In order to become a professional diver, even for leisure activities, one must get a diving license. The majority of the agencies require knowledge of physiology and the physics of diving, as the diving environment is hostile and relatively alien to humans. These basic notions are taught during the practice hours in the pool, with the scuba diving equipment, or at the theoretical courses where one must follow in order to understand the effect that water have on the human body, the risks and possibilities for accidents.
The physics knowledge implies notions of pressure, buoyancy, heat loss and light underwater. The physiology notions relate to the human body and the main causes of barotraumas, decompression sickness, hypothermia, drowning, gas toxicity and sensory variations. Some diving courses also teach first aid and rescue skills, which are related to diving equipments and the skills one must learn to correctly and safely dive.
The level of skills required and taught at these courses is directly related to the diving course level. Recreational divers will get less information, because they will be prepared to dive only at depth up to 30 meters, and they are not allowed to dive without assistance. The second levels though allow divers to explore wrecks, archaeological sites, and sunken ships and report the causes of accidents. There is a third category, even more demanding, which requires higher skills. These are for military applications, ship maintenance, even for instructing.
The divers’ beginning courses focuses on learning basic skills, which is the base for any further certification one wishes to take further. It starts with safe conduct in the underwater environment, procedures for the correct usage of the diving equipment, safety, self-help, and rescue procedures, notions of planning all the details for a dive, the use of dive tables or the personal decompression computer. Divers also use a special sign language, which allows them communicate underwater.