Diving is a human activity and stay below the water surface using air or a mixture of gases from an autonomous diving apparatus. The very beginnings of diving in the world date back to ancient Egyptian times, while the invention of the diving bell in the middle of the 16th century is considered as first serious steps of the diving system. In Croatia, diving is first developed on the island of Krapanj, where divers used soft spacesuits imported from neighboring Italy to catch sponges. Today, numerous world organizations deal with diving, the most prominent of which are listed below. Like any activity, diving requires a large amount of equipment and aids, of which the most basic components that divers use during every dive are listed and described in the paper. Given that divers are exposed to an aquatic environment that is not natural to the human body, it is necessary to know the specifics and dangers of diving. Also, considering the influence of pressure on the human body, it is necessary to know the gas laws well and thereby prevent a negative impact on health, as well as potential damage to the circulatory system and other vital organs. The divers of Fire Brigade Opatija have been working for several years on exercises and interventions under water surfaces, respecting all regulations and carrying out periodic medical examinations.