Scuba divers typically do not use 100% oxygen during their dives because breathing pure oxygen at increased atmospheric pressure can lead to a condition known as oxygen toxicity. The air we breathe at sea level consists of approximately 21% oxygen and 79% nitrogen. When diving, the concentration of gases divers breathe changes as they go to deeper depths.
At shallow depths, where most recreational scuba diving takes place, the concentration of oxygen in the air is generally safe. However, as divers descend to greater depths, the increased pressure causes the partial pressure of oxygen to rise. Breathing elevated partial pressures of oxygen for extended periods can lead to two types of oxygen toxicity:
Central Nervous System (CNS) Oxygen Toxicity: This condition affects the brain and central nervous system. Symptoms can range from mild dizziness, nausea, and twitching to seizures and unconsciousness.
Pulmonary Oxygen Toxicity: This condition affects the lungs and respiratory system. Symptoms can include coughing, chest pain, and difficulty breathing.
To avoid oxygen toxicity, divers use mixtures of gases other than air, such as Nitrox or Trimix. These mixtures have adjusted proportions of oxygen, nitrogen, and sometimes helium, depending on the depth and the desired bottom time. By carefully controlling the gas mixture, divers can reduce the risk of oxygen toxicity while still allowing for extended dive times and safer decompression profiles.
Recreational Nitrox, for example, has a higher percentage of oxygen than normal air (usually around 32% or 36%), which can extend the no-decompression limit, allowing for longer dives at shallower depths. Technical divers may use Trimix, which further reduces the percentage of nitrogen and replaces it with helium to manage narcosis at greater depths.
Using these gas mixtures, divers can explore the underwater world safely and enjoy longer bottom times without exposing themselves to the risks associated with breathing pure oxygen at depth. It's essential for scuba divers to undergo proper training and certification before using gas mixtures other than air to understand how to plan and execute their dives safely.