At what depth does oxygen toxicity become a concern for divers using air?

Oxygen toxicity becomes a concern for divers using air primarily due to the increasing partial pressure of oxygen as the depth increases. At around 30 meters (100 feet), the partial pressure of oxygen in the breathing gas significantly exceeds safe limits, which can lead to toxic effects on the central nervous system.

At this depth, the inspired oxygen pressure rises to approximately 1.4 ATA (atmospheres absolute), which is the level at which oxygen toxicity can start to cause symptoms such as visual disturbances, muscle twitching, and loss of consciousness. Staying within this depth range is crucial to mitigate the risks associated with oxygen toxicity while diving.

While the effects of oxygen toxicity can potentially start to emerge at depths shallower than 30 meters, they become a significant concern around this threshold, making 30 meters the critical point for divers using regular air as their breathing gas.