Scuba skills are skills required to dive safely using self-contained underwater breathing apparatus (scuba set). Most of these skills are relevant to both open-circuit scuba and rebreather scuba, and many are also relevant to surface-supplied diving. Certain scuba skills, which are critical to divers' safety, may require more practice than is provided during standard recreational training.
Some skills are generally accepted by recreational diver certification agencies as necessary for any scuba diver to be considered competent to dive without direct supervision. Others are more advanced, although some diver certification and accreditation organizations may consider some of these to also be essential for minimum acceptable entry-level competence. Divers are instructed and assessed on these skills during basic and advanced training, and are expected to remain competent at their level of certification, either by practice or refresher courses.
The skills include selection, functional testing, preparation and transport of scuba equipment, dive planning, preparation for a dive, kitting up for the dive, water entry, descent, breathing underwater, monitoring the dive profile (depth, time, and decompression status), personal breathing gas management, situational awareness, communicating with the dive team, buoyancy and trim control, mobility in the water, ascent, emergency and rescue procedures, exit from the water, removal of equipment after the dive, cleaning and preparation of equipment for storage and recording the dive, within the scope of the diver's certification.
Some scuba skills are only relevant to specific environments, activities, or equipment.
A certified scuba diver is expected to be able to assess what type of diving exposure suit is suitable for the planned dive, to check that it is in safe and usable condition, to check that it is the right size, and to dress correctly in it.
Entry-level skills usually cover wet suits, but in countries where the water and/or weather conditions are cold, dry suit skills may be considered to be entry-level skills. Using a dry suit safely during dives requires specific skills, including equalizing, buoyancy control, inversion recovery, emergency venting, and blowup recovery. Recreational divers trained in warm tropical waters may not acquire diving suit skills.
The set is usually stored and transported as separate major components: harness, cylinder(s) and regulator(s), buoyancy compensator, and assembled for each use. Correct assembly and function is critical to the dive, and in some cases to the survival of the user. All certification agencies require the diver to be competent to assemble their own set.
Scuba assembly generally entails mounting the cylinder(s) on the harness, connecting the regulator(s) to the cylinder valves, ensuring an uncontaminated and pressure-tight seal, and connecting the low pressure hose to the buoyancy compensator inflation valve. Validating the function of the regulator and inflation valve is part of scuba assembly, and reviewed as part of pre-dive checks. Given a significant interval between assembly and use, the check is commonly done twice.
Pre-dive checks include equipment inspection and testing and review of the dive plan with the dive team.
The final checks that all the equipment has been fitted correctly and is functioning without apparent flaw is the last opportunity before entering the water to avoid and correct problems which could make it necessary to abort the dive, including some which could be potentially fatal.
Recreational divers are personally responsible for the function of their equipment, and when diving as buddies with other divers, they are expected to ensure that they are at least familiar with any part of the buddy's equipment that they might need to operate in an emergency.
Some parts of the pre-dive checks are done as part of the process of kitting up on a boat. Equipment checks may be done as the equipment is fitted, or after it is fitted, and a routine for the order of fitting and checking can help avoid missing critical checks, though a written checklist is more reliable. The risk of missing a check is increased if the fitting procedure is interrupted, and it is considered good practice not to distract a diver unnecessarily during this process. The value of a written checklist increases with the complexity of the equipment used, and if there are distractions.
For a shore entry, kitting up may be broken up into stages, with the suit, scuba set and weights fitted at a convenient place, and the mask and fins just before entering the water. In this case some of the equipment may be checked twice. Once when it is fitted, and once just before committing to the water. If a long surface swim is necessary, the scuba set function and pressure may be checked again just before descent.
Responsibility for pre-dive checks for professional divers is more complex, based on the duty of care, and is usually defined in their organisational operations manual, which may stipulate recorded checklists for the equipment in use and the participation of other diving team members.
Getting into and out of the water with scuba gear in a range of circumstances appropriate to the certification is a necessary skill for all divers. Divers with disabilities or otherwise physically unable to make a safe entry or exit are expected to identify the conditions for which they need help, and to arrange for assistance, or to refrain from diving in those conditions.
The default condition for water entry is with positive buoyancy, but there are situations where a negatively buoyant entry is appropriate, for example given a strong surface current. Negative buoyancy is generally considered a higher risk procedure. It requires the buoyancy compensator and dry suit to be deflated, before entry, more precise control of weighting, confidence in the ability to equalise during rapid descent, and the ability to control descent rate and achieve neutral buoyancy without delay. An acceptably safe negative entry requires pre-dive checks on regulator and BC inflation function, and a sufficiently accurate balance of BC and/or suit inflation to ballast weight excess. This becomes more complex when large amounts of breathing gas are carried, as the weighting must allow neutral buoyancy at the shallowest decompression stop when the gas is expended, and the diver is therefore relatively more heavily weighted at the start of the dive.
Common entry and exit points include:
Standard water entries that are generally taught to entry level divers may include:
This section needs expansion with: describe surf, beach, and rocky shore entries. You can help by adding to it. (July 2021)
Standard exit procedures may include:
This section needs expansion with: describe exit techniques. You can help by adding to it. (July 2021)
Breathing from a demand valve must be done correctly to make effective use of a limited air supply, and to avoid drowning. Most recreational scuba diving is done with a half mask, so the demand valve is held in the mouth, gripped by the teeth, and sealed by the lips. Over a long dive this can induce jaw fatigue, and for some people, a gag reflex. Various mouthpiece styles are available off the shelf or as customised items, and one of them may work better if either of these problems occurs. Air is inhaled and exhaled through the mouth, and the diver must be able to seal off the nasal passages from the pharynx so that breathing remains possible with a flooded or dislodged mask. Under most circumstances scuba breathing differs little from surface breathing. A full-face mask may allow the diver to breathe through the nose or mouth as preferred.
The demand valve adds a little respiratory dead space to the airway, and the work of breathing is greater due to hydrostatic pressure differences between the depth of the demand valve and the lungs, and due to cracking pressure and flow resistance in the demand valve. These factors make a slow and deep breathing cycle more energy efficient and more effective at carbon dioxide elimination. Part of the skill is learning to relax under water, part is to minimize effort by learning good buoyancy, trim, maneuvering and propulsion skills and part is to breathe more slowly and deeply. Breathing too slowly or too shallow does not ventilate the lungs sufficiently and risks hypercapnia (carbon dioxide buildup). Breathing effort increases with depth, as density and friction increase in proportion to the increase in pressure, with the limiting case where all the diver's available energy may be expended on the task, leaving none for other purposes. This may cause carbon dioxide buildup. If this cycle is not broken, panic and drowning may follow. The use of a low density inert gas, typically helium, in the breathing mixture can reduce this problem (as well as diluting the narcotic effects of the other gases).
Scuba divers are typically taught to not to hold their breath underwater, as in some circumstances this can result in lung overpressure injury. This is a risk only during ascent, as that is when air expands in the lungs. During ascent the airways must remain open. Holding the breath at constant depth for short periods with a normal lung volume is generally harmless, providing there is sufficient ventilation on average to prevent carbon dioxide buildup, and is a standard practice by underwater photographers to avoid startling their subjects. Breath holding during descent can eventually cause lung squeeze, and may allow the diver to miss warning signs of a breathing gas supply malfunction until it is too late to correct.
Skilled open circuit divers make small adjustments to buoyancy by adjusting their average lung volume during the breathing cycle. This adjustment is generally in the order of a kilogram (corresponding to a litre of gas), and can be maintained for a moderate period, although it is more comfortable to adjust the volume of the buoyancy compensator over longer periods.
The practice of shallow breathing or skip breathing should be avoided as it may cause carbon dioxide buildup, which can result in headaches and a reduced capacity to recover from a breathing gas supply emergency. It is not an efficient method to conserve breathing gas.
Divers may remove their demand valves from their mouths under water for several reasons, both intentionally and unintentionally. In all cases, the casing may fill with water that must be removed before the diver can breathe again. This is known as clearing or purging the demand valve. The two clearing techniques are:
Divers may become nauseous and vomit underwater. Vomit left inside the DV must be cleared before breathing can resume. In this case it is usual to remove the DV from the mouth, flood it to rinse, and clear using the purge button. The process may be repeated as necessary. If the DV breathes wet after purging, something may be stuck in the exhaust valve. Flooding the DV and clearing again with the mouthpiece blocked usually clears the exhaust valve.
If the DV is dislodged from the diver's mouth unintentionally, it may end up in a place out of view of the diver. Three or more methods aid recovery:
If the diver has difficulty locating the demand valve by these methods, the octopus DV or bailout set can be used in the interim. Occasionally the DV gets snagged in such a way that it cannot be easily recovered. In some cases it may be prudent to abort the dive and surface, but this may not be practicable and it may be necessary to remove the harness partially or completely to recover the primary, after which the harness can be readjusted. A dive buddy can usually find the DV easily. If the DV cannot be reached it is prudent to terminate the dive, as a free-flow could empty the cylinder in minutes.
Water commonly leaks into the mask, which can interfere with clear vision, and the diver needs to flush the water. Reasons for leakage include poor fit, leaking through hair, facial muscle movement that causes temporary leaks, or impact of external objects against the mask. Most diving masks can fog up due to condensation on the inside of the faceplate. This is avoided by applying an anti-fog surfactant to the inner surface before the dive. Otherwise, the diver can deliberately flood it slightly to rinse off the droplets, and then clear the mask.
A half mask is not directly connected to the air supply. The only available source of air to displace the water is the diver's nose. The procedure involves exhaling through the nose into the mask until the water has been displaced by air. During this process, the air must be prevented from escaping at a high point, or the water will not be expelled. If the mask does not fit in such a way that the top of the skirt remains sealed, the diver must press the upper part against the face.
Several types of full-face mask exist, and the procedure for clearing them depends on the construction. In models that use an internal mouthpiece, the procedure is the same as with a half mask. Others automatically drain through the exhaust port of the demand valve provided the water can get to it. Models that use an oral/nasal internal seal usually drain to the demand valve or an additional drain valve at a low point when the diver's face is roughly upright or face down, and these clear during normal breathing for small leaks, and may be cleared of major flooding by using the DV's purge button to fill the mask with air.
The diver needs to be able to establish three states of buoyancy at different stages of a dive, using weights and a buoyancy compensator to control buoyancy. In the water the diver adjusts the BC's volume to increase or decrease buoyancy, in response to various effects that alter the diver's overall density.
To achieve negative buoyancy, divers must carry supplemental weight to counteract the buoyancy of the diver and buoyant equipment.
Neutral buoyancy matches the average density of the diver and equipment to that of the water. This is achieved by adding gas to the BC when the diver is too heavy, or venting from the BC when the diver is too buoyant. Any uncompensated change in depth from a position of neutrality accelerates the change, making buoyancy control a continuous procedure--the diving equivalent of balance, in a positive feedback environment.
It is always necessary to vent gas during ascent to maintain a moderate level of positive buoyancy and control the ascent. Similarly, during a descent, gas must be added to prevent a runaway descent.
Buoyancy control compensates for changes of volume of the diving suit and changes of mass due to using up the breathing gas.
Diver trim is the orientation and posture of the body, determined by the distribution of weight and buoyancy along the body as well as by the other forces acting on the diver. The stability and static trim of a scuba diver are important both at the surface and under water. Trim must be maintained under water at neutral buoyancy, while surface trim must be held at positive buoyancy.
When the BC is inflated at the surface to provide positive buoyancy, the centre of buoyancy and centre of gravity of the diver are generally different. The vertical and horizontal separation of these centroids determines the static trim. The diver can usually overcome the trimming moment of buoyancy, which requires directed effort. The diver can adjust trim to suit circumstances such as swimming face down or face up, or remaining vertical. The diver's centre of gravity is determined by the distribution of weight, and buoyancy is determined by the equipment in use, particularly supplemental weights and the buoyancy compensator, which can significantly influence centre of buoyancy as it is inflated and deflated. Stable trim implies that the centre of buoyancy is directly above the centre of gravity. Any horizontal offset generates a moment that rotates the diver until the equilibrium condition is restored.
In almost all cases, the centre of buoyancy with an inflated BC is nearer the head than the centre of gravity, and BCs are designed to provide this as the default condition, as an inverted diver floating at the surface is at risk of drowning. The offset in the forward/backward axis is quite frequently significant, and is usually the dominant factor in determining static trim. At the surface, it is generally undesirable to be trimmed strongly face down, but it is useful to be able to trim face down at will. Vertical trim is acceptable providing it can be overcome for swimming.
Underwater trim is the diver's attitude (orientation) in the water, in terms of balance and alignment with the direction of motion. The free-swimming diver may need to trim erect or inverted at times, but in general, a horizontal trim has advantages both for reduction of drag when swimming horizontally, and for observing the bottom. A slightly head down horizontal trim allows the diver to direct propulsive thrust from the fins directly to the rear, which minimizes disturbance of sediments on the bottom, and reduces the risk of striking delicate benthic organisms with the fins. A stable horizontal trim requires that diver's centre of gravity is directly below the centre of buoyancy (the centroid). Small errors can be compensated fairly easily, but large offsets may make it necessary for the diver to constantly exert significant effort towards maintaining the desired attitude. The position of the centre of buoyancy is largely beyond the control of the diver, though the cylinder(s) may be shifted in the harness by a small amount, and the volume of the BC has a large influence when inflated. Most of the control of trim available to the diver is in the positioning of ballast weights. Fine tuning of trim can be done by placing smaller weights along the length of the diver to bring the centre of gravity to the desired position.
The scuba diver usually usually uses legs and fins to move in the water, occasionally walking on the bottom as required by circumstances. Hands are occasionally used to grasp solid objects to remain in a position in a current, but are generally not used for propulsion and maneuvering by a competent diver, as they are often needed for other purposes while finning. Techniques for effective propulsion using fins include:
Ascent and descent are the phases of a dive where ambient pressure is changing, and this comes with hazards. Direct hazards include barotrauma, while indirect hazards include buoyancy instability and physiological effects of gas solubility changes, mainly the risk of bubble formation by supersaturated inert gas in body tissues, known as decompression sickness. The skill of equalization is essential to avoid injury during both activities.
Barotrauma of descent is caused by pressure differences between the increasing ambient pressure and the internal pressure of gas filled spaces of the diver's body and equipment. More complex, but also more straightforward in practice, is buoyancy control and descent rate. The diver must control descent rate by adjusting the buoyancy compensator and, if worn, the dry suit. The diver must be able to limit descent rate to match the ability to equalise, particularly the ears and sinuses, and must be able to stop the descent quickly without going into an uncontrolled ascent. In most cases the bottom provides a physical limit to descent, but this is not always the case, as in a wall dive or blue-water diving. A skilled diver can stop at the desired depth or distance above the bottom, adjust to neutral buoyancy, trim level, and be ready to proceed with the dive.
Barotrauma of ascent is caused by the same pressure differences, but during ascent. The two organs most susceptible to barotraumas of ascent are the sinuses and lungs, although both normally equalise automatically during ascent. Problems may arise in the middle ear if the Eustachian tubes become blocked during the dive, and the lungs can be injured if the diver forcibly holds their breath during ascent, which can occur during an emergency free ascent. As lung over-expansion is potentially life-threatening, entry level diver training emphasises developing the practice of not holding breath while diving on scuba, and slow continuous exhalation during emergency ascents. Techniques for clearing blocked Eustachian tubes during ascent are also taught at entry level.
Uncontrolled ascent can increase risk of decompression sickness and lung over-expansion injury even when diving within the no-stop limits of the decompression tables. The skills of controlling buoyancy during ascent are included in all entry level training, but the criteria for competence vary among the certification agencies. Most agencies require the diver to be able to limit ascent rate and to be able to achieve neutral buoyancy at a specified depth during an ascent without significantly overshooting the target depth, while using only a depth gauge or dive computer as a reference to depth and ascent rate, but this is a skill that usually requires more practice than is provided in recreational entry level training. The skills involve venting the buoyancy compensator and dry suit at a rate that provides neutral or slight negative buoyancy at all stages of the ascent, or a slightly positive buoyancy to assist ascent at the desired rate, and neutral buoyancy when a stop is required.
Most dry suits are fitted with an automatic dump valve, which can be adjusted to provide an approximately constant volume of gas in the suit, so the diver can concentrate on controlling ascent rate via the buoyancy compensator. These skills become critical when decompression stops are required, and even divers with excellent buoyancy control make use of aids to reduce risk. Shot lines are used at all levels of diving, and are in common use during entry level training, as a visual aid to ascent rate and depth control, and as a fall-back physical aid. The skills of deploying and using surface marker buoys and decompression buoys are generally considered advanced skills for recreational divers, but may be considered entry level skills for professional divers.
During ascent and descent, gas spaces in the diver and diving equipment experience pressure changes that cause the gas to expand or compress where possible, possibly damaging those pressurised spaces. Some spaces, such as the mask, release excess gas when the pressure breaks the seal to the face, but have to be equalised during compression to avert mask squeeze. Others, such as the buoyancy compensator bladder, expand until the over-pressure valve opens. The ears usually vent naturally through the Eustachian tubes, unless they are blocked. During descent they do not typically equalise automatically, and the diver must equalise deliberately.
Divers need to communicate underwater to co-ordinate their dive, to warn of hazards, to indicate items of interest and to signal distress.
Most professional diving equipment such as full-face diving masks and diving helmets include voice communication equipment, while recreational divers generally rely on hand signals and occasionally on light signals, touch signals and text written on a slate Through-water voice communications equipment is available for recreational diving, but requires full-face masks.
Rope signals can be used by a diver who is connected to another diver or tender by a rope or umbilical. A few codes using "pulls" and "bells" (a pair of short tugs) are partly standardised. These are mostly used as backup signals by professional divers should voice communications fail, but can be useful to recreational and particularly technical divers, who can use them on their surface marker buoy lines to signal to the surface support crew.
Hand signals are generally used when visibility allows. These signals are often also used by professional divers. A set of instructional hand signals is used during training. Recreational divers are expected to be familiar with the hand signals used by their certification agency. These have to a large extent been standardised internationally and are taught on entry level diving courses. A few additional hand signals are commonly used by technical divers.
Light signals are made using a dive light in dark places with reasonable visibility, although few have been standardised. A light can also be used to illuminate hand signals. There are also a few touch signals used by penetration divers in situations of extremely low visibility.
The diver has a limited ability to survive without breathing gas. Any interruption constitutes a life-threatening emergency. The diver must be prepared to cope with any reasonably foreseeable loss. Temporary interruptions due to flooding or dislodging the demand valve are addressed by recovery and clearing of the demand valve. More extensive interruptions require other skills. Ending the dive with an emergency ascent is appropriate in some circumstances. Other solutions involve accessing an alternative gas supply, either from an alternative source carried by the diver, or from another diver.
Emergency air sharing may involve sharing a single demand valve, or one diver providing a secondary air source to another. The gas may be from the same scuba set or from a separate cylinder. The preferred technique of air sharing is donation of a demand valve that is not needed by the donor.
The standard approach is "octopus donation" in which the buddy offers the secondary "octopus" demand valve to the diver in trouble, although this is not universal. A variation on this approach is for the buddy to offer their primary demand valve to the diver in trouble, while switching to the octopus. The reasoning is that this is more likely to calm a diver in trouble, and the gas will be appropriate for the depth.
Alternatively, two divers can share a single demand valve. This is known as buddy breathing. Buddy breathing is no longer taught as widely, although some groups still teach it. The standard buddy breathing technique is for the divers to alternately breathe from the demand valve, each taking two breaths, although since the receiver is likely to initially be out of breath, he/she may need a few more breaths to stabilise.
Once air sharing has been established, the dive terminates, unless the underlying problem can be resolved. Assisted ascents using a secondary demand valve are simpler than buddy breathing ascents, and this skill is quicker to learn.
An emergency ascent happens when no procedure allows a dive to continue safely.
Emergency ascents are independent ascents, where a single diver manages the ascent alone or is assisted by another diver, who provides gas, propulsion, buoyancy, or other assistance.
In an emergency ascent the diver initiates the ascent intentionally, and chooses the procedure. Ascents that are involuntary or unintentionally uncontrolled are classed as accidents.
Other forms of ascent which may be considered emergency ascents are:
Emergency ascent training policy differs considerably among the certification agencies, and has generated controversy regarding risk-benefit. Some agencies consider it irresponsible to fail to teach a skill which could allow a diver to safely manage a foreseeable emergency, others claim the probability of ever needing the skill to be low enough to disregard, and the risk of injury during training to be higher. Accident statistics are inconclusive.
It may be necessary for the diver to establish positive buoyancy if the buoyancy compensator fails. The following methods are available:
Given a continuous gas leak into the buoyancy compensator, the diver can continuously dump excess gas while disconnecting the low pressure supply hose. If upright or trimmed even slightly heads-up, this usually allows gas to exit faster than it enters. The ability to disconnect the inflation hose under pressure is an important safety skill, as an uncontrolled buoyant ascent puts the diver at risk of lung overpressure injury, and depending on decompression obligation, at severe risk of decompression sickness. Once disconnected, the diver can neutralise buoyancy by oral inflation or further deflation. If using a full-face mask, the hose can be temporarily reconnected to add gas when needed.
A dry suit leak can range from a trickle to a flood. Two aspects to a catastrophic flood put the diver at risk.
Damage to the lower part of the suit can admit cold water for winter users, or contaminated water or chemicals for hazmat divers. This may not materially affect buoyancy, and the risk is mainly hypothermia or contamination. A normal ascent is typically feasible, but exiting the water may be difficult due to the weight of trapped water.
Damage to the upper part of the suit can cause a sudden gas venting, destroying buoyancy and triggering uncontrolled descent and flooding. The buoyancy loss may exceed the buoyancy compensator's capacity. The simplest case is to drop sufficient weight to allow the buoyancy compensator to function. This requires sufficient detachable weight. Some divers do not prepare for this contingency in their weight distribution, and such planning is not covered by all training standards. Retaining more gas may compromise mobility.
A flooded suit may hold so much water that the diver cannot exit the water because of the weight and inertia. It may be necessary to cut a small slit in the lower part of each flooded leg to drain the water.
The possible consequences of a dry suit blowup are similar to a BCD blowup, and the method of management fairly similar. The instinctive reaction of trying to swim downwards is usually counterproductive, as it will prevent the automatic dump valve from releasing excess gas, while at the same time inflating the suit legs, making it difficult to fin, and if the boots slip off, impossible to fin. The diver must ensure that the dump valve is fully open, at the high point of the suit, and urgently disconnect the inflation hose. Many suits will release air at the neck or cuff seal if those are the highest point of the suit. It may be necessary to descend after this to compensate for rapid ascent, and to do this it may be necessary to dump gas from the BCD. After achieving neutral buoyancy, a normal ascent is usually possible, as it is seldom necessary to add air to the suit during ascent. The type of inflation hose connection can make a large difference to the urgency of the situation. The CEJN connector allows a much faster gas flow than the Seatec quick-disconnect fitting, and the Seatec is considered safer by the DIR community for this reason.
One of the standardised configurations used with manifolded twins was developed by the Doing It Right movement for cave exploration. The procedures are in general use by a many technical divers. The diver normally breathes from the right side primary second-stage regulator, mounted on a long hose which is tucked under at the waist and looped behind the head for quick deployment. A secondary second-stage regulator is carried just beneath the chin, suspended by a breakaway elastic loop around the neck, and supplied from the left side first stage cylinder by a shorter hose. The cylinder valves and manifold isolation valve are normally open:
Whenever a dive may require decompression stops, it is necessary to monitor dive depth and duration to ensure that appropriate decompression procedures are followed if necessary. This process may be automated via a dive computer, in which case the diver must understand how to read the output and respond correctly to the information displayed, and for more complex dive plans, to input the appropriate settings. The display and operation of dive computers is not standardised, so the user must learn to operate the specific model of computer. Accurate monitoring of depth and time is particularly important when diving using a schedule requiring decompression according to decompression tables, when a diving watch and depth gauge are used.
Management of breathing gas is a critical skill to avoid potentially fatal consequences. For the basic case of no-decompression open-water diving, which allows a free emergency ascent, this requires ensuring sufficient air remains for a safe ascent (plus a contingency reserve) and for the possibility of an assisted ascent, where the diver shares air with another diver. Gas management becomes more complex when solo diving, decompression diving, penetration diving, or diving with more than one gas mixture.
A submersible pressure gauge is used to indicate the remaining gas pressure in each diving cylinder. The amount of available gas remaining can be calculated from the pressure, the cylinder internal volume, and the planned reserve allowance. The time that he diver can dive on the available gas depends on the depth, gas mixture, work load, and the fitness of the diver. Breathing rates can vary considerably, and estimates are largely derived from experience. Conservative estimates are generally used for planning purposes. The diver must turn the dive and start the exit and ascent while there is enough gas to surface safely.
The two basic aspects of navigation are surface navigation to find the dive site, and underwater navigation, to find specific places underwater and to reach the fascent point.
Underwater navigation includes observing natural features, operating a compass, estimating distance travelled, and distance lines, used to navigate underwater. Basic navigation is normally taught as part of entry level certification. Advanced underwater navigation is usually part of advanced recreational diver training.
These are generally considered advanced techniques for recreational divers, but basic skills for professional divers.
Diver rescue is the process of avoiding or reducing further exposure to diving hazards and bringing a compromised diver to safety, such as a boat or shore, where first aid can be administered and additional medical treatment is available. Rescue skills are considered by some agencies to be beyond the scope of entry level divers, while others consider them entry level diving skills required as part of the professional skill set for a stand-by diver.
More than one technique may be taught for some of these skills.
Special applications require additional skills. In many cases such skills can be shared across applications, with only a few specific to that application. Many underwater work and activity skills are not directly related to the use of scuba equipment.
Scuba skills training is primarily provided by practical instruction directed by a registered or certified diving instructor. Additional practice and skills maintenance are the diver's responsibility. Recreational divers may attend refresher courses, which may involve revisions to earlier practices. Service providers such as dive shops and charter boats may require a checkout dive for divers unfamiliar with the region, or who haven't dived for some time. The checkout dive allows the diver to demonstrate basic skills relevant to the expected conditions.
It is the individual diver's responsibility to maintain sufficient skill and fitness to dive safely and not endanger themselves or others, and to judge whether they are ready to handle the anticipated conditions.
Many recreational diver training organizations offer diver training. Successful completion is shown by the issuance of a "diving certification", also known as a "C-card", or qualification card.
Recreational diver training courses range from minor specialties which require one classroom session and an open water dive, and which may be completed in a day, to complex specialties which may take days to weeks, and require classroom sessions, confined water skills training and practice, and an open-water dives, followed by assessment of knowledge and skills. Accurate schedules are generally only available from the specific school or instructor who presents that course, as this will depend on local conditions and other constraints.
The initial open water training for a person who is medically fit to dive and a reasonably competent swimmer is relatively short. Many dive shops in popular holiday locations offer courses intended to teach a novice to dive in a few days, which can be combined with diving on the vacation. Other instructors and dive schools provide longer and more thorough training.
Diving instructors affiliated to a diving certification agency may work independently, or through a university, a dive club, a dive school or a dive shop. They offer courses that satisfy the standards of a certification organization.
Technical diver training generally follows a similar pattern to recreational training, but provides more theoretical information, and in many cases, an exhaustive level of skill training, with higher standards for assessment, as the risks are higher and the necessary competence to manage reasonably foreseeable contingencies is more complex.
Professional diver training is typically provided by schools affiliated to or approved by one or more commercial, scientific or other professional diver certification or registration organisations  Professional diver training standards require significantly higher skill level than recreational certification. The professional diver is expected to manage most contingencies and still perform the planned work under difficult conditions. Professional training may include confidence training or stress training, where simulated emergencies are enacted, or unlikely contingencies are simulated, to develop the diver's confidence in their ability to safely manage contingencies. The amount of time spent on skill and confidence development is generally proportional to the length of the training programme, as basic skills are usually learned fairly quickly.
Although many scuba skills are safety critical, most are straightforward and are easily retained once learned given occasional practice.
This section needs expansion with: overlearning, muscle memory, ability to perform reliably under stress, refresher courses. You can help by adding to it. (May 2021)
Navigation by reference to terrain features, both natural and artificial, usually with the aid of an appropriate chart.