[Kamog]

What would happen if some of the crew are killed in battle, and the balance of Humans to Phong is changed? Now there's too much oxygen or too much carbon dioxide. Then the air would gradually become unbreathable for the race with more survivors. Then if some of the members of the larger race die from the bad air, equilibrium will be restored automatically and the air mixture would go back to normal.

For example:
Many humans die in battle -> less oxygen is used up and less carbon dioxide generated -> percentage of oxygen in air rises, carbon dioxide decreases -> bad for Phong -> Phong die -> ratio of Human / Phong restored.