Alternative Air Sources – Spare Air and Pony Bottles

What are alternative air sources?

Sometimes, divers underestimate how long they will be underwater for and how much air they will need. Other times, they encounter a problem while diving, like a gas leak in their scuba tank. Inevitably, even the safest, most knowledgeable divers will eventually find themselves in dire need of air. It’s a reality that should be planned for every time.

Though some people do swim with a second full-sized tank as their alternative air source, this method is cumbersome. For this reason, alternative air sources were designed. They are only meant to be used in the event of an emergency.

Each diver has their own preference for alternative air depending on the situation, with some preparing two different alternative sources for a single dive. We recommend practicing with all the options under safe circumstances, in order to understand the benefits and limitations of each source. The two types of alternative air sources we will be going over are both known as “bailout cylinders”.

What is Spare Air?

Spare Air is the brand name of the world’s smallest replacement air system for divers. Packaged in small aluminum tanks, about 8-12 inches tall and 2 inches in circumference, Spare Air offers a few quick breaths to a diver in an emergency through a standard rubber scuba mouthpiece.

Spare Air Bottle and accessories in Yellow

How long does Spare Air last?​

They are not fitted with hoses or pressure gages, but can be attached to the main scuba tank through a valve opposite to the mouthpiece on the regulator body. The idea behind Spare Air is to allow the diver enough time to get to the surface, unencumbered by equipment. Spare Air comes in two sizes. The small holds 1.7 cu ft of air and supplies about 30 breaths, while the large holds 3.0 cu ft of air and supplies about 50 breaths.

Spare Air is a good choice for new divers because it requires little training to use. Newly certified divers will stick to relatively shallow depths while they’re practicing their skills, anyway. Spare Air is only intended for dives that will not require decompression. If a diver should end up in a tricky situation, they can simply apply the nozzle to their mouth and safely ascend.

Are pony bottles the way to go?

Pony bottles are larger than Spare Air, but still smaller than a full-sized scuba tank. They act as an extension of the scuba set and are fitted with independent regulators and gauges. In the event of an emergency, the diver will have to attach the bottle to their main air supply using a connector and open the valve.

Catalina Pony Bottle Tanks in different sizes in yelllow

These bottles supply enough air to allow the diver to make a normal, safe ascent to the surface from mid to low depths. They are commonly sold in 6, 13, and 19 cu ft bottles, with 13 cu ft being the most popular size.

For deeper dives, bottles of both 30 and 40 cu ft are available. Smaller bottles will allow a safe ascent, while larger bottles will allow a safe ascent that includes decompression stops.

During a dive, a pony bottle should be fixed to the main scuba tank with clamps or straps. This allows convenient access and keeps them out of the way of the diver’s workspace.

Is one better than the other?

Both pony bottles and Spare Air are refillable while on land. Pony bottles are typically refilled via a scuba tank. Spare Air can be refilled using a scuba tank, personal breathing compressor, hand pump, or at your local dive shop.

Pony bottles definitely provide more air and are a safer choice if you know how to quickly change air supplies. They can save a diver’s life during a deep dive, but the air is not as easy to use in an emergency as Spare Air. Pony bottles are not safe for inexperienced divers to use, and one should never attempt to dive with a pony bottle without practicing with them first.

In shallow water dives with small space requirements, Spare Air is a good, safe choice. However, Spare Air is a small solution to a small problem. If caught at low depth with no extra supply, the diver would have to hurry to reach the surface, which can be very dangerous.

Ultimately, the choice comes down to experience. There is no perfect answer. A diver must look at the circumstances for each individual dive, and evaluate the risks. Dive tables are extremely helpful in calculating how much air one would need in an emergency, based on distance to the surface and rate of consumption.

It’s always best overestimate how much air will be needed. Adrenaline and fear typically cause people to breathe much more heavily, burning through their supply quickly. If space requirements are not an issue, we recommend using two alternative air sources: one pony bottle and one Spare Air.

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