What is it about Korea that is different than the rest of the world? Answer: Underfloor heating.
Why does it happen only during the summer? Answer: the underfloor heating system is off because it is not needed, so people will close up a room thinking that it is safe to do so (see below.)
Why does it happen only in a closed room? Answer: because the underfloor heating system is off, the normal ventilation system for that system is also off causing a buildup of gases. In buildings that have an older form of coal-based underfloor heating, carbon monoxide death is a well-known hazard causing modern buildings to have a water-based instead of coal based heating system.
Also note that in Korea, propane is the preferred source of heat for water, underfloor heating, and cooking. In general, anytime you are in Korea, it’s a bad idea to stay in a closed room.
This article shows a 201% spike in carbon monoxide deaths in Korea during winter, when the underfloor heating system is most utilized. When I was there, this was a known danger that we were warned about. However, in summer, when people think the underfloor system is off, that doesn’t mean it’s not being used. In some buildings (like the one I stayed in) the hot water for the shower went through the underfloor system. We had to turn it on when we wanted to take a shower, summer or winter.
Cecil says nothing about underfloor heating. Inasmuch as he gives an explanation at all, he seems to imply that the deaths that Koreans attribute to fans are most likely just random deaths from unrelated causes.
I don’t know if Superhal is right, but at least he has a theory, that does not sound too crazy, as to why people in Korea, in particular, might have an elevated tendency to die from sleeping in unventilated rooms. I would want to see more evidence than he gives, however, that underfloor heating is particularly common in Korea. The first link in the OP does suggest that it is traditional there, but also implies that its dangers are well recognized in modern Korea, and it is traditional in other places (including China, according to the link) where there is no tradition of belief in “fan death”.
I have a hard time sleeping without an electric fan blowing on my face. Unless I am the walking dead, I can assure you, sleeping with an electric fan in a closed room does not cause death. (Source- 36 years of sleeping with an electric fan running in a closed room).
I don’t know if they still use it but when I was in Korea I was warned about the rise in carbon monoxide due to floors heated with ondol (might have misspelled that but it is pretty close) which is pretty much a big piece of charcoal. Had nothing to do with fans.
I asked a friend of mine who grew up in South Korea, and is back there now, teaching ESL. She said the fans-are-dangerous urban legend is pretty widepread there.
I’m curious – what’s a coal-based underfloor heating system like? I would assume a coal-fired boiler and a water pump, but obviously that’s not what you mean because the coal-fired boiler wouldn’t be stupidly placed under the floor.
I live in China, and my cold water heater is also the floor heater, and I know where the natural gas vents to.
Your explanation in terms of carbon monoxide poisoning lends a sadly plausible air to the supersitious concept that a fan can cause death in a sealed room. However, it is merely a matter of semantics to show that it is not the fan that causes death at all, but in fact improperly combusted charcoal.
Now, if you can explain to me why Koreans actually believe (as confirmed by a taxi driver who claimed to be a traditional medic in his spare time) that eating gimchi will prevent the contraction of HIV, then I will gladly eat your suspicious pubic bacteria (for details on which, please see the relevant thread).