The instinct not to breathe underwater is so strong that it overcomes the agony of running out of air. No matter how desperate the drowning person is, he doesn’t inhale until he’s on the verge of losing consciousness. At that point there’s so much carbon dioxide in the blood, and so little oxygen, that chemical sensors in the brain trigger an involuntary breath whether he’s underwater or not. This is called the “break point”; laboratory experiments have shown the break point to come after eighty-seven seconds. It’s a sort of neurological optimism, as if the body were saying, Holding our breath is killing us, and breathing in might not kill us, so we might as well breathe in. If the person hyperventilates first - as free divers do, and as a frantic person might - the breakpoint comes as late as 140- seconds. Hyperventilation initially flushes carbon dioxide out of the system, so it takes much longer to climb back up to critical levels.
Until the break point, a drowning person is said to be undergoing “voluntary apnea,” choosing not to breathe. Lack of oxygen to the brain causes a sensation of darkness closing in from all sides, as in a camera aperture stopping down. The panic of a drowning person is mixed with an odd incredulity that this is actually happening. Having never done it before, the body - and the mind - do not know how to die gracefully. The process is filled with desperation and awkwardness. “So this is drowning,” a drowning person might think. ”So this is how my life finally ends.”
Along with the disbelief is an overwhelming sense of being wrenched from life at the most banal, inopportune moment imaginable. “I can’t die. I have tickets to next week’s game,” is not an impossible thought for someone who is drowning. The drowning person may even fell embarrassed, as if he’s squandered a great fortune. He has an image of people shaking their heads over his dying so senselessly. The drowning person may feel as if it’s the last, greatest act of stupidity of his life.
These thoughts shriek through the mind during the minute or so that it takes a panicked person to run out of air. When the first involuntary breath occurs most people are still conscious, which is unfortunate, because the only thing more unpleasant than running out of air is breathing water. At that point the person goes from voluntary to involuntary apnea, and the drowning begins in earnest. A spasmodic breath drags water into the mouth and windpipe, and then one of two things happen. In about ten percent of people, water - anything - touching the vocal cords triggers an immediate contraction of the muscles around the larynx. In effect, the central nervous system judges something in the voice box to be more of a threat than low oxygen levels in the blood, and acts accordingly. This is called a laryngospasm. It’s so powerful that it overcomes the breathing reflex and eventually suffocates the person. A person with laryngospasm drowns without any water in his lungs.
In the other ninety percent of people, water floods the lungs and ends any waning transfer of oxygen to the blood. The clock is running down now; half-conscious and enfeebled by oxygen depletion, the person is in no position to fight his way back up to the surface. The very process of drowning makes it harder and harder not to drown, an exponential disaster curve similar to that of a sinking boat.