Scuba skills
Scuba skills are skills required to dive safely using self-contained underwater breathing apparatus, known as a scuba set. Most of these skills are relevant to both open-circuit scuba and rebreather scuba, and many also apply to surface-supplied diving. Some scuba skills, which are critical to divers' safety, may require more practice than standard recreational training provides to achieve reliable competence.
Some skills are generally accepted by recreational diver certification agencies as basic and necessary in order to dive without direct supervision. Others are more advanced, although some diver certification and accreditation organizations may require these to endorse entry-level competence. Instructors assess divers on these skills during basic and advanced training. Divers are expected to remain competent at their level of certification, either by practice or through refresher courses. Some certification organizations recommend refresher training if a diver has a lapse of more than six to twelve months without a dive.
Skill categories 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 and progress of the dive, 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.
Basic open circuit equipment
Preparing and dressing in the diving suit
A scuba diver should be able to assess what type of diving exposure suit is preferable for the planned dive, to confirm that it is in safe, usable condition and the right size, and to put it on correctly. Entry-level skills usually include the use of wet suits, but in countries where the water and/or weather conditions are cold, beginners may need dry suit training. Recreational divers trained in warm tropical waters may not initially need to learn any diving suit skills. Using a dry suit safely requires special skills, including buoyancy control, inversion recovery, emergency venting, and blowup recovery.Preparing the equipment
Divers are individually responsible for the function of their personal equipment. When diving as buddies with other divers, they are expected to familiarize themselves with the functional aspects of the buddy's equipment as well, to be able to operate it in an emergency.Scuba assembly
The set is usually stored and transported as separate major components: harness and buoyancy compensator, and, and assembled for each use. Correct assembly and function are critical for safety and in some cases for survival. All certification agencies require all autonomous divers to be competent to assemble and test functionality of their own sets.Scuba assembly generally entails mounting the on the harness, connecting the 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 essential to proper scuba assembly, and always reviewed during pre-dive checks. Because there may be a significant interval between assembly and use, this check is commonly repeated just before putting the set on, and may be repeated just before descent.
Pre-dive checks
Pre-dive checks include equipment inspection and function testing, and review of the dive plan with the team. Such checks can reveal problems that could make it necessary to abort the dive, including some which could potentially be fatal.Some pre-dive checks are done while donning the dive equipment. Establishing a routine for the order of donning and checking can help avoid skipping critical checks; a written checklist may be more reliable. The risk of skipping a check is increased if the process is disrupted, and it is good practice never to distract a diver unnecessarily during a check. The value of a written checklist increases with the complexity of the equipment used, and even more so 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 added when entering the water. In this case, some of the equipment may be checked both when it is donned and again just before committing to the water. If a long surface swim is necessary, the scuba set function and pressure should be checked again just before descent. A swim through heavy kelp can roll the cylinder valve closed or partially closed.
Responsibility for pre-dive checks for professional divers is more complex, based on the concept of the duty of care. It is usually defined in an organizational operations manual, which may stipulate recorded checklists for the equipment in use, and norms for the participation of other diving team members.
Entry and exit
Certification standards often require a diver to be able to get in and out of the water under a range of circumstances. Divers with disabilities or who are otherwise physically unable to make a safe entry or exit are expected to be able to identify the conditions under which they need help. Then they are either to arrange for assistance, or to refrain from diving in those conditions.Common entry and exit points include:
- Poolside.
- Small/large boat.
- Beach or rocky shoreline.
- Jetty or dockside.
- Into/out of deep water.
- Into/out of shallow water.
- Through a surf line.
Positive and negative entry
In negative entries the diver establishes negative buoyancy before entering the water, allowing immediate descent. 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 to prevent rapid uncontrolled descent, confidence in the ability to equalize the ears and sinuses during rapid descent, and the ability to control the descent rate and achieve neutral buoyancy without delay. This procedure requires all pre-dive checks to be done before entering the water, and the consequences of getting buoyancy settings wrong or neglecting a breathing gas setup check can be serious. Failing to connect inflator hoses, to zip up a dry suit, or to open the cylinder valve sufficiently can quickly lead to an emergency. Other problems can arise if the diver is too negatively buoyant and has trouble equalizing, or sinks so fast that the inflator valves cannot fill the dry suit or BCD fast enough to compensate for the compression of descent. In poor visibility, buddy pairs may lose contact right at the start of the dive.
An acceptably safe negative entry requires pre-dive checks on the regulator and BC inflation function, and a sufficiently accurate balance of BC and/or suit inflation to ballast dive weights. This becomes more complex when the diver carries large amounts of breathing gas, because 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. The diver should be certain that the cylinder valve is fully open and the inflator hose connected. This requires testing the regulator flow, the work of breathing, and the inflation valve function immediately before entering the water. This all must be done while observing the pressure gauge, particularly if there is any possibility that anyone else has handled the valve after the set is on the diver's back. Extra care is required here because the diver may have inadvertently closed or partially closed the valve. Any movement of the gauge needle while inhaling is a warning of a partially closed valve.
Entries
Standard water entries that are generally taught to entry-level divers include:- Stride entry: this is the standard method of entry from a standing position at a moderately low height above sufficiently deep water. The diver simply steps forward and remains upright during the short drop into the water. The fins strike the water first and reduce impact. Depth of immersion can be limited by performing a scissor kick immediately after striking the water. If an unexpected obstacle is present or the water is shallower than expected, the feet will hit it first. Because the regulator and mask are vulnerable to water impact in this entry technique, they are held in place with one hand. If the buoyancy compensator is inflated, the buoyancy and drag will limit the depth of penetration. The diver may need to quickly clear the area below the entry point so that other divers can follow when there is a large group or a current.
- Seated entry: sometimes also known as a controlled seated entry or silent entry. This technique is suitable from a platform where the diver can sit facing the water with the legs hanging into the water, such as the side of a swimming pool, a floating jetty, or the swim platform of a large boat. Seated entry requires sufficient upper-body strength to support the diver's weight on the arms while rotating to face the platform, then lowering oneself into the water in a controlled manner. Divers sit at the waterside in full equipment with both feet over the side in the water, place both hands palm down on the deck on the same side of the body, and take the body weight on straight arms as they rotate their bodies to face the platform before lowering themselves into the water.
- Backward roll: this entry is used from small boats where divers complete preparations while seated on the side of the boat with their feet on the deck and the water behind them. It is particularly suited to inflatable boats and other small, open vessels with gunwale freeboards of about half a meter or less. Falling backward into the water from this position is relatively safe and easy, and can be done simultaneously by all divers seated along the gunwale. The backward roll is suitable when the distance to the water is short, when it is safe and comfortable to sit on the side deck, tube or gunwale, and when the diver will not rotate more than about 120° during the roll. It eliminates the need to stand up and walk to an alternative entry point on a moving platform while encumbered by equipment, and it can be done with back-mount or side-mount equipment. The back-mounted diving cylinder makes first contact with the water surface, and the more sensitive mask and demand valve, and any other delicate equipment, are shielded from the initial impact by the diver's body. Care must be taken not to fall on any divers already in the water. A multiple diver backward-roll entry is usually coordinated by a crew member who voices a countdown so all divers go at the same time. All delicate and loosely fitted equipment should be held securely in place while rolling. In the case of sling- or side-mount cylinders, these should be held in place by the arms to prevent them from hitting the diver in the face. The boat should be stationary relative to the water for a multiple diver simultaneous entry. If anchored in a current, divers nearest the stern should enter before divers further forward.
- Forward roll: this is an alternate entry that can be used from a low- to moderate-height standing position. It is seldom used, however, as the risk of injury, damage, or loss of equipment is greater than for the stride entry, and it rarely offers advantages. The technique is to stand at the edge of the deck, fully kitted, with the fins beyond the foot pocket overhanging the edge. The diver holds the mask and DV with one hand and bends forward at the hips, keeping the legs straight, curls in the head, and falls forward, rotating so that the top of the back-mounted cylinder strikes the water first.
- Ladder descent entry: this is a relatively controlled and low-impact entry method. Few ladders are suitable for descending while wearing fins, so fins are usually carried over an arm or clipped to the diver, and put on once in the water. Putting fins on in the water can be tricky in a seaway or current.
- Surf and beach entries: these are often complicated by breaking waves. A small break is not usually a problem, but a wave with sufficient energy to knock a diver over is usually best avoided, or managed by going under it if it cannot be avoided. The safe limit differs from diver to diver, and it depends on the equipment used. Going under the break requires wearing the mask and fins while the diver breathes through the regulator. It is easier to walk backward through a broken wave while wearing fins, and the type and height of the break will influence the difficulty. A plunging breaker is much more difficult and dangerous than a spilling breaker for both entries and exits.
- Entry from a steep rocky shore: proper approach depends on the details of the shoreline topography, water depth, and wave action. The diver may be able to jump in fully kitted, or sit at the water's edge to fit mask and fins, and then slide or step in. In some circumstances a diver may have to climb down into the water and fit the fins in the water. It is important both to know how to time the entry to minimize the effects of waves, and to know when entry is simply unacceptably risky. Risk is related to both the skill and fitness of the diver, and the equipment being used.
- Jump entries: some agencies teach jumps from heights of 3 meters or more. Relatively high jumps require the diver to strike the water upright with overlapped fins to reduce the risk of knocking them off, while simultaneously holding loose equipment in place, particularly the mask and demand valve. Demand valves should be desensitized where possible to reduce the risk of inducing a free-flow. High-jump entries may be unsuitable for rebreathers, sidemount configurations, or those configurations where a cylinder or other equipment is mounted in a way that may allow it to swing and strike the diver when it hits the water, or where the impact may damage equipment.