Thanks for playing! I didn't manage to include an in-game tutorial so I had to write the instruction in the game page, without that it can be quite confusing. The (poorly named) safety bar represent the dungeon stability, it will start depleting once you collect the key (or if enough time passes). Once it reaches zero it's game over, the dungeon collapses.The idea is to explore in the first 2 minutes and to plan an escape route using the beacons once you find the key and the exit.
If the bar was stuck and you died with a full bar it seems like you encountered a weird bug, unfortunately I can't seem to reproduce it :(