253.2 meters (831 feet) is the deepest free dive made by Austrian Herbert Nitsch.
Free diving can be done with various supporting equipment, but it must be done on a single breath – without use of the scuba equipment. There are numerous free-dive categories, such as with fins and without fins, length, static, and so on, with their individual records, but the most impressive by far is the so-called No-limits apnea (NLT), where any sort of equipment can be used to help diver descend and ascend. Naturally, this category is responsible for the deepest free-dive ever made.
This feat was accomplished by an Austrian free diver, Herbert Nitsch. Twice. He actually beat his own record he set in 2007, with his of 253.2 meters (831 feet) dive he made in 2012. In the no limit dives, motorized sleds have become the most popular means of descent and ascent, and Nitsch used a special, purpose built torpedo sled for his latest achievement. He had to train extensively for months, to prepare himself for a rapid shift in pressure that he was going to experience.
As one might notice, this depth is considerably greater than the scuba diving limit. This is because narcosis and oxygen toxicity only happen if we inhale gasses under pressure, not if we ourselves are subjected to it. However, Nitsch did suffer from several unpleasant effects: he suffered a blackout during the last 10 meters of his descent that he later described as “blackout through narcosis”, which was found strange by some, as the expected culprit would be oxygen starvation. He regained his consciousness on the ascent, but suffered from serious symptoms of decompression and had to be helped by the safety divers in the last 10 meters of the ascent, which was followed by an emergency transfer to a decompression chamber that was on alert for this particular dive.