Living in silos
The inhabitants of the silos live underground for their safety and survival because the outside world is deemed toxic and inhabitable. However, ironically, the silos become a sort of prison for the inhabitants, where information is controlled, and they are kept isolated. They are "protected" but at the cost of their freedom.
Cleaning
In the Silo series, the act of cleaning the lenses that provide a view of the outside world is ironic. The 'cleaning' is a death sentence, but those condemned to clean initially feel an overwhelming compulsion to do so. The outside view is manipulated to motivate the cleaners, so while they believe they're helping the silo by cleaning the lenses, they're victims of manipulation.
Donald Keene
Donald Keene, a character from the Shift series, continues to play a significant role in Dust. Donald was initially involved in designing the silos, believing he was creating a shelter for humanity. Ironically, he's unknowingly helping to create the very system that will become a prison for humanity.
Juliette's journey
Juliette's journey throughout the series also contains irony. She's originally a mechanic in the silos, which is seen as a lower-class job, but she becomes the leader and savior of her people. Her practical skills and lower status ironically give her the tools to understand and dismantle the oppressive system.
The outside volt
The outside world represents freedom but, at the same time, is toxic and deadly. The characters yearn for the freedom the outside world represents, but leaving the silo would mean certain death.
