to find, as they are at the far end of the umbilical, and it is extremely rare for the umbilical to be completely severed. The standard procedure for rescue of a surface supplied diver is for the standby diver to follow the umbilical to the diver, reporting back frequently to the supervisor on progress. Divers often use guidelines, surface marker buoys, diving shots, lightsticks and strobe lights to indicate their position to their surface support team. A standard precaution when entering enclosed spaces is to use a guideline; this marks the exit route, which may be needed after the diver's fins, wash, and bubbles dislodge silt and loose overhead materials such as rust which can reduce visibility to near zero. Common search techniques such as the circular search or jackstay search, need preparation and practice if they are to be used effectively and safely. The spiral box search and compass grid search require less preparation, but probably greater skill, and may be rendered ineffective by currents. Searches of enclosed spaces expose the rescuer to danger. The rescuers may need training and experience in cave diving, ice diving or wreck diving to minimise the risks of that type of rescue. Providing emergency gas Providing emergency gas to a diver who has run out is the highest priority after finding the diver. Without breathing gas the diver will die in minutes. Running out of gas is a major contributor to diving accidents. Many scuba accidents start in some other way and culminate in running out of gas. The main reasons for running out of scuba gas are: failing to monitor consumption of the gas - not watching the contents pressure gauge underestimating the amount of gas needed for the return and ascent and decompression stops consuming gas faster than estimated by going too deep, over-exercising or psychological stress delayed exit or ascent due to other problems, such as getting lost or entrapped equipment failure, such as a regulator freeze or blown o-ring, in the main breathing set leading to escape of gas. Even when the prime cause of an underwater emergency is not running out of gas, lack of gas can easily become another problem for the rescuers to overcome because more gas is consumed during the accident and its aftermath. This could be due to the diver remaining at depth for longer than planned or due to increases in the diver's