Decompression Sickness (DCS), commonly known as “the bends,” is a serious medical condition affecting divers, caisson workers, and high-altitude aviators. It occurs when a rapid reduction in ambient pressure causes inert gases, primarily nitrogen, to form bubbles within the body’s tissues and bloodstream. These gas bubbles can obstruct circulation, trigger inflammation, and cause damage to various organ systems, ranging from joint pain to severe neurological impairment. Prevention relies on managing the body’s nitrogen load through procedural discipline and physiological preparation.
Technical Dive Planning and Execution
The core of prevention involves strictly controlling the rate at which inert gas is eliminated from the body during ascent. This process is managed by adhering to the limits calculated by modern dive computers or established dive tables. These tools track theoretical nitrogen absorption, providing a no-decompression limit (NDL) that specifies the maximum time allowed at a given depth before mandatory decompression stops are necessary.
A fundamental safeguard is maintaining a slow and controlled ascent rate, typically not exceeding 30 feet (9 meters) per minute. This speed allows nitrogen to off-gas safely through the lungs without forming symptomatic bubbles. Divers must also perform a safety stop, generally a three- to five-minute pause at a depth of 15 feet (5 meters), even for dives within NDL limits. This brief hold near the surface enhances nitrogen elimination and provides a greater safety margin.
When planning multi-day or repetitive dives, the concept of residual nitrogen must be accounted for by the dive computer or tables. Nitrogen absorbed from previous dives remains in the body, which reduces the allowable bottom time for subsequent dives. Minimizing physical exertion during the deepest phase of a dive is also a prevention measure, as heavy exercise increases blood flow and the rate at which nitrogen is absorbed into tissues.
Pre-Dive Physiological Preparation
A diver’s physical state before entering the water significantly influences susceptibility to decompression sickness. Maintaining optimal hydration is important, as dehydration reduces blood plasma volume, impairing circulation and slowing the body’s ability to off-gas dissolved nitrogen. Divers should consume sufficient non-caffeinated and non-alcoholic fluids in the 24 hours leading up to a dive.
Avoiding alcohol consumption both before and immediately after diving is advised due to its dehydrating effects. Adequate rest and managing fatigue are also important factors, as exhaustion can compromise physiological functions and increase the risk of an incident. While general physical fitness is beneficial, obesity can increase risk because nitrogen is more soluble in fat tissue, leading to a greater gas load.
Thermal regulation plays a role in DCS prevention. While being warm at depth can increase nitrogen uptake, staying comfortably warm during the decompression phase and immediately afterward promotes better peripheral circulation. This enhanced blood flow facilitates the efficient removal of nitrogen from tissues, but divers should avoid rapid rewarming methods like hot showers immediately after surfacing.
Post-Dive Surface Safety Rules
The risk of decompression sickness does not end the moment a diver surfaces, as the body continues to off-gas residual nitrogen for many hours. Adhering to minimum surface intervals between dives is necessary to allow sufficient time for gas elimination before re-exposure to pressure. Conservative guidelines recommend a minimum surface interval of 12 hours for a single no-decompression dive.
For multiple dives per day or multi-day diving, the minimum recommended waiting period extends to at least 18 hours. This prolonged interval is designed to mitigate the cumulative nitrogen load in the body’s slower tissues. Any dive that required mandatory decompression stops dictates an even longer waiting period, often exceeding 24 hours before further diving.
A major post-dive safety rule involves avoiding significant altitude exposure, particularly flying, too soon after diving. Commercial aircraft cabins are pressurized to an equivalent altitude of 6,000 to 8,000 feet, which represents a pressure drop that can trigger bubble formation from residual nitrogen. The minimum recommended pre-flight surface interval is 18 hours for repetitive dives, with experts suggesting a full 24-hour wait to maximize the safety margin.
Recognizing Symptoms and Immediate Response
Even with conservative planning, a small risk of decompression sickness remains, requiring the recognition of symptoms and a swift response. Symptoms can manifest rapidly within minutes of surfacing, or they may be delayed for up to 12 hours. Common signs include joint pain, often described as a deep, boring ache, along with skin manifestations like a mottled rash or intense itching.
More severe symptoms, classified as Type II DCS, involve the central nervous system. These may include:
- Numbness
- Tingling
- Muscle weakness
- Paralysis
- Dizziness
- Loss of balance
Any unexplained symptom occurring after a dive must be treated as decompression sickness until proven otherwise. The immediate and most effective first aid is to place the affected person on 100% oxygen and keep them lying flat.
Following the administration of high-flow oxygen, emergency medical services or a specialized diving emergency network, such as the Divers Alert Network (DAN), must be contacted immediately. The definitive medical treatment for decompression sickness is recompression in a hyperbaric chamber. This treatment works by physically reducing the size of the nitrogen bubbles and simultaneously increasing the oxygen partial pressure to aid in the elimination of the inert gas.