Breathing high concentrations of oxygen can cause oxygen toxicity, which is usually fatal when diving. The concentration (or partial pressure) of oxygen in a diver’s breathing gas increases with depth. The higher the percentage of oxygen, the shallower the depth at which it becomes toxic. Divers calculate a MOD to be sure that they do not descend beyond the depth at which the oxygen in their tank may become toxic. The Scuba Diving Calculators Maximum Operating Depth Calculator is designed to help you calculate the math with ease.