NDL — No-Decompression Limit

The No-Decompression Limit (NDL) is the safe time window for a single dive. It tells you how long you can remain at a certain depth before nitrogen buildup becomes dangerous. Your dive computer calculates this value constantly based on your current depth and descent rate. For example, at 30 m, your NDL might be only 20 minutes. If you stay longer, you must perform mandatory decompression stops. This changes the dive from a recreational profile to a technical one. Many divers make the mistake of pushing too close to zero minutes. I saw a student in Koh Tao in 2019 try to squeeze one last minute out of his computer. He ended up needing a safety stop that lasted 10 minutes because he ignored the shrinking NDL. Always leave a 5-minute buffer for your ascent. This helps if you encounter unexpected currents or heavy surge.