Ascending and descending (diving)
Encyclopedia
In diving
, ascending and descending is done using strict protocols to avoid problems caused by the changes in ambient pressure
and the hazards of obstacles near the surface or collision with vessels. Diver training organizations place importance on these protocols early in their diver training
programmes.
When above the surface, the BCD is inflated and a signal is made, if a safety boat is waiting.
), allows a diver to perform an ascent in a controlled manner, breathing as normal.
When no redundant air supply is available, the diver carries out a controlled emergency swimming ascent. The diver starts to swim up exhaling
steadily and continuously along the entire ascent. The mouthpiece is kept in as the cylinder still contains some air and it may become available as the ambient pressure
decreases. It is important to exhale continuously, to avoid over-expansion of the air in the lungs (as the water pressure decreases while swimming up), which could cause the lungs to burst. The speed of ascent has to be a compromise between too slow (and running out of air before reaching the surface) and too fast (risking a burst lung).
Scuba diving
Scuba diving is a form of underwater diving in which a diver uses a scuba set to breathe underwater....
, ascending and descending is done using strict protocols to avoid problems caused by the changes in ambient pressure
Ambient pressure
The ambient pressure on an object is the pressure of the surrounding medium, such as a gas or liquid, which comes into contact with the object....
and the hazards of obstacles near the surface or collision with vessels. Diver training organizations place importance on these protocols early in their diver training
Diver training
Diver training is the process of developing skills and building experience in the use of diving equipment and techniques so that the diver is able to dive safely and have fun....
programmes.
Controlled ascent
When not ascending along a shot line or anchor line, the following steps should be taken when ascending in open water:- Before commencing the ascent manoeuvre, the signal buoy is released and inflated to notify any vessel in the vicinity of the ascent.
- The accompanying diver (buddy) is given the ascension signal (thumb up)
- The buoyancy compensator device (BCD) is set to neutral, inflater hose is pointed upwards and both divers slowly begin to swim up. The BCD is slowly filled with air using the inflater hose. Care is taken not to fill the BCD too rapidly, as the air will expand because of the reduced water pressure, increasing the buoyancyBuoyancyIn physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...
of the BCD. The divers keep looking up to avoid any obstacles. - Using the inflater hose to release air, the ascension speed is kept below 10 meters per minute. An ascent meter or dive computerDive computerA dive computer or decompression meter is a device used by a scuba diver to measure the time and depth of a dive so that a safe ascent profile can be calculated and displayed so that the diver can avoid decompression sickness.- Purpose :...
may be used to help judge this speed. - A safety stop of 1–3 minutes is made at 3–6 meters from the water surface.
- After the stop, the last part of the ascension is done very slowly (at no more than 5 meters per minute). The divers keep looking around and listen closely for any possible vessels.
When above the surface, the BCD is inflated and a signal is made, if a safety boat is waiting.
Controlled descent
When not descending along a shot line or anchor line, the following steps are performed:- The divers swim towards the point of descent and meet up with the companion diver ("buddy"). The OK-signal is given.
- The snorkel is removed and the second stage of the regulator is placed in the mouth (if not already done).
- The divers orient themselves towards the diving target, keeping their buddy in view.
- The divers give the signal to descend (thumb down).
- The inflater hose is held out of the water and the deflation button pressed. The BCD deflates, which will start the sinking process.
- Every few metres, the divers will "clear their ears"Ear clearingEar clearing or clearing the ears is any of various maneuvers to equalize the pressure in the middle ear with the outside pressure, by letting air enter along the Eustachian tubes, as this does not always happen automatically when the pressure in the middle ear is lower than the outside pressure...
to equalise pressure in the middle ear. - At a pre-arranged point in the descent, the divers halt and check their buddy's equipment for any air leaks. After this "bubble check", the descent is continued.
Emergency ascent
In emergencies when a person runs out of air and when there is no buddy around to donate air, the use of a redundant air supply (such as independent twins or a pony bottlePony bottle
A pony bottle is a small independently filled diving cylinder, often of only a few litres capacity, which forms an extended scuba set and which is fitted with its own independent regulator. In an emergency, such as exhaustion of the diver's main air supply, it can be used as an alternate air...
), allows a diver to perform an ascent in a controlled manner, breathing as normal.
When no redundant air supply is available, the diver carries out a controlled emergency swimming ascent. The diver starts to swim up exhaling
Exhalation
Exhalation is the movement of air out of the bronchial tubes, through the airways, to the external environment during breathing....
steadily and continuously along the entire ascent. The mouthpiece is kept in as the cylinder still contains some air and it may become available as the ambient pressure
Ambient pressure
The ambient pressure on an object is the pressure of the surrounding medium, such as a gas or liquid, which comes into contact with the object....
decreases. It is important to exhale continuously, to avoid over-expansion of the air in the lungs (as the water pressure decreases while swimming up), which could cause the lungs to burst. The speed of ascent has to be a compromise between too slow (and running out of air before reaching the surface) and too fast (risking a burst lung).