In this world, a mask is a representation of who you are. Your job is decided at birth, and you are trained such that your personality is stripped away and you become your job. Every day, people are moved around in housing to squash revolution. The coal miner mask is chosen due to the history of coal mining being an unsafe job, the random assignment of jobs is an allegory for the uncontrollable life situations leading someone to work in a job that harms them, and the personality being stripped away parallels the idea in the real world that individuality does not exist in jobs.