Penetration diving or overhead diving is a type of diving where the diver enters a space from which there is no direct, purely vertical ascent to the safety of breathable air of the atmosphere at the surface. Several types of dive meet this condition: cave diving, wreck diving, ice diving or diving other man-made, underwater structures or enclosures.
The fact that the diver cannot immediately ascend to breathe from the atmosphere at the surface makes this type of diving much more risky than open-water diving.
It is essential that divers doing penetration dives on scuba are appropriately equipped and trained in technical diving techniques such as:
- using redundant breathing gas sources
- using distance lines to guide the diver to the exit
When the dive depth and time are extended, the use of breathing gases other than air can reduce the risks. Nitrox is used for relatively shallow diving and accelerated decompression. Breathing gases containing helium such as trimix are used for deeper dives to reduce the enervating effects of nitrogen narcosis.
Famous quotes containing the word diving:
“A worm is as good a traveler as a grasshopper or a cricket, and a much wiser settler. With all their activity these do not hop away from drought nor forward to summer. We do not avoid evil by fleeing before it, but by rising above or diving below its plane; as the worm escapes drought and frost by boring a few inches deeper.”
—Henry David Thoreau (1817–1862)