Lee, W.D.; Lee, J., and Lee, J.H., 2019. Applicability of nitrox diving for improved safety and efficiency of underwater operations. In: Lee, J.L.; Yoon, J.-S.; Cho, W.C.; Muin, M., and Lee, J. (eds.), The 3rd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 91, pp. 206-210. Coconut Creek (Florida), ISSN 0749-0208.

Most underwater divers, including recreational participants, use compressed air with a composition of 21% oxygen and 78% nitrogen for breathing while submerged. Deep underwater diving often requires a lengthy decompression time shortly after surfacing, especially if the operator was submerged for an extended period, or descended to a considerable depth. This process is required to remove nitrogen which dissolves into the body with the increase in pressure with depth. If this intervention is not taken, the diver's safety cannot be ensured, and the likelihood of ensuing decompression sickness increases. This means that in the case of air diving, there is significant risk associated with working in deep sea conditions or remaining submerged for a prolonged period of time. To address this issue, a new type of breathing gas with a higher oxygen-to-nitrogen ratio called nitrox has been formulated, which has resulted in an increased use by the recreational diving community. In addition, the use of nitrox in the case of commercial diving has also recently increased. Nitrox diving results in a significantly reduced decompression time since the amount of nitrogen dissolved in the body is drastically reduced due to the high oxygen-to-nitrogen ratio in nitrox. Correspondingly, the risk of suffering from decompression sickness is reduced. In this report, the applicability of nitrox diving using the Varying Permeability Model (VPM) to improve diver safety and work efficiency is discussed. The study results indicate that the beneficial effects of nitrox are nonexistent for shallow diving operations, regardless of the breathing gas used. This is because the no-interval-decompression limit is too long. However, using a 36%-oxygen nitrox in deep diving scenarios can decrease the total work time by 33% and the decompression time by up to 73% compared to air. Therefore, for scenarios in which the depth does not exceed the maximum operating depth, nitrox is both safer and more efficient than diving with air.