inherent in the equipment, but to improper use, incorrect configuration, poor maintenance or unfamiliarity with the equipment. It is more often the diver's response to equipment malfunction than the malfunction itself which results in injury or death. The triggering event, if not managed effectively, leads to a harmful action that exacerbates the situation, and the most commonly identified harmful action is an emergency ascent, which shows that most of the divers chose to try to escape to the surface instead of dealing with the problem underwater. The next stage of the cascade/sequence is an incapacitating injury, which prevents the diver from further efforts to control the incident, most commonly asphyxia, followed by the official cause of death as the final stage. In freediving and scuba diving this is usually found to be drowning. In an analysis of recreational closed circuit rebreather deaths between 1998 and 2010, a somewhat arbitrary risk rating for each dive was allocated: low risk, for open water dives to depths not exceeding , where all checks and tests were done moderate risk, for penetration dives to depths not exceeding , where all checks and tests were done, intermediate risk, open water dives to depths between and , where all checks and tests were done high risk, for penetration dives to depths between and , where all checks and tests were done, extreme risk, for all dives to depths exceeding , or where checks and tests were not done, or alarms were ignored. When applied to the database this indicated that about two thirds of the deaths appear to be associated with high risk behaviour. The annual rebreather death rate of approximately 4 per 10 000 dives is approximately 10 times the rate for non-technical recreational scuba diving. Some deep diving problems have been associated with excessive work of breathing, which can reduce the capacity of the diver to deal with problems where physical exertion is required, and in extreme cases can be overwhelming even at low exertion levels. Analysis of recreational diver behaviour indicates that using a sufficiently specific written checklist for pre-dive checks reduces the incidence of dives started in unsafe conditions in comparison with pre-dive checks following a memorised checklist, and a corresponding reduction of mishaps during the dive that might have triggered incidents with harmful consequences. There were not enough observations to correlate with actual harmful incidents such as fatalities, which are much