Among other things, David T. discusses that fateful day. Please read the following and come to your own conclusions. Instead of protecting the moms and kids, the concrete room became their tomb. The story worried me from the beginning.
Mothers are practical people.
When the air is poisoned, the practical solution is to get away from it. But the concrete room was a catch basin for poisoned air. It was windowless. It had a doorway, but no door. Poisoned air entering the room from the doorway would have nowhere to escape.