Penetration diving or no clear surface diving is a type of diving where the scuba diver

Scuba diving

Scuba diving is a form of underwater diving in which a diver uses a scuba set to breathe underwater....

 enters a space from which there is no direct, purely vertical ascent to the safety of breathable air of the atmosphere

Earth's atmosphere

The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...

 at the surface. Several types of dive meet this condition: cave diving

Cave diving

Cave diving is a type of technical diving in which specialized equipment is used to enable the exploration of caves which are at least partially filled with water. In the United Kingdom it is an extension of the more common sport of caving, and in the United States an extension of the more common...

, wreck diving

Wreck diving

Wreck diving is a type of recreational diving where shipwrecks are explored. Although most wreck dive sites are at shipwrecks, there is an increasing trend to scuttle retired ships to create artificial reef sites...

, ice diving

Ice diving

Ice diving is a type of penetration diving where the dive takes place under ice. Because diving under ice places the diver in an overhead environment typically with only a single entry/exit point, it is considered an advanced type of diving requiring special training...

 or diving other man-made, underwater structures or enclosures.

The fact that the diver cannot immediately ascend to breathe from the atmosphere at the surface makes this type of diving much more risk

Risk

Risk is the potential that a chosen action or activity will lead to a loss . The notion implies that a choice having an influence on the outcome exists . Potential losses themselves may also be called "risks"...

y than the usual types recreational diving

Recreational diving

Recreational diving or sport diving is a type of diving that uses SCUBA equipment for the purpose of leisure and enjoyment. In some diving circles, the term "recreational diving" is used in contradistinction to "technical diving", a more demanding aspect of the sport which requires greater levels...

 or open-water diving

Open-water diving

Open-water diving has at least two different meanings in scuba diving:* In the later stages of initial diver training, divers progress from diving in swimming pools to "open water", which normally implies the sea or a lake, including quarries....

.

It is essential that divers doing penetration dives are specially equipped and trained in technical diving

Technical diving

Technical diving is a form of scuba diving that exceeds the scope of recreational diving...

 techniques such as:

• using redundant diving cylinder
  Diving cylinder
  A diving cylinder, scuba tank or diving tank is a gas cylinder used to store and transport high pressure breathing gas as a component of a scuba set. It provides gas to the scuba diver through the demand valve of a diving regulator....
  
  s
• using distance line
  Distance line
  A distance line, penetration line or guideline is an item of diving equipment used by SCUBA divers as a means of returning to a safe starting point in conditions of low visibility, water currents or where pilotage is difficult...
  
  s to guide the diver to the exit
• using breathing gas
  Breathing gas
  Breathing gas is a mixture of gaseous chemical elements and compounds used for respiration.Air is the most common and only natural breathing gas...
  
  es other than air. Nitrox is used for shallow diving and trimix for deeper dives.

External links

• GUE - Global Underwater Explorers (http://www.gue.com/)
• IANTD - International Association of Nitrox and Technical Divers (http://www.iantd.com/)
• NACD - National Association for Cave Diving (http://www.safecavediving.com/)
• NSS-CDS - National Speleological Society Cave Diving Section (http://www.nsscds.com/)
• WKPP Woodville Karst Plain Project (http://www.wkpp.org)