A new air decompression table has been developed for a dive to 40 msw for one hour, which employs a switch to a helium and oxygen mixture and oxygen during decompression The safety of the table has been validated using two types of ultrasonic monitoring
The problem of neurological decompression sickness In the air range has now been acknowledged In the UK and action taken to limit exposures to both compressed-air and nitrox mixtures[1] However the restrictions applied to in-water and surface-decompression air dives severely limit the useful work that can be done They also force more dives to be undertaken In order to complete the same amount of work increasing the number of dives Increases the risks from hazards other than decompression sickness [2] About half of all the diving fatalities in the oil and gas Industry have been related to surface-orientated diving Fortunately this has led to the successful development of transfer-under-pressure techniques in the air diving range
Unfortunately, dlving on air well within the current limits as not guarantee that subtle neurological damage will not occur and, from an examination of the data there IS no safety margin The recommended limits for in-water decompression only slightly exceed the no-stop decompression curve for air dives However even adherence to the no-stop decompression limit doses not provide protection against neurological decompression sickness as the case of a diver who developed symptoms after a dive of 30 minutes at 30 fsw has demonstrated [3]
A second problem is that the therapy of decompression illness, especially In the air range, is unsatisfactory In 1964 it was found that the air therapy tables recorded a failure rate of about 46% In the treatment of serious decompression sickness [4] The minimal-recompression oxygen breathing tables USN 5 and 6 were Introduced to solve this problem In 1965 It was soon recognised that oxygen at an equivalent pressure to 18 msw (60fsw) may paradoxically cause deterioration of a diver suffering from decompression sickness and this was recorded In the US Navy Diving Manual released In 1970 Both human and experimental studies indicate that there may be an irreversible component of severe dysbaric illness Currently, therefore, the Industry has both unsatisfactory working procedures and Inadequate schedules for therapy
Compressed-air as a diving gas has been limited to 50 msw (165 fsw) by UK legislation, because of decompression sickness, but because at greater depths narcosis becomes significant Clearly, because it IS inexpensive and the diving equipment needed IS simple, many would st111 prefer to retain compressed-air In shallow-water diving However, it can only be retained if the problem of decompression sickness can be solved
The risk of decompression sickness was recognised by Bert In 1875 [5] to be due to nitrogen being released from solution that is, gas phase, due to super saturation He observed bubbles In the blood from a severed jugular vein in a dog following a decompression
