The fumes from this non-catastrophic failure are like all combustion byproducts -- toxic. Keeping people in a confined space with toxic fumes is not conducive to their health. People with asthma, allergies and other respiratory pathologies are at particular risk.
Many fires do self-extinguish, but without clairvoyance there is nothing to distinguish the first waft of smoke/fumes between a small release of toxic fumes or the beginnings of a conflagration that will in the next several seconds consume the entire aircraft.
If the CC waits for visible flames or heavy smoke, lives will be lost.