Scuba Diving: Scuba diving is a mode of underwater diving where the diver uses a self-contained underwater breathing apparatus(scuba) which is completely independent of surface supply, to breathe underwater. Scuba divers carry their own source of breathing gas usually compressed air. Open circuit scuba systems discharge the breathing gas into the environment as it is exhaled, and consist of one or more diving cylinders containing breathing gas at high pressure which is supplied to the diver through a regulator.
The volume of gas used is reduced compared to that of an open circuit, so a smaller cylinder or cylinders may be used for an equivalent dive duration. Rebreather extends the time spent underwater compared to open circuit for the same gas consumption; they produce fewer bubbles and less noise than open circuit scuba which makes them attractive to covert military divers to avoid detection, scientific divers to avoid disturbing marine animals, and media divers to avoid bubble interference.
Breathing Apparatus: The equipment used by a scuba diver is the eponymous scuba the self-contained underwater breathing apparatus which allows the diver to breathe while diving, and is transported by the diver. Most recreational scuba diving is done using a half mask which covers the diver’s eyes and nose, and a mouthpiece to supply the breathing gas from the demand valve or rebreather. Inhaling from a regulator’s mouthpiece becomes second nature very quickly. The other common arrangement is a full face mask which covers the eyes, nose, and mouth, and often allows the diver to breathe through the nose. Professional scuba divers are more likely to use full face masks.
Rebreather: Less common are a closed circuit (CCR) and semi-closed (SCR) Rebreather which, unlike open-circuit sets that vent off all exhaled gases, process all or part of each exhaled breath for re-use by removing the carbon dioxide and replacing the oxygen used by the diver. In a closed-circuit rebreather, the oxygen partial pressure in the rebreather is controlled, so it can be maintained at a safe continuous maximum, which reduces the inert gas (nitrogen and/or helium) partial pressure in the breathing loop. A semi-closed circuit rebreather injects a constant mass flow of a fixed breathing gas mixture into the breathing loop or replaces a specific percentage of the respired volume, so the partial pressure of oxygen at any time during the dive depends on the diver’s oxygen consumption and/or breathing rate.
Gas Mixtures: For some diving, gas mixtures other than normal atmospheric air can be used., so long as the diver is competent in their use The most commonly used mixture is nitrox, also referred to as Enriched Air Nitrox, which is air with extra oxygen, often with 32% or 36% oxygen, and thus less nitrogen, reducing the risk of decompression sickness or allowing longer exposure to the same pressure for equal risk. For dives requiring long decompression stops, divers may carry cylinders containing different gas mixtures for the various phases of the dive, typically designated as Travel, Bottom, and Decompression gases. These different gas mixtures may be used to extend bottom time, reduce inert gas narcotic effects, and reduce decompression times.
Buoyancy control and trim: To dive safely, divers must control their rate of descent and ascent in the water and be able to maintain a constant depth in mid-water. Ignoring other forces such as water currents and swimming, the diver’s overall buoyancy determines whether they ascend or descend. Equipment such as diving weighting systems, diving suits, and buoyancy compensators can be used to adjust the overall buoyancy. When divers want to remain at constant depth, they try to achieve neutral buoyancy. This minimizes the effort of swimming to maintain depth and therefore reduces gas consumption.
Diving suits made of compressible materials decrease in volume as the diver descends, and expand again as the diver ascends, causing buoyancy changes. Diving in different environments also necessitates adjustments in the amount of weight carried to achieve neutral buoyancy. The diver can inject air into dry suits to counteract the compression effect and squeeze.
Underwater Vision: Divers who need corrective lenses to see clearly outside the water would normally need the same prescription while wearing a mask. Masks tend to fog when warm humid exhaled air condenses on the cold inside of the faceplate. To prevent fogging many divers spit into the dry mask before use, spread the saliva around the inside of the glass and rinse it out with a little water.
Monitoring and Navigation: Unless the maximum depth of the water is known, and is quite shallow, a diver must monitor the depth and duration of a dive to avoid decompression sickness. Traditionally this was done by using a depth gauge and a diving watch, but electronic dive computers are now in general use, as they are programmed to do real-time modeling of decompression requirements for the dive, and automatically allow for surface interval.
Safety Equipment: Cutting tools such as knives, line cutters or shears are often carried by divers to cut loose from entanglement in nets or lines. A surface marker buoy on a line held by the diver indicates the position of the diver to the surface personnel. This may be an inflatable marker deployed by the diver at the end of the dive, or a sealed float, towed for the whole dive. A surface marker also allows easy and accurate control of ascent rate and stop depth for safer decompression. A bailout cylinder provides breathing gas sufficient for a safe emergency ascent.
Preparation for the Dive: Before starting a dive both the diver and their dive mate do equipment checks to ensure everything is in good working order and available. Recreational divers are responsible for planning their own lives, unless in training when the instructor is responsible. Dive masters may provide useful information and suggestions to assist the divers, but are generally not responsible for the details unless specifically employed to do so. In professional diving teams all team members are usually expected to contribute to planning and to check the equipment they will use, but the overall responsibility for the safety of the team lies with the supervisor as the appointed on-site representative of the employer.
Diving Procedures: Divers cannot talk underwater unless they are wearing a full-face mask and electronic communications equipment, but they can communicate basic and emergency information using hand signals, light signals, and rope signals, and more complex messages can be written on waterproof slates.
Emergency Procedures: The most urgent underwater emergencies usually involve a compromised breathing gas supply. Divers are trained in procedures for donating and receiving breathing gas from each other in an emergency and may carry an independent alternative air source if they do not choose to rely on a diver.
Above mentioned are the diving equipment and the diving procedure and also the precautions.