The scene that really caught my eyes was when Freder first discovered the Heart Machine and sees the sight of all the workers toil at the machinery relentlessly without break.
Here the workmen put in all their effort into keeping the machinery alive, “feeding” them their labor. The rhythm of their movements keeps itself in sync to the beat of the accompanying music. Almost like clockwork. The matching of movement and music itself makes feelings of tension arise. It greatly does so by intensifying the pace of the music, thus placing the workers into a hyper mode of work.
The scene is first shot as a long shot frame that shows the entirety of the Heart Machine and the workers that toil at its body. It then alternates between different portions of the machine and the workers tending to the parts. Similar to an accelerated montage that quickly transitions to the eventual explosion that occurs in front of Freder.
The aftermath of the explosion includes majority of the workers scalded by the searing steam/flames released from the machine. I believe this enforces my own thought that the workers city is symbolic of hell: an underground area where men toil relentlessly and are burned by the flames. In Freder’s eyes, the machine becomes akin to a demon that eats away at the workers.