Decompression sickness (DCS), commonly known as “the bends,” results from the formation of gas bubbles within the body’s tissues and bloodstream. This occurs when a person, such as a diver, experiences a rapid reduction in ambient pressure after exposure to a high-pressure environment. The gas involved is primarily nitrogen, an inert component of the air we breathe. Understanding the relationship between diving depth and time spent there is fundamental to managing the risk of bubble formation.
Understanding Pressure and Gas Saturation
The physics governing DCS risk centers on how inert gas, like nitrogen, behaves under pressure. As a diver descends, ambient pressure increases dramatically, doubling every 33 feet (10 meters) of saltwater depth. This increased pressure forces more gas into the body’s tissues, a principle described by Henry’s Law.
During a dive, the body absorbs nitrogen into the blood and tissues, with the amount increasing the deeper the diver goes. Nitrogen is inert and accumulates until the tissues are saturated at the surrounding pressure. The danger arises upon ascent, when the pressure on the body rapidly decreases.
This pressure reduction causes the dissolved nitrogen to come out of solution and form bubbles, similar to opening a can of carbonated soda. The expansion of these bubbles is governed by Boyle’s Law, which states that as pressure decreases, gas volume increases. If the ascent is too fast, the nitrogen cannot be exhaled through the lungs, and the expanding bubbles can cause tissue damage or block blood vessels, leading to the bends.
The Relationship Between Depth and Time Limits
To prevent bubble formation, divers must manage nitrogen absorption by adhering to No-Decompression Limits (NDLs). The NDL is the maximum time a diver can remain at a specific depth and ascend directly to the surface without mandatory decompression stops. Risk accelerates the deeper a diver ventures.
For instance, at 33 feet (10 meters), a diver can stay for over two hours before reaching the NDL. At 60 feet (18 meters), the safe bottom time shortens to around 56 minutes. Dropping to 100 feet (30 meters) reduces this time to 20 minutes, and at 130 feet (40 meters), the NDL can be five to eight minutes.
This exponential shortening demonstrates how depth is the primary factor determining the risk of the bends. Even shallow dives carry risk if the exposure time is long enough to supersaturate the tissues with nitrogen.
Controlling Ascent to Mitigate Risk
Regardless of the maximum depth, the controlled ascent is the final step in preventing DCS. Divers must maintain a slow ascent rate, typically no faster than 30 feet (9 meters) per minute, to allow nitrogen to off-gas safely. This slow rate transforms the entire ascent into a gradual decompression process.
A mandatory safety stop is performed near the end of the dive, usually for three to five minutes at 15 feet (5 meters). This pause is located in the shallowest part of the water column, where the pressure change is most significant. The stop provides a window for the body to eliminate dissolved nitrogen before reaching the surface.
These preventative measures allow nitrogen to be exhaled through the lungs rather than forming symptomatic bubbles in the tissues. Controlling buoyancy and releasing air from the buoyancy control device (BCD) are continuous actions required to maintain this slow, steady ascent. The combination of a slow rate and a safety stop is an effective protocol for managing absorbed inert gas.
Recognizing and Responding to Decompression Sickness
If decompression sickness is suspected, recognizing the signs and symptoms quickly is necessary. Symptoms can range from mild joint pain, often described as a deep, “boring” ache, to serious neurological issues. Common manifestations include:
- Skin rashes
- Unusual fatigue
- Numbness
- Tingling
- Muscle weakness
In severe cases, DCS can lead to paralysis, difficulty breathing, or symptoms resembling a stroke. Symptoms usually appear within one hour of surfacing, though they can be delayed for up to 24 hours. Immediate first aid involves laying the individual flat and administering 100% oxygen, which accelerates the removal of nitrogen from the body.
The definitive treatment for the bends is recompression therapy in a hyperbaric chamber. Inside the chamber, the patient is returned to a higher pressure, forcing the nitrogen bubbles back into a dissolved state. The pressure is then slowly reduced over a monitored schedule, allowing the gas to be eliminated safely.