When divers ascend too rapidly, they risk developing Decompression Sickness (DCS), commonly called “the bends.” This injury occurs because the rapid reduction in ambient pressure forces dissolved gases within the body’s tissues and bloodstream to come out of solution prematurely. The resulting gas bubbles cause mechanical and inflammatory damage, leading to a wide range of symptoms. DCS is one of two disorders known as Decompression Illness (DCI); the other is the more serious Arterial Gas Embolism (AGE).
Decompression Sickness: The Physiological Mechanism
The cause of decompression sickness is explained by the physics of gas solubility under pressure, primarily Henry’s Law. As a diver descends, ambient pressure increases, causing inert gases—predominantly nitrogen—to dissolve into the body’s tissues. The amount of gas absorbed is proportional to the partial pressure, meaning deeper or longer dives lead to greater gas loading.
The issue arises during ascent, when the ambient pressure decreases rapidly. Nitrogen elimination through the lungs cannot keep pace with the swift drop in pressure, causing the tissues to become “supersaturated.” This state causes the dissolved nitrogen to transition out of solution and form bubbles within the tissues and blood vessels, similar to opening a carbonated drink.
A rapid ascent can also lead to Arterial Gas Embolism (AGE) through a different mechanism. If a diver holds their breath or fails to exhale adequately during a swift ascent, the expanding air in the lungs can rupture lung tissue. This barotrauma releases gas bubbles directly into the pulmonary veins, which then travel to the arterial circulation and can obstruct blood flow to the brain and other vital organs.
Recognizing the Symptoms and Severity
The symptoms of decompression sickness are variable, ranging from mild discomfort to neurological impairment. Symptoms usually appear within one hour of surfacing in about half of all cases, and within six hours in 90% of cases. DCS is classified into two main categories.
Type I DCS is the milder form, often involving the musculoskeletal system, skin, and lymphatic system. The most recognizable symptom is joint pain, particularly in the elbows and shoulders, which is the source of the term “the bends.” Other signs include localized itching, skin mottling, or a rash.
Type II DCS is severe and involves the central nervous system, inner ear, or cardiorespiratory system. Neurological symptoms include numbness, tingling, weakness, or paralysis. Inner ear involvement may manifest as vertigo, dizziness, or hearing loss. Rare, severe cardiorespiratory symptoms—known as “the chokes”—include shortness of breath, chest pain, and coughing.
Emergency Response and Recompression Therapy
Immediate first aid for suspected decompression sickness begins with contacting emergency medical services. The diver should be placed in a horizontal position and kept still to prevent further bubble movement. The most important field treatment is the administration of 100% oxygen via a non-rebreather mask.
Breathing pure oxygen helps create a concentration gradient that encourages inert gas, such as nitrogen, to leave the body’s tissues more quickly. This temporary measure reduces symptoms and stabilizes the patient for transport. Hydration with oral or intravenous fluids is also recommended to support circulation and aid in gas elimination.
The definitive medical treatment for DCS is Hyperbaric Oxygen Therapy (HBOT), which takes place in a specialized recompression chamber. The pressure is increased to a level equivalent to a significant depth, often 60 feet of seawater. This increased pressure physically reduces the size of the gas bubbles, forcing them back into a dissolved state. The patient then breathes 100% oxygen, speeding up nitrogen elimination while the pressure is slowly reduced over several hours.
Essential Safety Protocols for Ascent
The most effective way to prevent decompression sickness is by adhering to safety protocols during ascent. Divers must maintain a slow, controlled ascent rate, generally no faster than 30 feet (9 meters) per minute. Modern dive computers often provide an alarm if this rate is exceeded.
For all dives, including those within “no-decompression limits,” a safety stop is standard practice. This involves pausing the ascent for three to five minutes at a shallow depth, typically between 15 and 20 feet (5 to 6 meters). The safety stop allows dissolved nitrogen to off-gas harmlessly before the final ascent.
For deeper or longer dives, mandatory decompression stops are required, calculated based on the dive profile using tables or a computer. These stops occur at specific depths and durations to manage the significant inert gas load absorbed. Following these schedules and managing the ascent rate are the primary tools divers use to mitigate bubble formation risk.