Revealing mistake: When the builders are committing suicide the guy in charge keeps turning earlier to the areas of the falling instead of after they land. A special FX and timing error I guess. (00:06:20)
Revealing mistake: When they are sitting down for dinner at the old lady's home, it is clear that a very white light source is in the room brightening things up - something that non-electric oil/kerosene light sources cannot do.
Chosen answer: If it would/could wear off would be debatable. As far as sending troops in wearing gas masks: The masks are simply filters that block molecules of certain sizes. If the neurotoxin molecular structure was small enough, it could pass through the filters. And then there is, if you really wanted to die, you will find a way regardless of the situation.
Rlvlk