What is the maximum O2 concentration allowed in a Decompression Chamber (DDC)?

The maximum oxygen concentration allowed in a Decompression Chamber (DDC) is 21%. This corresponds to the oxygen levels present in ambient air at sea level. Decompression chambers are used to treat decompression sickness and facilitate the safe ascent of divers after deep dives. The pressure within a DDC is regulated to ensure that divers receive the necessary treatment without introducing risks associated with higher oxygen concentrations.

At concentrations above 21%, the risk of oxygen toxicity increases significantly. Oxygen toxicity can lead to a range of serious symptoms, including visual disturbances, muscle twitching, and even convulsions, which can be dangerous, especially in high-pressure environments like a DDC. Maintaining the oxygen concentration at this level maximizes safety while still providing the therapeutic benefits needed for dives requiring decompression.

In contrast, higher concentrations, such as those indicated by the other choices, could lead to complications and are not considered safe for use within a DDC. The use of pure oxygen or elevated oxygen levels should only be done under controlled circumstances and often with specific protocols that take into account the diver's health status and diving profile.