Most people or scuba divers do not know who or what Dalton’s Law is. Those that have gone through some technical diving or military training, you have heard of this law. What it states is that the pressure of a gas is made up of of the partial pressures of the gases contained within. It will also go on to state that if left independent, the partial gas will maximize the space remaining and act independent of the other gas. That can be a confusing mouthful. What does it mean and what does it have to do with scuba diving. Now, when you were getting your scuba diver certification, we talked about pressures and what decompression sickness. In a nutshell, Dalton’s Law is the bases of decompression sickness. As we dive, we are breathing an air mixture of 79% nitrogen and 21% oxygen. Our bodies need oxygen to feed our muscles and keep us alive underwater. So just like on the surface, oxygen feeds our muscles and then is converted to carbon dioxide and we exhale it. Unlike being on the surface, while underwater the nitrogen is absorbed into our bodies. While we are on the surface, nitrogen is not adsorbed into the body anymore than what it already is. We are at what is considered “saturated”. Because we have changed the pressure against our bodies by scuba diving, we create the ability to adsorb more nitrogen. Thus the partial pressure of a gas is maximizing the space and creating the pressure to offset the amount of pressure against our bodies. Same as what Dalton’s Law was going to predict. So are bodies absorb nitrogen and the partial pressure of the gas keeps increasing the deeper we go and the longer we stay down. Thus begins the cycle of nitrogen loading and managing our exposure. As divers, we know we need to manage our exposure to nitrogen or we run the risk of decompression sickness. Since that is not a desired effect, we understand Dalton’s Law and keep things in check. While this was a really simple explanation of Dalton’s Law. It does help to illustrate how decompression sickness can start if we don’t manage our dive profiles correctly. If you are going to acquire your scuba diving certification, your instructor should have a general idea about how nitrogen loading and decompression sickness can happen. Mike Shea
www.ScubaShea.com