SCUBA Gas Laws

Earth's atmosphere is composed of a mixture of gasses that obey the famous chemistry "Gas Laws." Some of these laws become matters of life and death when using a Self Contained Underwater Breathing Apparatus (SCUBA) device. Understanding just four of these laws will help you stay alive and out of trouble while SCUBA diving.

Boyle's Law

For SCUBA divers, the most important of the gas laws--and the most deadly one to ignore--is Boyle's law. Boyle's law says that as long as temperature is constant, pressure and volume are inversely proportional--when one goes up the other goes down and vice versa. If you have an inflatable container--such as your lungs-- decreasing the pressure increases the volume. So if you take a deep breath and then move toward the surface while holding your breath, your lungs expand. If you hold it too long your lungs will explode. This is why you should never hold your breath while SCUBA diving--not even briefly. If you breathe consistently the volume of air in your lungs will constantly adjust to the changing pressure.

Amonton's Law

Amonton's law says that if the volume of a gas is constant--as it is in a SCUBA tank--the pressure and temperature are directly proportional. If one increases so does the other, and vice versa. If you fill up your tank on a summer day and then jump in water that's 40 degrees cooler, you are going to have less pressure than you might think. Therefore, the tank will not last as long. If you fill up a tank and then put it in the trunk of the car where it is 60 degrees hotter, the pressure might rise to dangerous levels and damage your equipment.

Henry's Law

Henry's law describes how pressure determines a liquid's ability to absorb gasses. As pressure increases, more of a gas will dissolve in a liquid. When a diver dives, the pressure increases and more gasses dissolve in the diver's tissues. Most of Earth's atmosphere is nitrogen, which is relatively inert so it does no real harm. If the diver ascends slowly the nitrogen comes out of the tissues as the pressure decreases. If the diver with nitrogen-saturated tissues (too deep, too long) ascends too quickly, the nitrogen comes out too fast--in bubbles. This causes a very dangerous condition known as the "bends," which can cause permanent damage or even death.

Dalton's Law

Dalton's law says that if a gas is a mixture, the pressure of each component depends on the percentage of that component in the mixture. Earth's atmosphere is about 78% nitrogen, 21% oxygen, and one or two percent other gasses--depending on where you live. If your tank is filled using faulty equipment, you might be getting a lethal dose of something that is relatively safe at low pressures. Even oxygen can be toxic at high pressures. Nitrogen at high pressures can have a narcotic effect (known as "rapture of the deep") that can cause a deadly loss of judgement.

By Carlos Mano, eHow Contributor

Kathy Dowsett
www.kirkscubagear.com

Why You Might Remove Your Regulator When You Shouldn’t

Thanks to Undercurrents

Many divers trying to save a buddy from drowning report afterwards that, against all reason, their buddies removed their regulators from their mouths while they struggled for air. Over the years, Undercurrent has reported on many drowning deaths in which divers are found on the bottom with their second stages hanging free, but plenty of air still in their tanks. In one article, we reported that many firefighters breathing from air tanks have been found dead in the aftermath, with their regulators no longer in their mouths.

Recently, I came across the book Deep Survival by Laurence Gonzalez, in which he reports on research by Ephimia Morphew, a psychologist and founder of the Society for Human Performance in Extreme Environments. Gonzalez writes that she has "studied a series of accidents in which scuba divers were found dead with air in their tanks and perfectly functional regulators. 'Only they had pulled the regulators out of their mouths and drowned. It took a long time for researchers to figure out what was going on.' It appears that certain people suffer an internal feeling of suffocation when their mouths are covered. That led to an overpowering impulse to uncover the mouth and nose.



"The victims had followed an emotional response that was in general a good one for the organism, to get air. But it was the wrong response under the special, non-natural, circumstances of scuba diving. It's possible that the impulse, the feeling of suffocation, was formed as an implicit memory by some previous experience that was not available to conscious (explicit) memory. And the divers had no way of knowing that the one thing that would keep them alive, covering the nose and mouth, was the one thing the organism would not tolerate. At the critical moment of decision, reason was not enough to overcome emotion. For no one would say that those divers believed they could breathe under water without a regulator.

"Morphew and the other researchers wanted to know what divers were thinking when they removed their regulators and tried to breathe without them. The answer is: you don't need to think. That's what emotions and implicit memories are all about. By tradition, reason is regarded as the highest function. But from the point of view of an organism in desperate trouble, an organism that evolved by relying on emotions as the first line of defense, cognition is irrelevant and gets set aside. It's slow and clunky. As Remarque said, there's no time for it.

"Most of the mystifying accidents that happen in the course of risky recreation, the seemingly illogical decisions, actions, and outcomes, can be explained by the same interplay of emotions and cognition that shapes all human behavior. What the scuba divers did made perfect sense from the point of view of the organism's survival: The impulse to get air is automatic, and can be overpoweringly strong. Those who can control that impulse to survive, live. Those who can't, die. And that's the simplest way to explain survival."

As for the dead divers, says Gonzalez, "If you had magically transported them to the surface a moment before they removed their regulator and asked them about their impulse, they would have told you that it made no sense: The regulator was necessary for their survival. If you were able to ask them afterward, they would tell you that they didn't intend to take it out. They intended to live."

Kathy Dowsett

www.kirkscubagear.com