Deep Stops and Scuba Diving in 2017: Do I need to do a Deep Stop?
The theory and practice of Deep Stops remains a controversial issue among many within the diving community. Deep Stops should never be added at the expense of reducing the shallower stop times of a decompression dive.
Deep stops should be considered when diving to depths below 65.6 feet (20 meters). Click the item in the table below to skip to your most pressing question, or continue to read the whole article.
What is a Deep Stop?
There's one big important thing about Deep Stops that entry level and many recreational divers need to note. Deep Stops don't need to be considered in a plan until you're diving to a depth of 65.5 feet (20 meters) or greater.
At the Open Water Diver level, divers gain basic skills, knowledge and theory for diving to a recommended depth of about 60 feet (18 metres). Once you're qualified to dive to past these depths, Deep Stops should be considered when planning your plan.
A Deep Stop is an short stop of between 1-3 minutes taken during your ascent. These are additional stops taken at depths well below the mandatory decompression stops. The thinking is that additional short stops taken during your ascent will help naturally disperse the nitrogen that has built up in your body.
The History Behind the Deep Stop
In the 1980s, an ichthyologist (someone who studies fish) named Richard Pyle often made deep reef dives in search of fish species to collect. His dives were to depths of between 180 and 220 feet (50 and 70 meters).
Over time, Pyle began to notice that at times after a deep dive he felt post-dive fatigue, and at other times he felt quite normal. Pyle reviewed his dive profile and realized he always felt better after a dive where he'd caught fish specimens. During these dives, he made a stop during his ascent to deflate the swim bladders of the fish.
After dives where he hadn’t caught any fish, Pyle didn't need to stop to deflate the swim bladders so ascended directly to the first mandatory decompression stop before stopping. It was after these dives that he felt fatigue symptoms once back on the surface. Pyle started including a brief stop halfway to the surface on all his deep dives, whether he'd caught fish or not.
This stop was well below the normal decompression stops mandated by conventional dive algorithms at the time.
Pyle's later formulated a system of including a brief 2-3 minute stop at a position half-way between the previous stop (or the bottom depth) and the first stop mandated by his decompression schedule. Based on his personal experience, Richard Pyle formed the strong opinion that this deep stop greatly reduced his post-dive fatigue.
In 1989 Pyle received some justification on his findings when he found that his pattern of ascent was very similar to that of Dr. David Yount's Varying Permeability Model (VPM) of decompression calculations.
Pyle shared his theory and technique with his fellow divers. Before it could be scientifically tested, the practice of deep stops became widespread among technical divers from the late 1990’s.
This is why Deep Stops are also known as Pyle Stops.
At what depths are Deep Stops taken?
The first Deep Stop is at the midway point between the bottom depth and the 1st decompression stop depth. The next Deep Stop is taken at the midway depth between the last Deep Stop depth and the 1st decompression stop depth. The table below helps shows this clearly.
Which Dive Computers have a Deep Stop function?
Most dive computers on the market, now have Deep Stops to cover the practices now adopted by many technical and professional divers. These can be adjusted or turned off altogether.
If you have a dive computer that has a Deep Stop feature, you should probably follow it. The Suunto D4i and D4i Novo, and the Suunto D6i dive computers have a Deep Stop function. This is activated when diving deeper than 65.6 feet (20 meters). This is ON by default in Air and Nitrox modes and can be turned OFF.
Of the entry-level dive computers, the Suunto Zoop doesn't have a Deep Stop function. Other entry-level computers such as the Cressi Leonardo, Mares Puck Pro and Suunto Zoop Novo all have Deep Stops built in.
What's the effectiveness of Deep Stops?
Opinions on the effectiveness of Deep Stops remain varied among those in the diving community. There is research that shows a reduced venous bubble count after including both Deep Stops and standard decompression stops into a dive plan. This is when compared to stopping at decompression stops only.
The length of a Deep Stop is generally 1 or 2 minutes. Adding a Deep Stop while still following the mandated shallower decompression stops has not been shown to be harmful. Many divers do report a better post-dive feeling when including Deep Stops into their dive plan.
As part of their program, the Sub-Aqua Association of the UK now includes training on deep stops for all deep dive ascents.
After more than a hundred years of working on decompression theory and safety, we still can't say with certainty what the ideal decompression profile is. In fact, the ideal profile may be slightly different for each of us.
We know that a range of profiles with first stops at different depths have been reasonably successful. Scientific studies will continue to give us better evidence over time that will help us find that ideal.
The bottom line at the end of the day is to plan and dive as safely as possible to reduce the risk of getting bent.
As individuals, we have to look at the slowly mounting evidence and make our own decisions. If you're feeling fatigued in the afternoon after a morning spent on a long dive, then try incorporating a deep stop of 2 minutes at your half depth, and see how you feel. After all, it's only a minute or two.
While researching this article, I found a lot of confusing or overly technical posts on Deep Stop theory. This article has been written in an attempt to help others understand what Deep Stops are, even if they remain controversial. Knowledge is power. Please share this post if you've enjoyed it.
Below is a video on Safety Stops by Dive Training Magazine. It shows the various options for safety stops and the procedures.