Dive
A dive ( TG for short ) is a planned stay under water that is usually carried out with technical aids. It can have different goals and reasons: For recreational divers , the focus is on fun or diving training . Apnea divers are looking for a sporty challenge. Professional and research divers do work underwater.
The Professional Association of Diving Instructors (PADI) defines the minimum requirements for a dive that the diver descends at least 5 meters deep for at least 20 minutes or breathes at least 1400 normal liters of breathing gas below the surface of the water. A recreational divers dive typically lasts between 20 minutes and 2 hours.
preparation
information gathering
As a rule, all dives have a largely uniform preparation in common. First, information about the dive site is collected:
- Entry / exit
- Diving boat
- maximum depth
- Underwater topography
- flow
- Visibility
- temperature
- Dangers under water
- Weather
- Arrival and departure routes
- necessary permits
- Participants in the dive
- next filling stations
- next decompression chamber
- Emergency services
planning
Then the dive is planned. The level of detail depends heavily on the destination of the dive, the experience of the divers and the prevailing conditions. The following points are usually determined:
- equipment needed
- Planning the course of the dive (dive profile)
- Calculation of the composition of the breathing gases ( air , nitrox , trimix and others.)
- Calculation of the required decompression levels ( decompression stops) and safety stops , taking into account the diving tables
- Calculation of the breathing gas requirement
- Determine and organize the necessary safety measures (e.g. oxygen suitcase, lines, safety divers , orientation aids, reserve air supplies ...)
- Emergency scenario plan
At the dive site
When you arrive at the dive site, you can distinguish between three phases: Before and after the dive and the dive itself.
Before the dive
- Inspection of the water and the entry and exit points.
- Unpack and assemble the equipment
- Briefing , a brief discussion of the dive with everyone involved.
- Putting on equipment
- Checking the equipment , the completeness and the condition of the equipment.
- Checking the cylinder pressures.
Dive
The dive itself begins after entering and leaving the water surface. It is divided into three phases:
- Compression (diving)
- Isocompression
- Decompression (surfacing)
Together, these three phases are also referred to as TUP (Time Under Pressure). The compression and isocompression phases together make up the bottom time .
compression
As a rule, in shallow water (~ 3 m), your own equipment and that of your buddy are checked for faults. It is also important that every diver can equalize the pressure in his airways. If this is not possible and you continue to dive, barotrauma can result. Once at the agreed depth, each diver establishes neutral buoyancy or initiates the decompression phase again, as is sometimes the case with apnea diving.
Isocompression
The diving depth is kept more or less the same. Now the destination of the dive is controlled and viewed, the exercises in the training dive are carried out or the planned underwater work is done. Due to the increased ambient pressure, a diver saturates parts of the breathing gas mixture in his tissue during the isocompression phase. Usually too high a concentration of dissolved nitrogen is reached first. This can lead to a deep intoxication that can result in unconsciousness. Depending on the breathing gas mixture, oxygen or helium poisoning can occur. In order to avoid diving accidents, the diver usually uses a dive computer to check during the isocompression phase that he does not exceed any of the permissible limit values. These limits may have been determined by the previous dive calculation or, in the case of simpler dives, result from the remaining no-stop time and the remaining breathing gas supply.
decompression
This is followed by the decompression phase. A continuous, slow ascent (recommended max. Ascent speed: 10 m / min) and observing waiting times at a certain depth should exhale the respiratory gas components dissolved in the body. The necessary safety and deco stops are either specified by the dive computer or have been calculated beforehand using a diving table. If the max. Ascent rate or failure to comply with the decompression stop threatens the formation of gas bubbles in the body. This can cause decompression sickness , which is often fatal. Incorrect behavior (e.g. stopping breathing for a long time) also creates the risk of barotrauma in various parts of the body during the decompression phase.
If a diver has to surface unplanned because of an emergency, he can carry out an emergency ascent in disregard of the limits. The emergency ascent involves great risks, depending on the diving depth.
After the dive
After leaving the water, the equipment and especially the team are checked for completeness and damage. In addition to storing and storing the equipment, a debriefing is usually held, during which the dive is discussed and evaluated, and the log is kept and often mutually confirmed.
Up to 72 hours after the dive, symptoms resulting from exceeding a limit or a diving accident may occur. Therefore, even if there are no symptoms, a doctor should be consulted immediately after an accident or exceeding a limit .
Repetitive dives
A dive in the broader sense also includes the reduction of the residual desaturation of the tissue with respiratory gas on or above the water surface. If several dives are planned within the time required to reduce the desaturation, one speaks of repetitive dives . Sufficiently long surface breaks must be planned between these dives so that the dissolved gases in the body can be broken down. If the surface interval is too short, this will greatly reduce the maximum permissible limits for the repetitive dive. Dive tables or dive computers usually take these surface intervals into account.
Changes in altitude
After a dive, divers should not ascend higher than 400 m above the water level of the diving water, otherwise there is a risk of developing decompression sickness for up to 24 hours after the dive. This is particularly important if the return journey from the dive site leads over hills or passes or if a trip by plane is planned. The term DNF time (English for: do not fly ) is often used in this context .
See also
Web links
Individual evidence
- ↑ PADI (Ed.): Instuctor Manual . German. 02/15 edition. Rancho Santa Margarita 2015, p. 28-29 .
- ↑ Divers FAQ. How long is a dive? dive.steha.ch, accessed on April 17, 2020 : "Basically, one can say that dives by recreational divers usually last between around 20 minutes and 2 hours."
- ↑ a b c d Andreas Nowotny: Selection of the diving water / diving area. In: www.tauchtheorie.nowotaucher.de. Andreas Nowotny, Augsburg, archived from the original on December 7, 2013 ; accessed on January 31, 2018 .
- ↑ a b c d e f Thomas Kromp , Hans J. Roggenbach , Peter Bredebusch : Practice of diving . 3. Edition. Delius Klasing Verlag, Bielefeld 2008, ISBN 978-3-7688-1816-2 , p. 252-284 .
- ↑ a b c Andreas Nowotny: Planning + calculating the diving profile. In: www.tauchtheorie.nowotaucher.de. Andreas Nowotny, Augsburg, archived from the original on December 7, 2013 ; accessed on January 31, 2018 .
- ↑ a b c Organization of the dive. In: www.tauchtheorie.nowotaucher.de. Andreas Nowotny, Augsburg, archived from the original on December 7, 2013 ; accessed on January 31, 2018 .
- ^ Drew Richardson: Divemaster Manual - German Version. PADI Europa AG, Hettlingen December 2007, edition 09/07, p. 120.