Maximum operating depth

Abstract: Device for and method of dive monitoring, wherein the pressure in a diving flask of a breathing equipment and the ambient pressure which the diver is exposed to at the respective water depth are detected. A decompression computing means is used to determine the respective decompression stops which the diver has to observe in surfacing, and how much time surfacing will require altogether. A performance index is derived from the variation of the pressure versus time in the diving flask, which index is a measure of the physical work performed by the diver. This performance index is supplied to the decompression computing means and is considered in the calculation of the total surfacing period.

Abstract: Clear differences between professional and recreational deep diving are disappearing, at least when taking into account the types of breathing mixtures (oxygen, nitrox, heliox, and trimix) and range of dive parameters (depth and time). Training of recreational deep divers is conducted at depths of 120–150 metres and some divers dive to 180–200 metres using the same diving techniques. Extremely deep recreational divers go to depths of more than 200 metres, at which depths the physical and chemical properties of breathing gases create some physiological restrictions already known from professional deep diving. One risk is carbon dioxide retention due to limitation of lung ventilation caused by the high density of breathing gas mixture at great depths. This effect can be amplified by the introduction of the additional work of breathing if there is significant external resistance caused by a breathing device. The other risk for deep divers is High Pressure Neurological Syndrome (HPNS) caused by a direct compression effect, presumably on the lipid component of cell membranes of the central nervous system. In deep professional diving, divers use a mixture of helium and oxygen to decrease gas density, and nitrogen is used only in some cases for decreasing the signs and symptoms of HPNS. The same approach with decreasing the nitrogen content in the breathing mixture can also be observed nowadays in deep recreational diving. Moreover, in extremely deep professional diving, hydrogen has been used successfully both for decreasing the density of the breathing gas mixture and amelioration of HPNS signs and symptoms. It is fair to assume that the use of hydrogen will be soon “re-invented” by extremely deep recreational divers. So the scope of modern diving medicine for recreational divers should be expanded also to cover these problems, which previously were assigned exclusively to professional and military divers. (Int Marit Health 2012; 63, 1: 49–55)

Abstract: The paper discusses the finite-element modelling and performance of ring-shell projectors, a particular type of flextensional projector. A ring-shell projector can be used near its resonance frequency as a high-power source, or as a moderate-power broadband source. The most recent design of ring-shell projector has a resonance frequency of 349 Hz, a mechanical Q-factor of 10.6 and a source level of 205 dB relative to 1 μPa at 1 m. Finite-element predictions of the transmitting response and admittance show good agreement with the measured values. Ring-shell projectors that are passively pressure compensated have a maximum operating depth in excess of 300 m and a safe immersion depth of at least 450 m.

Abstract: To the Editor.— The advice given by Drs Jules-Elysee and Stover in Questions and Answers 1 regarding safe return to scuba diving following bleomycin sulfate therapy is not entirely correct. While most scuba divers breathe compressed air (21% oxygen), the partial pressure of oxygen in the inspired air is a direct function of the depth of the dive. 2 For every 9.9 m of sea water dive depth, the ambient barometric pressure to which the diver is exposed increases by 1 atm. At a dive depth of 19.8 m of sea water (3 atm total pressure), the partial pressure of inspired oxygen in a scuba diver breathing compressed air is 0.63 atm, equivalent to breathing 63% oxygen on the surface. At a dive depth of 29.7 m of sea water, not an unusual depth for many sport divers, the partial pressure of oxygen is 0.84 atm, equivalent to breathing 84%