What is the difference between non-decompression limits (NDLs) and stop times?

The rationale behind the distinction between non-decompression limits (NDLs) and stop times revolves around safety in diving practices. NDLs specifically indicate how long a diver can remain at a certain depth without needing to perform mandatory decompression stops upon ascent. This signifies that if a diver exceeds the NDL, they risk developing decompression sickness, which is caused by insufficient ascent time and pressure changes creating nitrogen bubbles in the body.

In contrast, stop times refer to mandatory decompression stops that are required if a diver exceeds the NDL on their ascent. These stops provide a controlled and safe way for divers to off-gas nitrogen and reduce the risks associated with rapid changes in pressure.

Therefore, the correct answer reflects that NDLs give divers crucial information about safe diving durations without the need for decompression stops, while stop times become necessary for those who exceed those limits, enhancing diver safety and understanding of decompression procedures.