NDL (No Decompression Limit) Tables
The No Decompression Limit (NDL) or no stop time, is the interval that a scuba diver can theoretically spend at a given depth without having to perform decompression stops. When divers breathe air under pressure, inert gases, such as nitrogen and helium, dissolve into their body tissues. As the diver ascends from a dive the ambient pressure reduces and the dissolved inert gases in their tissues come out of solution. If this process occurs too quickly decompression sickness can result. The No decompression limit helps divers plan dives so that they can stay at a given depth and ascend without stopping without significant risk of decompression sickness (the bends).
Decompression sickness (DCS), the diver’s disease, the bends, or caisson disease is the name given to a variety of symptoms suffered by a person exposed to a decrease (nearly always after a big increase) in the pressure around the body. It is a type of diving hazard and dysbarism.
No decompression limits are typically printed on dive tables in a grid that can be used to plan scuba dives. There are many different tables available as well as software programs and calculators, which will calculate no decompression limits. Dive tables allow scuba divers to plan multiple dives by allowing the diver to calculate the residual inert gases remaining in their body after Surface Interval Time, a period of time at the surface during which excess nitrogen leaves the body.
It should be noted that the No Decompression Limits are theoretical. Although there is a science to calculating no decompression limits there is still much that is unknown about how inert gas enter and leave the human body. In addition, every individual's body is unique and may absorb and release inert gases at different rates. For this reason dive tables typically have a degree of safety built into their recommendations. Divers can and do suffer decompression sickness while remaining inside No Decompression Limits.
The History of No Decompression Limits
Dr. John Scott Haldane created the first tables for scuba diving based on his research for the British Royal Navy. Based on his understanding of Henry's Law and through experimentation with goats, Haldane developed the first dive table which was used by the Royal Navy to prevent decompression sickness in divers. In 1912, Chief Gunner George D. Stillson of the United States Navy created a program to test and refine Haldane's tables. This program ultimately led to the first publication of the United States Navy Diving Manual and the establishment of a Navy Diving School in Newport, Rhode Island. Diver training programs were later cut at the end of World War I.
In 1925 a United States submarine, the USS S-51, was sunk after a collision with a passenger liner. Public interest in raising the submarine sparked renewed interest in diving and, in 1927, the Naval School, Diving and Salvage was re-established at the Washington Navy Yard. At this time the US Navy moved their Experimental Diving Unit (EDU) to the same naval yard. In the following years, the Experimental Diving Unit developed the US Navy Air Decompression Tables which have become the accepted world standard for diving with compressed air.
NDL (No Decompression Limit) Table
The Kingfisher Diver-Pro Swiss Movement Divers Watch is one of the first in the world to incorporate a ‘No Decompression Limit' (NDL) table engraved on its back.
Watch Back Engraved with NDL (No Decompression Limit) Table
This valuable feature is designed as a back-up device for experienced divers, for use with Recreational Dive Planner Tables to ensure a safety first dive.
NDL (No Decompression Limit) Table Engraved on Watch Back
