As a diving expert with years of experience in various underwater environments, I can provide a detailed explanation on the limits of diving depth and the necessity of decompression stops.

Diving is an activity that requires a deep understanding of physics, physiology, and safety protocols. The human body is not designed to withstand the pressures encountered at great depths, and as such, divers must be cautious about how deep they go and for how long they stay at those depths.

Depth and Pressure
The pressure in the water increases by approximately 1 atmosphere for every 10 meters (33 feet) of depth. This means that at 20 meters (66 feet), a diver is already experiencing twice the atmospheric pressure at the surface. This increase in pressure has significant implications for a diver's body and the gases they breathe.

Nitrogen Absorption
When a diver breathes compressed air, which is primarily composed of nitrogen and oxygen, the nitrogen dissolves in the body's tissues. At shallow depths, the body can off-gas this nitrogen without issue. However, as depth increases, the nitrogen dissolves more rapidly and in greater quantities, leading to a higher risk of decompression sickness (DCS), also known as "the bends."

Decompression Stops
To mitigate the risk of DCS, divers must make decompression stops as they ascend. These stops allow the body to gradually release the absorbed nitrogen. The need for decompression stops increases with depth. As you mentioned, a diver at 6 meters (20 feet) may be able to dive for many hours without needing to make decompression stops. However, at depths greater than 40 meters (130 feet), a diver may have only a few minutes at the deepest part of the dive before decompression stops are required.

No-Decompression Limit (NDL)
The no-decompression limit is the maximum depth and time a diver can stay without needing to make decompression stops. This limit varies based on the dive profile, including depth, duration, and the rate of ascent. Recreational divers are typically advised to stay within the no-decompression limits to avoid the risk of DCS.

Maximum Operating Depth (MOD)
Different types of diving have different maximum operating depths. For example, recreational scuba diving is generally limited to a maximum depth of 40 meters (130 feet), while technical diving can go much deeper, with some divers reaching depths of 100 meters (330 feet) or more. However, technical diving requires advanced training, specialized equipment, and strict adherence to safety protocols.

Safety and Training
Safety is paramount in diving. Divers must be properly trained and certified for the depths they intend to reach. Training includes learning about decompression theory, dive planning, and emergency procedures. Divers must also be in good physical health and be aware of their personal limits.

Conclusion
In conclusion, the depth a diver can safely reach is limited by several factors, including the body's ability to tolerate pressure, the rate of nitrogen absorption, and the need for decompression stops. Recreational divers should always stay within their training limits and follow safety guidelines to prevent decompression sickness and ensure a safe and enjoyable diving experience.

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To put these depths into perspective, three American football fields laid end to end would measure 900 feet (274.32 m) long -- less than the distance these divers reached underwater. Most recreational scuba divers only dive as deep as 130 feet (40 meters), according to the Professional Association of Diving Instructors.read more >>