Essentials of the GUE equipment configuration

Using extra cylinders to extend dive time or to accelerate decompression is fundamental to technical diving. In fact, the presence of extra tanks is essential to the definition of technical diving: diving in ceiling/overhead environments and breathing multiple gases during the dive.

To ensure a safe and effective dive, it’s important to understand the proper configuration of the extra tanks, the selection criteria for size and material, and the proper protocols for handling stage and deco tanks.

Terminology

There are a few different names for compressed gas cylinders that are not worn on the back, so let’s clarify some terminology. These containers are commonly referred to as cylinders, tanks, or bottles. In this text, we will use the term “tank” to refer to all of them. When we add a prefix to “tank,” it becomes a bit more complicated. We encounter terms such as stage tanks, decompression (or deco) tanks, sling tanks, sidemount tanks, pony-tanks, and bailout tanks. We also have argon tanks or suit inflation tanks. For now, we’ll focus on stage and deco tanks. Stage tanks are primarily intended to extend bottom time by providing an extra volume of gas. Typically, a stage tank will contain the same gas mixture as the back gas for that dive. On the other hand, deco tanks contain gas mixtures specifically designed to accelerate decompression. The contents of a deco tank will vary depending on the depth and duration of the planned decompression stops.

In short, a stage tank provides longer bottom time, while a deco tank is used to reduce decompression time. Although some people use the terms “stage tank” and “deco tank” interchangeably, they have distinct purposes. For the sake of simplicity, we will use the term “stage tank” throughout the rest of this article. The configuration and markings of these tanks are the same, so this simplification is justified.

Material and sizes

Typical stage tanks are usually 40cf or 80cf aluminum tanks. An alternative option is the 7 L tank, which falls between the two sizes. Aluminum tanks are preferred for stage use because they have superior buoyancy characteristics. When empty, they are positively buoyant and will float up and out of the way, and when full, they are slightly negative, which helps them stay in the proper position. In contrast, steel tanks should be avoided for stage use because they are very negative when empty and even more so when full. Using steel stage tanks as part of a weighting strategy can cause a diver to become dangerously over-weighted. If a diver loses or is forced to let go of a steel tank, they may become dangerously light, making it challenging to maintain mandatory decompression stops or exit a cave.

The ideal size of a stage tank depends on the gas requirements of the dive. For bottom gas, a large S80 or its equivalent is usually preferred. However, for shorter decompression times, smaller tanks are easier to carry. In a situation where multiple stage tanks are required, stages of different sizes can be deployed. For example, a diver might use an S80 tank for the bottom stage, an S80 tank filled to 50%, and an S40 tank filled to 100% for decompression stops. By selecting appropriate tank sizes, divers can optimize their gas supply for the dive while minimizing the weight and bulk of their equipment.

Stage rigging

The purpose of the stage kit is to attach two bolt snaps to the stage tank and to define the ideal distance between the attachment points. The stage kit also provides a way to stow the stage regulator when it is not in use.

There are a number of stage rigging kits available from several different manufacturers, but the job can be just as easily accomplished using locally purchased materials. The nice part of the factory kits is that they have all the necessary hardware in one easily assembled package.

The hose clamp end and its tightening device require special attention. They must be covered by either plastic or nylon tubing to prevent sharp edges to perforate drysuits or cut other equipment.

Factory stage kits provide all the necessary hardware in one package, saving time and effort.

Take special care that the bottom retainer loop is below the hose clamp. This placement reduces the possibility of the bottom bolt snap getting threaded through the loop of hose that is left at the bottom of the tank, thus making proper deployment practically impossible.

It is important to ensure that the stickers and markings on a tank are relevant and accurate to avoid confusion and potential safety hazards. The only relevant stickers are the mandatory MOD and analysis stickers (and VIP sticker, where required) and the optional name sticker. It is important to remove all other extraneous stickers and markings from the tank. Decals saying NITROX or any irrelevant information can be misleading and confusing.

Get a grip

It is important to handle a stage tank properly to ensure safety and prevent damage. Gripping the garden hose on the stage kit is a bad habit and should be discouraged. It is not a handle, and holding it as such can cause the hose clamp to slide and negatively affect the positioning of the tank during the dive. Instead, the stage should be handled either by gripping the valve or using the bolt snaps on each end of the stage kit. This will help ensure that the tank is secure and in the correct position during the dive.