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Everything to know about a depleted air supply

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In this article, we will discuss a number of aspects regarding the state of a depleted air supply when diving. We will present 10 facts that are not always taught during the diving course and are important to know. We will also discuss differences in air distribution methods between partners.

Fact 1: It is almost impossible to reach the “no air” state during a dive: in most situations of “no air” there is actually air in the tank but at low pressure. Tests conducted after diving accidents caused by lack of air revealed that in most cases there is air in the tank and the valve is still functioning. It is the diver who makes a number of human errors leading to a situation where the air pressure in the tank is too low, preventing the regulator to provide air to the diver with the normal ease he is used to.

According to the literature, this condition is caused when the pressure in the tank is the same as the atmospheric pressure (for example, 3 atmospheres at 20 meters) but in fact this may vary according to other factors such as the regulator structure, the breathing of the diver, regulator maintenance, accuracy of the pressure gauge and more. Therefore, the recommended and common practice is to get out of the water while the container has 50 atmospheres.

Fact 2: Equipment can break down but this also happens very rarely: a malfunctioning regulator is often expressed in air leakage, water leakage or free-flow. In the case of a regulator problem, it is almost always designed in the form of the Fail Safe, which means that it still provides air, although with a little discomfort compared to critical air deprivation. Despite what is written, we do not learn to carry out controlled emergency ascensions due to equipment problems, but rather because of human errors.

Fact 3: The inflator will still work when it is no longer possible to breathe through the second level: the inflator can keep working with a tank pressure lower than what allows the diver to breathe with is so despite the feeling that there is no air in the tank the inflator will keep working.

Fact 4: Sometimes the surface of the water is preferable to the partner’s face: before you rush to the partner in a state of “no air”, consider what is closer to you: your partner or the water surface. Remember that in order to share air with your partner, you not only need to reach him, but also communicate with him about your needs, and then take or get another a regulator to breathe from. This may take longer than a controlled emergency ascension. Of course, if there is a something in the way of getting to the surface, including “decompression ceiling”, swimming for a partner may be the best step. Should you reach such a situation, you will need to use you own better judgement.

Fact 5: Successful air distribution requires practice and repetition: no matter which air source or regulator you share, you should agree with your partner before diving how each will operate in an air distribution situation. It is possible to rehearse above the water before diving and also to practice in the water, although very few divers do so. An alternative air source can be practiced during a safety or decompression stop. Another way to practice with your partner is to dive one by the other during an easy part of the dive, and give the diver with less air to breathe from the air source of the partner. It also helps to balance the air supply between the couple and thus extend the dive.

Fact 6: “The Golden Triangle”: An important principle in the location of alternative air source and the regulator is the “Golden Triangle Rule”. According to this principle, any means of breathing that can be divided with another diver should be visible on the front of the diver in a triangle formed by the vertices located on the right and left sides of the pelvis and the mouth. This way, the backup is available to both divers.

Fact 7: Alternately breathing can prevent over-breathing: One of the concerns when sharing the air supply with the partner is the possibility of over-breathing of the first degree of the regulator (i.e., beyond the capacity by the first step) when breathing from two levels of second and using the balance inflator and / or a dry suit. Over-breathing may occur more often as the depth is greater and the pressure in the tank is lower. One way to prevent this is alternating breathing: when your partner exhales, you aim and alternately. A gentle use of an inflator with short clicks may also help.

Fact 8: Taking “sips” can help you breathe: Since you are likely to be in a situation with low air pressure rather than no air, breathing slowly and calmly can give you more time to reach your partner and share air. As noted above, the compensator’s inflator will continue to work, so there is no need to inflate the inflator with your mouth or to plunge into negative float to the surface.

Fact 9: The regulator tube should be long enough: no matter which regulator you share with your partner (Second Class or Octopus) the tube should be long enough (between 80 cm to 1 meter).

Fact 10: Resuscitation is not recommended! The old-fashioned skill of a partner’s respiraton (a division of air with a single second degree) does not make sense in the diving world today. At best, resuscitation was a difficult skill to learn and preserve. In many cases, this skill failed in emergency situations with very serious consequences. With the new standards that every diver should have an alternative air source, there should be no reason for a diver equipped to perform resuscitation of to their partner.

If so, the question arises: What is the best way to use the alternative air source? Opinions are divided on this issue and there are no clear standards for how to produce or locate the alternative air source, nor even how to share the alternative air source when needed, including the substantive issue of what second level the donor should transfer to the partner when air needs to be shared. As a result, there are alternative air sources that can be used in one way and some can be used in several ways. As a result, you must make decisions based on an understanding of what is right for you, and what is not. 

Reports from diving accidents show that confusion with regulators is a major cause of air distribution problems, with over-breathing of the donor’s regulator, air supply depletion, and poor underwater balance. Therefore you should plan and practice these situations in advance. You can also add a spare respiratory system (such as Spare-Air) to your diving equipment so that you can have a compact and reliable backup equipment without the need for a partner, and therefore will be able to finish the dive in a safer fashion.

Two scuba divers training in a swimming pool Two scuba divers training in a swimming pool

The donor transfers the source of the alternative air to the partner:

  • Less risk to the donor because there is no disruption to his air supply.
  • With a longer tube, the donor can safely secure the alternative air source (as long as it passed to the partner correctly).
  • Colors and markings on the alternative air source can be used to improve accessibility.
  • Your partner can take the alternative air source without the help of your partner.

The donor transfers the main regulator to the partner:

  • The donor is more in control.
  • Only the donor should know the location and operation of the alternative air source.
  • The main regulator is easier to find by the partner because it is already in the donor’s mouth and it works.
  • The partner cannot take the regulator without the donor being aware of it.
  • The main regulator is usually better for breathing.
  • Most of the donors will have more diving experience, sometimes even a professional diver, and will therefore be better able to change the regulator and maintain control of the situation.

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