A method for for assessing severity of an underwater dive includes calculating a dive severity index by: (a) determining the gas breathed by the diver; (b) measuring the dive time; (c) determining the depth profile of the dive; (d) calculating a dive severity index based on a function of steps (a), (b) and (c); and (e) assessing severity based on the dive severity index calculated in step (d), wherein the steps (a), (b), (c), (d) and (e) are carried out in real time, at each instant of the dive time of the diver, and step (d) is performed according to the formula: DSI=k1*f(GAS)*f(D)*f(T), where: DSI is the dive severity index, k1 is an arbitrary constant, f(GAS) is a function of the inhaled gas, f(D) is a function of the dive depth, and f(T) is a function of the dive time.
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