Some scuba diving curricula may apply the terms "shallow-water blackout" and "deep-water blackout" differently; deep-water blackout being applied to the final stage of nitrogen narcosis while shallow water blackout may be applied to a blackout from a deep free dive. Nitrogen narcosis does not normally apply to freediving as free-divers start and finish the dive with only a single lungful of air and it has long been assumed that free divers are not exposed to the necessary pressure for long enough to absorb sufficient nitrogen. Where these terms are used in this manner there is usually little or no discussion of the phenomenon of blackouts not involving depressurisation and the cause may be variously attributed to either depressurisation or hypocapnia or both. This problem may stem from the origin of the term "latent hypoxia" in the context of a string of fatal, shallow water accidents with early military, closed-circuit rebreather apparatus prior to the development of effective oxygen partial pressure measurement. In the very different context of dynamic apnea sports careful consideration of terms is needed to avoid potentially dangerous confusion between two phenomena that actually have different characteristics, mechanisms and prevention measures. The application of the term "shallow water blackout" to deep dives and its subsequent association with extreme sports has tended to mislead many practitioners of static apnea and dynamic apnea distance diving into thinking that it does not apply to them even though isobaric shallow water blackout kills swimmers every year, often in shallow swimming pools.