NARD Diving MedicineDiving MD

Oxygen Poisoning

Oxygen at an elevated partial pressure may have a toxic effect. Surplus oxygen affects the central nervous system (CNS) or the pulmonary system during extended exposure, as in medical therapy. Ordinary air is 21% oxygen at 1 ATM, or sea level with a pressure of 3.09 psi (Dalton's Law 21% of 14.7 = 3.09). Oxygen toxicity can take place at a partial pressure equal to 29.4 psi. If the diver is utilizing pure oxygen this will occur at 2 ATM or 33 feet, with compressed air it would be 297ft. Oxygen poisoning will never be a hindrance to a diver who dives within the 130 feet limit. However with Nitrox the incidence of oxygen poisoning is increasing. Where the rescue diver may encounter it is in chamber therapy, scene calls to commercial divers, or divers utilizing Nitrox and closed circuit systems. The toxic affect can induce convulsions so the rescuer should be attentive.

Warning Signs:
  • Visual field reduction, an abnormality comparable to tunnel vision.

  • Tinnitus (ringing or roaring sound inside the ear)

  • Nausea, which may be intermittent.

  • Changes in behavior such as irritability or confusion.

  • Dizziness

  • Tingling or numb feeling around the mouth.

  • Muscle twitching usually in the face.

  • Unusual fatigue

Not all symptoms will materialize and most are not exclusively symptoms of oxygen poisoning. Muscle twitching is the best warning of oxygen toxicity. Convulsions can befall without warning. Do not give the victim 100% oxygen. After a convulsion, recovery is rapid with no lingering aftermath. If a victim is in a recompression chamber and starts convulsing, he should be protected from injury and have his airway guarded.

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