in the air passages will minimise the work of breathing for a given gas mixture composition and density, and respiratory minute volume. Procedures The underwater environment is unfamiliar and hazardous, and to ensure diver safety, simple, yet necessary procedures must be followed. A certain minimum level of attention to detail and acceptance of responsibility for one's own safety and survival are required. Most of the procedures are simple and straightforward, and become second nature to the experienced diver, but must be learned, and take some practice to become automatic and faultless, just like the ability to walk or talk. Most of the safety procedures are intended to reduce the risk of drowning, and many of the rest are to reduce the risk of barotrauma and decompression sickness. In some applications getting lost is a serious hazard, and specific procedures to minimise the risk are followed. Preparation for the dive The purpose of dive planning is to ensure that divers do not exceed their comfort zone or skill level, or the safe capacity of their equipment, and includes gas planning to ensure that the amount of breathing gas to be carried is sufficient to allow for any reasonably foreseeable contingencies. Before starting a dive both the diver and their buddy do equipment checks to ensure everything is in good working order and available. Recreational divers are responsible for planning their own dives, unless in training when the instructor is responsible. Divemasters 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. Standard diving procedures Some procedures are common to almost all scuba dives, or are used to manage very common contingencies. These are learned at entry level and may be highly standardised to allow efficient cooperation between divers trained at different schools. Water entry procedures are intended to allow the diver to enter the water without injury, loss of equipment, or damage to equipment. Descent procedures cover how to descend at the right place, time, and rate; with the correct breathing gas available; and without losing contact with the other divers in the