Wreck diving

Wreck diving is recreational diving where the wreckage of ships, aircraft and other artificial structures are explored. Although most wreck dive sites are at shipwrecks, there is an increasing trend to scuttle retired ships to create artificial reef sites. Diving to crashed aircraft can also be considered wreck diving. The recreation of wreck diving makes no distinction as to how the vessel ended up on the bottom.

Some wreck diving involves penetration of the wreckage, making a direct ascent to the surface impossible for a part of the dive.

A shipwreck may be attractive to divers for several reasons:

In his seminal work on the subject, The Advanced Wreck Diving Handbook,Gary Gentile sub-divides wreck diving into three categories:

Each subsequent level involves additional hazards and greater risk, and therefore will normally require additipnal training and experience to develop the required competence, and may also require additional equipment and the competence to use it effectively.

Non-penetration wreck diving is the least hazardous form of wreck diving, although divers still need to be aware of the entanglement risks presented by fishing nets and fishing lines which may be snagged to the wreck (wrecks are often popular fishing sites), and the underlying terrain may present greater risk of sharp edges.

Penetration within the light zone presents greater hazards due to overhead and greater proximity of the wreck's structure, but because of the proximity of a visible exit point, and some amount of external light, those hazards are more manageable. However, there is clearly a much greater risk of entanglement and silt out inside of the structure, as well as the requirement to move laterally to a defined exit point before one can surface in the event of an emergency.

Full penetration involves the greatest level of risks, including the risk of getting lost within the structure, the risk of complete darkness in the event of multiple light failures, and the inability to escape unassisted in the event of a complete disruption to breathing gas supply.

These categorisations broadly coincide with the traditional division between "recreational" wreck diving (taught as a specialty course by recreational diver training agencies and normally limited to the "light zone" and/or 100-130 cumulative feet of depth plus penetration) and "technical" wreck diving (taught as a stand-alone course by technical diver training agencies).

...
Wikipedia