or higher.

Update:The International Association of Nitrox and Technical Divers (IANTD) is the largest technical diving certification authority in the United States. The IANTD is providing a standardized curriculum and teaching materials to divemasters to certify technical divers. Plus, they give you a nifty card to carry around.