Anyone who purchases an electric fan in South Korea may notice something unusual; an automatic shut-off timer. This is one popular method for preventing what a number of South Koreans refer as fan death. Fan death allegedly occurs whenever an electric fan is used for many hours in a sealed room.
It's not the fan itself which causes fan death through physical injury or electrical shock, but rather the cumulative effect of the circulating air. Some believe the fan's rotating blades create a partial vacuum or vortex near a sleeper's face, causing a disruption in normal breathing and ultimately fatal suffocation. Others suggest the fan somehow uses up the available oxygen, allowing the room to fill up with deadly carbon dioxide. A third theory blames fan death on a gradual hypothermia as the circulating air lowers the sleeper's body temperature. Paradoxically, others believe fan death is caused by hyperthermia as the hot circulating air raises a sleeper's body temperature during a heat wave.
The urban legend of fan death seems to be limited to South Korea. Stories have circulated in that country for decades concerning victims being discovered in small, enclosed rooms with no obvious contributing factors except the presence of an electric fan. Depending on the circumstances, a victim of fan death may have frozen to death, suffered heatstroke or suffocated for no apparent reason. These accounts tend to be attributed to a very small newspaper or a "friend of a friend" who heard about such an incident of fan death years earlier. Skeptics of the fan death phenomenon suggest that the real cause of death in these cases may have been carbon monoxide poisoning, an existing physical condition or electrocution from an improperly wired appliance. The fact that an appliance as common as an electric fan happened to be in the room could very well be coincidental.
While an electric fan can certainly create a circulating vortex of disturbed air, there is very little evidence to support the suffocation theory of fan death. Such a vortex would have to be exceptionally powerful in order to suffocate an average human being, and most users position an electric fan in a direction which blows air towards their faces as they sleep. While this constant stream of air may cause minor dehydration, it would not be powerful enough to complete disrupt normal breathing. Even if the fan were positioned in the opposite direction, the air displaced by the fan would be replaced immediately by other air. Since it would be extremely difficult to seal off a room's doors and windows completely, fresh air is also likely to enter the room and disrupt any suffocating vortex.
A circulating fan also cannot convert oxygen into carbon dioxide through mechanical methods alone. The sleeper's respiration would be more responsible for introducing carbon dioxide into the atmosphere, and all the electric fan would do is mix the oxygen and carbon dioxide together. Eventually the concentration of carbon dioxide could reach toxic levels if the room were perfectly sealed, but the chances of such a lethal event happening within a few hours would be very low. The electric fan itself could not be held responsible for a death caused by carbon dioxide exposure. A better argument could be made for dehydration after hours of exposure to a constant stream of air, but the odds of an electric fan removing enough fluid from the sleeper's body to cause fan death would be extremely low.
The circulating air generated by an electric fan does have a cooling effect on a sleeper's body as sweat evaporates and lowers body temperature. Conceivably, a powerful air conditioning unit set for maximum cooling could cause a dangerous drop in the sleeper's body temperature over time, but an electric fan does not use coolants. The ambient room temperature would also have to fall to dangerously cold levels in order for the fan's circulating air to become a factor. Fan death caused by hypothermia could just as easily be attributed to the room's ambient temperature or exposure to outside elements. The same holds true for an electric fan circulating hot air during a heatwave. The fan does not affect the temperature of the air itself, so a person's death could be attributed to the effects of heat exhaustion or heat stroke.
While many other countries consider fan death to be little more than a South Korean urban legend, the South Korean government and many health officials still issue warnings on the use of electric fans in small rooms with limited ventilation. The timer units on South Korean electric fans are supposed to prevent fan death by stopping the circulation of air after a number of hours. This would allow the heavier carbon dioxide gases to remain separate from the breathable oxygen in the room. A sleeper would also not risk dehydration after hours of exposure to a constant stream of air, and his or her body temperature would not be raised or lowered to dangerous levels overnight.