When diving we all know it is imperative we meet the correct decompression requirements otherwise we expose ourselves to the risk of Decompression Illness (DCI) and a Cerebral Arterial Gas Embolism (CAGE).
When diving on Air, the rate nitrogen diffuses into our body is determined by the depth and duration of our dive. It is important that when we ascend to the surface on the completion of our dive, we allow the nitrogen to expel from our body at a controlled rate otherwise an excessive number of bubbles of nitrogen gas form in our tissues and blood, which can result in the development of DCI or CAGE.
To expel the nitrogen from our body we use decompression stops, which can be carried out in-water, in a recompression chamber (RCC) or a mixture of both. A decompression stop is a time spent at a nominated depth to allow our body to expel nitrogen. Saturation divers who dive at extreme depths will decompress in a recompression chamber because it will generally take days for them to decompress. When diving at reasonably shallow depths it is more common to complete decompression stops in-water. Another option to decompress is to use in water stops and a RCC. This method is good for deeper dives because they require longer decompression times and it is more comfortable sitting in a RCC on the surface or in a boat rather than being in the water in ocean swells, exposed to hazards or being cold. It is also very effective when diving surface supplied breathing apparatus (helmet diving). In this instance divers can be decompressing in a chamber, and whilst doing so the equipment they just used can be set up for the following dive.
To give you an idea of how surface decompression is carried out. Lets say you are completing a dive to 6o meters breathing air. You have finished your task, left bottom and are ascending to the surface. You carry out your required in-water decompression stops as per your decompression table up to and including the 9 meter stop. On completion of the 9-meter stop you will ascend directly to the surface, onto a boat (for example), undress from all your diving equipment down to your wetsuit, enter a RCC and recompress on oxygen to a depth 12 meters. The time between leaving the 9-meter stop in the water and descending to 12 meters in the RCC is 7 minutes. This eliminates the chances of omitted decompression. Every 30 minutes breathing oxygen in the chamber you will carry out a 5-minute air break to prevent oxygen toxicity. Apart from that all you need to do is relax and allow the chamber operator to bring you safely back to the surface as per the decompression table requirements.
There are risks involved with surface decompression procedures however when the correct procedures are followed it's a safe, comfortable method of decompressing divers and effective in running productive diving operations.
Prepping the 2 Man RCC for Diving using Surface Decompression