In the story, the cause of the falling of chronos was a outbreak of the NX element. But its not just that.
The two lead scientists behind the NX compound, were to blame. Cyraak and Lehnstoch are best friends even when parting ways. They swore an oath, that oath was to keep their creation safe and contained. It had too much promise, but was too dangerous. The cause of the outbreak was an error by Cyraak who failed to properly seal the element in the container. This error costed his body, and some of the element to seep out into the room. Lehnstoch operated on Cyraak and saved him just in time before the taint reached past his heart and lungs. Cyraak was just a severed head, Lehnstoch sought to that a body was made and he then installed Cyraaks dying head into the body when it was finished.
Though things were seeming to be fine for now, Lehnstoch was infected when he cut off Cyraaks head, exposing him to the taint. Lehnstoch soon realized he was infected when his fleshed started to peel, exposing black rotted muscle flesh. He tried to hide it and vanished.
When Cyraak woken he came to realize what befalls him in his new body, but comes to agony when he finds out Lehnstoch vanished. Several years later, a surveyor came across a sealed room not marked on his map. When he pried the door open with help from his colleagues, they come to realize that they breached the quarantine keeping the NX element inside. The workers soon fallen ill on the spot and past away suffocating to death. The taint soon got into the ventilation system then soon into the atmospheric distribution system. The taint spread like wild fire.
Cyraak caught the spread, but was too late. He issued a total lockdown. All bulkheads and blast doors sealed shut and all hatches and doors locked all across the station. In a desperate attempt to keep it contained and from spreading even further, Cyraak shut down all of Chronos's reactors. This sudden drop in power seised the spread, and killed all crew, preventing it to spread even more. But the cost was too great. With his mind full of regret, shame, and sorrow, Cyraak soon died due to his life support shutting down.
The taint was all across the station except several isolated locations that were sealed off just in time.