From here:
More at the link. The ventilation grate on which they were standing was not designed for that and was, in fact, about shoulder-height. The people climbed up to stand on it so they could get a better view of the performance.
I took out the link because, as far as I can tell, it has nothing to do with the story you posted. Maybe you posted the wrong link? Not sure.
They should have used a fan instead.
(Link)
Okay, these should work.
16 killed in pop concert mishap
On the one hand, it was pretty rash of them to climb up and stand on something that is clearly not designed to support any weight. It’s different from the ones on street level because obviously they expect people to be walking over them.
On the other hand, the organizers should have expected someone would try and climb up on them (this being Korea) and posted someone there to keep people off.
I haven’t been out of Korea in so long that I’ve lost my perspective. Is this one of those things that could have happened in the US?
Back in the 70’s, 11 people died and over 20 seriously injured at a Who concert in Cincinnati. They were crushed by other concert goers. The short version is that there wasn’t reserved seating so the first in got the best seats. And there were only a couple of doors opened for the venue.
Wow, looking at the photo in one of the links, I can definitely see people climbing on that without worrying.
This is what America lacks – a sense of personal responsibility.
Wow, it really sucks that no one told them not to gather up there. What a scary way to die!
HazelNutCoffee I don’t see why this couldn’t happen in America too. Seems like it was something that never occurred to anyone - that 27 people would have reason to stand on this grate. It’s not like it was a concert venue, it’s just an office campus. So you wouldn’t really need to put a sign up about not standing on it because it could probably very well hold 2 people, 5 people…who would ever imagine 27 people ending up there?
Very tragic 
Update on the safety awareness situation: I’m on vacation now in South Korea and I’ve walked around three cities (Seoul, Daegu, and Busan) a bit. My last vacation here was in September and October last year. The difference now is that between my last vacation and this vacation, the three city governments managed to have warning signs in Korean, English, and Chinese posted on every horizontal grating I saw. The warning was: “Danger! Do not stand on grate!”
Most people over the years thought they were trampled to death. They weren’t; they suffocated in the crowd before the doors opened.
1964
May 24, Lima, Peru: more than 300 soccer fans killed and over 500 injured during riot and panic following unpopular ruling by referee in Peru vs. Argentina soccer game. It is worst soccer disaster on record.
1980
Jan. 20, Sincelejo, Colombia: bleachers at a bullring collapsed, leaving 222 dead.
Clearly what our parents said about sports being “good” and that loud rock and roll music being “bad” isn’t all that clear cut.
There’s also The Hillsborough disaster in which 96 people died. They also died of suffocation, not trampling. The reason it’s notorious is not just because of the death toll or the location but because of lies by the police and the newspapers after the event.
Basically policing large groups of people is really difficult but it’s one of the reasons for high ticket costs.
As an individual you don’t know if you’re going to be the one that breaks the vent’s back, so to speak, but any accessible vent really should be checked for safety before letting people have unrestricted access to it - even warning signs would deter a lot of people. South Korea is not exactly a dangerous, unregulated country full of habitual rule-breakers, so the lack of warning signs would understandably make some people believe that the vent was safe.