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The Silent Threat: Understanding Decompression Sickness Risk Factors

Updated: Apr 23


An illustration of a scuba diver ascending and the bubbles that are in his tissues

Scuba diving allows us to explore a breathtaking underwater world. But like any exhilarating activity, it comes with inherent risks. Decompression sickness (DCS), or "the bends," is a severe medical condition that can occur after a dive. It happens when nitrogen bubbles form in your bloodstream and tissues as you ascend too quickly. While you significantly reduce the risk of decompression sickness by following safe diving practices, certain factors can make you more susceptible to DCS. Let's delve into the top 5 culprits and how to mitigate them for a secure and unforgettable dive experience.


1. Exertion: How you move your body during a dive can significantly impact decompression sickness (DCS) risk. Exertion, or workload, refers to the intensity and timing of your physical activity underwater. Let's explore how exertion affects DCS risk throughout your dive.


Minimizing Exertion is Key:  Imagine your body like a sponge; the deeper you dive and the harder you work, the more nitrogen your tissues absorb. Excessive exertion, particularly during descent and at the deepest part of your dive, increases blood flow and its capacity to carry inert gas (primarily nitrogen). This translates to more nitrogen absorbed by your tissues, requiring more decompression time later to eliminate excess gas safely and avoid DCS. Alternatively, you can proactively make your dive shorter. 

Finding the Right Pace:  While minimizing exertion throughout your dive is essential,  gentle movement during decompression stops can be beneficial in promoting the off-gassing of nitrogen and reducing DCS risk.

After the Dive:  Avoid strenuous exercise for as long as possible after surfacing. Physical exertion can stimulate bubble formation and increase the likelihood of bubbles bypassing the lungs, which act as a natural filter.

By following these tips and taking control of your dive pace, you can significantly reduce your risk of DCS. Remember, you're in charge of your dive, so take your time and explore at a leisurely pace.


2. Thermal Stress: Our bodies are complex systems, and maintaining a comfortable temperature underwater is crucial for preventing decompression sickness (DCS). Thermal stress, caused by being too cold or hot during a dive, can significantly impact your DCS risk.

A diver's body temperature plays a significant role in managing inert gas, primarily nitrogen. According to Henry's Law, the amount of gas dissolved in a liquid is directly proportional to the pressure. During descent, as pressure increases, the volume of gas that your tissues can absorb also increases. This is why maintaining a cooler body temperature during descent and at depth helps restrict the expansion of your blood vessels and minimize inert gas uptake.

Here's where things get interesting. The same principle applies during ascent. As you rise towards the surface, the pressure decreases, and the absorbed gas needs to escape your tissues. Warmer body temperatures promote the expansion of blood vessels, allowing for better circulation and a more efficient release of inert gas. Therefore, aiming for a warmer body temperature during ascent and decompression stops facilitates the elimination of excess gas and reduces DCS risk.

Another culprit is dehydration. You can become dehydrated if you get too hot before, during, and after a dive, and don't replace lost fluids. Dehydration thickens your blood, making it more difficult for your body to circulate blood and eliminate nitrogen waste products. Think of it like pushing thick mud through a pipe—it takes more effort!


Staying Comfortable for Safe Diving

  • Divers using protective suits without active heating should choose a thickness appropriate for the water temperature to avoid getting chilled, especially toward the end of the dive.

  • Divers with heated suits should aim for a comfortable coolness at depth and prioritize staying warm during decompression stops. Staying warmer at this dive stage promotes optimal gas elimination and reduces DCS risk.

  • Maintain thermal comfort throughout your dive. While staying warm is essential, avoid the urge to rapidly rewarm after surfacing, such as taking a hot shower or bath. This sudden temperature change can increase your risk of DCS. Here's why: During decompression, the body works hard to eliminate inert gas. Rapid rewarming causes blood vessels to dilate, which can lead to a sudden release of inert gas bubbles back into the bloodstream. If these bubbles are too big to filter out by the lungs, they can lodge in tissues and cause DCS symptoms.

Hydration is Key: Remember to stay hydrated before, during (if possible), and after your dive. Proper hydration helps maintain blood flow and circulation, aiding in nitrogen elimination.

Prioritizing a thermal profile that emphasizes cooler temperatures during descent and depth and warmer temperatures during ascent and decompression can significantly reduce your risk of DCS.


3. Post-Dive Air Travel: Not the Best Post-Dive Plan! The allure of a tropical diving adventure often includes a quick getaway flight home. However, this seemingly convenient plan can pose a severe risk of decompression sickness.


The Rapid Rise Risk:  During your dive, your body absorbs inert gas, primarily nitrogen. While a slow ascent with proper decompression stops allows this gas to be eliminated safely, airplanes present a different scenario. Cabin pressure at high altitudes is significantly lower than sea level, mimicking a rapid ascent from the depths. This rapid pressure change can trap residual nitrogen bubbles in your body, potentially causing them to expand and migrate to your tissues, exposing you to a higher DSC risk.


Planning for a Safe Return: To minimize your DCS risk after diving, ensure sufficient surface time before flying. Here are the recommended guidelines:

  • Single no-decompression dive: Wait at least 12 hours before flying.

  • Multiple dives per day or multiple days of diving: Wait at least 18-24 hours before flying.

  • Dives requiring decompression stops: Wait more than 24 hours before flying (consult a professional).


Remember: These are guidelines and effective measures to reduce your DCS risk. Extending your surface interval can further enhance your safety. Following these recommendations significantly reduces your DCS risk. However, there's no guaranteed 'safe' waiting period. Always prioritize your safety and listen to your body. If you experience any DCS symptoms after diving, seek medical attention immediately.

By carefully planning your post-dive travel and prioritizing safety measures, you can ensure a smooth and enjoyable return home after a diving vacation.


4. Medical Fitness: Ensuring a safe and enjoyable diving experience requires careful consideration of several factors, including your overall health and physical fitness. Certain medical conditions, medications, and even your physical fitness level can significantly increase your risk of decompression sickness (DCS).


Medical Conditions and DCS Risk: Pre-existing respiratory problems like asthma can make breathing difficult during ascent, potentially leading to air trapping in your lungs and complications during decompression. Likewise, heart and lung disease can compromise your body's ability to eliminate nitrogen efficiently, increasing the risk of bubble formation. Some medications, like certain diuretics, can also pose a risk, as they can affect your hydration and potentially alter gas absorption or elimination.


How to Mitigate the Risk:

  • Be honest about your health: If you have any concerns, consult your doctor before diving, especially if you have any pre-existing medical conditions or take medications regularly. A thorough medical evaluation can identify potential risks and ensure you're fit to dive safely. Be sure to understand your physical condition, medications, and their potential impact on diving.

  • Maintain good physical fitness: Regular exercise, including cardiovascular activity and strength training, can significantly reduce your DCS risk. Follow established guidelines from reputable health organizations like the Centers for Disease Control and Prevention (CDC) for optimal health benefits.


5. The Breathing Gas Mixture: The gas you breathe underwater significantly affects your risk of decompression sickness (DCS). Air, the most common recreational diving gas, contains a high percentage of nitrogen (around 78%). As discussed earlier, higher nitrogen content exposes you to a higher risk. Fortunately, we have safer alternatives for deeper dives: Enriched Air Nitrox (Nitrox). This breathing gas mixture blends oxygen and nitrogen with a reduced percentage of nitrogen compared to air. Nitrox can significantly reduce your DCS risk by decreasing your overall nitrogen load. However, it's essential to be aware of the trade-offs involved with Nitrox. While the reduced nitrogen content benefits DCS prevention, Nitrox also has a higher oxygen content. While beneficial in some ways for deeper dives, exceeding safe depth limits with Nitrox can increase the risk of oxygen toxicity, a severe medical condition.


How to Mitigate the Risk:

  • Consider the type of diving you'll be doing. Nitrox can be safer for deeper dives, reducing your DCS risk. However, Nitrox is unsuitable for all dives, so consulting a professional is crucial.

  • Always adhere to safe depth limits when using Nitrox to avoid oxygen toxicity. Nitrox diving requires specific training and adherence to designated depth tables to ensure safety.

  • Other mixed gases and a rebreather are also options, but they are typically used in more advanced applications and less in recreational diving.


Individual susceptibility to DCS may vary, and DCS is a preventable condition. By being aware of the risk factors and following these safety tips, you can significantly reduce your chances of experiencing it:

  • Ascend Slowly and Follow Decompression Stops

  • Stay Hydrated

  • Plan Your Post-Dive Travel Wisely

  • Get Proper Training and Certification

  • Listen to Your Body


Remember, safe diving is not just about the destination; it's about enjoying the journey every step of the way!




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