On Dwarven Oxygen Tolerance

Dwarves are frequently described as possessing “underground lungs,” a phrase which is scientifically useless without being entirely wrong. Populations with long histories of subterranean habitation demonstrate unusually efficient tolerance for elevated carbon dioxide and modest reductions in oxygen. Their blood chemistry adjusts rapidly, ventilation response differs from that of Humans, and panic triggered by poor air appears less pronounced under equivalent conditions.

The mistake is assuming this makes Dwarves immune to bad ventilation. It does not. Carbon monoxide, severe oxygen deprivation, and mine gases all kill Dwarves perfectly well; the difference is that conditions which cause a Human worker to become distressed may leave a Dwarf functioning normally long enough to underestimate the danger. This has produced a grim pattern in mixed mining crews, where the Humans often become symptomatic first and flee while the Dwarves remain because they feel fine. They are not fine.

A useful survival rule therefore exists in several modern mines: if the Humans begin complaining about the air, the Dwarves are required to believe them. Many Dwarves consider this humiliating. They nevertheless continue breathing.