What prevents scuba divers form going deeper than 40 meters below the surface?

Scuba divers are generally advised not to exceed depths of 40 meters due to the increased risks of nitrogen narcosis and oxygen toxicity. At greater depths, the partial pressure of nitrogen rises, which can impair cognitive function and motor skills. Additionally, high levels of oxygen at depths beyond 40 meters can become toxic, potentially leading to seizures and other serious health issues. These factors, along with the challenges of ascent and decompression, make deep diving hazardous without specialized training and equipment.