Freediving and Decompression Sickness
Freediving and decompression sickness is a frequent topic of discussion within the dive community. While decompression sickness is often thought of in relation to scuba diving, it’s also something we need to be aware of in freediving. It may not be highly likely, but it is possible if we don't take the correct steps to mitigate the risk. Taking the appropriate amount of time at the surface and planning our dives should be prioritized for all freedivers.
In this article, we will cover exactly what you need to know about decompression sickness in freediving and how you can avoid it. Educating yourself about safe freediving practices regarding decompression sickness allows you to properly relax and enjoy your dives to the full potential without worrying about exposure to risk.
What is Decompression Sickness
Decompression sickness is a medical condition that arises from nitrogen bubbles forming in the blood and tissues. The bubbles can become lodged in various parts of the body, creating discomfort, pain, or other symptoms.
When exposed to higher pressures, such as being underwater, the gases in our lungs become more concentrated. The higher concentration of gas begins to dissolve into our tissues over time. While this happens with all gasses, the primary concern is nitrogen. The air we breathe is comprised primarily of nitrogen, an inert gas. This means our body cannot metabolize or use the gas, so it just sits in our tissues.
The issue, and risk of DCS, arises when the pressure drops or returns to normal, such as surfacing from a dive. As the surrounding pressure decreases, the dissolved nitrogen comes out of solution. If there is an excess of nitrogen or this process happens too quickly, nitrogen bubbles may form in our bodies. This is known as decompression sickness.
The resulting bubbles can become lodged in various parts of the body such as joints, blood vessels, or under the skin. If nitrogen bubbles become lodged in joints, it can cause pain and discomfort. Blood vessels blocked by bubbles can have far more severe ramifications depending on the location. The result of the blockage can range from mild effects such as numbness or tingling to more serious conditions such as paralysis or stroke-like symptoms.
Signs and Symptoms of DCS
Signs and symptoms of DCS include the following:
Extreme fatigue
Nausea or feeling of illness
Headache
Numbness and tingling
Joint pain
Paralysis
Confusion
Speech difficulties
Blurred vision
Can Freediving Cause Decompression Sickness?
Freediving can cause decompression sickness, but it is easily avoided. Freedivers are not at as high of a risk for DCS as scuba divers because we spend a relatively short amount of time underwater in relation to our depth.
The amount of nitrogen dissolved in our tissues coincides with the amount of pressure we are exposed to and the time spent under pressure. Therefore the deeper the dive and the more time spent at depth, the more nitrogen dissolves into tissues.
This is why scuba divers are more concerned with the possibility of DCS, as they spend up to an hour or more breathing compressed gas at depth. Spending this much time under pressure allows more nitrogen to be absorbed into the body compared to freediving.
Freediving, on the other hand, exposes us to pressure for significantly less time on a single breath. This means less nitrogen dissolves into our tissues. However, the trade-off is that freedivers are constantly up and down. Although we have less nitrogen in our system, the pressure change is far more dramatic as we ascend much faster than scuba divers. The abrupt drop in surrounding pressure as we ascend can contribute to the formation of bubbles with a relatively small amount of dissolved nitrogen compared with scuba. Therefore doing repetitive dives over a short time can increase our risk of decompression sickness.
Luckily, this is easily avoided by spending sufficient time on the surface in between dives. This time at the surface allows the nitrogen to safely leave our body before the next dive, and it is known as a “surface interval.” In scuba diving, surface intervals of an hour or more may be required for subsequent dives, but this isn't the case in freediving. Safe and conservative surface intervals for freediving can be done in a matter of minutes. In fact, most of the time, the surface interval is completed in the time it takes to let your buddy perform a dive and do a nice relaxation phase before your subsequent dive.
So don’t worry it won’t interfere with the number of dives you’ll have or your enjoyment. If you find you need additional time on the surface, utilize the time to fall deeper into relaxation, which only stands to improve your next dive.
Do You Need to Decompress When Freediving
You do not need to “decompress” in the usual understanding of the word when it comes to freediving. The term Decompression, or “deco stops,” is often used in scuba diving to imply that divers need to stop at shallower depths to allow nitrogen to leave the body before surfacing.
We do not absorb enough nitrogen during our dives to require decompression stops. This is great news as we are limited by our breath-hold, and deco stops would complicate the matter. The issue arises from repetitive dives over a short period which does not allow enough gas to be released between dives, and nitrogen builds up throughout the session. That being said, surface intervals in themselves can be considered a type of “decompression” in freediving.
Surface Intervals in Freediving
Surface intervals in freediving are the time we spend on the surface between dives. Surface intervals are necessary to conduct safe dive sessions without concern or DCS risk. If freedivers do not follow appropriate surface interval practices, they significantly increase their risk of getting decompression sickness.
Rather than viewing surface intervals as something that is preventing you from doing your next dive, know that they are an opportunity to relax longer. This will only increase the ease of the following freedives.
Calculating Freedive Surface Intervals
Calculating freedive surface intervals is done by multiplying the maximum atmospheric pressure reached by the total time of the previous dive. This is why having a dive computer is critical for freedivers who arent out with a guide or instructor.
To calculate surface intervals, divers must understand how to convert the dive depth to the total pressure. Total pressure accounts for the pressure at the surface, 1 atmosphere (ATM), and the pressure underwater, which is 1 ATM per 10 meters of seawater.
For instance, the pressure on a dive to 20 meters is 3 ATM:
1 ATM (surface pressure) + 2 ATM (20 meters) = 3 ATM
Should the depth of your dive fall between multiples of 10, it's easiest and most conservative to round up to the next even increment of 10. IE: 25 meters = 3 ATM
Following this, we simply multiply the total pressure (P), by the dive time (T), and you will get your minimum surface interval (SI).
P x T = SI
For example:
If a diver performs a freedive to a depth of 20 meters for 1 minute. The surface interval calculation is as follows:
3 ATM x 1 min. = 3 min. surface interval
The only exception to this rule is for extremely deep dives. For dives to a depth of 60 meters or deeper, only one dive should be performed every 24 hours. This is due to the extreme pressure at those depths for which we need to allow ample time for decompression.
Freediving and Scuba Diving
Freediving and scuba diving together has special considerations that should be followed closely. Freediving before scuba diving is acceptable however, freediving after scuba diving is not recommended.
Because of the build of nitrogen in our bodies during scuba diving, performing a subsequent freedive without waiting for the appropriate amount of time puts divers at exceptionally high risk of DCS. The rapid and abrupt increase and decrease in pressure during freediving can cause bubbles to form from the nitrogen dissolved during previous scuba dives, which would otherwise be of no concern.
Therefore it is recommended to wait 24 hours after scuba diving before performing any freediving activities.
Final Thoughts
As prudent freedivers, we should all be aware of freediving and decompression sickness. Although freedivers do not have the same exposure to nitrogen as scuba divers, we can still put ourselves at risk if we do not follow the proper procedures. We can easily mitigate the risk of DCS in freediving by simply spending sufficient time at the surface between dives.
As freedivers, we are all very familiar with the highly addictive nature of the sport. Most of us can’t wait to get back beneath the surface in search of the joy and serenity only freediving can provide. But remember, more time on the surface is never a bad thing. Use the time to drop deeper into relaxation, reflect on your previous dive, and anticipate the meditative experience of your next venture below the surface.