Some 1.2 cubic kilometers of CO2 was released in roughly 20 seconds. This massive wave of deadly gas swept over the countryside. Villages nearby the lake had almost no chance of survival, and in the nearby Nyos only six out of 800 survived. (Those that did survive usually did so by quickly escaping to higher ground on motorcycles.) As the CO2 settled, every flame and fire was immediately extinguished, a sign of the doom descending all around Lake Nyos.
The cloud spread far and wide killing people who were as far as 25 km away from the lake. Nearby villagers who came out of their houses to find out what the sound they had heard was were overtaken by wafting clouds of gas and fell dead at their doorsteps. People taking naps were killed without their relatives even realizing anything had happened, as the gas settled on the ground with enough concentration to kill, but left those standing unaffected.
Nature is scary.