Eu encontrei este artigo . Traduzido livremente:
Station Schiphol disallows balloons since recently. The reason for this is that it has happened a few times last year that a kid's ballon hit the overhead power lines, often resulting in smoke and smouldering particles.
Because the smoke alarm is very sensitive, because of safety concerns with the long train tunnel, this will set off the alarm very quickly. When that happens, the tunnel and the entire train station have to be evacuated. This leads to major discomfort for travellers who will face delays.
Eu viajo de trem e lembro que os trens Schiphol foram cancelados com bastante frequência por causa da fumaça no túnel no ano passado, mas eu não sabia que os balões eram a causa ...