Decompression Sickness (DCS), commonly referred to as “the bends,” is a serious medical condition affecting divers and others who experience a significant reduction in surrounding pressure. It occurs when inert gas dissolved in the body forms bubbles within tissues and the bloodstream. Preventing DCS requires strict adherence to established safety guidelines and an understanding of the underlying physical principles. This article details the actionable prevention strategies necessary to mitigate the risk of decompression sickness.
The Science of Inert Gas Absorption
The root cause of decompression sickness lies in the physics of gas solubility under pressure, described by Henry’s Law. This principle explains that the amount of gas dissolved in a liquid is directly proportional to the partial pressure of that gas above the liquid. When a diver descends, ambient pressure increases, causing inert gases, primarily nitrogen, to dissolve into the body’s blood and tissues at higher concentrations.
This absorption is not instantaneous; nitrogen gradually loads into the body’s tissues during the dive. The deeper and longer the dive, the greater the amount of nitrogen absorbed. The danger arises when external pressure is suddenly reduced, such as during an ascent, causing the dissolved nitrogen to rapidly come out of solution. If the diver ascends too quickly, the nitrogen comes out of solution too fast for the lungs to eliminate it efficiently, leading to bubble formation in the blood and tissues. These bubbles can obstruct blood flow or damage nerve tissue, resulting in the symptoms of DCS.
Critical In-Dive Safety Protocols
The primary defense against the bends involves meticulous management of the ascent profile, which directly controls the rate of pressure reduction. Current safety standards for recreational diving recommend a maximum ascent rate of no more than 30 feet (9 meters) per minute. Adhering to this slow, controlled speed is paramount to allow nitrogen to off-gas safely through the lungs without forming bubbles.
A mandatory safeguard near the end of every dive is the safety stop. This pause requires the diver to halt their ascent at a depth between 15 and 20 feet (5 to 6 meters) for three to five minutes. The safety stop is performed in the shallow zone where the greatest pressure change occurs relative to the surface, enhancing the elimination of excess nitrogen before the final ascent.
Dive planning relies on calculating No-Decompression Limits (NDLs). NDLs define the maximum time a diver can remain at a given depth and still ascend directly to the surface (plus the safety stop) without requiring mandatory decompression stops. Modern dive computers continuously monitor depth and time, calculating the exact NDL in real-time. Never violating the NDL is a foundational rule, as exceeding it necessitates mandatory decompression stops to avoid DCS.
Managing Personal and Environmental Risk Factors
Preventing decompression sickness extends beyond managing the dive itself to include personal physiological factors and the environment. Dehydration is a significant risk factor because it reduces blood plasma volume, thereby increasing blood viscosity. Thicker blood impairs circulation, which in turn slows the transport of nitrogen from the tissues to the lungs for elimination. Divers should prioritize adequate hydration before, during, and after a dive.
Thermal stress is another element that must be managed, as exposure to cold water is a known contributor to DCS risk. Being cold, especially during the decompression phase, causes peripheral blood vessels to constrict. This restricts blood flow to the extremities and slows down nitrogen off-gassing. Conversely, rapid external warming, such as a hot shower immediately after a cold dive, can quickly increase blood flow to the skin, potentially triggering bubble formation from supersaturated tissue.
Managing repetitive dives requires careful attention to the surface interval, which is the time spent out of the water between dives. This interval allows the body to continue the off-gassing process and is crucial for calculating the residual nitrogen level before the next dive. For multi-day diving, the cumulative nitrogen load increases, making longer surface intervals and conservative dive profiles necessary.
A critical rule is the prohibition on flying or ascending to high altitudes too soon after diving. Commercial aircraft cabins are pressurized to an equivalent altitude of 6,000 to 8,000 feet, which represents a significant drop in ambient pressure. Experts recommend a minimum surface interval of 12 hours for a single no-decompression dive and at least 18 hours for repetitive dives before flying.
Recognizing Symptoms and Immediate Action
Despite the best precautions, understanding the signs of DCS and the correct emergency response is a final safety measure. Symptoms can range from mild joint pain, often described as a deep ache, to neurological signs like numbness, tingling, or muscle weakness. Other indications include skin rashes, extreme fatigue, or difficulty with balance and coordination.
The onset of symptoms typically occurs within minutes to a few hours after surfacing, and any unusual physical change should be immediately investigated. The immediate first response for a suspected case of decompression sickness is to administer 100% oxygen via a tight-fitting mask. This rapidly accelerates the elimination of nitrogen from the body. The affected person must be kept lying flat and still to prevent bubble migration or worsening of the condition.
The definitive treatment for decompression sickness is Hyperbaric Oxygen Therapy (HBOT), which requires immediate transport to a hyperbaric recompression chamber. The chamber increases the ambient pressure, which physically shrinks the nitrogen bubbles back into a dissolved state, allowing for their safe elimination. Prompt first aid and rapid transport to a specialized facility are necessary to achieve a full recovery and minimize the chance of permanent tissue damage.