Carbon monoxide is an odorless, colorless gas that forms when there is incomplete combustion of fuels. Everything we burn for fuel (wood, coal, oil, gas, alcohol, etc.) contains carbon and the process of burning combines the carbon with oxygen to form one of two combinations. Complete combustion produces carbon dioxide (CO2). The reaction of oxygen with carbon to form CO2 is one of the fundamental energy producing chemical reactions. All forms of animals used this reaction to produce metabolic energy. Anytime we burn fuel, this reaction occurs to produce energy. Incidentally, the carbon dioxide has to go somewhere. If it weren’t removed from the air we would by now have an atmosphere laden with it. We are saved by the trees and plants that use the energy of the sun to convert carbon dioxide back to carbon and oxygen. The carbon becomes part of the plant structure, the oxygen is released into the air.
You can see why we are so interested in keeping our forests healthy. It is not just for looks, we need the trees to replenish the oxygen used when we burn fuels in furnaces or in our body.
When there is not enough oxygen to completely burn the carbon in our fuels, then a different product is formed – carbon monoxide (CO). Note that only one oxygen atom is combined with one carbon atom. This small difference converts the gas from a relatively harmless one (carbon dioxide is not entirely harmless, but it is much less toxic that carbon monoxide) to a deadly, silent killer.
Unlike carbon dioxide, which is the product of combustion in the cells of the body and is handled by normal body processes, carbon monoxide adheres tightly to the hemoglobin in the blood and prevents oxygen from being carried to the body from the lungs. If the hemoglobin cannot carry oxygen, the cells and tissues essentially suffocate. CO also blocks the action of certain cell enzymes that are necessary for utilization of oxygen by the cell. When the blood vessels of the brain sense the lack of oxygen, they dilate to allow more flow into it. This causes a headache. It is likely that nausea comes from abnormal impulses originating from areas of the brain that are sensing the lack of oxygen. If allowed to continue, the buildup of CO in the brain and other body tissues ultimately causes the cells to die and the function of many of the organs of the body becomes abnormal. The heart cannot function very long without oxygen and in severe CO poisoning, death may be owing to heart stoppage. Before that happens, the brain becomes involved and unconsciousness occurs. In severe CO poisoning (for example in a house fire) once unconsciousness occurs, the victim is unlikely to survive unless rescued.
As divers, we should be concerned with CO contamination of our breathing air. Drawing exhaust fumes from an internal combustion engine into a compressor intake is a classic example of how diving air can become contaminated. After several bad experiences early in sport diving, the compressor problem is nearly gone. CO poisoning can come from other sources, however. Faulty stoves, heaters or furnaces can cause CO poisoning; burning a gas or charcoal stove or a catalytic heater in a closed space will use up the oxygen to the point that incomplete combustion will produce carbon monoxide. Car exhaust is heavily laden with carbon monoxide and situations which have caused prolonged exposure to engine exhaust have caused people to die.
If you are exposed to CO, the chances are you won’t know it; many victims die in their sleep because you cannot smell, taste or see the gas.
Treatment of CO poisoning first requires removal from the source. You should get to fresh air as soon as possible. We now use hyperbaric oxygen to rapidly remove CO from the body and restore function to tissues and organs. Use of 100 percent oxygen on the surface only also speeds the rate of removal from the body.
Avoiding CO poisoning is easy. Be sure of your air supply; be sure stoves or furnaces are properly vented; do not use stoves, heaters or fires in closed spaces where you share your air supply with the fire; avoid prolonged exposure to auto exhaust; and stay out of burning buildings. You might also give up smoking cigarettes, because the burning cigarette also produces carbon monoxide, although the amounts are small and don’t appear to have any obvious effects.
Knowledge about carbon monoxide sources, effects and avoidance is a necessary part of diving training. Learn as much as you can about it so that you can avoid this deadly, silent killer.