1At a glance
- Primary function
- Extended bottom time, decompression, specific gas mixtures
- Attachment method
- Side-mounted via straps and clips
- Common gas types
- Enriched Air Nitrox (EANx), Trimix, Oxygen
- Typical capacities
- 5.7 litre (40 cu ft) to 11.1 litre (80 cu ft)
- Used in
- Technical diving, cave diving, wreck diving, prolonged recreational dives
- Required training
- Specific technical diving certifications (e.g., Decompression Procedures, Cave Diver)
- Alternative names
- Staging cylinder, stage bottle, deco bottle
2How stage tanks work for technical divers
Stage tanks are typically rigged with a dedicated regulator set, including a first stage, second stage, and pressure gauge. They are attached to a diver's harness or buoyancy compensator (BC) D-rings using bolt snaps and straps, allowing them to be easily donned, doffed, or 'staged' (left at a specific depth for later retrieval). This modular approach allows divers to customise their gas supply according to the demands of the dive profile.
During a technical dive requiring multiple gases, a diver might start with one stage tank containing a specific bottom gas, switch to another stage with a different blend for decompression stops, and even use a third stage with 100% oxygen for the shallowest decompression. The ability to carry and manage these separate gas supplies is crucial for safely executing complex dive plans, especially those involving extended time at depth or mandatory decompression.
Effective management of stage tanks includes proper labelling of gas contents, careful planning of gas switches, and practicing emergency procedures. Technical divers undergo rigorous training to master the skills required for safe stage tank deployment, retrieval, and gas switching, ensuring they can handle potential issues underwater while maintaining buoyancy and trim.
3Comparison: Stage Tank vs. Other Auxiliary Cylinders
| Feature | Stage Tank | Pony Bottle | Sidemount Tank |
|---|---|---|---|
| Primary Purpose | Extended bottom time, decompression, specific gas | Emergency air supply (bailout) | Primary breathing gas, alternative to backmount |
| Typical Capacity | 5.7-11.1 litre (40-80 cu ft) | 1.9-5.7 litre (13-40 cu ft) | 11.1-15 litre (80-100 cu ft) |
| Gas Type | Air, Nitrox, Trimix, Oxygen | Air or Nitrox | Air, Nitrox, Trimix |
| Attachment | Side-mounted (removable/stageable) | Small, often back-mounted or clip-on | Primary tanks, side-mounted (non-removable mid-dive) |
| Required Training | Technical diving certifications | Recreational diving (often recommended) | Sidemount specialty, technical diving certifications |
4What stage tanks mean for your liveaboard trip
For most recreational divers on a liveaboard, stage tanks are not a standard part of their equipment. However, for those interested in technical diving or participating in specialised liveaboard itineraries, stage tanks become a focal point. Some liveaboards cater specifically to technical divers, offering amenities like onboard gas blending facilities for custom nitrox or trimix fills, and ample deck space for managing multiple cylinders.
If you plan to undertake technical diving training or a technical diving trip on a liveaboard, verifying the availability and cost of stage tank rentals, gas fills, and any associated logistics with the liveaboard operator is crucial. These considerations ensure that your equipment needs are met and that the vessel supports the demanding requirements of technical diving operations.
Even if you are not a technical diver, being aware of stage tanks can enhance your understanding of diving practices, especially when sharing a liveaboard with technical divers. Observing their gear setup and dive planning can offer insight into the complexities and safety protocols involved in advanced underwater exploration. Blue Rides lists liveaboards worldwide, some of which cater to the technical diving community and its specific equipment needs.
5Stage Tank Usage Scenarios
| Scenario | Purpose | Typical Gas | Benefit |
|---|---|---|---|
| Decompression Dive | Provides optimal gas for specific depth stops | Enriched Air Nitrox (e.g., EAN50), 100% Oxygen | Accelerates decompression, reduces inert gas loading |
| Deep Wreck Penetration | Extended bottom time, gas redundancy | Trimix (hypoxic or normoxic) | Mitigates nitrogen narcosis, extends exploration time |
| Cave Exploration | Longer penetration, redundancy, specific gas for sections | Air, Nitrox, Trimix | Ensures sufficient gas for complex routes and egress |
| Gas Switching Course | Practical training for handling multiple gas cylinders | Various EANx blends | Develops critical skills for technical diving |
| Extended Bottom Time | Supplementary gas for prolonged exposure at depth | Air or bottom Trimix | Allows more time for photography or scientific observation |
6Common misconceptions
Myth: Stage tanks are only for 'extreme' divers. Fact: While stage tanks are essential for advanced technical diving, the concept of carrying additional gas for specific purposes, such as an extra safety margin or a richer nitrox for conservative decompression, can also be applied by experienced recreational divers with appropriate training.
Myth: Stage tanks are unwieldy and difficult to manage. Fact: With proper training and practice, technical divers learn efficient methods for donning, doffing, and managing stage tanks underwater. Modern rigging techniques make them streamlined and relatively easy to handle, even in confined spaces.
Myth: Any diver can use a stage tank. Fact: Using a stage tank, especially for decompression or carrying different gas mixtures, requires specific training and certification beyond recreational open water diving. Incorrect use can lead to serious safety issues, such as oxygen toxicity or missed decompression.
Myth: A stage tank replaces your primary back-mounted cylinder. Fact: A stage tank is supplementary. It provides additional gas or a different gas mixture to be used in conjunction with a diver's primary breathing supply, which could be a single back-mounted tank, a twinset, or a sidemount configuration.
FAQ
What is the main difference between a stage tank and a pony bottle?
A stage tank is typically a larger cylinder used for extended bottom times, planned decompression, or carrying specific gas mixtures like Trimix or high-percentage Nitrox. A pony bottle is generally smaller, intended purely as an emergency air supply (bailout gas) for recreational dives.
Do I need special training to use a stage tank?
Yes, using a stage tank requires specific technical diving training. Courses such as Decompression Procedures, Extended Range, or Trimix Diver certifications are necessary to learn the proper planning, gas switching, and safety protocols associated with stage tank diving.
How is a stage tank attached to a diver?
A stage tank is usually attached to the diver's side using a set of clips and straps. A bolt snap on the tank's neck clips to a chest D-ring, and another bolt snap on the bottom of the tank clips to a hip D-ring, keeping it streamlined and accessible.
Can I rent stage tanks on a liveaboard?
On liveaboards that cater to technical diving, stage tank rentals are often available. However, it's crucial to confirm availability, sizes, and associated costs with the liveaboard operator well in advance, especially if you require specific gas fills like Trimix.
What type of gas is typically put in a stage tank?
The gas in a stage tank depends on its intended use. For decompression stops, it might be enriched air nitrox (EANx) or 100% oxygen. For deeper sections of a dive, it could contain a different Trimix blend than the primary cylinders, or simply extra air/bottom mix for extended duration.
Are stage tanks only for very deep dives?
While commonly used for deep technical dives, stage tanks are also employed for shallower dives that require extended bottom times, complex penetration, or extensive decompression. They provide modular gas supply, allowing divers to carry precisely what's needed for any demanding dive profile.