List of diving hazards and precautions
Breathing gases at high ambient pressure

List of diving hazards and precautions

Section Title: Breathing gases at high ambient pressure
Table Section Text: None

Hazard	Consequences	Cause	Avoidance and prevention

Medium to long term exposure to high partial pressures (>c1.3 bar) of inert gas (usually N2 or He) in the breathing gas.	Decompression sickness ("the bends"): Injury due to gas bubbles expanding in the tissues and causing damage, or gas bubbles in the arterial circulation causing emboli and cutting off blood supply to tissues downstream of the blockage.	Gas dissolved in tissues under pressure during the dive according to Henry's Law coming out of solution and forming bubbles if the ascent and decompression is too fast to allow safe elimination of the gas by diffusion into the capillaries and transport to the lungs where it can diffuse into the respiratory gas.	Decompress to suit the dive profile and gas mixtures used. Use appropriate ascent rates and decompression stops.

Short term (immediate onset) exposure to high partial pressure (>c2.4 bar) of nitrogen in the breathing gas:	Nitrogen narcosis: A reversible alteration in consciousness that occurs while diving at depth. A state similar to alcohol intoxication or nitrous oxide inhalation.	A high partial pressure of nitrogen in the nerve tissues. (other gases may also have narcotic effect, to varying degrees).	Use of less narcotic gases to dilute the breathing gas, or Limit the partial pressure of narcotic gases at maximum depth by limiting the depth of the dive.

Short term (minutes to hours) exposure to high partial pressure (>c1.6 bar) of oxygen in the breathing gas.	Acute oxygen toxicity: Convulsions similar to epileptic seizure. Loss of consciousness may occur with no warning, or may be preceded by any of the following symptoms: Muscle twitching, Tinnitus, Blurred or tunnel vision, Disorientation, Aphasia, Nystagmus, Incoordination.	Breathing gas with too high a partial pressure of oxygen, risk becomes significant at partial pressures exceeding 1.6 bar (partial pressure depends upon proportion of oxygen in the breathing gas, and depth).	Appropriate training before using a rebreather or oxygen enriched gases such as nitrox. Correct labeling of cylinders containing mixed breathing gases, specifying oxygen fraction and maximum operating depth.

Long term (hours to days) exposure to moderately raised partial pressure (>0.5 bar) of oxygen in the breathing gas.	Chronic oxygen toxicity: Signs of pulmonary toxicity begin with inflammation of the upper airways. Temporarily reduced lung capacity.	Breathing gas at too high a partial pressure of oxygen, Risk is significant at a partial pressure in excess of 0.5 atmospheres pressure for long periods and increases with higher partial pressure even for shorter exposures.	Not normally a risk for recreational divers due to short exposures. Limit use of rich nitrox mixtures and pure oxygen for accelerated decompression.

Exposure to a high partial pressure(>15 bar) of helium in the breathing gas.	High Pressure Nervous Syndrome (HPNS): Symptoms include: visual disturbance nausea dizziness decreased mental performance tremors myoclonic jerking somnolence EEG changes	HPNS has two components: The compression effects may occur when descending below 500 feet (150 m) at rates greater than a few metres per minute, but reduce within a few hours once the pressure has stabilised.	The susceptibility of divers to HPNS varies over a wide range depending on the individual, but has little variation between different dives by the same diver.

Sentence(s)

DCS is known as a diving disorder that affects divers having breathed gas that is at a higher pressure.

final_sentence: DCS is known as a diving disorder that affects divers having breathed gas that is at a higher pressure.