Although diving as a purposeful activity has been going on since at least 5000 BC and almost certainly predates any recorded history, the decompression illnesses which can result from diving are a comparatively recent phenomenon and were not even described in detail until well into the 19th century. The reason for this is that despite many attempts to produce a practical means of breathing underwater, most of which were positively dangerously with little or no understanding of the physics and physiology involved, breath-hold diving from the surface or from submerged diving bells was the only way of venturing underwater. However, the advent of an effective and relatively safe underwater breathing capability came with the 1819 introduction of Augustus Siebe’s diving helmet, a device which allowed the diver to be provided with compressed air from a pump on the surface. Apart from the much greater freedom given to the diver by this equipment, divers were provided with a much easier means of achieving depth-time limits underwater which were capable of causing what came to be known as decompression sickness (DCS) which, in its more acute forms, involves the central nervous system (CNS). Indeed, it is said that when Greek sponge divers began to use the 1839 version of Siebe’s helmet, which by now was combined with a suit and heavy boots, 50% of them died within the first year! Equally, the very fact that it was now possible to breathe underwater made divers vulnerable to decompression pulmonary barotrauma, the second decompression illness capable of damaging the CNS.