What is the increased risk when a diver pushes the Doppler no-decompression limits?

When a diver exceeds the no-decompression limits, the primary concern is the increased likelihood of experiencing Decompression Sickness (DCS). DCS occurs due to the formation of nitrogen bubbles in the body when a diver ascends too quickly after spending time at depths that require decompression stops during ascent. This can happen when nitrogen, which has been absorbed by the tissues during the dive, is released too rapidly when ascending.

Pushing the no-decompression limits means that the diver is not allowing enough time for the nitrogen that has been absorbed in the body to safely eliminate itself as they ascend. The deeper and longer the dive, the more nitrogen the body absorbs. Rapid ascent without decompression stops can lead to bubbles forming in the bloodstream or tissues, which can cause a variety of symptoms ranging from joint pain to more severe neurological effects.

While nitrogen narcosis and oxygen toxicity are valid concerns for divers, they relate to different aspects of diving. Nitrogen narcosis occurs at greater depths due to the effects of increased pressure on inert nitrogen and does not have a direct correlation with exceeding no-decompression limits. Oxygen toxicity is a risk at higher partial pressures of oxygen, especially during deeper dives while breathing enriched gases like nitrox, but again, this is