Diving chamber

Abstract: The difference in risk of decompression sickness (DCS) between dry chamber subjects and wet, working divers is unknown and a direct test of the difference would be large and expensive. We used probabilistic models and maximum likelihood estimation to examine 797 dry (and generally resting and comfortable) and 244 wet (and generally working and cold) chamber dives from the Defence and Civil Institute of Environmental Medicine, supplemented with 483 wet (working, cold) dives from the Navy Experimental Diving Unit. Several analyses considered whether dry and wet data were distinguishable using several models, whether models obtained from one set of exposure conditions would correctly predict the occurrence of DCS in the other condition, and whether a single wet-dry risk difference parameter was different from zero. Although the two conditions may not produce identical risks, immersion appears to change relative risk of DCS by less than 30% and certainly involves less than a doubling of DCS risk. Uncontrolled differences in exercise and temperature stresses unavoidably complicate interpretation. Several methods are presented to extrapolate results from dry-test subjects in decompression trials to expected at-sea performance.

Abstract: The crew of a disabled submarine can be rescued by means of free ascent through the water to the surface. Pulmonary gas exchange was studied during simulated rapid free ascent in subjects standing immersed to the neck in a pressure chamber. The pressure was rapidly increased to 1.1 MPa [100 meters seawater (msw)] followed by decompression at 0.03 MPa/s (3 msw/s). Effective inspired tidal volume, as estimated by an Ar dilution method, fell gradually to zero during decompression from 20 to 0 msw. Directly determined expired tidal volumes were increased up to two to three times at the time of return to surface pressure compared with pre- and postdecompression volumes. End-tidal PCO2 was increased on compression and fell to a nadir of 3.4 kPa (25 Torr) at the time of return to surface pressure. Thus, intrapulmonary gas expansion caused simultaneous inspiratory hypoventilation and expiratory hyperventilation. If O2-enriched gas is to be used to reduce the risk of decompression sickness, it should be administered early during decompression to alter the intrapulmonary gas composition. The time course of arterial PCO2 changes as reflected by end-tidal values during short-lasting compression/decompression would act to promote inert gas supersaturation in the brain.

Abstract: : US Navy submarines rarely become disabled The first disablement and loss occurred in 1914 when leaking battery acid in USS F-4 corroded hull rivets that caused progressive flooding, chlorine off gassing, loss of depth control and eventual catastrophic hull failure Then, after another accident in 1927 when the US Submarine S-4 became disabled and was lost with all hands, rescue procedure planning, equipment and training have continuously been undergoing improvement As a result, 12 years later, in 1939 off the shore of Portsmouth, NH Sailors were successfully rescued from the USS Squalus, which quickly sank after a rear compartment flooded (Stewart, 2008) The disabled Squalus was located on the sea floor at a depth of 240 ft in 29 F (-17 C) water, a rescue ship with a diving chamber came to the site and the 33 crew in the non-flooded compartments were transferred to the surface within 40 hours via 4 trips of the diving chamber A major thermal hazard in such a disabling has been the threat of hypothermia from the environment caused by cold ocean water while waiting the sub s rescue (Castellani et al, 2005)