If there are items that are explicitly banned in Hong Kong’s subway systems, it’s not bombs, bladed weapons or prohibited drugs. Instead it makes an effort to notify the public with public broadcast and posters than metallic balloons are no way allowed inside the MTR.
So for the uninformed, what in the first place is a metallic balloon?
Metallic balloons are commonly found at parties as ones that serve both as decoration and occasionally as a toddler magnet. They are almost always filled with helium gas that is colorless, odorless, tasteless and has the lowest boiling point among all elements.
Like many other subway systems in the world, Hong Kong’s MTR is constructed with power transmitted across additional rail on the tracks. The MTR has its cables running overhead and they carry high voltages, that is why the railway company expedited the construction of gates so these cables will be out of reach to those who decide to take their lives in public.
If you have a child carrying a metallic balloon inside the MTR, however, such cables can easily be reached by the balloon should it likely gets let go by the child. The balloon could soon get in contact with the cables and short-circuit power lines. And that’s where a piece of history reminds MTR to be very vigilant about it.
In 1996, a metallic balloon floated inside an MTR tunnel on the Island line during lunch hour. The resulting short circuit halted all trains between Admiralty and Quarry Bay for an hour and a half, affecting 100,000 commuters.
Since then, the MTR transport system expanded further while serving more passengers. Imagine the level of chaos if a short-circuit caused by contact between the balloon and overhead cables disrupts the service.
So when you hear such announcement banning the entry of metallic balloons inside the MTR, just comply. It’s for your own good.