a number of small problems promptly and correctly before the situation escalates. Dealing with such problems as a dislodged or flooded mask, or free-flowing regulator, or correctable buoyancy fault should be done before the situation deteriorates to an emergency. A basic understanding of the physics and physiology of diving should give the diver the ability to predict the consequences of possible responses to unfamiliar contingencies. A diver with inadequate understanding may respond inappropriately to an emergency outside of their training and experience, which though unlikely remains possible. Repeated practice beyond initial competence of standard responses to the more likely contingencies develops a "muscle memory" response, which helps the diver perform the correct response under stress, and when more than one problem occurs simultaneously. It is possible to never experience one of these problems, and some divers may never need the skills in practice, but divers who do not practice the skills are more likely to be overtaken by circumstances if something does go wrong. The practice of stress exposure training in controlled conditions, where the diver is task loaded with an increasing level of simulated problems and must deal with them, is thought to develop the diver's confidence in their ability to manage an emergency effectively, which may give them the ability to avoid panic and continue to respond usefully to the situation, giving a better chance of survival. Continued occasional practice of emergency procedures after initial training ensures that the skills are not lost due to lack of use. Divers who have not practiced their skills for several months or years are at higher risk of accidents when first returning to the water, and refresher courses and checkout dives in benign conditions are available to get the skills back to standard and thereby reduce risk of an accident. Personal protective equipment A large part of personal diving equipment can be classified as personal protective equipment. Breathing apparatus allows the diver to breathe under water, where they would otherwise drown. Exposure suits - Wetsuits, Dry suits, and hot-water suits provide thermal protection to the diver. Where thermal protection is not necessary, divers may wear overalls as protection against stings, cuts and abrasions which could be caused by contact with the environment. Diving helmets provide thermal protection and impact protection for the diver's head, and protect the diver's airway. Neoprene hoods provide protection against high volume sound, often produced by the