You may have heard of them, or experienced divers – especially those who are technically trained – might have mentioned them to you in a conversation, you may even have read a thing or two about them. But the question remains, what the heck are deep stops, and why is it useful to know about them as a recreational diver?
In the last 15 years or so, deep stops have made a slow but steady progress on their way from the closeted realm of technical diving into the everyday recreational scuba diving. Their progress has been so pervasive that even computer manufacturers have relented, and today many recreational dive computers have deep stops built into their algorithms.
Today’s diving computers utilize a very simple method to indicate a deep stop to the user. Most computers indicate a decompression ceiling for the diver as he begins his ascent, even if the diver has no decompression obligation. This ceiling, which is much deeper than any decompression stop ceiling, only lasts for one to two minutes once the diver reaches it. The diver can then resume his ascent as normal. But what we want to know is why all the fuss about deep stops, what are they and what do they do?
Casting an eye back in time, it becomes quite apparent that this whole new part of decompression theory and its development is mainly due to the genius of one man.
The early 90’s was a great time in our understanding of decompression theory, as well as some big jumps in the quality and technological innovation of dive equipment. One of the biggest contributors to decompression theory was Dr Richard Pyle. The Doctor, who is an Ichthyologist (someone who studies fish), regularly conducted dives while working for a museum and research center in Hawaii. His diving, which was a mix of recreational and technical, resulted in him making a few observations that piqued his scientific curiosity, and the end result was the creation of deep stops.
The question that Dr Pyle tried to answer was a curious one, since over time he had noticed that although he conducted thousands of dives, sometimes he felt very fatigued after dives, and sometime he felt absolutely fine. This question really bothered the enterprising doctor since the event occurred on many dives that for all intents and purposes where identical. There had to be a reason why.
Like any self-respecting scientist, Dr Pyle began by applying his scientific method to the problem, and the first thing he had to do was amass a large solid data set to enable him to reach any viable conclusion. Dr Pyle began to meticulously record in great detail the events of every dive he was doing. After collating the data and studying it, he came to one stunning conclusion: the dives that resulted in less fatigue were the ones he collected a fish sample on. Dives where he did not collect a sample were the dives that made him feel fatigued post dive.
At first, the solution seemed psychosomatic – surely, Dr Pyle reasoned, it could not be a psychological high that “getting a fish” led to less fatigue! After all, he was an experienced scientist who had collected hundreds if not thousands of specimens, he was not a giddy new researcher happy with a fish. He would have to dig deeper to find out the truth.
After going back and looking at the data again the enterprising doctor finally had his eureka moment. He realized it was nothing to do with psychology, and had everything to do with exploding fish.
Fish have a unique way of controlling their buoyancy; inside the fish, there is a swim bladder that the fish uses like a BCD. The fish adds and removes gas from this bladder to control its buoyancy. When you capture a fish specimen and starts to ascend with it, you have to stop for a minute or so and use a syringe to release some of the expanding gas from the specimen’s swim bladder. If the diver does not do this, the swim bladder will explode on ascent and ruin the sample, and this is exactly what Dr Pyle was doing every time he collected a sample. He realized that these stops, which were much deeper than his normal decompression stops, not only allowed the doctor to bleed out gas from the fish, but also allowed his own body to release small amounts of gas from his fast tissues. Thus preventing the formation of micro bubbles later in the dive or post ascent.
The doctor went on to publish his findings and develop a mathematical formula for calculating his way of doing deep stops, and from that day on Pyle stops and deep stops were born. Needless to say, since those heady days there has been more and more research as divers have taken a keen interest in developing this new branch of decompression theory.
Find out more about decompression theory.