What does the term 'no decompression limit' (NDL) refer to?

The term 'no decompression limit' (NDL) is defined as the maximum time a diver can spend at a specific depth without needing to make any mandatory decompression stops during ascent. This concept is critical for divers to understand because it helps ensure their safety by minimizing the risks associated with decompression sickness, commonly referred to as "the bends."

When divers exceed the NDL for a particular depth, they may need to stop at various depths during their ascent to allow gases that have dissolved in their body tissues to safely escape. By adhering to the NDL, divers can ascend directly to the surface without the need for these additional decompression stops, making their dives simpler and less risky.

The other choices, while related to diving, do not accurately describe the concept of no decompression limits. The maximum depth a diver can reach without special equipment pertains more to the dive training level and environmental conditions and does not relate to decompression. The average time for a dive at any depth does not provide specific insights into safety limits at various depths. Similarly, the required time to ascend safely from any depth is a separate consideration and is not directly described by the term NDL.