Bill the philosopher had a bit of a heavy breathing problem. No matter how shallow the dive, no matter how large the cylinder, he could suck it down to nothing in 15 minutes flat. It was while considering this problem, assisted by several pints of decompression fluid, that he offered one of those profound philosophical statements that in biblical times would have placed him alongside the famous Greeks “I suppose running out of air is like premature ejaculation, one of the partners remains unsatisfied.”
I was reminded of this gem of modern philosophy on a trip to DDRC a while back. I asked about sources of diving accidents and they remarked that running out of decompression gas and subsequently missing stops was one of the commonest technical diving problems.
It is not just techies who make this mistake. Looking at sports diving accident reports, poor gas planning seems to be prevalent at all levels of experience from newly qualified open water divers upwards.
We all learn how to plan our gas consumption during training. But be honest, how many of us really plan our gas requirements to the same extent as we plan for tides or decompression schedules? I know that for the average dive I don’t, I depend upon past experience, then just look at my computer and cylinder pressure regularly and let that tell me when it is time to come up. I also normally dive with either a pony cylinder or twin set. Nevertheless, for any serious dive and certainly for technical dives I calculate gas requirements fully in advance.
The factors governing a divers gas consumption can be broken into three categories: physical, physiological and psychological.
Basic diver training teaches Boyle’s law, that the volume of a gas is inversely proportional to pressure. Amongst other things, this has an impact on a diver’s gas consumption. The deeper you go, the more gas each breath will take from a diving cylinder. This is a physical component of a diver’s gas consumption.
We all know that if we swim hard we breathe more. The heavy metal collectors amongst us will also know that any form of underwater work, such as hammering the rivets out of a porthole, also increases gas consumption. The reason for this is that our bodies metabolise food and oxygen to produce energy. The harder we work, the more energy we need, the more oxygen we need to provide the energy, and the more gas we need to breathe. We also need energy to keep our bodies warm, so a cold diver will also breathe harder. These are physiological components of a diver’s gas consumption.
The third component of a diver’s gas consumption is psychological. Have you noticed that worried or nervous diver’s tend to get through their gas faster? If a diver is nervous, uncomfortable, or unsettled in any way, they will tend to breathe faster than they need to.
Whatever you do, don’t try to save gas by holding your breath or deliberately breathing shallowly. At the least you will surface with a headache, and you could end up with a burst lung or worse. The way to use less gas is to address the root of the problem, not its symptoms.
A good place to start is with buoyancy control. This may seem like a topic for novices, but the buoyancy control of many “experienced” divers is less than perfect. A buoyant diver will be swimming down all the time. A heavy diver will have to swim upwards or bounce along the bottom, reducing the visibility for everyone else or damaging the marine life. Maintaining neutral buoyancy throughout a dive, avoids unnecessary effort, improves comfort, and hence reduces gas consumption.
Closely related is the amount of weight that a diver carries. An over-weighted diver will have to put extra gas into a BC or dry suit to maintain neutral buoyancy. By itself, this is insignificant compared to the amount of gas a diver breathes, but it will have a bad effect on a divers position in the water, tending to turn the diver upright. Swimming requires greater effort due to an unnatural angle in the water and increased water resistance, with a consequent increase in gas consumption.
Poor finning technique such as a bicycle kick wastes effort and increases a diver’s gas consumption. It can be difficult to spot problems in your own finning technique, so ask your buddy to keep an eye on it and give you some feedback; you may be surprised at the results. Efficient finning uses strong gentle stokes of the whole leg, taking each kick through to completion.
Think about the equipment you carry and how it is adjusted. A poorly adjusted regulator with a high breathing resistance will require extra effort just to breathe, again increasing gas consumption. A loose weight belt will often rotate round a diver’s waist, pulling the diver off balance, making the dive uncomfortable and causing the diver to expend effort to compensate. A loose weight belt can also slip downwards, pulling a diver upright and making swimming more difficult. In both cases the consequence will be an increased gas consumption, not just from the effort, but also because a diver will feel generally awkward and uncomfortable.
Any loose, badly sized or poorly adjusted equipment can have a similar effect, pulling a diver off balance or making control difficult. While on the subject of equipment, having the right diving suit for the water temperature will also help to reduce a diver’s gas consumption, because a cold diver breathes more.
Overall be comfortable and happy in the water. Become familiar with your equipment. Learn to move gracefully and economically with good buoyancy control and finning technique. Once these factors are under control your breathing will take care of itself. Good gas consumption is a Zen thing.